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Power–duration relationship: Physiology, fatigue, and the limits of human performance
Abstract
The duration that exercise can be maintained decreases as the power requirements increase. In this review, we describe the power–duration (PD) relationship across the full range of attainable power outputs in humans. We show that a remarkably small range of power outputs is sustainable (power outputs below the critical power, CP). We also show that the origin of neuromuscular fatigue differs considerably depending on the exercise intensity domain in which exercise is performed. In the moderate domain (below the lactate threshold, LT), fatigue develops slowly and is predominantly of central origin (residing in the central nervous system). In the heavy domain (above LT but below CP), both central and peripheral (muscle) fatigue are observed. In this domain, fatigue is frequently correlated with the depletion of muscle glycogen. Severe-intensity exercise (above the CP) is associated with progressive derangements of muscle metabolic homeostasis and consequent peripheral fatigue. To counter these effects, muscle activity increases progressively, as does pulmonary oxygen uptake (
), with task failure being associated with the attainment of
max. Although the loss of homeostasis and thus fatigue develop more rapidly the higher the power output is above CP, the metabolic disturbance and the degree of peripheral fatigue reach similar values at task failure. We provide evidence that the failure to continue severe-intensity exercise is a physiological phenomenon involving multiple interacting mechanisms which indicate a mismatch between neuromuscular power demand and instantaneous power supply. Valid integrative models of fatigue must account for the PD relationship and its physiological basis.
... Four domains of exercise intensity have been identified based on power outputs associated with specific metabolic thresholds, namely the lactate threshold (LT) and the critical power (CP) (Burnley & Jones, 2018). The four exercise intensity domains are: moderate (below the LT), heavy (between LT and CP), severe (above CP until VȮ2max is attained), and extreme (task failure occurs before VȮ2max is attained) (Burnley & Jones, 2018). ...
... Four domains of exercise intensity have been identified based on power outputs associated with specific metabolic thresholds, namely the lactate threshold (LT) and the critical power (CP) (Burnley & Jones, 2018). The four exercise intensity domains are: moderate (below the LT), heavy (between LT and CP), severe (above CP until VȮ2max is attained), and extreme (task failure occurs before VȮ2max is attained) (Burnley & Jones, 2018). ...
... The conceptual framework of CP allows to study and understand metabolic and physiological mechanisms underpinning exercise performance, including high-intensity intermittent exercise (Burnley & Jones, 2018). The two-parameter CP model describes the hyperbolic relationship between power output (intensity) and time to task failure (duration) within the severe-intensity domain . ...
This PhD thesis by Published Works consists of six peer-reviewed journal articles relating to the overall theme of all-out sprint testing and training. The purpose of the thesis was, firstly, to investigate the performance reliability and test sensitivity of the 6- and 30-s Wingate Anaerobic Tests (WAnT), and secondly, to measure the effects of work-to-rest (W:R) ratios and exercise modality (cycling and running) during all-out training on physiological and performance adaptations in healthy participants.
In Publication 1, no significant differences in peak power output (PPO) and mean power output (MPO) across four trials of a 6- and 30-s WAnT were found in physically active males and females. Furthermore, test sensitivity of both WAnT protocols was generally marginal in both sexes, and only male MPO in the 30-s test displayed good test sensitivity. Publication 2 was a 2-week cycling repeated sprint training (RST) intervention in competitive runners. The results showed that the type and magnitude of adaptations is dependent on the prescribed W:R ratio. Specifically, greater improvements in endurance performance tests, as measured by the 3-km running time-trial (TT), time-to-exhaustion (TTE) and peak oxygen uptake (V̇O2peak) were demonstrated with shorter rest periods (1:3 W:R ratio), whereas longer rest periods (1:8 and 1:12 W:R ratios) resulted in higher power outcomes (PPO and MPO). Publication 3 demonstrated improvement in tests requiring endurance intensive efforts (10-km cycling TT, TTE and critical power), following a 4-week cycling sprint interval training (SIT) in female-only participants. However, twice weekly cycling SIT sessions did not provide adequate stimulus to significantly increase cardiorespiratory fitness (V̇O2peak) in healthy young females. Publication 4 reported a significant change in lactate kinetics following a 6-week cycling RST in adolescent academy level male football players. These changes were associated with the improvements in different performance measures. Specifically, maximal blood lactate kinetics was shown to correlate with sprint and power parameters, while endurance performance was related to maximal blood lactate clearance. Publication 5 directly compared acute physiological adaptations in response to two weeks of cycling SIT and uphill run sprint training (UST) in recreationally active males. While there was no significant improvement in V̇O2peak following either training modality, the UST was effective at improving TTE and ventilatory threshold by 11% and 3%, respectively. Finally, Publication 6 measured the effectiveness of a longer, 6-week UST to improve physical characteristics in competitive male footballers. Twice weekly UST performed alongside normal football training significantly enhanced endurance measures (YYIR1 distance: +11.9%; estimated V̇O2peak: +2.9%; 3-km TT: -4%), increased leg and back strength (+10%) and decreased time taken to complete change of direction test (-3.2%).
Collectively, these findings have practical implications for testing selection and training prescription in research and practice. One of the key outcomes was provision of valuable data on testing and training responses during all-out sprinting in female participants. Specifically, both WAnT protocols (i.e., 6- or 30-s) can be reliably used when testing male and female participants. With regards to training prescription, the 1:8 W:R ratio during cycling all-out training appears to be optimal when targeting adaptations associated with explosive, high-intensity, and endurance intensive efforts. If access to a cycle ergometer is not possible, though, then the UST performed on a 6-10% slope offers an effective and freely accessible alternative. Finally, recommendations for future research are also presented to facilitate further advancement on this topic.
... During exercise, the utilization of energy substrates and the accumulation of metabolic by-products leads to the transition between different exercise intensity domains [9]. The most commonly used exercise intensity domains are identified as moderate (below the gas exchange threshold (GET) (a non-invasive assessment of lactate threshold)), heavy (between GET and critical power (CP), and severe (above CP with the attainment of VO 2 peak) which are anchored by metabolic events [9]. ...
... During exercise, the utilization of energy substrates and the accumulation of metabolic by-products leads to the transition between different exercise intensity domains [9]. The most commonly used exercise intensity domains are identified as moderate (below the gas exchange threshold (GET) (a non-invasive assessment of lactate threshold)), heavy (between GET and critical power (CP), and severe (above CP with the attainment of VO 2 peak) which are anchored by metabolic events [9]. The metabolic response to exercise varies by the domain in which exercise is performed [9]. ...
... The most commonly used exercise intensity domains are identified as moderate (below the gas exchange threshold (GET) (a non-invasive assessment of lactate threshold)), heavy (between GET and critical power (CP), and severe (above CP with the attainment of VO 2 peak) which are anchored by metabolic events [9]. The metabolic response to exercise varies by the domain in which exercise is performed [9]. The moderate intensity domain is primarily characterized by blood lactate values and respiratory exchange ratios remaining at or near resting values during exercise, with VO 2 values rising but at a slower rate than the slow component of VO 2 and reaching a metabolic steady state within two to three minutes [9,10]. ...
Persons with multiple sclerosis (PwMS) experience a variety of physical impairments that can present in an asymmetrical pattern, resulting in significant differences between contralateral limbs (i.e., >10%). Asymmetries in PwMS have been associated with walking impairment and postural instability. Exercise intensity has been shown to influence the degree of asymmetry outcomes in healthy populations, and may have an impact on appropriate exercise prescriptions. The purpose of the current pilot study was to investigate the potential presence of asymmetry in metabolic events demarcating exercise intensity domains during single-leg cycling in PwMS. Five PwMS (Expanded Disability Status Scale range 2.0 to 4.5) completed a single leg incremental cycling test (SLICT) and a series of single-leg constant power time-to-exhaustion trials to determine gas exchange threshold (GET), peak oxygen consumption (VO2peak), peak power output (PPO), critical power (CP), and W’ (exercise tolerance above CP) for both lower limbs. Statistical analysis revealed no significant between-limb differences for VO2peak, GET, CP, PPO, and W’. Only W’ asymmetry score was significantly (49.5 ± 28.7 vs. 10.0, p = 0.04) greater than 10%. No significant differences between asymmetry scores at the GET, CP, and PPO were observed. Results from the current pilot investigation suggest that exercise intensity may not influence asymmetry outcomes in PwMS. Future studies with larger sample sizes and those with higher disability levels are required to fully understand the influence of exercise intensity on asymmetry in PwMS.
... The intensity of muscular contractions plays an important role in the development of neuromuscular fatigue and, therefore, has a significant effect on the consequent loss of force control. The critical torque (CT; analogous to the critical power measured during whole-body tasks) represents a critical neuromuscular fatigue threshold (or, as has recently been demonstrated, phase transition [54]) that separates the heavy and severe exercise domains [55,56]. During contractions performed above the CT, it is not possible to achieve a metabolic steady state, in contrast to contractions performed below it [56]. ...
... The critical torque (CT; analogous to the critical power measured during whole-body tasks) represents a critical neuromuscular fatigue threshold (or, as has recently been demonstrated, phase transition [54]) that separates the heavy and severe exercise domains [55,56]. During contractions performed above the CT, it is not possible to achieve a metabolic steady state, in contrast to contractions performed below it [56]. A consequence of this metabolic non-steady state is the development of peripheral fatigue~4-5 times faster above CT compared with below it [18,54,55]. ...
... A consequence of this metabolic non-steady state is the development of peripheral fatigue~4-5 times faster above CT compared with below it [18,54,55]. Indeed, metabolite-mediated peripheral is thought to be the dominant mechanism of MVC force losses above CT [56]. Thus, contraction intensity, specifically whether contractions are performed below or above the CT, can provide important insights into the mechanisms underpinning neuromuscular fatigue-induced loss of force control. ...
Neuromuscular fatigue is characterised not only by a reduction in the capacity to generate maximal muscle force, but also in the ability to control submaximal muscle forces, i.e., to generate task-relevant and precise levels of force. This decreased ability to control force is quantified according to a greater magnitude and lower complexity (temporal structure) of force fluctuations, which are indicative of decreased force steadiness and adaptability, respectively. The “loss of force control” is affected by the type of muscle contraction used in the fatiguing exercise, potentially differing between typical laboratory tests of fatigue (e.g., isometric contractions) and the contractions typical of everyday and sporting movements (e.g., dynamic concentric and eccentric contractions), and can be attenuated through the use of ergogenic aids. The loss of force control appears to relate to a fatigue-induced increase in common synaptic input to muscle, though the extent to which various mechanisms (afferent feedback, neuromodulatory pathways, cortical/reticulospinal pathways) contribute to this remains to be determined. Importantly, this fatigue-induced loss of force control could have important implications for task performance, as force control is correlated with performance in a range of tasks that are associated with activities of daily living, occupational duties, and sporting performance.
... Hazard scores below 1.5 and above 3 arbitrary units are associated with a reduction and an increase in the running speed, respectively [79]. Critical power delimits the transition between heavy and severe exercise intensity domains [80,81]. In the exercise above the critical power (i.e., severe-intensity domain), fatigue-related metabolites accumulate (e.g., inorganic phosphate and hydrogen ions) over time in the skeletal muscle [81][82][83], limiting the capacity to sustain the exercise for a prolonged time [81]. ...
... Critical power delimits the transition between heavy and severe exercise intensity domains [80,81]. In the exercise above the critical power (i.e., severe-intensity domain), fatigue-related metabolites accumulate (e.g., inorganic phosphate and hydrogen ions) over time in the skeletal muscle [81][82][83], limiting the capacity to sustain the exercise for a prolonged time [81]. Therefore, critical power is a valuable tool for continuous or interval endurance training prescription, and it is considered an important indicator of performance in endurance sports [80,81,84]. ...
... Critical power delimits the transition between heavy and severe exercise intensity domains [80,81]. In the exercise above the critical power (i.e., severe-intensity domain), fatigue-related metabolites accumulate (e.g., inorganic phosphate and hydrogen ions) over time in the skeletal muscle [81][82][83], limiting the capacity to sustain the exercise for a prolonged time [81]. Therefore, critical power is a valuable tool for continuous or interval endurance training prescription, and it is considered an important indicator of performance in endurance sports [80,81,84]. ...
The perceived exertion construct creation is a landmark in exercise physiology and sport science. Obtaining perceived exertion is relatively easy, but practitioners often neglect some critical methodological issues in its assessment. Furthermore, the perceived exertion definition, neurophysiological basis, and practical applications have evolved since the perceived exertion construct’s inception. Therefore, we revisit the careful work devoted by Gunnar Borg with psychophysical methods to develop the perceived exertion construct, which resulted in the creation of two scales: the rating of perceived exertion (RPE) and the category-ratio 10 (CR10). We discuss a contemporary definition that considers perceived exertion as a conscious perception of how hard, heavy, and strenuous the exercise is, according to the sense of effort to command the limbs and the feeling of heavy breathing (respiratory effort). Thus, other exercise-evoked sensations would not hinder the reported perceived exertion. We then describe the neurophysiological mechanisms involved in the perceived exertion genesis during exercise, including the influence of the peripheral feedback from the skeletal muscles and the cardiorespiratory system (i.e., afferent feedback) and the influence of efferent copies from the motor command and respiratory drive (i.e., corollary discharges), as well as the interaction between them. We highlight essential details practitioners should consider when using the RPE and CR10 scales, such as the perceived exertion definition, the original scales utilization, and the descriptors anchoring process. Finally, we present how practitioners can use perceived exertion to assess cardiorespiratory fitness, individualize exercise intensity prescription, predict endurance exercise performance, and monitor athletes’ responses to physical training.
... The hyperbolic relationship between power (P) and duration (T lim ) is a well-established framework for human performance modeling (4,22,23). Commercially available power meters greatly expanded the knowledge on the P-T lim relationship in competitive cycling by recording the maximal mean power output (MMP) over different durations and allowing the collection of a large amount of data from training, testing, and competition (14,25). Racing MMPs have been often collected without further modeling attempts, both in single-day events (6,18) and in multistage "Grand Tours" (7,26,30,37,38), with the main aim of quantifying the physical strain imposed by the race. ...
... Racing MMPs have been often collected without further modeling attempts, both in single-day events (6,18) and in multistage "Grand Tours" (7,26,30,37,38), with the main aim of quantifying the physical strain imposed by the race. When such modeling occurred, the 2-parameter (2-p) hyperbolic model was generally used, where the power asymptote (critical power [CP]) is the upper limit of the metabolic steady state (8,12), whereas the curvature constant (W9) is the amount of energy available above CP in the severe exercise-intensity domain (i.e., where maximal values of oxygen consumption, intramuscular metabolites, and blood lactate concentration are reached at exhaustion) (4,34). ...
... In so doing, performance with a T lim below 1-2 minutes is no more overestimated, whereas estimations of CP are comparable with that of 2-p (35). This allows 3-p to accurately describe performance not only in the severe but also in the extreme exercise-intensity domain, i.e., where T lim is so low that exhaustion occurs before of oxygen consumption and blood lactate concentration can reach their maximal values (4,35). Although only a few studies tested the 3-p in the extreme intensity domain, in particular with T lim , 60 seconds (27,35), they promisingly showed a well-preserved goodness of fit to experimental data up to a T lim of 20 (35) to 1 second (27). ...
Vinetti, G, Pollastri, L, Lanfranconi, F, Bruseghini, P, Taboni, A, and Ferretti, G. Modeling the power-duration relationship in professional cyclists during the Giro d'Italia. J Strength Cond Res XX(X): 000-000, 2022-Multistage road bicycle races allow the assessment of maximal mean power output (MMP) over a wide spectrum of durations. By modeling the resulting power-duration relationship, the critical power (CP) and the curvature constant (W') can be calculated and, in the 3-parameter (3-p) model, also the maximal instantaneous power (P0). Our aim is to test the 3-p model for the first time in this context and to compare it with the 2-parameter (2-p) model. A team of 9 male professional cyclists participated in the 2014 Giro d'Italia with a crank-based power meter. The maximal mean power output between 10 seconds and 10 minutes were fitted with 3-p, whereas those between 1 and 10 minutes with the 2- model. The level of significance was set at p < 0.05. 3-p yielded CP 357 ± 29 W, W' 13.3 ± 4.2 kJ, and P0 1,330 ± 251 W with a SEE of 10 ± 5 W, 3.0 ± 1.7 kJ, and 507 ± 528 W, respectively. 2-p yielded a CP and W' slightly higher (+4 ± 2 W) and lower (-2.3 ± 1.1 kJ), respectively (p < 0.001 for both). Model predictions were within ±10 W of the 20-minute MMP of time-trial stages. In conclusion, during a single multistage racing event, the 3-p model accurately described the power-duration relationship over a wider MMP range without physiologically relevant differences in CP with respect to 2-p, potentially offering a noninvasive tool to evaluate competitive cyclists at the peak of training.
... The inability to achieve an oxygen consumption steady-state due to the increased cardiovascular strain from severe intensity exercise, resulting in higher accumulations of blood lactate and eventual exercise cessation (Burnley & Jones, 2018;Burnley et al., 2012). ...
... Moderate-intense exercise is performed below the LT and is characterized by a V O2 steady state within approximately two to three minutes of the onset of exercise (Burnley & Jones, 2018). The production and clearance of lactate below the LT during moderateintensity exercise indicates sufficient energy production from both the aerobic and anaerobic systems, resulting in high potential volumes/distances performed (Burnley & Jones, 2018;Poole et al., 2020). ...
... Moderate-intense exercise is performed below the LT and is characterized by a V O2 steady state within approximately two to three minutes of the onset of exercise (Burnley & Jones, 2018). The production and clearance of lactate below the LT during moderateintensity exercise indicates sufficient energy production from both the aerobic and anaerobic systems, resulting in high potential volumes/distances performed (Burnley & Jones, 2018;Poole et al., 2020). Heavy-intensity exercise is above the LT but below the CP/CV thresholds, resulting in higher V O2 needs, faster-accumulating central and peripheral fatigue, and a V O2 steady-state within approximately 10-20 minutes (Burnley & Jones, 2018;Poole et al., 2020). ...
As performance and competition levels increase in soccer, so does the need for efficient training programs. High-intensity interval training is an effective exercise modality that can improve both the aerobic and anaerobic energy systems, but its efficacy in well-trained soccer players is unknown. The purpose of this study was to evaluate a bodyweight high-intensity interval training program and its effects on critical velocity via a 50-meter 3-minute all-out test and maximal sprint speed by a 40-yard dash in well-trained soccer players during the competitive season. The experimental subjects performed a progressive series of exercises consisting of backward sprints, lower body plyometrics, and an alternating series of sprints/walking, twice per week for four consecutive weeks, in addition to their regular practice and match schedules. A 2 x 2 ANOVA was used for both performance tests, along with the smallest worthwhile change and smallest real difference to measure practical significance. No statistically significant differences were found between time or groups for the 40-yard dash or 50-m 3-minute all-out tests; however, significant small and trivial interactions were found, respectively. Considerable differences between both groups were also observed regarding the smallest worthwhile change and smallest real differences for both performance tests. The results obtained can serve as a practical option for strength and conditioning coaches to improve sprinting and critical velocity in well-trained soccer players within a four-week in-season training period, along with foundations for future replication or follow-up research to further determine the training program’s effectiveness.
... Skinner and Mclellan 8 already classified intensities into three phases related to the physiological responses observed during exercise with progressively increasing intensity. However, Burnley and Jones 9 are currently proposing four intensity domains to explain bioenergetic responses to exercise and how they relate to task failure. This refers to the point that a participant cannot or does not want to continue a physical task. ...
... This refers to the point that a participant cannot or does not want to continue a physical task. 9 These four intensity domains are marked out by three physiological milestones (lactate threshold (LT), critical power/velocity (PC/VC) and maximum oxygen consumption (VO 2max )), that will separate the sustainable entities for hours, even minutes or seconds: moderate intensity (power or velocity below the LT), heavy (power or speed between LT and PC/VC), severe (power or speed over the PC/VC that can be sustained until the VO 2max is reached), and extreme (power or velocity over VO 2max ). 9 The moderate intensity field includes intensities under the LT (between 50-60% of the VO 2max in young subjects and between 70-80% in highly-trained subjects). 10 These intensities can be sustained beyond 3 hours (e.g. ...
... 9 These four intensity domains are marked out by three physiological milestones (lactate threshold (LT), critical power/velocity (PC/VC) and maximum oxygen consumption (VO 2max )), that will separate the sustainable entities for hours, even minutes or seconds: moderate intensity (power or velocity below the LT), heavy (power or speed between LT and PC/VC), severe (power or speed over the PC/VC that can be sustained until the VO 2max is reached), and extreme (power or velocity over VO 2max ). 9 The moderate intensity field includes intensities under the LT (between 50-60% of the VO 2max in young subjects and between 70-80% in highly-trained subjects). 10 These intensities can be sustained beyond 3 hours (e.g. ...
Review Resumen El ejercicio físico induce un aumento de la temperatura corporal que se ve influenciado por la intensidad de este, además de por las condiciones de estrés térmico en las que se realice. La relación potencia/velocidad-duración (PD/VD) muestra cómo el tiempo que un ejercicio puede ser mantenido depende de la potencia o velocidad producida, pudiendo diferenciarse 4 dominios de intensidad que estarán delimitados por el umbral láctico (LT), la potencia/velocidad crítica (PC/VC) y el consumo máximo de oxígeno (VO 2max). Esta revisión tiene como objetivo analizar los efectos del estrés térmico sobre el rendimiento en los diferentes dominios de intensidad-duración, así como identificar los principales mecanismos fisiológicos responsables. En los dominios de intensidad moderado (por debajo del LT) y duro (entre LT y PC/VC), el calor perjudica el rendimiento en los ejercicios que comprenden duraciones de ~40 min hasta por encima de 3h, siendo los mecanismos centrales y la depleción del glucógeno los principales contribuyentes a esa fatiga. En el dominio severo (por encima de la PC/VC), el calor afecta negativamente al rendimiento de los ejercicios máximos que van de los ~25 a ~2 min de duración, siendo los factores cardiovasculares y periféricos los limitantes principales. Sin embargo, en el dominio extremo (por encima del VO 2max), el calor se ha visto como un elemento clave en la consecución de mejores registros de rendimiento en esfuerzos máximos inferiores a ~2 min de duración, debiéndose estas mejoras a factores centrales y de disponibilidad energética. El calor influye en gran medida en el rendimiento de los deportes de resistencia, acelerando el fracaso de la tarea en aquellos que tienen duraciones superiores a los ~2 min, y favoreciendo aquellos de duraciones inferiores. Conocer estos mecanismos de actuación puede ayudarnos a identificar distintas estrategias para reducir o aprovechar sus efectos durante el entrenamiento y la competición. Palabras clave: Resistencia. Rendimiento. Fatiga. Hipertermia. Fisiología. Revisión. Summary Physical exercise induces an increase in body temperature that is influenced by the exercise intensity, as well as by the heat stress conditions in which it is performed. Power/velocity-duration relationship (PD-VD) shows how long an exercise can be sustained depending on the power output or the velocity output. Four intensity domains can be differentiated, which will be delimited by the lactic threshold (LT), the critical power/velocity (CP/CV) and the maximum oxygen consumption (VO 2max). This review aims to analyze the effects of heat stress on performance in the different intensity-duration domains, as well as to identify the main physiological mechanisms responsible. In the moderate (below LT) and hard (between LT and CP/CV) intensity domains, heat impairs the performance of exercises ranging from ~40min to over 3h, with central mechanisms and glycogen depletion being the major contributors to this fatigue. In the severe domain (above CP/CV), heat negatively affects the performance of maximum exercises ranging from ~25 to ~2 min duration, with cardiovascular and peripheral factors being the main limitations. However, in the extreme domain (above VO 2max), heat has been considered as a key element in achieving better performance records in maximum efforts of less than 2 min, associating these improvements with central and energy availability factors. Heat greatly influences the performance of endurance sports, accelerating task failure in those efforts longer than ~2 min, and favoring those with shorter durations. Knowing these mechanisms of action can help us to identify different strategies to reduce or take advantage of their effects during training and competition. Efectos del calor en el rendimiento en deportes de resistencia en los diferentes dominios de intensidad-duración: artículo de revisión
... The current study determined maximal power output and neuromuscular fatigue resistance of the KE under isotonic conditions (maximal effort isotonic "power" contractions) along with various indices of fatigue, such as maximal voluntary contraction (MVC) torque, evoked torque, surface electromyography (EMG), and muscle stiffness evaluated by muscle shear modulus (e.g., Akagi et al., 2019), before, during, and after a fatigue task for older men. Furthermore, to better understand the association between prefatigue maximal power output and neuromuscular fatigue resistance, individual differences in the relationship between power and reciprocals of the number of contractions during the fatiguing task were investigated with reference to previously reported power-duration relationships (Burnley & Jones, 2018;Neder et al., 2000;Poole et al., 2016). It was hypothesized that older people with a higher prefatigue power output have greater neuromuscular fatigue resistance. ...
... At Pre and the 46th-50th contractions, RMS-EMGs of the RF, VL, VM, and BF were also evaluated. Furthermore, a relationship between power and number of contractions was investigated for each participant with reference to previously reported power-duration relationships (Burnley & Jones, 2018;Neder et al., 2000;Poole et al., 2016). The torque and angle data were obtained using a dynamometer (CON-TREX MJ, Physiomed), and the EMG was assessed using a standard EMG system (Bagnoli 8 EMG System, DELSYS). ...
... Previous studies (Burnley & Jones, 2018;Neder et al., 2000;Poole et al., 2016) have reported that the hyperbolic powerduration relationship (y-axis: power; x-axis: time) can be transformed into a linear relationship (y-axis: power, x-axis: 1/time). Here, the slope and the intercept are considered to be the curvature constant (fatigability constant) and the critical power (fatigue threshold) of the power-duration relationship, respectively (Poole et al., 2016). ...
This study investigated associations of fatigue resistance determined by an exercise-induced decrease in neuromuscular power with prefatigue neuromuscular strength and power of the knee extensors in 31 older men (65-88 years). A fatigue task consisted of 50 consecutive maximal effort isotonic knee extensions (resistance: 20% of prefatigue isometric maximal voluntary contraction torque) over a 70° range of motion. The average of the peak power values calculated from the 46th to 50th contractions during the fatigue task was normalized to the prefatigue peak power value, which was defined as neuromuscular fatigue resistance. Neuromuscular fatigue resistance was negatively associated with prefatigue maximal power output (r = -.530) but not with prefatigue maximal voluntary contraction torque (r = -.252). This result highlights a trade-off between prefatigue maximal power output and neuromuscular fatigue resistance, implying that an improvement in maximal power output might have a negative impact on neuromuscular fatigue resistance.
... The most comprehensive way to measure exercise tolerance is by measuring the maximum duration that a broad range of power outputs can be sustained in the severe intensity domain [i.e., power-duration relationship (PDR)] (13). The relationship between power output and duration is hyperbolic, with the maximum duration of exercise decreasing exponentially beyond a certain intensity. ...
... W 0 is strongly related to the amount of metabolic disturbance that can be tolerated (14)(15)(16). Some of the most influential components determining an individual's capacity to perform exercise across the PDR are an individual's cardiovascular and muscular systems, and their mediating effects on V _ O 2max , known determinants of CP, and fatigability (13). To date, very few studies have investigated sex differences in the shape of the PDR, described by CP and W 0 (17,18). ...
Purpose:
To investigate the effect of the menstrual cycle (MC) on exercise performance across the power-duration relationship (PDR). We hypothesized females would exhibit greater variability in the PDR across the MC than males across a similar timespan, with critical power (CP) and Work-prime (W') being lower during the early follicular phase than the late follicular and mid-luteal phases.
Methods:
Seven eumenorrheic, endurance-trained female adults performed multiple constant-load-to-task-failure and maximum-power tests at three time points across the MC (early follicular, late follicular, mid-luteal phases). Ten endurance-trained male adults performed the same tests approximately 10 days apart.
Results:
No differences across the PDR were observed between MC phases (CP: 186.74 ± 31.00 W, P = 0.955, CV = 0.81 ± 0.65 %) (W': 7,961.81 ± 2,537.68 J, P = 0.476, CV = 10.48 ± 3.06 %). CP was similar for male and female subjects (11.82 ± 1.42 W • kg-1 vs. 11.56 ± 1.51 W • kg-1, respectively) when controlling for leg lean mass. However, W' was larger (P = 0.047) for male subjects (617.28 ± 130.10 J • kg-1) than female subjects (490.03 ± 136.70 J • kg-1) when controlling for leg lean mass.
Conclusion:
MC phase does not need to be controlled when conducting aerobic endurance performance research on eumenorrheic female subjects without menstrual dysfunction. Nevertheless, several sex differences in the power-duration relationship exist, even after normalizing for body composition. Therefore, previous studies describing the physiology of exercise performance in male subjects may not perfectly describe that of female subjects.
... During high-intensity exercise, several neural mechanisms cooperate to sustain muscle activity and delay the development of neuromuscular fatigue. Throughout the years, several concepts have been proposed in order to understand the metabolic and neural mechanisms determining exercise tolerance (1)(2)(3)(4). Among these, the sensory tolerance limit theory postulates that central motor drive and associated corollary discharges, and feedback (i.e., afferent activity) mechanisms, both contribute to achieving a threshold at which exercise becomes unsustainable (1,5). ...
... Factors that may contribute to limitations in endurance performance are O 2 delivery and utilization (3,48). The observation that R and V E (i.e., central factors) as well as femoral blood flow and TOI (i.e., peripheral factors) were similar between all conditions at exhaustion ( Figure 4), represent indirect evidence that convective O 2 transport and utilization were likely similar between the three conditions, and therefore not the root cause of the widely different time to exhaustion between pre-fatigue conditions and control. ...
... Then, by smoothly connecting the points, we can find the relationship between power and duration and conclude the power profile. Power is inversely proportional to duration due to lactate tolerance and maximum lactate capacity [2]. When the duration approaches infinity, the average maximum power the cyclists can maintain is around FTP. Hence, the relationship between power and duration is approximately an inverse proportional function with a constant. ...
... Moreover, the rolling friction is proportional to the support force. 2 1 2 ...
Individual Time Trial (ITT) is a road bicycle race where cyclists race alone against the clock. To minimize the total time cost, cyclists need to focus on the output power. In this paper, we develop models to analyze the output power of cyclists determine how to adjust the output power at every position of the course. Firstly, this article collects the real data of cyclists, which is used to find the power profile related to power and duration. Reasonable expressions of different types of cyclists of different gender are also concluded. Secondly, this article considers the cyclists in competition as a constantly charged battery and discharged. FTP is the power at which cyclists can work steadily for a long time. Therefore, this article uses FTP to represent the recovery rate of cyclists approximately. There is two basis of our model. First, maintaining a steady speed is the key to reducing the total time loss in the time trial. The next basis of our model is to divide the course into three types: uphill, downhill, and sharp turn and do the force analysis. Then, this article builds up a model which tells the cyclists how to adjust output power in the whole time trial. Fatigue is also considered in our model. the model applies to two real Individual Time Trials and one course designed by us and draws the power-distance curve correspondingly. Finally, this article analyzes the potential impact of the wind. The wind will affect the cyclists' air resistance fA. The time cost at every part is calculated to determine the proposed model's accuracy. This article also analyzes the impact of improper power adjustment.
... Noteworthy, Burnley and Jones [17] investigated the duration-power relationship describing three intensity domains (i.e., power zones) with different physiological events explaining the onset of fatigue for each of them. While moderate-intensity exercise (i.e., below aerobic threshold) can be sustained for more than three hours and fatigue appears to have its origin in the central nervous system, a severe-intensity activity (i.e., above Critical Power) is only tolerable up to 40 min and metabolite-mediated processes seem to trigger the subsequent peripheral fatigue. ...
... Amidst these power domains, the inability to endure heavy-intensity tasks (i.e., above lactate threshold but below critical power) is explained by a combination of central and peripheral physiological phenomenon. These physiological boundaries highly depend upon the athlete aerobic profile and, as stated previously [17], need to be set on an individual basis. ...
Background
The advent of power meters for running has raised the interest of athletes and coaches in new ways of assessing changes in running performance. The aim of this study is to determine the changes in power-related variables during and after a strenuous endurance running time trial.
Methods
Twenty-one healthy male endurance runners, with a personal record of 37.2 ± 1.2 min in a 10-km race, completed a 1-h run on a motorized treadmill trying to cover as much distance as they could. Before and after the time trial the athletes were asked to perform a 3-min run at 12 km h ⁻¹ . Normalized mean power output, step frequency, form power and running effectiveness were calculated using the Stryd™ power meter. Heart rate (HR) and rating of perceived exertion (RPE) were monitored, and data averaged every 5 min.
Results
Despite high levels of exhaustion were reached during the time trial (HRpeak = 176.5 ± 9.8 bpm; RPE = 19.2 ± 0.8), the repeated measures ANOVA resulted in no significant differences ( p ≥ 0.05), between each pair of periods for any of the power-related variables. The pairwise comparison ( T test) between the non-fatigued and fatigued constant 3-min runs showed an increase in step frequency ( p = 0.012) and a decrease in form power ( p < 0.001) under fatigue conditions, with no meaningful changes in normalized mean power output and running effectiveness.
Conclusions
Trained athletes are able to maintain power output and running effectiveness during a high demanding extended run. However, they preferred to reduce the intensity of vertical impacts under fatigue conditions by increasing their step frequency.
... During high-intensity exercise, several neural mechanisms cooperate to sustain muscle activity and delay the development of neuromuscular fatigue. Throughout the years, several concepts have been proposed in order to understand the metabolic and neural mechanisms determining exercise tolerance (1)(2)(3)(4). Among these, the sensory tolerance limit theory postulates that central motor drive and associated corollary discharges, and feedback (i.e., afferent activity) mechanisms, both contribute to achieving a threshold at which exercise becomes unsustainable (1,5). ...
... Factors that may contribute to limitations in endurance performance are O 2 delivery and utilization (3,48). The observation that R and V E (i.e., central factors) as well as femoral blood flow and TOI (i.e., peripheral factors) were similar between all conditions at exhaustion ( Figure 4), represent indirect evidence that convective O 2 transport and utilization were likely similar between the three conditions, and therefore not the root cause of the widely different time to exhaustion between pre-fatigue conditions and control. ...
Purpose: This study evaluated whether central motor drive during fatiguing exercise plays a role in determining performance and the development of neuromuscular fatigue during a subsequent endurance task.
Methods: On separate days, 10 males completed 3 constant-load (80% peak-power output), single-leg knee-extension trials to task failure in a randomized fashion. One trial was performed without pre-existing quadriceps fatigue (CON), and 2 trials were performed with pre-existing, quadriceps fatigue induced either by voluntary (VOL; involving central motor drive) or electrically-evoked (EVO; without central motor drive) quadriceps contractions (~20% maximal voluntary contraction (MVC)). Neuromuscular fatigue was assessed via pre-post changes in MVC, voluntary activation (VA), and quadriceps potentiated twitch force (Qtw,pot). Cardiorespiratory responses and rating of perceived exertion were also collected throughout the sessions. The two pre-fatiguing protocols were matched for peripheral fatigue and stopped when Qtw,pot declined by ~35%.
Results: Time-to-exhaustion was shorter in EVO (4.3 ± 1.3 min) and VOL (4.7 ± 1.5 min) compared to CON (10.8 ± 3.6 min, p < 0.01) with no difference between EVO and VOL. ΔMVC (EVO:-47 ± 8%, VOL:-45 ± 8%, CON:-53 ± 8%), ΔQtw,pot (EVO:-65 ± 7%, VOL:-59 ± 14%, CON:-64 ± 9%), ΔVA (EVO:-9 ± 7%, VOL:-8 ± 5%, CON:-7 ± 5%) at the end of the dynamic task were not different between conditions (all p > 0.05). Compared to EVO (10.6 ± 1.7) and CON (6.8 ± 0.8), rating of perceived exertion was higher (p = 0.05) at the beginning of VOL (12.2 ± 1.0).
Conclusions: These results suggest that central motor drive involvement during prior exercise plays a negligible role on the subsequent endurance performance. Therefore, our findings indicate that peripheral fatigue-mediated impairments are the primary determinants of high-intensity single-leg endurance performance.
... Thus, different exercise speed/power throughout Sprint and Olympic triathlons might produce different levels of central and peripheral fatigue after each exercise modality, but there is currently no experimental data supporting this assumption. Due to its short distance, the average speed/power might be above the critical speed (CS) or respiratory compensation point (RCP) in the Sprint triathlon, which could increase peripheral fatigue (Black et al., 2017;Burnley & Jones, 2018;Thomas, Elmeua, Howatson, & Goodall, 2016). On the other hand, due to its long distance, the average speed/power might be below the CS/RCP in Olympic triathlon (Aoyagi, Ishikura, & Nabekura, 2021;Burnley & Jones, 2018), where central fatigue is higher, and the peripheral fatigue is lower than exercise above CS/RCP (Krüger, Aboodarda, Jaimes, Samozino, & Millet, 2019;Thomas et al., 2016). ...
... Due to its short distance, the average speed/power might be above the critical speed (CS) or respiratory compensation point (RCP) in the Sprint triathlon, which could increase peripheral fatigue (Black et al., 2017;Burnley & Jones, 2018;Thomas, Elmeua, Howatson, & Goodall, 2016). On the other hand, due to its long distance, the average speed/power might be below the CS/RCP in Olympic triathlon (Aoyagi, Ishikura, & Nabekura, 2021;Burnley & Jones, 2018), where central fatigue is higher, and the peripheral fatigue is lower than exercise above CS/RCP (Krüger, Aboodarda, Jaimes, Samozino, & Millet, 2019;Thomas et al., 2016). In addition, as running may be performed at higher intensities in Sprint than Olympic triathlon, the documented peripheral fatigue recovery after running when completed after cycling (Pageaux et al., 2017) might be lower in Sprint than Olympic triathlon. ...
This study compared central and peripheral fatigue development between the Sprint and Olympic distance triathlon. Fifteen male triathletes performed Sprint and Olympic triathlon simulations in a randomized and counterbalanced order. Central and peripheral fatigue was evaluated from changes in voluntary activation level (VAL) and twitch responses of quadriceps muscle (Qtw,pot), respectively. Qtw,pot reduced from baseline to post-swimming similarly between triathlon simulations (Sprint,−17±11%; Olympic, −13±9%). In post-cycling, Qtw,pot further declined to a similar extent between triathlon distances (Sprint, −31±15%; Olympic, −28±11%). In post-running, Qtw,pot was fully recovered in the Olympic triathlon (−4±10%), whereas there was only a partial recovery of Qtw,pot in the Sprint triathlon (−20±11%). VAL was not reduced in post-swimming, but reduction was similar between triathlon distances in post-cycling (Sprint, −10±9%; Olympic, −8±8%) and post-running (Sprint, −15±14%; Olympic, −16±8%). In the Sprint triathlon, the swimming speed (1.07±0.13m.s⁻¹) was above (p <.001) critical speed (1.01±0.14m.s⁻¹), the cycling power (179.7±27.2W) was below the respiratory compensation point (216.3±27.8W, p <.001) and running speed (13.7±1.05km.h⁻¹) similar to the respiratory compensation point (13.2±0.70km.h⁻¹, p =.124). In the Olympic triathlon, swimming speed (1.03±0.13m.s⁻¹) was similar to critical speed (p =.392), and cycling power (165.3±27.3W) and running speed (12.6±1.05km.h⁻¹) were below the respiratory compensation point (p ≤.007). In conclusion, peripheral fatigue progressed until post-cycling regardless of triathlon distances. However, peripheral fatigue was fully recovered after running in Olympic but not in Sprint triathlon. The central fatigue started in post-cycling and progressed until post-running regardless of triathlon distances.
• Highlights
• The quadriceps muscle peripheral fatigue progresses similarly in Sprint and Olympic triathlons until post-cycling.
• The quadriceps muscle peripheral fatigue is completely recovered after running in the Olympic triathlon, whereas it is partially recovered in the Sprint triathlon.
• The central fatigue starts in post-cycling and progresses similarly until post-running in Sprint and Olympic triathlons, regardless of triathlon distances.
... 15 All riders were informed about the importance of the zero calibration of power meters and were instructed to do the zero calibration before every ride. The field-derived physical performance parameters considered were RPOs over different time durations (10 s, 1 min, 5 min, and 20 min) and RPOs after certain amounts of work done (10,20,30,40, and 50 kJ·kg −1 ). For each of these parameters, the highest value of the season was considered. ...
... Furthermore, the same levels of prior accumulated work can be reached through different duration and intensity efforts. As the physiological mechanisms (central and/or peripheral) linked to fatigue depend on the intensity domain in which exercise is performed, 30 we cannot exclude that the same amount of work completed at different intensities lead to a different percentage decline in power output (ie, fatigue resistance). In this scenario, the higher percentage decline in RPOs after the different levels of work observed in JUN compared with both U23 and PRO could be a Figure 4 -Differences in percentage decline of record power outputs after 10, 20, 30, 40, and 50 kJ·kg −1 between high-ranked JUN, U23, and PRO climbers. ...
Purpose: To investigate the relationship of field-derived power and physical performance parameters with competition success in road cycling climbing specialists of age-related categories and to explore cross-sectional differences between high-ranked (HIGHR) climbing specialists of each category. Methods: Fifty-three male climbers participated in this study (junior [JUN], n = 15; under 23 [U23], n = 21; professional [PRO], n = 17). Training and racing data collected during the 2016–19 competitive seasons were retrospectively analyzed for record power outputs (RPOs) and RPOs after prior accumulated work. Results: In JUN, body mass, absolute RPOs, and relative RPOs were higher in HIGHR compared with low ranked (d = 0.97–2.20, large; P = .097–.001); in U23 and PRO, the percentage decrease in RPOs after 20, 30, 40, and 50 kJ·kg−1 was less in HIGHR compared with low ranked (d = 0.77–1.74, moderate–large; P = .096–.004). JUN HIGHR presented lower absolute and relative RPO-
20 min (η2p = .34 − .38, large; P = .099–.001) and higher percentage decrease in RPOs after prior accumulated work compared with U23 and PRO HIGHR (η2p = .28 − .68, large; P = .060–.001); percentage decrease in RPOs after prior accumulated work was the only parameter differentiating U23 and PRO HIGHR, with PRO declining less in relative RPO-1 min, RPO-5 min, and RPO-20 min after 20 to 50 kJ·kg−1 (η2p = .28 − .68, large; P = .090–.001). Conclusions: Superior absolute and relative RPOs characterize HIGHR JUN climbing specialists. Superior fatigue resistance differentiates HIGHR U23 and PRO climbers
compared with low ranked, as well as PRO versus U23 climbers.
... 12 In the development of neuromuscular fatigue, the percentage contribution of central (ie, limitation of the synaptic input to the motoneuronal pool) and peripheral (impaired excitation-contraction coupling in muscle fibers) factors varies, depending on exercise intensity and duration. 13 Central fatigue is more exacerbated when exercise duration increases and exercise intensity decreases, whereas peripheral fatigue is more pronounced under opposite circumstances. 14,15 However, it is not clear whether the ergogenic effects of bilateral HD-tDCS over the DLPFC observed by Pollastri et al 10 in a 15-to 20-minute cycling TT could be extended also to a shorter cycling TT performed at the upper limit of severe-intensity exercise domain (2-4 min of duration). ...
... The fact that a central neuromodulator technique like HD-tDCS might improve performance was unexpected. In fact, peripheral fatigue is greater than central fatigue in these kinds of maximal efforts, 13 and the vast majority of physiological factors positively correlating with a superior performance in the upper limit of severeintensity exercise could be found within the muscles (ie, intracellular pH regulation, 27 Na + -K + pump β1-subunit expression, 28 muscle capillarity density, 28 skeletal muscle carnosine content, 29 rate of phosphocreatine resynthesis 30 ). This suggests that central fatigue may contribute to determining performance even at the upper limit of the severe-intensity exercise domain. ...
Purpose:
To investigate the effects of bilateral dorsolateral prefrontal cortex high-definition transcranial direct-current stimulation (HD-tDCS) on physiological and performance responses during exercise at the upper limit of the severe-intensity exercise domain in elite-level road cyclists.
Methods:
Eleven elite-level road cyclists (VO2peak: 71.8 [3.1] mL·kg-1·min-1) underwent the HD-tDCS or SHAM condition in a double-blind, counterbalanced, and randomized order. After 20 minutes of receiving either HD-tDCS on dorsolateral prefrontal cortex (F3 and F4) or SHAM stimulation, participants completed a 10-minute constant-load trial (CLT1) at 90% of the first ventilatory threshold and a 2-minute CLT (CLT2) at peak power output. Thereafter, they performed a simulated 2-km time trial (TT). Maximal oxygen uptake, respiratory exchange ratio, heart rate, and rating of perceived exertion were recorded during CLT1 and CLT2, whereas performance parameters were recorded during the TT.
Results:
In 6 out of 11 cyclists, the total time to complete the TT was 3.0% faster in HD-tDCS compared to SHAM. Physiological and perceptual variables measured during CLT1 and CLT2 did not change between HD-tDCS and SHAM.
Conclusions:
HD-tDCS over the dorsolateral prefrontal cortex seemed to improve cycling TT performance within the upper limit of the severe-intensity exercise domain, suggesting that an upregulation of the prefrontal cortex could be critical even in this exercise intensity domain. However, the limited dimension and the high interindividual variability require further studies to test these putative ergogenic effects.
... During severe-intensity endurance exercise accurate prediction of performance can be obtained using the hyperbolic relationship between exercise duration and work rate (Monod & Scherrer, 1965;Moritani et al., 1981;Poole et al., 1988;Jenkins & Quigley, 1991;Hill et al., 2002;Chidnok et al., 2012;2013;Black et al., 2014). In cycling, this relationship is mathematically determined by two parameters: the critical power which represents the asymptote of the hyperbolic relationship and corresponds to the limit between the heavy and severe intensity domains, and the curvature constant (W') which represents a fixed amount of work that can be performed above the critical power (Poole et al., 1988;Burnley & Jones, 2016;Black et al., 2017). Because task failure in the severe intensity domain (i.e. ...
... This result contrast with our previous findings showing an accelerated recovery for MVC peak force and VA following a 10 min time-trial compared to a 1 min timetrial (Ducrocq et al., 2021). This discrepancy might be explained by the fact that the 1 min time-trial belong to the extreme intensity domain (Burnley & Jones, 2016) and might elicit a different fatigue response than exercise tests performed in the severe intensity (such as the ones performed in the present study). For example, the greater reduction in MVC was observed immediately after exercise termination (i.e. 10 s) following the 3minTT while MVC progressively decreased during the first part of the recovery period (i.e. up to 2 min) after the 1 min time trial in our previous experiment (Ducrocq et al., 2021). ...
New findings:
What is the central question of this study? Does the work done above critical power (W') or muscle activation determine the degree of peripheral fatigue induced by cycling time-trials performed in the severe intensity domain? What is the main finding and its importance? We found that peripheral fatigue increased when power output and muscle activation increased whereas W' did not change between the time-trials. Therefore, no relationship was found between W' and exercise-induced peripheral fatigue such as previously postulated in the literature. In contrast, we found a significant association between EMG amplitude during exercise and exercise-induced reduction in the potentiated quadriceps twitch, suggesting that muscle activation plays a key role in determining peripheral fatigue during severe intensity exercise.
Abstract:
In order to determine the relationship between peripheral fatigue, muscle activation and the total work done above critical power (W'), ten men and four women performed, on separated days, self-paced cycling time-trials of 3, 6, 10, and 15 min. Exercise-induced quadriceps fatigue was quantified using pre- to post-exercise (15 s through 15 min recovery) changes in maximal voluntary contraction peak force (MVC), voluntary activation (VA) and potentiated twitch force (QT). VA was measured using the interpolated twitch technique, and QT was evoked by electrical stimulations of the femoral nerve. Quadriceps muscle activation was determined using the root mean square of surface electromyography of vastus lateralis (VLRMS ), vastus medialis (VMRMS ) and rectus femoris (RFRMS ). Critical power and W' were calculated from the power/duration relationship from the four time-trials. Mean power output and mean VLRMS , VMRMS and RFRMS were greater during shorter compared to longer exercises (P<0.05) whereas no significant between-trials change in W' was found. The magnitude of exercise-induced reductions in QT increased with the increase in power output (P<0.001) and were associated with mean VLRMS and VMRMS (P<0.001, r2 >0.369) but not W' (P>0.150, r2 <0.044). Reduction in VA tended (P = 0.067) to be more pronounced with the lengthening in time-trial duration while no significant between-trials change in MVC were found. Our data suggest that peripheral fatigue is not related to the amount of work done above the critical power but rather to the level of muscle activation during exercise the severe intensity domain. This article is protected by copyright. All rights reserved.
... The physiological response to exercise varies as a function of the intensity at which it is performed. 17 These responses have been characterized into exercise intensity domains, 17,18 which are delineated by specific physiological thresholds. The moderate intensity domain refers to intensities below the so-called first lactate threshold, defined as the intensity after which there is a sustained increase in blood lactate concentration above resting values (LT1). ...
... The physiological response to exercise varies as a function of the intensity at which it is performed. 17 These responses have been characterized into exercise intensity domains, 17,18 which are delineated by specific physiological thresholds. The moderate intensity domain refers to intensities below the so-called first lactate threshold, defined as the intensity after which there is a sustained increase in blood lactate concentration above resting values (LT1). ...
Purpose
The desire-goal motivational conflict helps explain endurance performance, however, the physiological concomitants are unknown. The present study examined disturbances in desire to reduce effort and performance goal value across moderate, heavy, and severe exercise intensity domains, demarcated by the first (LT1) and second (LT2) lactate thresholds. In addition, the within-person relationships between blood lactate concentration, heart rate and desire-goal conflict were examined.
Methods
Thirty participants (53% female, Mage = 21.03 years; SD = 2.06 years) completed an incremental cycling exercise test, in which work-rate was increased by 25 watts every four minutes, until voluntary exhaustion or sufficient data from the severe intensity domain had been collected. Desire to reduce effort, performance goal value, blood lactate concentration (for determination of LT1 and LT2) and heart rate were measured at the end of each stage and analyzed using multilevel models.
Results
The desire to reduce effort increased over the exercise test with additional shifts and accelerations after each lactate threshold. The performance goal did not show general declines, nor did it shift at LT1. However, the performance goal value shifted at LT2, and the rate of change increased at both thresholds. Within-person variation in blood lactate concentration positively correlated with the desire to reduce effort and negatively correlated with the performance goal. Within-person variation in heart rate correlated with desire to reduce effort but not the performance goal.
Conclusion
Transitioning through both lactate thresholds are important phases for motivation during progressive exercise, particularly for the desire to reduce effort. Within-person variation in blood lactate concentration is more influential for motivation, compared to heart rate.
... The glycogen could be broken down to glucose and used for energy during prolonged exercise, and its content could reflect the degree of fatigue (Burnley et al. 2018). The in vitro study in C2C12 myoblasts showed that the PAP could increase glycogen content, so we further investigated the effect of PAP on glycogen contents in vivo. ...
The polysaccharides were isolated from apple
pomace by hot-water extraction, and their anti-fatigue activity
was evaluated in C2C12 muscle myoblasts and male
Kunming mice. The purified polysaccharides from apple
pomace (PAP) have a molecular weight of 1.74 × 105
Da and
were composed of mannose, rhamnose, glucose, galactose
and arabinose. In C2C12 myoblasts, PAP showed no cytotoxicity
in the concentrations of 0–300 μg/ml. PAP treatment
increased the glycogen content, while the ATP content was
not affected in C2C12 myoblasts. Further investigation found
that the activity and gene expression of glycogen synthase,
rather than glycogen phosphorylase, were upregulated by
PAP treatment. The studies in vivo showed that PAP treatment
did not affect the food intake and weight again in mice.
Importantly, PAP prolonged the exhaustive swimming time,
increased hepatic and skeletal muscle glycogen levels, and
effectively inhibited the accumulation of blood lactic and
blood urea nitrogen in mice. Taken together, the results
suggested that PAP exhibit anti-fatigue activity in vitro and
in vivo through increasing glycogen content.
... It was surprising that high-volume LIT, which mimics very closely the durability test and challenges the same origins of fatigue (Black et al., 2017;Burnley and Jones, 2018), did not induce larger increases in durability. Earlier, 65% VO 2max -intensity training produced quite clear changes in the VO 2 drifts (Phillips et al., 1996;Carter et al., 2001), suggesting that durability may also be intensity dependent and one cannot simply compensate lower intensity with longer exercise bouts. ...
Introduction: This is one of the first intervention studies to examine how low- (LIT) and high-intensity endurance training (HIT) affect durability, defined as ‘time of onset and magnitude of deterioration in physiological-profiling characteristics over time during prolonged exercise’. Methods: Sedentary and recreationally active men (n = 16) and women (n = 19) completed either LIT (average weekly training time 6.8 ± 0.7 h) or HIT (1.6 ± 0.2 h) cycling for 10 weeks. Durability was analyzed before and after the training period from three factors during 3-h cycling at 48% of pretraining maximal oxygen uptake (VO2max): 1) by the magnitude and 2) onset of drifts (i.e. gradual change in energy expenditure, heart rate, rate of perceived exertion, ventilation, left ventricular ejection time, and stroke volume), 3) by the ‘physiological strain’, defined to be the absolute responses of heart rate and its variability, lactate, and rate of perceived exertion. Results: When all three factors were averaged the durability was improved similarly (time x group p = 0.42) in both groups (LIT: p = 0.03, g = 0.49; HIT: p = 0.01, g = 0.62). In the LIT group, magnitude of average of drifts and their onset did not reach statistically significance level of p < 0.05 (magnitude: 7.7 ± 6.8% vs. 6.3 ± 6.0%, p = 0.09, g = 0.27; onset: 106 ± 57 min vs. 131 ± 59 min, p = 0.08, g = 0.58), while averaged physiological strain improved (p = 0.01, g = 0.60). In HIT, both magnitude and onset decreased (magnitude: 8.8 ± 7.9% vs. 5.4 ± 6.7%, p = 0.03, g = 0.49; onset: 108 ± 54 min vs. 137 ± 57 min, p = 0.03, g = 0.61), and physiological strain improved (p = 0.005, g = 0.78). VO2max increased only after HIT (time x group p < 0.001, g = 1.51). Conclusion: Durability improved similarly by both LIT and HIT based on reduced physiological drifts, their postponed onsets, and changes in physiological strain. Despite durability enhanced among untrained people, a 10-week intervention did not alter drifts and their onsets in a large amount, even though it attenuated physiological strain.
... Exercise intensity is commonly divided into three exercise-intensity domains: moderate-, heavy-, and severe-intensity domains [10,11]. The moderate-intensity domain is characterized by exercise intensities below the gas exchange threshold (GET) [12]. The performance fatigability during whole-body exercise within moderate-intensity develops slowly and is mostly of central origin [13,14], given that muscle metabolic perturbation (e.g., lactate and H + ) is low and rapidly reach a steady state [15]. ...
Objectives. — Whether performance fatigability and its determinants (i.e., peripheral and central fatigue) after cycling exercise performed at extreme- and severe-intensity domains are
of similar magnitude is unknown. In the current study, we investigated the levels of performance fatigability and peripheral and central fatigue in nine young female after a cycling
exercise performed until the limit of tolerance at extreme- (i.e., 140% of peak power output) and severe-intensity domains (80% of the difference between gas exchange threshold and peak
power output). Equipment and methods. — The level of maximal voluntary isometric contraction (MVC), potentiated quadriceps twitch force evoked by single pulse (Q tw ), and voluntary activation (VA) were measured pre- and post-exercise. Results. — The MVC (a marker of performance fatigability) decreased from pre- to post-exercise (P < 0.05) in the extreme- (−10 ± 8%) and severe-intensity (−10 ± 10%) exercises. The Q tw (a marker of peripheral fatigue) reduced similarly from pre- to post-exercise (P < 0.05) in the extreme- (−18 ± 15%) and severe-intensity (−10 ± 17%) exercises. The VA (a marker of central fatigue) did not reduce from pre- to post-exercise in either severe- (2 ± 7%) or extreme-intensity (−2 ± 7%) exercises (P > 0.05). Conclusions. — These findings suggest a similar amount of performance fatigability and peripheral fatigue after severe- and extreme-intensity cycling exercises in young female, which is in
accordance with the concept that exercises performed above critical power until task failure attain a common level of peripheral fatigue regardless of exercise intensity.
... Because participants have a 30-hour training week and maximal test pre and post with an aggressive weight loss protocol. This could be due to glycogen depletion and central fatigue [21][22][23]. ...
... Fatigue is defined as any reduction in the body's maximum capacity to produce power or output (performance). In general, fatigue is actually a feeling of weakness, inability, and lack of energy in all activities of the body so that it appears as a physical and mental disability (Burnley & Jones, 2018). There are several methods for measuring fatigue, which is divided into two categories: objective and subjective methods. ...
The aim of this study is to investigate the relationship between noise exposure, fatigue and subjective mental workload (SMWL) in bank employees. This study was performed on 113 bank employees in Iran. Noise pollution in the studied banks was estimated in accordance with the standard ISO 9612 (1997). To determine the SMWL, NASA-TLX method was used. The level of job fatigue of employees was determined using the Swedish Job Fatigue Questionnaire (SOFI-20) and the sensitivity of people to noise was measured using the Weinstein questionnaire. Finally, the predictor variables of mental workload were analyzed using simultaneous multiple linear regression test in SPSS-V16 software. The level equivalent to the noise exposure (Mean ±SD) in the workstations of bank employees was 61.30 dB-A. The Mean ±SD of the final score of SMWL in the studied employees was 71.91±12.79. The results of the simultaneous regression analysis test showed that the fatigue, noise sensitivity, and level of noise exposure predict a total of 0.61 of the variances of SMWL (P < 0.05, df = 112, f = 16.43). Increasing the noise can increase the SMWL of employees by having the effect of increasing fatigue, and this effect is increased by the sensitivity of employees to noise.
... These intensity domain transitions are used to assess performance capability, regulate training and competition intensities, monitor training load, and quantify adaptations to training (Maunder et al. 2021). The moderate and heavy exercise intensity domains are defined by physiological responses, including distinct blood lactate and whole-body oxygen uptake (V·O 2 ) kinetics profiles (Burnley and Jones 2018;Jones et al. 2019). ...
Purpose
To determine the effect of prolonged exercise on moderate-to-heavy intensity transition power output and heart rate.
Methods
Fourteen endurance-trained cyclists and triathletes took part in the present investigation (13 males, 1 female, V·O2peak 59.9 ± 6.8 mL.kg−1.min⁻¹). Following a characterisation trial, participants undertook a five-stage incremental step test to determine the power output and heart rate at the moderate-to-heavy intensity transition before and after two hours of cycling at 90% of the estimated power output at first ventilatory threshold (VT1).
Results
Power output at the moderate-to-heavy intensity transition significantly decreased following acute prolonged exercise when determined using expired gases (VT1, 217 ± 42 W vs. 196 ± 42 W, P < 0.0001) and blood lactate concentrations (LoglogLT, 212 ± 47 W vs. 190 ± 47 W, P = 0.004). This was attributable to loss of efficiency (VT1, -8 ± 10 W; LoglogLT, − 7 ± 9 W) and rates of metabolic energy expenditure at the transition (VT1, − 14 ± 11 W; LoglogLT, − 15 ± 22 W). The heart rate associated with the moderate-to-heavy intensity transition increased following acute prolonged exercise (VT1, 142 ± 9 beats.min⁻¹ vs. 151 ± 12 beats.min⁻¹, P < 0.001; LoglogLT, 140 ± 13 beats.min⁻¹ vs. 150 ± 15 beats.min⁻¹, P = 0.006).
Conclusion
These results demonstrate the external work output at the moderate-to-heavy intensity transition decreases during prolonged exercise due to decreased efficiency and rates of metabolic energy expenditure, but the associated heart rate increases. Therefore, individual assessments of athlete ‘durability’ are warranted.
... 2C), confirming previous findings that CAF prolongs the time maintained at the maximal oxidative metabolic rate, without affecting the speed of the V O2 response (2). Exhaustion during exercise performed within the severe-intensity domain, as performed in the present study, typically occurs soon after the attainment of V O2max(44). Our finding of a prolongation of exercise time within the severe-intensity domain with CAF ingestion, even after the attainment of V O2max, suggests the cause of exhaustion at this intensity is not the attainment of a maximal oxidative metabolic rate.Copyright © 2022 by the American College of Sports Medicine. Unauthorized reproduction of this article is prohibited. ...
Purpose:
In the present study, we tested the hypothesis that caffeine would increase endurance performance via attenuation of neural and muscular determinants of performance fatigability during high-intensity, whole-body exercise.
Methods:
Ten healthy males cycled until exhaustion (89% ± 2% of V̇O2max) after the ingestion of caffeine or placebo. During another four visits, the same exercise was performed after either caffeine or placebo ingestion but with exercise discontinued after completing either 50% or 75% of the duration of placebo trial. An additional trial with caffeine ingestion was also performed with interruption at the placebo time to exhaustion (isotime). Performance fatigability was measured via changes in maximal voluntary contraction, whereas neural and muscular determinants of performance fatigability were quantified via preexercise to postexercise decrease in quadriceps voluntary activation (VA) and potentiated twitch force, respectively.
Results:
Compared with the placebo, caffeine increased time to exhaustion (+14.4 ± 1.6%, P = 0.017, 314.4 ± 47.9 vs 354.9 ± 40.8 s). Caffeine did not change the rate of decline in maximal voluntary contraction (P = 0.209), but caffeine reduced the twitch force decline at isotime when stimulating at single twitch (-58.6 ± 22.4 vs -45.7 ± 21.9%, P = 0.014) and paired 10 Hz electrical stimuli (-37.3 ± 13.2 vs -28.2 ± 12.9%, P = 0.025), and reduced the amplitude of electromyography signal during cycling at isotime (P = 0.034). The decline in VA throughout the trial was lower (P = 0.004) with caffeine (-0.5 ± 4.2%) than with placebo (-5.8 ± 8.5%). Caffeine also maintained peripheral oxygen saturation at higher levels (95.0 ± 1.9%) than placebo (92.0 ± 6.2%, P = 0.016).
Conclusions:
Caffeine ingestion improves performance during high-intensity, whole-body exercise via attenuation of exercise-induced reduction in VA and contractile function.
... The ability to delineate sustainable from non-sustainable exercise intensities is of considerable interest to exercise physiologists, coaches, and athletes alike. In this light, the critical speed (CS) associated with running is a metric which has emerged as a 'critical metabolic threshold' that differentiates the heavy from the severe intensity domains, and thereby more clearly defines exercise tolerance [1][2][3]. The study of CS is intricately linked to a second parameter termed D' (D-prime) which is associated with a finite energy reserve for covering distances when running at speeds above CS [4,5]. ...
Force-velocity-power (FVP) profiling offers insights related to key factors that may enhance or hinder sprinting performances. Whether the same FVP principles could be applied to the sprinting portion of the 3-minute all-out test for running (3MT) has not been previously investigated. Twenty moderately trained participants volunteered for the study (age: 24.75 ± 3.58 yrs; height: 1.69±0.11 m; mass: 73.74±12.26 kg). After familiarization of all testing procedures, participants completed: (i) a 40-m all-out sprint test, and (ii) a 3MT. Theoretical maximal force and power, but not velocity, were significantly higher for the 40-m sprint test. Most FVP variables from the two tests were weakly to moderately correlated, with the exception of maximal velocity. Finally, maximal velocity and relative peak power were predictive of D’, explaining approximately 51% of the variance in D’. Although similar maximal velocities are attained during both the 40-m sprint and the 3MT, the underlying mechanisms are markedly different. The FVP parameters obtained from either test are likely not interchangeable but do provide valuable insights regarding the potential mechanisms by which D’ may be improved.
... In addition, absolute running speeds were used, which enables generalisability with findings from other studies using absolute speeds. However, future studies might seek to examine the consistency in running patterns based on DF and SF variables across relative speeds [i.e., percent of maximal aerobic speed or maximal oxygen uptake, or percent of maximal lactate steady state to avoid influencing motor unit recruitment strategy (Burnley & Jones, 2018;Fletcher et al., 2009)] to establish whether sudden changes in DF and/or SF could take place at given relative intensities. Moreover, the eligibility criteria about the level of running performance was independent of the sex of the runners, implying that women were of a higher relative standard than men. ...
Duty factor (DF) and step frequency (SF) are key running pattern determinants. However, running patterns may change with speed if DF and SF changes are inconsistent across speeds. We examined whether the relative positioning of runners was consistent: 1) across five running speeds (10-18 km/h) for four temporal variables [DF, SF, and their subcomponents: contact (t c) and flight (t f) time]; and 2) across these four temporal variables at these five speeds. Three-dimensional whole-body kinematics were acquired from 52 runners , and deviations from the median for each variable (normalised to minimum-maximum values) were extracted. Across speeds for all variables, correlations on the relative positioning of individuals were high to very high for 2-4 km/h speed differences, and moderate to high for 6-8 km/h differences. Across variables for all speeds, correlations were low between DF-SF, very high between DF-t f , and low to high between DF-t c , SF-t c , and SF-t f. Hence, the consistency in running patterns decreased as speed differences increased, suggesting that running patterns be assessed using a range of speeds. Consistency in running patterns at a given speed was low between DF and SF, corroborating suggestions that using both variables can encapsulate the full running pattern spectrum. ARTICLE HISTORY
... Indeed, independent validation studies predominantly reported noticeable inaccuracy of 1-RM predictions based on complete-pooling models, especially when using lower relative loads (Reynolds et al., 2006;Mayhew et al., 2008;LeSuer et al., 1997;Brechue & Mayhew, 2009;Ware, Clemens, Mayhew, & Johnston, 1995). Several researchers have sought to overcome this issue and improve model validity by transposing the concept of critical power (Burnley & Jones, 2018) to dynamic resistance training (Bergstrom et al., 2021;Morton, Redstone, & Laing, 2014). The socalled critical load model, also referred to as critical lift or critical resistance model, introduced the idea of modelling strength endurance on an individual level (i.e. ...
Purpose:
To identify the relationship between load and the number of repetitions performed to momentary failure in the pin press exercise, the present study compared different statistical model types and structures using a Bayesian approach.
Methods:
Thirty resistance-trained men and women were tested on two separate occasions. During the first visit, participants underwent assessment of their one-repetition maximum (1-RM) in the pin press exercise. On the second visit, they performed sets to momentary failure at 90%, 80% and 70% of their 1-RM in a fixed order during a single session. The relationship between relative load and repetitions performed to failure was fitted using linear regression, exponential regression and the critical load model. Each model was fitted according to the Bayesian framework in two ways: using an across-subjects pooled data structure and using a multilevel structure. Models were compared based on the variance explained (R²) and leave-one-out cross-validation information criterion (LOOIC).
Results:
Multilevel models, which incorporate higher-level commonalities into individual relationships, demonstrated a substantially better fit (R²: 0.97-0.98) and better predictive accuracy compared to generalized pooled-data models (R²: 0.89-0.93). The multilevel 2-parameter exponential regression emerged as the best representation of data in terms of model fit, predictive accuracy and model simplicity.
Conclusion:
The relationship between load and repetitions performed to failure follows an individually expressed exponential trend in the pin press exercise. To accurately predict the load that is associated with a certain repetition maximum, the relationship should therefore be modeled on a subject-specific level.
... library(R2jags) # download JAGS at https://sourceforge.net/projects/mcmc-jags/files/ library(MASS) ############ enter the data in Table 1 (7) estimates given in Table 2 ############ # define the parameters and the data: n = length(yt) data = list("yt" =yt,"t"=time, "n" = n) # identify data # model definition: [3] }",sep = ""), file="CV3Model2.txt") 13,12833.37), nrow = 3)), pp = runif(1, min = 0, max = 1),tu = 1)} # generate sample from posterior: jags.m <-jags.model(file = "CV3Model2.txt",data ...
In sports science, critical power and related critical velocity models have been widely investigated, and are being increasingly applied to field-based team sports. A challenge associated with these models is that laboratory experiments that yield accurate measurements of maximal sustainable velocity are expensive. Alternatively, inexpensive field data (from training and matches) are being used to fit such models. However, the intermittent nature of efforts in field-based sports implies that the dependent variable concerning maximum sustainable velocity is reliably calibrated only for short time durations. This paper develops methods where field data based on short time durations is combined with prior knowledge to fit the three-parameter critical velocity model. This is accomplished in a Bayesian framework for which Markov chain methods are required for model fitting and inference.
... This observation, as a group, was however not unexpected as the mechanisms and extent of fatigue are exercise domain dependent. Fatigue resulting from prolonged activity in the moderate domain has been shown to be mostly of central origin (Burnley and Jones, 2016) while the HIIT was in the severe domain, inducing both central and peripheral decrements. This study is the first to report individual impairments in neuromuscular function immediately and 24-h post HIIT. ...
PurposeTo examine the time course of recovery for gait and neuromuscular function immediately after and 24-h post interval training. In addition, this study compared the impact of different statistical approaches on detecting changes.Methods
Twenty (10F, 10M) healthy, recreational club runners performed a high-intensity interval training (HIIT) session consisting of six repetitions of 800 m. A 6-min medium intensity run was performed pre, post, and 24-h post HIIT to assess hip and knee kinematics and coordination variability. Voluntary activation and twitch force of the quadriceps, along with maximum isometric force were examined pre, post, and 24-h post significance HIIT. The time course of changes were examined using two different statistical approaches: traditional null hypothesis significance tests and “real” changes using minimum detectable change.ResultsImmediately following the run, there were significant (P < 0.05) increases in the hip frontal kinematics and coordination variability. The runners also experienced a loss of muscular strength and neuromuscular function immediately post HIIT (P < 0.05). Individual assessment, however, showed that not all runners experienced fatigue effects immediately post HIIT. Null hypothesis significance testing revealed a lack of recovery in hip frontal kinematics, coordination variability, muscle strength, and neuromuscular function at 24-h post, however, the use of minimum detectable change suggested that most runners had recovered.Conclusion
High intensity interval training resulted in altered running kinematics along with central and peripheral decrements in neuromuscular function. Most runners had recovered within 24-h, although a minority still exhibited signs of fatigue. The runners that were not able to recover prior to their run at 24-h were identified to be at an increased risk of running-related injury.
... Combined, these physiological traits result in a 'performance metabolic rate', the highest oxidative metabolic rate that can be sustained for the marathon. Critical speed (CS) is the physiological threshold delineating the heavy-and severe-intensity domains, and therefore defines the point at which the maximal metabolic steady-state (MMSS) can be attained, and exercise can be supported mainly from oxidative metabolism [7][8][9][10]. It is worth noting that several other terms or approaches have been suggested to correspond with, or permit the approximation of, the MMSS including ventilatory or respiratory thresholds, or thresholds derived from blood lactate concentration, such as the maximal lactate steady state [8]. ...
Aim
This study characterised the decoupling of internal-to-external workload in marathon running and investigated whether decoupling magnitude and onset could improve predictions of marathon performance.
Methods
The decoupling of internal-to-external workload was calculated in 82,303 marathon runners (13,125 female). Internal workload was determined as a percentage of maximum heart rate, and external workload as speed relative to estimated critical speed (CS). Decoupling magnitude (i.e., decoupling in the 35–40 km segment relative to the 5–10 km segment) was classified as low (< 1.1), moderate (≥ 1.1 but < 1.2) or high (≥ 1.2). Decoupling onset was calculated when decoupling exceeded 1.025.
Results
The overall internal-to-external workload decoupling experienced was 1.16 ± 0.22, first detected 25.2 ± 9.9 km into marathon running. The low decoupling group (34.5% of runners) completed the marathon at a faster relative speed (88 ± 6% CS), had better marathon performance (217.3 ± 33.1 min), and first experienced decoupling later in the marathon (33.4 ± 9.0 km) compared to those in the moderate (32.7% of runners, 86 ± 6% CS, 224.9 ± 31.7 min, and 22.6 ± 7.7 km), and high decoupling groups (32.8% runners, 82 ± 7% CS, 238.5 ± 30.7 min, and 19.1 ± 6.8 km; all p < 0.01). Compared to females, males’ decoupling magnitude was greater (1.17 ± 0.22 vs. 1.12 ± 0.16; p < 0.01) and occurred earlier (25.0 ± 9.8 vs. 26.3 ± 10.6 km; p < 0.01). Marathon performance was associated with the magnitude and onset of decoupling, and when included in marathon performance models utilising CS and the curvature constant, prediction error was reduced from 6.45 to 5.16%.
Conclusion
Durability characteristics, assessed as internal-to-external workload ratio, show considerable inter-individual variability, and both its magnitude and onset are associated with marathon performance.
... oxygen consumption, heart rate) and peripheral haemodynamics (e.g. muscle oxygenation, blood flow), we cannot determine whether the sensory enhancement of warm-up affected cardiovascular adjustments, which are highly linked to exercise performance (i.e., VO2 max at task failure (Burnley and Jones 2018)). ...
Purpose
In sport and exercise, warm-ups induce various physiological changes that facilitate subsequent performance. We have shown that delivering patterned stimulation to cutaneous afferents during sprint cycling mitigates fatigue-related decrements in performance, and that repeated sensory stimulation amplifies spinal reflex excitability. Therefore, the purpose of this study was to assess whether sensory enhancement of warm-up would affect subsequent high-intensity arm cycling performance.
Methods
Participants completed three experimental sessions, in which they randomly performed either a control, stim, or sleeve warm-up condition prior to maximal duration arm cycling. During the control condition, warmup consisted of low-intensity arm cycling for 15 min. The stim condition was the same, except they received alternating pulses (400 ms, 50 Hz) of stimulation just above their perceptual threshold to the wrists during warm-up. The third condition required participants to wear custom fabricated compression sleeves around the elbow during warm-up. Grip strength and spinal reflex excitability were measured before and after each warm-up and fatigue protocol, which required participants to arm cycle at 85% of peak power output until they reached volitional fatigue. Peak power output was determined during an incremental test at minimum 72 h prior to the first session.
Results
Both sensory enhanced warm-up conditions amplified subsequent high-intensity arm cycling performance by ~ 30%. Additionally, the stim and sleeve warm-up conditions yielded improvements in grip strength (increased by ~ 5%) immediately after the sensory enhanced warm-ups. Ergogenic benefits from the sensory enhanced warm-up conditions did not differ between one another.
Conclusion
These findings demonstrate that enhanced sensory input during warm-up can elicit improvements in both maximal and submaximal performance measures.
... The metabolic climate of NZBC supplemented athletes suggests a need for further NZBC research in intermittent and team sports athletes, preferably with a trained comparator group, employing a replicated crossover design or in an extended tournament setting. In aerobic disciplines, future research should focus on exercise tasks in the severe domain (Burnley & Jones, 2016), where an increased lactate production, as observed in the present study, may improve performance via priming (Ingham et al., 2013). When assessing female participants, menstrual cycle phase should also be considered and where possible controlled for too, due to potential oestrogen-mediated antioxidant and glycogen sparing effects (McNulty et al., 2020). ...
Blackcurrants are an excellent source of antioxidant and anti-inflammatory agents, and recent studies have found them to facilitate performance and recovery in aerobic activities. However, limited research exists in intermittent or anaerobic settings despite known oxidative and inflammatory stresses. Therefore, we examined the effects of New Zealand Blackcurrant (NZBC) on repeated sprint ability (RSA) and recovery parameters. Sixteen recreationally active females were supplemented with either NZBC (1.6mg.kg-1 anthocyanin content; ViBERi, Timaru, New Zealand) or a matched placebo (artificial sweetener) for 7 days in a randomized, double-blind, parallel-group design. On day 7 participants performed the RSA test which consisted of ten 30m shuttle sprints interspersed with a 30 second recovery period. Blood lactate was assessed 1-, 3-, 5-, and 10-minutes post-test. The same protocol was then replicated the following day. NZBC improved mean sprint time from baseline by 2.0% and fastest sprint time by 2.7%. Placebo also improved sprint time by 2.3%. Compared to the placebo group the NZBC group typically performed better in all RSA test outcomes, however the differences were deemed unclear and non-significant. Lactate responses post RSA on average tended to be higher on both days for the NZBC group compared to placebo group (15.1-32.5%). A moderate difference (ES:-0.64) was observed between groups post 7-days of supplementation for lactate clearance from 5-minutes to 10-minutes post-test with NZBC leading to a decrease of 23.7%. In conclusion, NZBC supplementation for 7-days does not improve repeated sprint ability when compared to placebo.
... However, the depletion of muscle glycogen seems to be critic for the peripheral fatigue, also considering that, fatigue-related metabolites (such as ADP, Pi, and H+) do not accumulate as exercise progresses, in spite of the fact that peripheral fatigue gradually develops [5]. ...
Background: Sambo is a martial art and combat sport that originated in the Soviet Union.
There are two main stiles, Sport Sambo and Combat Sambo which resembles modern mixed martial
arts. Very little literature is available about physiological aspects of Sambo and, in particular, on the
possible effects on cognitive domains. The purpose of the present research was to determine if there
is a correlation between a blood lactate increase and the intensity and/or selectivity of attentions.
Methods: Sixteen male athletes practicing Sambo for at least 5 years participated voluntarily in
the study. Each athlete had to sustain, with an interval of one week, both a Sport Sambo match
and a Combat Sambo match, each lasting 5 min. Blood lactate levels as well as attentive capacities
were evaluated at three different times: at rest, i.e., 5 min before the start of the session (pre), at
end of the session and 15 min after its conclusion. Reaction time protocol was used to evaluate the
intensity of attention, whereas divided attention was assessed for analyzing the selectivity of attention
together with errors and omissions. Results: Concerning Sport Sambo, blood lactate was 1.66 mmol/L
(�0.55 SD) before the session, reached a mean value of 3.40 mmol/L (�0.45 SD) at the end of the
session (end) and returned to values similar to initial ones (a mean value of 1.98 mmol/L (�0.37 SD)
after 15 min (15-end). None of the attentive parameters examined, showed statistically significant
differences. Conversely, for Combat Sambo, it was found a significant increase in blood lactate levels
that went from 1.66 mmol/L (�0.55 SD) before the session (pre), to 4.76 mmol/L (�0.60 SD) at
the end (end) and then back to values similar to those observed before the session 15 min after its
conclusion (15-end), i.e., 1.97 mmol/L (�0.37 SD); however, after a Combat Sambo session increases
in blood lactate were associated with significant worsening of attentional mechanisms. Conclusions:
In conclusion, in all the participants, the worsening of attentional mechanisms was observed only
after the Combat Sambo session in which blood lactate values exceeded 4 mmol/L. This figure, also
known as the Onset of Blood Lactate Accumulation (OBLA), is commonly used to determine the
anaerobic threshold.
... However, the depletion of muscle glycogen seems to be critic for the peripheral fatigue, also considering that, fatigue-related metabolites (such as ADP, Pi, and H+) do not accumulate as exercise progresses, in spite of the fact that peripheral fatigue gradually develops [5]. ...
Background:
Sambo is a martial art and combat sport that originated in the Soviet Union. There are two main stiles, Sport Sambo and Combat Sambo which resembles modern mixed martial arts. Very little literature is available about physiological aspects of Sambo and, in particular, on the possible effects on cognitive domains. The purpose of the present research was to determine if there is a correlation between a blood lactate increase and the intensity and/or selectivity of attentions.
Methods:
Sixteen male athletes practicing Sambo for at least 5 years participated voluntarily in the study. Each athlete had to sustain, with an interval of one week, both a Sport Sambo match and a Combat Sambo match, each lasting 5 min. Blood lactate levels as well as attentive capacities were evaluated at three different times: at rest, i.e., 5 min before the start of the session (pre), at end of the session and 15 min after its conclusion. Reaction time protocol was used to evaluate the intensity of attention, whereas divided attention was assessed for analyzing the selectivity of attention together with errors and omissions.
Results:
Concerning Sport Sambo, blood lactate was 1.66 mmol/L (±0.55 SD) before the session, reached a mean value of 3.40 mmol/L (±0.45 SD) at the end of the session (end) and returned to values similar to initial ones (a mean value of 1.98 mmol/L (±0.37 SD) after 15 min (15-end). None of the attentive parameters examined, showed statistically significant differences. Conversely, for Combat Sambo, it was found a significant increase in blood lactate levels that went from 1.66 mmol/L (±0.55 SD) before the session (pre), to 4.76 mmol/L (±0.60 SD) at the end (end) and then back to values similar to those observed before the session 15 min after its conclusion (15-end), i.e., 1.97 mmol/L (±0.37 SD); however, after a Combat Sambo session increases in blood lactate were associated with significant worsening of attentional mechanisms.
Conclusions:
In conclusion, in all the participants, the worsening of attentional mechanisms was observed only after the Combat Sambo session in which blood lactate values exceeded 4 mmol/L. This figure, also known as the Onset of Blood Lactate Accumulation (OBLA), is commonly used to determine the anaerobic threshold.
... When energy is depleted and the supply and demand are imbalanced, the by-products of fatigue will increase, including the accumulation of lactic acid, inorganic phosphorus, and ammonia. This makes it difficult for muscles to maintain continuous contraction, resulting in an inability to maintain or a loss of their original exercise performance [14]. Therefore, in addition to improving physical fitness through regular scientific training, the use of nutritional supplements to improve the utilization of energy in the body, reduce consumption, delay the accumulation of fatigue metabolites, and accelerate the elimination of fatigue is one effective strategy [15]. ...
Silver perch (Bidyanus bidyanus) has many nutrition and health benefits, being a rich source of macro and micronutrients, phospholipids, polyunsaturated fatty acids, and a variety of essential minerals while having a high protein content. In addition to direct consumption, it is often made into a soup as an important nutritional supplement for strengthening the body and delaying fatigue. By extracting the essence, its quality can be controlled, and it is convenient to supplement. This study aimed to evaluate the effect of supplementation with Santé premium silver perch essence (SPSPE) on improving exercise performance and anti-fatigue. Fifty male institute of cancer research (ICR) mice were divided into five groups (n = 10/group): (1) vehicle (vehicle control or water only), (2) isocaloric (0.93 g casein/kg/mice/day), (3) SPSPE-1X (0.99 g/kg/mice/day), (4) SPSPE-2X (1.98 g/kg/mice/day), and (5) SPSPE-5X (4.95 g/kg/mice/day). A sample or an equal volume of liquid was fed orally for four consecutive weeks. Grip strength and swimming exhaustion tests were used as exercise performance assessments. After 10 and 90 min of unloaded swimming, biochemical parameters of fatigue were evaluated. We found that supplementation with SPSPE for four consecutive weeks could significantly improve mice’s grip strength, exercise endurance performance, and glycogen content (p < 0.05), and significantly reduced post-exercise fatigue biochemical parameters, such as lactate, blood ammonia (NH3), blood urea nitrogen (BUN) concentration, and muscle damage index creatine kinase (CK) activity (p < 0.05). In summary, supplementation with SPSPE for 4 weeks could effectively improve exercise performance, reduce sports fatigue, and accelerate fatigue recovery. In addition, it did not cause any physiological or histopathological damage.
... It is well established that the relative contributions to fatigue by peripheral and central factors are intensity-dependent (see refs: (Burnley and Jones 2018)). These differences may also be apparent with maximal exercise, including extreme-intensity exercise (Alexander et al. 2019;Hill et al. 2002). ...
Maximal voluntary contraction force (MVC), potentiated twitch force (Q pot ), and voluntary activation (%VA) recover to baseline within 90 s following extreme-intensity exercise. However, methodological limitations mask important recovery kinetics. We hypothesized reductions in MVC, Q pot , and %VA at task failure following extreme-intensity exercise would be less than following severe-intensity exercise, and Q pot and MVC following extreme-intensity exercise would show significant recovery within 120 s but remain depressed following severe-intensity exercise. Twelve subjects (6 men) completed 2 severe-intensity (40, 50% MVC) and 2 extreme-intensity (70, 80% MVC) isometric knee-extension exercise bouts to task failure (T lim ). Neuromuscular function was measured at baseline, T lim , and through 150 s of recovery. Each intensity significantly reduced MVC and Q pot compared with baseline. MVC was greater at T lim (p < 0.01) and at 150 s of recovery (p = 0.004) following exercise at 80% MVC compared with severe-intensity exercise. Partial recovery of MVC and Q pot were detected within 150 s following T lim for each exercise intensity; Q pot recovered to baseline values within 150 s of recovery following exercise at 80% MVC. No differences in %VA were detected pre- to post-exercise or across recovery for any intensity. Although further analysis showed sex-specific differences in MVC and Q pot , future studies should closely examine sex-dependent responses to extreme-intensity exercise. It is clear, however, that these data reinforce that mechanisms limiting exercise tolerance during extreme-intensity exercise recover quickly.
Novelty: Severe- and extreme-intensity exercise cause independent responses in fatigue accumulation and the subsequent recovery time courses. Recovery of MVC and Q pot occurs much faster following extreme-intensity exercise in both men and women.
... where F(v) is the fatigue-free F/v profile and τF denotes the time constant of its decline due to fatigue. Since the results of Burnley and Jones [20], among others, described a steady state of power output after an exponential drop, a limiting value c was included in the function to represent this steady state. As the F/v profile shifted, the characteristic parameters of the fatigue-free profiles also decreased, allowing the three-dimensional model to be reduced to a two-dimensional model by eliminating the dependence on cadence. ...
In track cycling sprint events, optimal cadence PRopt is a dynamic aspect of fatigue. It is currently unclear what cadence is optimal for an athlete’s performance in sprint races and how it can be calculated. We examined fatigue-induced changes in optimal cadence during a maximal sprint using a mathematical approach. Nine elite track cyclists completed a 6-s high-frequency pedaling test and a 60-s isokinetic all-out sprint on a bicycle ergometer with continuous monitoring of crank force and cadence. Fatigue-free force-velocity (F/v) and power-velocity (P/v) profiles were derived from both tests. The development of fatigue during the 60-s sprint was assessed by fixing the slope of the fatigue-free F/v profile. Fatigue-induced alterations in PRopt were determined by non-linear regression analysis using a mono-exponential equation at constant slope. The study revealed that PRopt at any instant during a 60-s maximal sprint can be estimated accurately using a mono-exponential equation. In an isokinetic mode, a mean PRopt can be identified that enables the athlete to generate the highest mean power output over the course of the effort. Adding the time domain to the fatigue-free F/v and P/v profiles allows time-dependent cycling power to be modelled independent of cadence.
Many organisational officials agree that most of the incidents in the field happen due to undesirable human performance (or human error). So, to maintain safety and efficiency at work where human subjects are involved, it is necessary to have in-depth knowledge about human performance analysis and assessment. This article reviewed human performance from its different facets to understand it and find techniques available to help manage it. To review this subject, we have followed a user-friendly, replicable technique. After the intense review, we noticed a need for more adaptable technologies in system safety, where the work can only be accomplished with human involvement. This review helps researchers and has the capability to advance studies both in the engineering psychology and human reliability fields. It also assists the novice in the organisational management team in understanding essential parameters responsible for human performance in order to improve human work safety and efficiency.
The power-time relationship is an important concept in exercise physiology because it provides a systematic framework for understanding the mechanical bases of fatigue and exhaustion during exercise, as well as a tool for diagnosing physical fitness and monitoring training. This relationship is well known during high intensity exercise, sustainable with stable critical power (CP) values, reaching maximum work rates over time until exercise intolerance is reached. This amount of work above the CP (W ́) is constant at different speeds depending on the proximity of the power output to CP. The appeal of this concept of CP in recent years has been broadened through its application to high intensity intermittent exercise, however, there are no intermittent training programs (IWC) based on CP/W ́ that can evaluate and optimize the exercise. athletic performance in road cycling.
Therefore, the objective of this Doctoral Thesis is to analyze the power-time relationship (CP) and the metabolic thresholds for the evaluation and optimization of sports performance during intermittent exercise through a reconstitutive model (W'BAL) in road cyclists. For this, a systematic review and Meta-Analysis has been carried out that determines the degree of correspondence between CP and VT1, MLSS, VT2 and RCP (Article I), in addition a study has been carried out that determines the influence between the load based on the weight body and muscle mass during the WAnT performance test above CP in the severe intensity domain (Article II), in order to develop a reconstitutive intermittent training program (Article III), which can estimate, evaluate and monitor the CP during training (Article IV).
The main results of this Doctoral Thesis suggest that a) VT1 and MLSS underestimate CP while RCP and VT2 overestimate it, and MLSS and MMSS do not mean the same thing. b) In the WAnT test, the protocols can be used interchangeably in the conditions of body weight (BW) and muscle mass or fat-
XIII
free (LBM) that evaluate anaerobic capacity above CP. c) IWC significantly improves CP and MMP in field tests TT12min, TT7min and TT3min after 4 weeks of training. d) Estimated CP3p and CP2p of the MMP values during the sessions of the IWC training program, differ from the CP extracted from the formal field test. e) IWC can estimate CP from 7min MMP values, track and monitor its changes during 4 weeks of training.
This Doctoral Thesis shows that the development of a CP training program applied to intermittent reconstitutive exercise (WBAL) has important applications in the optimization of sports performance in road cyclists.
Functional Threshold Power (FTP) has been considered a valid alternative to other performance markers that represent the upper boundary of the heavy intensity domain. However, such a claim has not been empirically examined from a physiological perspective.This study examined the blood lactate and VO2 response when exercising at and 15 W above the FTP (FTP+15W). Thirteen cyclists participated in the study. The VO2 was recorded continuously throughout FTP and FTP+15W, with blood lactate measured before the test, every 10 minutes and at task failure. Data were subsequently analysed using two-way ANOVA. The time to task failure at FTP and FTP+15W were 33.7 ± 7.6 and 22.0 ± 5.7 minutes (p < 0.001), respectively. The VO2peak was not attained when exercising at FTP+15W (VO2peak: 3.61 ± 0.81 vs FTP+15W 3.33 ± 0.68 L·min⁻¹, p < 0.001). The VO2 stabilised during both intensities. However, the end test blood lactate corresponding to FTP and FTP+15W was significantly different (6.7 ± 2.1 mM vs 9.2 ± 2.9 mM; p < 0.05). The VO2 response corresponding to FTP and FTP+15W suggests that FTP should not be considered a threshold marker between heavy and severe intensity.
The parameters of the hyperbolic speed-duration relationship (the asymptote critical speed, CS, and the curvature constant, D') provide estimates of the maximal steady state speed (CS) and the distance an animal can run, swim, or fly at speeds above CS before it is forced to slow down or stop (D'). The speed-duration relationship has been directly studied in humans, horses, mice and rats. The technical difficulties with treadmill running in dogs and the relatively short greyhound race durations means that, perhaps surprisingly, it has not been assessed in dogs. The endurance capabilities of lizards, crabs and salamanders has also been measured, and the speed-duration relationship can be calculated from these data. These analyses show that 1) raising environmental temperature from 25 °C to 40 °C in lizards can double the CS with no change in D'; 2) that lungless salamanders have an extremely low critical speed due, most likely, to O2 diffusion limitations associated with cutaneous respiration; and 3) the painted ghost crab possesses the highest endurance parameter ratio (D'/CS) yet recorded (470 s), allowing it to maintain high speeds for extended periods. Although the speed-duration relationship has not been measured in fish, the sustainable swimming speed has been quantified in a range of species and is conceptually similar to the maximal steady state in humans. The high aerobic power of birds and low metabolic cost of transport during flight permits the extreme feats of endurance observed in bird migrations. However, the parameters of the avian speed-duration relationship have not been quantified.
Hurd, KA, Surges, MP, and Farrell, JW. Use of exercise training to enhance the power-duration curve: a systematic review. J Strength Cond Res 37(3): 733-744, 2023-The power/velocity-duration curve consists of critical power (CP), the highest work rate at which a metabolic steady state can obtained, and W' (e.g., W prime), the finite amount of work that can be performed above CP. Significant associations between CP and performance during endurance sports have been reported resulting in CP becoming a primary outcome for enhancement following exercise training interventions. This review evaluated and summarized the effects of different exercise training methodologies for enhancing CP and respective analogs. A systematic review was conducted with the assistance of a university librarian and in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Ten studies met the criteria for inclusion and were reviewed. Four, 2, 2, 1, and 1 articles included swimming, cycling, resistance training, rowing, and running, respectively. Improvements in CP, and respective analogs, were reported in 3 swimming, 2 cycling, and 1 rowing intervention. In addition, only 2 cycling and 1 swimming intervention used CP, and respective analogs, as an index of intensity for prescribing exercise training, with one cycling and one swimming intervention reporting significant improvements in CP. Multiple exercise training modalities can be used to enhance the power/velocity-duration curve. Significant improvements in CP were often reported with no observed improvements in W' or with slight decreases. Training may need to be periodized in a manner that targets enhancements in either CP or W' but not simultaneously.
The relationship between the applied load and the number of repetitions performed to momentary failure (i.e., the strength-endurance relationship) in a given exercise has repeatedly drawn the interest of researchers over the past decades. While this relationship was commonly assumed to be virtually identical across individuals and, thus, described by unified equations, there is evidence that it may actually differ between individuals. The present thesis aimed to investigate the concept of “strength-endurance profiles”, which describe the strength-endurance relationship on an individual level. The main objective was to identify a model function that yields good descriptive and predictive validity while being robust across test-retest trials. Since strength-endurance profiles require the completion of multiple repetitions-to-failure tests, the thesis further aimed to compare different strategies for data acquisition to evaluate whether they may be used interchangeably. Based on the findings, it was concluded that the individual strength-endurance relationship can be best represented by a 2-parameters exponential regression or a reciprocal regression function. Data acquisition should be completed in multiple separate sessions distributed across different days, rather than a single session with 22 min breaks in between repetitions-to-failure tests.
Duration is a rarely investigated marker of exercise prescription. The aim of this study was to test the feasibility of the methodological approach, assessing effects of different duration constant-load exercise (CLE) on physiological responses (internal load) and recovery kinetics. Seven subjects performed an incremental exercise (IE) test, one maximal duration CLE at 77.6 ± 4.8% V˙O2max, and CLE’s at 20%, 40%, and 70% of maximum duration. Heart rate (HR), blood lactate (La), and glucose (Glu) concentrations were measured. Before, 4, 24, and 48 h after CLE’s, submaximal IE tests were performed. HR variability (HRV) was assessed in orthostatic tests (OT). Rating of perceived exertion (RPE) was obtained during all tests. CLE’s were performed at 182 ± 27 W. HRpeak, Lapeak, V˙Epeak, and RPEpeak were significantly higher in CLE’s with longer duration. No significant differences were found between CLE’s for recovery kinetics for HR, La, and Glu in the submaximal IE and for HRV or OT. Despite no significant differences, recovery kinetics were found as expected, indicating the feasibility of the applied methods. Maximum tests and recovery tests closer to CLE’s termination are suggested to better display recovery kinetics. These findings are a first step to prescription of exercise by both intensity and duration on an individual basis.
Background:
Physical fitness optimization and injury risk-reducing require extensive monitoring of training loads and athletes' fatigue status. This study aimed to investigate the effect of a 6-month training program on the training-related stress indicators (creatine kinase - CK; cortisol - COR; serotonin - SER; brain-derived neurotrophic factor - BDNF) in youth soccer players.
Methods:
Eighteen players (17.8 ± 0.9 years old, body height 181.6 ± 6.9 cm, training experience 9.7 ± 1.7 years) were blood-tested four times: at the start of the preparation period (T0), immediately following the preparation period (T1), mid-competitive period (T2), and at the end of the competitive period (T3). CK activity as well as concentrations of serum COR, SER and BDNF were determined. Training loads were recorded using a session rating of perceived exertion (sRPE).
Results:
Statistical analyzes revealed significant effects for all biochemical parameters in relation to their time measurements (T0, T1, T2, T3). The statistical analyzes of sRPE and differences of biochemical parameters in their subsequent measurements (T0-T1, T1-T2, T2-T3) also demonstrated significant effects observed for all variables: sRPE (HKW = 13.189 (df = 2); p = 0.00), COR (HKW = 9.261 (df = 2); p = 0.01), CK (HKW = 12.492 (df = 2); p = 0.00), SER (HKW = 7.781 (df = 2); p = 0.02) and BDNF (HKW = 15.160 (df = 2); p < 0.001).
Discussion:
In conclusion, it should be stated that the most demanding training loads applied in the preparation period (highest sRPE values) resulted in a significant increase in all analyzed biochemical training stress indicators. The reduction in the training loads during a competitive period and the addition of recovery training sessions resulted in a systematic decrease in the values of the measured biochemical indicators. The results of the study showed that both subjective and objective markers, including training loads, are useful in monitoring training stress in youth soccer players.
La identificación de las respuestas agudas y crónicas inducidas por el ejercicio físico resultan ser las características más recordadas en la fisiología del ejercicio por quienes hemos realizado cursos relacionados a esta área, ya sea como estudiantes de pre o posgrado, lo que está bien si se considera que son los hallazgos más relevantes que debemos reconocer si nos gusta el deporte y, por tanto, lo vivenciamos en primera persona, o realizamos actividad asistencial con deportistas o pacientes. Sin embargo, muchas veces nos olvidamos del marco teórico que sustentan dichos cambios; aspecto crucial, dados los diferentes tipos de actividad física y programas de entrenamiento que se pueden realizar. Esto hace que para algunos se transforme en una verdadera odisea recordar conceptos clásicos, y mas complejo aún poder relacionarlos e integrarlos en el fenómeno que se está evaluando; mientras que para otros se transforma en el pretexto ideal para reencontrarse con libros de ciencias básicas, como aquellos de biología, química, física, bioquímica, fisiología general, análisis del movimiento, etc.
Con la finalidad de ayudar a que los contenidos teóricos de fisiología del ejercicio se plasmen en actividades prácticas que se orienten hacia el logro de objetivos de aprendizaje gracias al “aprender haciendo”, incentivando la autorreflexión y el pensamiento crítico, es que se desarrolló el presente manual de actividades prácticas. En este se incorporan las unidades más frecuentes de los programas académicos de universidades e institutos de formación profesional. En cada unidad se presenta el marco teórico que sustenta el tópico principal a tratar, englobando contenidos de diferentes libros y artículos científicos, y finaliza con actividades prácticas a desarrollar en forma personal o en grupos pequeños, tanto en ambientes libres como en el laboratorio, siempre bajo la guía de los académicos responsables de la asignatura.
En la creación de este manual participaron académicos de la carrera de Kinesiología UC, aportando a través de su experiencia docente, las mejores actividades en las que se pueda vivenciar lo explicitado previamente en forma teórica. Espero que los contenidos y la forma en que son presentados faciliten el desarrollo de la docencia en el área de la fisiología del ejercicio, tanto a académicos como a estudiantes. De igual manera, los invito a comentar respecto del entendimiento de las actividades prácticas, con la finalidad de incorporar mejoras y potenciar el objetivo principal de la creación de este libro. Por ello, invitamos a los lectores a disfrutar el “aprender haciendo” en fisiología del ejercicio.
The hyperbolic form of the power-duration relationship is rigorous and highly conserved across species, forms of exercise and individual muscles/muscle groups. For modalities such as cycling, the relationship resolves to two parameters, the asymptote for power (critical power, CP) and the so-called W' (work doable above CP), which together predict the tolerable duration of exercise above CP. Crucially, the CP concept integrates sentinel physiological profiles - respiratory, metabolic and contractile - within a coherent framework that has great scientific and practical utility. Rather than calibrating equivalent exercise intensities relative to metabolically distant parameters such as the lactate threshold or V˙O2 max, setting the exercise intensity relative to CP unifies the profile of systemic and intramuscular responses and, if greater than CP, predicts the tolerable duration of exercise until W' is expended, V˙O2 max is attained, and intolerance is manifested. CP may be regarded as a 'fatigue threshold' in the sense that it separates exercise intensity domains within which the physiological responses to exercise can (<CP) or cannot (>CP) be stabilized. The CP concept therefore enables important insights into 1) the principal loci of fatigue development (central vs. peripheral) at different intensities of exercise, and 2) mechanisms of cardiovascular and metabolic control and their modulation by factors such as O2 delivery. Practically, the CP concept has great potential application in optimizing athletic training programs and performance as well as improving the life quality for individuals enduring chronic disease.
Purpose:
The aim of this study was to determine if exercise time trials (TT) of different durations would cause different levels of peripheral and central fatigue during exercise.
Methods:
Twelve trained subjects (11 men, 1 woman) performed TTs lasting 3, 10 and 40 min with repetitive self-paced concentric right knee extension at 60 deg[BULLET OPERATOR]s on an isokinetic dynamometer. Neuromuscular function was assessed prior to, during, and immediately after the TTs using voluntary and electrically evoked forces.
Results:
Maximal voluntary contraction (MVC) force, evoked peak force for single stimulus (SS), and rating of perceived exertion reached similar levels at termination of all TTs. Evoked peak force for paired stimuli of 100 Hz (PS100) decreased more for the 40-min compared to the 3-min TT (-42 ± 15% vs -37 ± 13%, P < 0.05) and central fatigue was significant for the 40-min and 10-min but not for the 3-min TT. SS and PS100 decreased while voluntary electromyography normalized to M-wave for self-paced contractions increased during the end-spurt in all TTs.
Conclusion:
These data demonstrate that the extent of peripheral and central fatigue that contribute to reductions in force of single limb dynamic contractions depend on the duration and intensity of self-paced exercise. There was no evidence for a critical threshold in peripheral fatigue that was common to all time trials.
To determine the mechanisms causing task failure during incremental exercise to exhaustion (IE) sprint performance (10 s all-out isokinetic) and muscle metabolites were measured before (control) and immediately after IE in normoxia (Nx, PI O2 :143 mmHg) and hypoxia (Hyp, PI O2 :73 mmHg) in 22 men (22 ± 3 years). After IE, subjects recovered for either 10 or 60 s, with open circulation or bilateral leg occlusion (OC, 300 mmHg) in random order. This was followed by a 10 s sprint with open circulation. Post-IE peak power output (Wpeak) was higher than IE-Wmax (P < 0.05). After 10 and 60 s recovery in Nx, Wpeak was reduced by 38 ± 9 and 22 ± 10% without OC, and 61 ± 8 and 47 ± 10% with OC (P < 0.05). Following 10 s OC, Wpeak was 20% higher in Hyp than Nx (P < 0.05), despite similar muscle lactate accumulation ([La]) and phosphocreatine and ATP reduction. Sprint performance and anaerobic ATP resynthesis were greater after 60 than 10 s occlusions, despite the higher [La] and [H(+) ] after 60 s than 10 s OC recovery (P < 0.05). The mean rate of ATP turnover during the 60 s OC was 0.180 ± 0.133 mmol.kg wet.(-1) .s(-1) , i.e. equivalent to 32% of leg VO2 peak (ion pumps expended energy). A greater degree of recovery is achieved, however, without occlusion.In conclusion, during incremental exercise task failure is not due to metabolite accumulation or lack of energy resources. Anaerobic metabolism, despite the accumulation of lactate and H(+) , facilitates early recovery even in anoxia. This points to central mechanisms as the principal determinants of task failure both in normoxia and hypoxia, with lower peripheral contribution in hypoxia. This article is protected by copyright. All rights reserved.
This article is protected by copyright. All rights reserved.
We investigated the influence of altered muscle duty cycle on the performance decrements and neuromuscular responses occurring during constant-load, fatiguing bouts of knee extension exercise. We experimentally altered the durations of the muscularly inactive portion of the limb movement cycle, and hypothesized that greater relative durations of inactivity within the same movement task would 1) reduce the rates and extent of muscle performance loss and 2) increase the forces necessary to trigger muscle fatigue. In each condition (Duty Cycle=0.6 & 0.3), male subjects (age = 25.9±2.0 yr(SEM); mass = 85.4±2.6 kg), completed 9-11 exhaustive bouts of two-legged knee extension exercise, at force outputs that elicited failure between 4 and 290 s. The novel duty cycle manipulation produced two primary results; first, we observed two-fold differences in both the extent of muscle performance lost (DC0.6=761±35 N vs DC0.3=366±49 N) and the time course of performance loss. For example, exhaustive trials at the midpoint of these force ranges differed in duration by more than 30 s (t0.6=36±2.6 vs t0.3=67±4.3 s). Second, both the minimum forces necessary to exceed the peak aerobic capacity and initiate a reliance on anaerobic metabolism, and the forces necessary to elicit compensatory increases in EMG were 300% greater in the lower vs higher duty cycle condition. These results indicate that the fatigue-induced compensatory behavior to recruit additional motor units is triggered by a reliance on anaerobic metabolism for ATP resynthesis, and is independent of the absolute level or fraction of the maximum force produced by the muscle.
Copyright © 2014, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology.
The parameters of the power-duration relationship for severe-intensity exercise (i.e., the critical power (CP) and the curvature constant (W')) are related to the kinetics of pulmonary O2 uptake, which may be altered by pacing strategy. We tested the hypothesis that the CP would be higher when derived from a series of self-paced time-trials (TT) than when derived from the conventional series of constant work-rate (CWR) exercise tests. Ten male subjects (age, 21.5 ± 1.9 years; mass, 75.2 ± 11.5 kg) completed 3-4 CWR and 3-4 TT prediction trial protocols on a cycle ergometer for the determination of the CP and W'. The CP derived from the TT protocol (265 ± 44 W) was greater (P < 0.05) than the CP derived from the CWR protocol (250 ± 47 W), while the W' was not different between protocols (TT: 18.1 ± 5.7 kJ, CWR: 20.6 ± 7.4 kJ, P > 0.05). The mean response time of pulmonary O2 uptake was shorter during the TTs than the CWR trials (TT: 34 ± 16, CWR: 39 ± 19 s, P < 0.05). The CP was correlated with the total O2 consumed in the first 60 s across both protocols (r = 0.88, P < 0.05, n = 20). These results suggest that in comparison with the conventional CWR exercise protocol, a self-selected pacing strategy enhances CP and improves severe-intensity exercise performance. The greater CP during TT compared with CWR exercise has important implications for performance prediction, suggesting that TT completion times may be overestimated by CP and W' parameters derived from CWR protocols.
Group III and IV muscle afferents originating in exercising limb muscle play a significant role in the development of fatigue during exercise in humans. Feedback from these sensory neurons to the central nervous system (CNS) reflexively increases ventilation and central (cardiac output) and peripheral (limb blood flow) hemodynamic responses during exercise and thereby assures adequate muscle blood flow and O2 delivery. This response depicts a key factor in minimizing the rate of development of peripheral fatigue and in optimizing aerobic exercise capacity. On the other hand, the central projection of group III/IV muscle afferents impairs performance and limits the exercising human via its diminishing effect on the output from spinal motoneurons which decreases voluntary muscle activation (i.e. facilitates central fatigue). Accumulating evidence from recent animal studies suggests the existence of two subtypes of group III/IV muscle afferents. While one subtype only responds to physiological and innocuous levels of endogenous intramuscular metabolites (lactate, ATP, protons) associated with ?normal?, predominantly aerobic exercise, the other subtype only responds to higher and concurrently noxious levels of metabolites present in muscle during ischaemic contractions or following, for example, hypertonic saline infusions. This review discusses the mechanisms through which group III/IV muscle afferent feedback mediates both central and peripheral fatigue in exercising humans. We also briefly summarize accumulating evidence from recent animal and human studies documenting the existence of two subtypes of group III/IV muscle afferents and the relevance of this discovery for the interpretation of previous work and the design of future studies.
Intense muscle contraction induces high rates of ATP hydrolysis with resulting increases in inorganic phosphate (Pi), H(+) and ADP, factors thought to induce fatigue by interfering with steps in the cross-bridge cycle. Force inhibition is less at physiological temperatures; thus the role of low pH in fatigue has been questioned. Therefore, effects of pH 6.2 and collective effects with 30 mM Pi on the pCa-force relationship were assessed in skinned fast and slow rat skeletal muscle fibers at 15 and 30°C. At 30°C, the pH 6.2 and 30 mM Pi condition significantly depressed peak force in all fiber types with the greatest effect in type IIx fibers. Across fiber types, Ca(2+) sensitivity was depressed by low pH and low pH plus high Pi, with the greater effect at 30°C. For type IIx fibers at 30°C, the pCa50 was 5.36 at pH 6.2 (no added Pi) and 4.98 at pH 6.2, 30 mM Pi, compared to 6.58 for control (pH 7, no added Pi). At 30°C, n2, reflective of thick filament cooperativity, was unchanged by low cell pH but was depressed from 5.02 to 2.46 in type IIx fibers with pH 6.2, 30 mM Pi. With acidosis, activation thresholds of all fiber types required higher free Ca(2+) at both 15 and 30°C. With the exception of type IIx fibers, the Ca(2+) required to reach activation threshold increased further with added Pi. In conclusion, it is clear that fatigue-inducing effects of low cell pH and elevated Pi at near-physiological temperatures are substantial.
We investigated the responses of intramuscular phosphate-linked metabolites and pH (as assessed by (31)P-MRS) during intermittent high-intensity exercise protocols performed with different recovery-interval durations. Following estimation of the parameters of the power-duration relationship (i.e., CP and W') for severe-intensity constant-power exercise, eight male subjects completed three intermittent exercise protocols to exhaustion where periods of high-intensity exercise (60-s) were separated by different durations of passive recovery (18-s, 30-s and 48-s). The tolerable duration of exercise was 304 ± 68 s, 516 ± 142 s and 847 ± 240 s for the 18-s, 30-s and 48-s recovery protocols, respectively (P<0.05). The work done >CP (W>CP) was significantly greater for all intermittent protocols compared to the subjects' W' and this difference became progressively greater as recovery-interval duration was increased. Similarly, the degree of intramuscular phosphocreatine restoration during recovery was greatest, intermediate and least for 48-s, 30-s and 18-s of recovery, respectively (P<0.05). The W>CP in excess of W' increased with greater durations of recovery and this was correlated with the mean magnitude of muscle phosphocreatine reconstitution between work intervals (r = 0.61; P<0.01). During intermittent high-intensity exercise, recovery intervals allow intramuscular homeostasis to be restored, with the degree of restoration being related to the duration of the recovery interval. Consequently, the ability to perform W>CP during intermittent high-intensity exercise and, therefore, exercise tolerance, increases in a predictable manner when recovery-interval duration is extended.
Muscular exercise requires transitions to and from metabolic rates often exceeding an order of magnitude above resting and places prodigious demands on the oxidative machinery and O2-transport pathway. The science of kinetics seeks to characterize the dynamic profiles of the respiratory, cardiovascular, and muscular systems and their integration to resolve the essential control mechanisms of muscle energetics and oxidative function: a goal not feasible using the steady-state response. Essential features of the O2 uptake (VO2) kinetics response are highly conserved across the animal kingdom. For a given metabolic demand, fast VO2 kinetics mandates a smaller O2 deficit, less substrate-level phosphorylation and high exercise tolerance. By the same token, slow VO2 kinetics incurs a high O2 deficit, presents a greater challenge to homeostasis and presages poor exercise tolerance. Compelling evidence supports that, in healthy individuals walking, running, or cycling upright, VO2 kinetics control resides within the exercising muscle(s) and is therefore not dependent upon, or limited by, upstream O2-transport systems. However, disease, aging, and other imposed constraints may redistribute VO2 kinetics control more proximally within the O2-transport system. Greater understanding of VO2 kinetics control and, in particular, its relation to the plasticity of the O2-transport/utilization system is considered important for improving the human condition, not just in athletic populations, but crucially for patients suffering from pathologically slowed VO2 kinetics as well as the burgeoning elderly population. © 2012 American Physiological Society. Compr Physiol 2:933-996, 2012.
Studies performed already in the beginning of the last century revealed the importance of carbohydrate as a fuel during exercise and the importance of muscle glycogen on performance has subsequently been confirmed in numerous studies. However, the link between glycogen depletion and impaired muscle function during fatigue is not well understood and a direct cause-and-effect relationship between glycogen and muscle function remains to be established. The use of electron microscopy has revealed that glycogen is not homogeneously distributed in skeletal muscle fibres, but rather localized in distinct pools. Further, each glycogen granule has its own metabolic machinery with glycolytic enzymes and regulating proteins. One pool of such glycogenolytic complexes is localized within the myofibrils in close contact with key proteins involved in the excitation-contraction coupling and Ca2+ release from the sarcoplasmic reticulum (SR). We and others have provided experimental evidence in favour of a direct role of decreased glycogen, localized within the myofibrils, for the reduction in SR Ca2+ release during fatigue. This is consistent with compartmentalized energy turnover and distinctly localized glycogen pools being of key importance for SR Ca2+ release and thereby affecting muscle contractility and fatigability.
We tested the hypothesis that muscle high-energy phosphate compounds and metabolites related to the fatigue process would be recovered after exhaustion during recovery exercise performed below but not above critical power (CP) and that these changes would influence the capacity to continue exercise. Eight male subjects completed single-leg knee-extension exercise to exhaustion (for ~ 180 s) on three occasions, followed by a work-rate reduction to either severe-intensity exercise (>CP), heavy-intensity exercise (<CP), or a 10 min passive recovery period, in a random order. The muscle metabolic responses to exercise were assessed using (31)P magnetic resonance spectroscopy. There was a significant difference between the sustainable exercise duration during the recovery from exhaustive exercise between the CP conditions (at least 10 min and 39 ± 31 s, respectively; P<0.05). During passive recovery and <CP recovery exercise, muscle phosphocreatine concentration ([PCr]) increased rapidly after the exhaustion point reaching ~ 96 % and ~ 76 % of baseline values, respectively, after 10 min (P<0.05). Moreover, pH increased abruptly, reaching 7.0 ± 0.0 and 7.0 ± 0.2, respectively, after 10 min recovery (P<0.05). However, during >CP recovery exercise, neither muscle [PCr] nor pH recovered, reaching ~37 % of the initial baseline and 6.6 ± 0.2, respectively. These results indicate that the muscle metabolic dynamics in recovery from exhaustive severe-intensity exercise differ according to whether the recovery exercise is performed below or above the CP. These findings confirm the importance of the CP as an intramuscular metabolic threshold which dictates the accumulation of fatigue-related metabolites and the capacity to tolerate high-intensity exercise.
The amplitude of the surface EMG does not reach the level achieved during a maximal voluntary contraction force at the end of a sustained, submaximal contraction, despite near-maximal levels of voluntary effort. The depression of EMG amplitude may be explained by several neural and muscular adjustments during fatiguing contractions, including decreased net neural drive to the muscle, changes in the shape of the motor unit action potentials, and EMG amplitude cancellation. The changes in these parameters for the entire motor unit pool, however, cannot be measured experimentally. The present study used a computational model to simulate the adjustments during sustained isometric contractions and thereby determine the relative importance of these factors in explaining the submaximal levels of EMG amplitude at task failure. The simulation results indicated that the amount of amplitude cancellation in the simulated EMG (∼ 40%) exhibited a negligible change during the fatiguing contractions. Instead, the main determinant of the submaximal EMG amplitude at task failure was a decrease in muscle activation (number of muscle fiber action potentials), due to a reduction in the net synaptic input to motor neurons, with a lesser contribution from changes in the shape of the motor unit action potentials. Despite the association between the submaximal EMG amplitude and reduced muscle activation, the deficit in EMG amplitude at task failure was not consistently associated with the decrease in neural drive (number of motor unit action potentials) to the muscle. This indicates that the EMG amplitude cannot be used as an index of neural drive.
Existing evidence suggests that exercise-induced alterations of the metabolic milieu of locomotor muscle and associated peripheral muscle fatigue affect the central projection of thin-fiber muscle afferents. These neurons provide inhibitory feedback to the CNS and thereby influence the magnitude of central motor drive during high-intensity whole-body endurance exercise. The purpose of this proposed feedback loop would be to regulate and restrict the development of exercise-induced peripheral muscle fatigue and/or associated sensory feedback to an "individual critical threshold." This centrally mediated restriction in the development of peripheral locomotor muscle fatigue might thereby help to prevent excessive disturbance of muscle homeostasis and potential harm to the organism. It seems that the regulatory mechanism is dominant during exercise under "normal" conditions but might become secondary in the face of extreme environmental influences such as severe hypoxia or heat. Most recent data are used to emphasize how the proposed feedback loop might be a key factor limiting performance during high-intensity whole-body endurance exercise.
Increased brain dopamine availability improves prolonged exercise tolerance in the heat. It is unclear whether supplementing the amino-acid precursor of dopamine increases exercise capacity in the heat. Eight healthy male volunteers [mean age 32 ± 11 (SD) years; body mass 75.3 ± 8.1 kg; peak oxygen uptake ([Formula: see text]) 3.5 ± 0.3 L min(-1)] performed two exercise trials separated by at least 7 days in a randomised, crossover design. Subjects consumed 500 mL of a flavoured sugar-free drink (PLA), or the same drink with 150 mg kg body mass(-1) tyrosine (TYR) in a double-blind manner 1 h before cycling to exhaustion at a constant exercise intensity equivalent to 68 ± 5% [Formula: see text] in 30°C and 60% relative humidity. Pre-exercise plasma tyrosine:large neutral amino acids increased 2.9-fold in TYR (P < 0.01), while there was no change in PLA (P > 0.05). Subjects cycled longer in TYR compared to PLA (80.3 ± 19.7 min vs. 69.2 ± 14.0 min; P < 0.01). Core temperature, mean weighted skin temperature, heart rate, ratings of perceived exertion and thermal sensation were similar in TYR and PLA during exercise and at exhaustion (P > 0.05) despite longer exercise time in TYR. The results show that acute tyrosine supplementation is associated with increased endurance capacity in the heat in moderately trained subjects. The results also suggest for the first time that the availability of tyrosine, a nutritional dopamine precursor, can influence the ability to subjectively tolerate prolonged submaximal constant-load exercise in the heat.
Tolerance to high-intensity constant-power (P) exercise is well described by a hyperbola with two parameters: a curvature constant (W') and power asymptote termed "critical power" (CP). Since the ability to sustain exercise is closely related to the ability to meet the ATP demand in a steady state, we reasoned that pulmonary O(2) uptake (Vo(2)) kinetics would relate to the P-tolerable duration (t(lim)) parameters. We hypothesized that 1) the fundamental time constant (τVo(2)) would relate inversely to CP; and 2) the slow-component magnitude (ΔVo(2sc)) would relate directly to W'. Fourteen healthy men performed cycle ergometry protocols to the limit of tolerance: 1) an incremental ramp test; 2) a series of constant-P tests to determine Vo(2max), CP, and W'; and 3) repeated constant-P tests (WR(6)) normalized to a 6 min t(lim) for τVo(2) and ΔVo(2sc) estimation. The WR(6) t(lim) averaged 365 ± 16 s, and Vo(2max) (4.18 ± 0.49 l/min) was achieved in every case. CP (range: 171-294 W) was inversely correlated with τVo(2) (18-38 s; R(2) = 0.90), and W' (12.8-29.9 kJ) was directly correlated with ΔVo(2sc) (0.42-0.96 l/min; R(2) = 0.76). These findings support the notions that 1) rapid Vo(2) adaptation at exercise onset allows a steady state to be achieved at higher work rates compared with when Vo(2) kinetics are slower; and 2) exercise exceeding this limit initiates a "fatigue cascade" linking W' to a progressive increase in the O(2) cost of power production (Vo(2sc)), which, if continued, results in attainment of Vo(2max) and exercise intolerance. Collectively, these data implicate Vo(2) kinetics as a key determinant of high-intensity exercise tolerance in humans.
In exercise physiology, it has been traditionally assumed that high-intensity aerobic exercise stops at the point commonly called exhaustion because fatigued subjects are no longer able to generate the power output required by the task despite their maximal voluntary effort. We tested the validity of this assumption by measuring maximal voluntary cycling power before (mean +/- SD, 1,075 +/- 214 W) and immediately after (731 +/- 206 W) (P < 0.001) exhaustive cycling exercise at 242 +/- 24 W (80% of peak aerobic power measured during a preliminary incremental exercise test) in ten fit male human subjects. Perceived exertion during exhaustive cycling exercise was strongly correlated (r = -0.82, P = 0.003) with time to exhaustion (10.5 +/- 2.1 min). These results challenge the long-standing assumption that muscle fatigue causes exhaustion during high-intensity aerobic exercise, and suggest that exercise tolerance in highly motivated subjects is ultimately limited by perception of effort.
For high-intensity muscular exercise, the time-to-exhaustion (t) increases as a predictable and hyperbolic function of decreasing power (P) or velocity (V ). This relationship is highly conserved across diverse species and different modes of exercise and is well described by two parameters: the "critical power" (CP or CV), which is the asymptote for power or velocity, and the curvature constant (W') of the relationship such that t = W'/(P - CP). CP represents the highest rate of energy transduction (oxidative ATP production, V˙O2) that can be sustained without continuously drawing on the energy store W' (composed in part of anaerobic energy sources and expressed in kilojoules). The limit of tolerance (time t) occurs when W' is depleted. The CP concept constitutes a practical framework in which to explore mechanisms of fatigue and help resolve crucial questions regarding the plasticity of exercise performance and muscular systems physiology. This brief review presents the practical and theoretical foundations for the CP concept, explores rigorous alternative mathematical approaches, and highlights exciting new evidence regarding its mechanistic bases and its broad applicability to human athletic performance.
This experiment investigated the fatigue induced by a 24-h running exercise (24TR) and particularly aimed at testing the hypothesis that the central component would be the main mechanism responsible for neuromuscular fatigue. Neuromuscular function evaluation was performed before, every 4 h during, and at the end of the 24TR on 12 experienced ultramarathon runners. It consisted of a determination of the maximal voluntary contractions (MVC) of the knee extensors (KE) and plantar flexors (PF), the maximal voluntary activation (%VA) of the KE and PF, and the maximal compound muscle action potential amplitude (Mmax) on the soleus and vastus lateralis. Tetanic stimulations also were delivered to evaluate the presence of low-frequency fatigue and the KE maximal muscle force production ability. Strength loss occurred throughout the exercise, with large changes observed after 24TR in MVC for both the KE and PF muscles (-40.9+/-17.0 and -30.3+/-12.5%, respectively; P<0.001) together with marked reductions of %VA (-33.0+/-21.8 and -14.8+/-18.9%, respectively; P<0.001). A reduction of Mmax amplitude was observed only on soleus, and no low-frequency fatigue was observed for any muscle group. Finally, KE maximal force production ability was reduced to a moderate extent at the end of the 24TR (-10.2%; P<0.001), but these alterations were highly variable (+/-15.7%). These results suggest that central factors are mainly responsible for the large maximal muscle torque reduction after ultraendurance running, especially on the KE muscles. Neural drive reduction may have contributed to the relative preservation of peripheral function and also affected the evolution of the running speed during the 24TR.
Mental fatigue is a psychobiological state caused by prolonged periods of demanding cognitive activity. Although the impact of mental fatigue on cognitive and skilled performance is well known, its effect on physical performance has not been thoroughly investigated. In this randomized crossover study, 16 subjects cycled to exhaustion at 80% of their peak power output after 90 min of a demanding cognitive task (mental fatigue) or 90 min of watching emotionally neutral documentaries (control). After experimental treatment, a mood questionnaire revealed a state of mental fatigue (P = 0.005) that significantly reduced time to exhaustion (640 +/- 316 s) compared with the control condition (754 +/- 339 s) (P = 0.003). This negative effect was not mediated by cardiorespiratory and musculoenergetic factors as physiological responses to intense exercise remained largely unaffected. Self-reported success and intrinsic motivation related to the physical task were also unaffected by prior cognitive activity. However, mentally fatigued subjects rated perception of effort during exercise to be significantly higher compared with the control condition (P = 0.007). As ratings of perceived exertion increased similarly over time in both conditions (P < 0.001), mentally fatigued subjects reached their maximal level of perceived exertion and disengaged from the physical task earlier than in the control condition. In conclusion, our study provides experimental evidence that mental fatigue limits exercise tolerance in humans through higher perception of effort rather than cardiorespiratory and musculoenergetic mechanisms. Future research in this area should investigate the common neurocognitive resources shared by physical and mental activity.
Isolated skeletal muscle triads contain a compartmentalized glycolytic reaction sequence catalyzed by aldolase, triosephosphate isomerase, glyceraldehyde-3-phosphate dehydrogenase, and phosphoglycerate kinase. These enzymes express activity in the structure-associated state leading to synthesis of ATP in the triadic junction upon supply of glyceraldehyde 3-phosphate or fructose 1,6-bisphosphate. ATP formation occurs transiently and appears to be kinetically compartmentalized, i.e., the synthesized ATP is not in equilibrium with the bulk ATP. The apparent rate constants of the aldolase and the glyceraldehyde-3-phosphate dehydrogenase/phosphoglycerate kinase reaction are significantly increased when fructose 1,6-bisphosphate instead of glyceraldehyde 3-phosphate is employed as substrate. The observations suggest that fructose 1,6-bisphosphate is especially effectively channelled into the junctional gap. The amplitude of the ATP transient is decreasing with increasing free [Ca2+] in the range of 1 nM to 30 microM. In the presence of fluoride, the ATP transient is significantly enhanced and its declining phase is substantially retarded. This observation suggests utilization of endogenously synthesized ATP in part by structure associated protein kinases and phosphatases which is confirmed by the detection of phosphorylated triadic proteins after gel electrophoresis and autoradiography. Endogenous protein kinases phosphorylate proteins of apparent Mr 450,000, 180,000, 160,000, 145,000, 135,000, 90,000, 54,000, 51,000, and 20,000, respectively. Some of these phosphorylated polypeptides are in the Mr range of known phosphoproteins involved in excitation-contraction coupling of skeletal muscle, which might give a first hint at the functional importance of the sequential glycolytic reactions compartmentalized in triads.
For high-intensity cycling, power (P) can be well described as a hyperbolic function of tolerable work duration (t): P=(W'/t) + PLL W' is a constant and PLL is the lower limit (asymptote) for P which is shown to occur at an O2 uptake ([Vdot]O2) lying above the estimated threshold for sustained blood [lactate] increase (ΘIac) but below the maximum [Vdot]O2 ([Vdot]O2max) obtained during incremental cycling. This relation suggests that, above PLL, only a certain amount of work (W') can be accomplished regardless of its rate of performance, with [Vdot]O2 max being attained at fatigue. Hence, PLL defines a point of discontinuity in the [Vdot]O2-P relation for supra-ΘIac exercise. In order to determine the factors responsible for the continued increase in [Vdot]O2 (to the maximum fatiguing value) at power outputs >PLL, we documented the temporal profiles of metabolic (rectal temperature; blood [lactate], [pyruvate], [norepinephrine], [epinephrine]) and respiratory ([Vdot]E; [Vdot]O2; [Vdot]CO2; blood pH, PCO2, [HCO3 ]) responses to constant-load cycling in eight healthy males at PLL (24 min) and slightly above PLL (to exhaustion, i.e. < 24 min). [Vdot]O2 manifested a delayed steady state at PLL, despite catecholamine levels and core temperature continuing to increase throughout; blood [lactate] and pH plateaued, however. In contrast, [Vdot]O2 continued to increase slowly for the duration of the exercise > PLL and attained [Vdot]O2max. The response patterns at PLL, and > PLL suggest that the slow phase of the [Vdot]O2 response is best correlated with the temporal profile of blood [lactate], and hence the site and route of metabolism of this variable may play a major role in the [Vdot]O2 kinetics for high-intensity exercise.
