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Prediction of performance reduction in self-paced exercise as modulated by the rating of perceived exertion
Abstract
Rating of perceived exertion (RPE) is a scale of exercise difficulty and has been hypothesized to be a regulator of work rate during self-pacing. The goal of this work was to develop a dynamic prediction of RPE and to characterize the control strategy employed to reduce work rate during self-paced exercise using RPE as feedback.
Training and test data were acquired from the literature to develop a linear regression of RPE as a function of four physiological variables: core temperature, mean-weighted skin temperature, metabolic rate, and integral of relative oxygen consumption (R (2) = 0.85). A thermoregulatory model was used to predict core and mean-weighted skin temperature. Utilizing self-paced cycling and running data from the literature, we characterized reductions in work rate with a proportional-derivative control algorithm with RPE as feedback.
Bland-Altman analysis revealed the necessity to parameterize RPE equations for untrained and endurance-trained individuals. Afterwards, dynamic predictions of RPE were accurate for a wide range of activity levels and air temperatures for walking, running, and cycling (LoA and bias of 2.3 and -0.03, respectively). For self-paced exercise, the control algorithm characterized the trend and magnitude of work rate reductions for cycling and running, and showed regulated RPE to be less conservative for shorter vs. longer duration exercise.
A novel methodology to characterize self-paced work intensity, based upon dynamic physiologic response, is provided. The complete model is a useful tool that estimates performance decrements during self-paced exercise and predicts tolerance time for exhaustive fixed-rate exercise.
... We previously developed a TRM to predict body temperature, evaporative heat loss, and shivering heat response for a wide range of environmental conditions, clothing types, and exercise levels. 35 However, our TRM was validated against male data only. Therefore, the overall objective of this work was to expand the TRM to model the thermoregulatory response of women to make predictions which in the future can assist in understanding performance limitations for women performing physical tasks in cold to hot environments. ...
... A full description of the TRM is provided in the supplementary materials of Iyoho et al. 35 The TRM consists of passive and active components that govern heat exchange within the human body and the environment. The human anatomy is approximated with 10 body segments, where each segment is composed of a core, muscle, fat, and skin layer. ...
... 17,[40][41][42][43] Therefore, vasomotor calculations were kept the same for men and women. A mathematical description of vasomotor changes in skin blood flow is shown in the supplementary materials of Iyoho et al. 35 TRM Validation for Women TRM predictions have already been shown to be accurate for male subjects over a wide range of air temperatures, activity levels, and clothing. 35 For the simulations, the intrinsic clothing heat resistance for soaked clothing is assumed to be 7% of the dry intrinsic clothing resistance. ...
In January 2013, the Department of Defense lifted a ban that had prevented women from holding combat positions in the military. However, innate differences in physical traits and physiology between men and women likely will result in differences in physical performance. Sex differences in thermoregulation is a key area that needs to be examined due to the potential impact on physical performance. Therefore, we expanded our previously developed thermoregulation model (TRM) to include the effects of gender. Women have been found to have a lower sweat output in heat stress and lesser shivering in cold stress than men; therefore, the equations for sweat mass loss rate and shivering heat generation were modified for women accordingly. The updated TRM showed good agreement with female data collected from exercise in cool to hot conditions, cold air exposure, and cold water immersion. Gender differences in sweat evaporation appear minimal except for sufficiently high exercise-heat combinations. Gender differences in core temperature and heat generation during cold stress are significant. The expanded TRM can be used to assess gender-specific thermal response with future application to predicting performance differences and optimizing warfighter effectiveness for a wide range of military relevant tasks. © Association of Military Surgeons of the U.S. All rights reserved.
... The minimum and maximum values for initial skin temperature and core temperature were determined by simulating cold (minimum values) and heat-exercise (maximum values) stress with a thermoregulatory model developed by the authors. 19 A core temperature of 39.5°C can be achieved during rigorous exercise without reaching heat exhaustion if the ambient temperature is cool. 20 Skin thicknesses and blood flow values are derived from Lee and Hwang 21 and Johnson et al, 22 respectively. ...
... The authors have developed such a model under the sponsorship of the U.S. Army Medical Research and Materiel Command. 19 BURNSIM's probabilistic dose response has been applied to thermal injury predictions from furnace fires (i.e., USAARL data) and carbon arc sources (i.e., University of Rochester data); but has application to other types of thermal injury. BURNSIM can already be simulated for purely radiant, convective, and conductive source (or for any combination of these heat transfer modes) and contact burns. ...
Objective:
The objective was to augment a burn injury model, BURNSIM, with probabilistic dose-response risk curves.
Methods:
To develop the dose-response, we drew on a considerable amount of historical porcine burn injury data collected by U.S. Army Aeromedical Research Laboratory in the 1970s. The experimental parameters of each usable data point served as inputs to BURNSIM to calculate the burn damage integral (i.e., the internal dose) for 4 severities (mild, intermediate, deep second- and third-degree burns). The binary probability response was constructed and logistic regression was applied to generate the respective dose-response. Historic data collected at the University of Rochester in the 1950s were used for validation.
Results:
Four dose-response curves were generated, ranging from mild to third degree, with tight 95% confidence bands for mild to deep second degree, and slightly wider bands for third degree. Parametric sensitivity analysis revealed that epidermal and whole skin thicknesses, skin temperature, and blood flow rate have a large effect on predicted outcomes.
Conclusions:
Addition of dose-response curves provides a critical augmentation to BURNSIM to improve operational risk assessments of burn hazard. Future recommendations for BURNSIM include the use of body location- and gender-specific parameters with coupling to a thermoregulatory model.
... The future of marathon performed with the integrity of human homeostasis is now more and more considered to be associated with the concept of self-paced run rather than having to follow a constant target speed [169,89,95]. This strategy is adopted in elite runners especially because they have a sufficient metabolic scope [138], a high speed reserve between average marathon and 1000 meters paces [30]. ...
... The future of marathon performed with the integrity of human homeostasis is now more and more considered to be associated with the concept of self-paced run rather than having to follow a constant target speed [169,89,95]. This strategy is adopted in elite runners especially because they have a sufficient metabolic scope [138], a high speed reserve between average marathon and 1000 meters paces [30]. ...
L'amélioration de la performance en course à pied, lors de courses sur du plat, raisonne avec l'actualité et l'objectif de voir un athlète descendre en dessous des deux heures sur Marathon. Cependant, il existe peu d'équipes travaillant de façon transverse sur les sujets de préparation et de stratégie de course à destination du grand public. Les programmes d'entraînement, fondés sur l'expérience des entraîneurs, ne sont pas, ou peu, personnalisés ce qui conduit à des risques de blessures et une perte de la motivation. Une limite de l'analyse actuelle des programmes d'entraînement semble avoir été atteinte et l'entreprise BillaTraining® a pour objectif de construire un pont entre la recherche scientifique et les coureurs amateurs.L'objectif principal de ce travail de thèse est double. Premièrement, nous avons essayé d'apporter une contribution à la recherche dans le domaine de la course à pied. Après avoir accumulé et formaté des données d'entraînements et de courses provenant de différentes sources, nous avons cherché à décrire des phénomènes tels que l'accélération humaine ou encore les différentes stratégies de course employées sur Marathon pour des coureurs dont les performances de durée de course sont comprises entre 2h30 et 4 heures.Deuxièmement, nous avons développé une application web intégrant les trois phases de la méthode BillaTraining®. La première étape est un audit énergétique qui n'est autre qu'un entraînement de trente minutes à la sensation, permettant de connaitre les capacités physiques d'un coureur. La second étape, le radar énergétique, est le bilan de l'audit et agit comme point d'entrée de l'entraînement sur-mesure qui est la troisième et dernière étape.Afin de répondre à ces deux objectifs, nous avons intégré des notions de physiologie, de mathématiques et d'informatique.Les connaissances en physiologie sont basées sur l'état de l'art ainsi que les recherches passées et présentes du professeur Véronique Billat. Par extension, il s'agit du coeur de métier de l'entreprise BillaTraining®. Les idées de recherche présentent dans cette thèse émanent de la physiologie.Les mathématiques, quand à elles, nous ont permis de décrire certains phénomènes physiologiques grâce notamment aux statistiques. Nous avons eu l'occasion d'utiliser le modèle d'Ornstein-Uhlenbeck de retour à la moyenne ou encore la méthode PELT (Pruned Exact Linear Time) pour la détection d'instants de ruptures dans une série temporelle.Finalement, l'informatique permet de faire communiquer les mathématiques et la physiologie à des fins de recherche scientifique et commerciales.
... The future of marathon performed with the integrity of human homeostasis is now more and more considered to be associated with the concept of self-paced run rather than having to follow a constant target speed [35][36][37]. This strategy is adopted in elite runners especially because they have a sufficient metabolic scope [20], a high speed reserve between average marathon and 1000 m paces [38]. ...
Lately, the sub two-hour marathon attempt in Monza was still based on the belief that constant speed is the best way of running. This idea is relayed by marathon organizers who offer pace-group leaders to help the runners to maintain a target race speed. The purposes of this study are to verify the hypotheses that 1. The mass runners try to maintain a constant speed without succeeding. 2. Marathoners run in an asymmetric way and this turns out to be visible in the speed time series. Those two points are independent of the gender, the level of performance (2h30–3h40) and the profile of the race (Paris vs Berlin). Before considering a predictive running strategy for optimizing personal marathon running performance, here we shed light on some significant statistical features by analyzing speed time series data recorded by 273 runners’ GPS. We started with looking for a trend in the speed time series. By means of Kendall's non-parametric rank correlation coefficient we exhibited a decreasing trend in speed data, whichever the level of performance, gender (Male and Female) and race profile (Berlin and Paris marathons). Going deeper in the study we applied a systematic analysis of the asymmetry of speed via classical statistical measures of skewness. Among them the quantiles of the average speed, i.e. the proportion of the race run above or below the final average The combination of the trend and the asymmetry lead to building up a statistical signature for the speed time series which is identical regardless the level of performance, gender and race profile.
During prolonged exercise, ratings of perceived exertion (RPE) and affect (pleasure; activation) play an important role in performance, especially in hot conditions. Although various mechanisms have been tried to manage the effects of heat (e.g. cooling jackets), the purpose of the current research was to assess the effect of a cooling collar on RPE, affect, thermal sensation, and running performance in the heat. Participants (n = 8) wore a cold collar, uncooled collar or no collar as they completed three 90-min preloaded treadmill time-trials in the heat (30.5±0.1°C), which included 75 min at ~60% [Vdot]O2max followed by a 15-min time-trial. Affect, RPE, and thermal sensation were measured throughout. Performance during the time-trial was significantly improved in the cold collar compared with the uncooled collar and no-collar trials; however, pleasure and activation ratings were highest for the no-collar trial. Findings suggest that a cooling collar may improve performance, but not necessarily “feel good”. Practically, it seems necessary to ensure sufficient education about the benefits, on balance, of the cold collar, while the performance improvements outweighed the reported discomfort of athletes in this study. In addition, the cold collar may prove quite beneficial for individuals who work in hot climates and or conditions, as it may be effective in minimizing discomfort associated with heat for other groups as well.
Two studies tested the hypothesis that teleoanticipatory mechanisms regulate the perception of exertion (RPE) in the context of expected exercise duration by the adjustment of attentional focus. Study 1 involved 22 runners who participated in a short (8-mile) run and a long (10-mile) run on separate days. Pace did not differ between conditions (M = 6.3 mph). Runners reported on their attentional focus (proportion of associative to dissociative thoughts) and RPE at regular intervals. Study 2 involved 40 participants who ran twice on a treadmill at the same speed and gradient: once when they expected to run for 10 min (short condition) and once when they expected to run for 20 min (long condition). In both studies, RPE was lower throughout the long condition. In Study 1 there were more dissociative thoughts in the long condition. Study 2 showed the same trend, although the results were nonsignificant. In both studies RPE was inversely correlated with dissociative thoughts, supporting the hypothesis that runners pace themselves cognitively by manipulating their attentional focus.
Core temperature (CT) in combination with heart rate (HR) can be a good indicator of impending heat exhaustion for occupations involving exposure to heat, heavy workloads, and wearing protective clothing. However, continuously measuring CT in an ambulatory environment is difficult. To address this problem we developed a model to estimate the time course of CT using a series of HR measurements as a leading indicator using a Kalman filter. The model was trained using data from 17 volunteers engaged in a 24 h military field exercise (air temperatures 24-36 °C, and 42%-97% relative humidity and CTs ranging from 36.0-40.0 °C). Validation data from laboratory and field studies (N = 83) encompassing various combinations of temperature, hydration, clothing, and acclimation state were examined using the Bland-Altman limits of agreement (LoA) method. We found our model had an overall bias of -0.03 ± 0.32 °C and that 95% of all CT estimates fall within ±0.63 °C (>52 000 total observations). While the model for estimating CT is not a replacement for direct measurement of CT (literature comparisons of esophageal and rectal methods average LoAs of ±0.58 °C) our results suggest it is accurate enough to provide practical indication of thermal work strain for use in the work place.
This article examines how pacing strategies during exercise are controlled by information processing between the brain and peripheral physiological systems. It is suggested that, although several different pacing strategies can be used by athletes for events of different distance or duration, the underlying principle of how these different overall pacing strategies are controlled is similar. Perhaps the most important factor allowing the establishment of a pacing strategy is knowledge of the endpoint of a particular event. The brain centre controlling pace incorporates knowledge of the endpoint into an algorithm, together with memory of prior events of similar distance or duration, and knowledge of external (environmental) and internal (metabolic) conditions to set a particular optimal pacing strategy for a particular exercise bout. It is proposed that an internal clock, which appears to use scalar rather than absolute time scales, is used by the brain to generate knowledge of the duration or distance still to be covered, so that power output and metabolic rate can be altered appropriately throughout an event of a particular duration or distance. Although the initial pace is set at the beginning of an event in a feedforward manner, no event or internal physiological state will be identical to what has occurred previously. Therefore, continuous adjustments to the power output in the context of the overall pacing strategy occur throughout the exercise bout using feedback information from internal and external receptors. These continuous adjustments in power output require a specific length of time for afferent information to be assessed by the brain's pace control algorithm, and for efferent neural commands to be generated, and we suggest that it is this time lag that crates the fluctuations in power output that occur during an exercise bout. These non-monotonic changes in power output during exercise, associated with information processing between the brain and peripheral physiological systems, are crucial to maintain the overall pacing strategy chosen by the brain algorithm of each athlete at the start of the exercise bout.
The objective of this study was to investigate pacing strategy, perceived exertion and heart rate during a competitive run simula-tion. Eight recreational runners ran a 10 km distance in an outdoor 400 m track with 28-30 o C temperature. Before the run they were asked to run the 10 km as faster as possible. The run velocity, the perceived exertion and the heart rate were measured each 400 m. The speed of run decreased on 19 th and 20 th laps (p < 0.05). The heart rate increased significantly on 7 th and 10 th laps (p < 0.05) and achieved steady state afterwards, while the perceived exertion increased statistically until the 13 th lap (p < 0.05). These data su-ggest that pacing strategy, perceived exertion and heart rate have different temporal adjustments during a competitive run. Possibly the run strategy is established before the competition simulation and has an economic aspect to the last lap. This economic effect of run strategy is determined until the half of the distance is com-pleted by rate of perceived exertion modulation, which is a result of metabolic, context and cognitive feedbacks.
This randomized, double-blind, placebo-controlled study was designed to determine the influence of exercise mode, and 6%
carbohydrate (C) versus placebo (P) beverage ingestion, on ratings of perceived exertion (RPE) and hormonal regulation to
2.5 h of high-intensity running and cycling (≈75% maximum oxygen uptake) by ten triathletes who acted as their own controls.
Statistical significance was set at P ≤ 0.05. The pattern of change in RPE over time was significantly different between C and P ingestion (P < 0.001) and between running and cycling modes (P = 0.001). The lowest RPE values were seen in the C-cycling sessions and the highest in the P-running sessions. The pattern
of change in the respiratory exchange ratio and fat and carbohydrate oxidation rates were significantly different between
the C and P conditions but not between the running and cycling modes. C relative to P ingestion (but not exercise mode) was
associated with higher plasma levels of glucose and insulin and lower plasma cortisol and growth hormone levels. The pattern
of change in plasma levels of catecholamines and lactate did not differ between the C and P conditions. These data indicate
that a lower RPE was associated with a higher level of carbohydrate oxidation, higher plasma glucose and insulin levels, and
lower plasma cortisol and growth hormone levels during cycle exercise following C supplementation as compared to P feeding.
These findings support a physiological link between RPE and carbohydrate substrate availability as well as selected hormonal
regulation during cycle exercise.
The rating of perceived exertion (RPE) is a recognized marker of intensity and of homeostatic disturbance during exercise. It is typically monitored during exercise tests to complement other measures of intensity. The purpose of this commentary is to highlight the remarkable value of RPE as a psychophysiological integrator in adults. It can be used in such diverse fashions as to predict exercise capacity, assess changes in training status, and explain changes in pace and pacing strategy. In addition to using RPE to self-regulate exercise, a novel application of the intensity:RPE relationship is to clamp RPE at various levels to produce self-paced bouts of exercise, which can be used to assess maximal functional capacity. Research also shows that the rate of increase in RPE during self-paced competitive events of varying distance, or constant-load tasks where the participant exercises until volitional exhaustion, is proportional to the duration that remains. These findings suggest that the brain regulates RPE and performance in an anticipatory manner based on awareness of metabolic reserves at the start of an event and certainty of the anticipated end point. Changes in pace may be explained by a continuous internal negotiation of momentary RPE compared with a preplanned "ideal rate of RPE progression" template, which takes into account the portion of distance covered and the anticipated end point. These observations have led to the development of new techniques to analyze the complex relationship of RPE and pacing. The use of techniques to assess frontal-cortex activity will lead to further advances in understanding.
Precooling is the pre-exercise reduction of body temperature and is an effective method of improving physiologic function and exercise performance in environmental heat. A practical and effective method of precooling suitable for application at athletic venues has not been demonstrated.
To confirm the effectiveness of pre-exercise ingestion of cold fluid without fluid ingestion during exercise on pre-exercise core temperature and to determine whether pre-exercise ingestion of cold fluid alone without continued provision of cold fluid during exercise can improve exercise performance in the heat.
Randomized controlled clinical trial.
Environmental chamber at an exercise physiology laboratory that was maintained at 32°C, 60% relative humidity, and 3.2 m/s facing air velocity.
Seven male recreational cyclists (age = 21 ± 1.5 years, height = 1.81 ± 0.07 m, mass = 78.4 ± 9.2 kg) participated.
Participants ingested 900 mL of cold (2°C) or control (37°C) flavored water in 3 300-mL aliquots over 35 minutes of pre-exercise rest.
Rectal temperature and thermal comfort before exercise and distance cycled, power output, pacing, rectal temperature, mean skin temperature, heart rate, blood lactate, thermal comfort, perceived exertion, and sweat loss during exercise.
During rest, a greater decrease in rectal temperature was observed with ingestion of the cold fluid (0.41 ± 0.16°C) than the control fluid (0.17 ± 0.17°C) over 35 to 5 minutes before exercise (t(6) = -3.47, P = .01). During exercise, rectal temperature was lower after ingestion of the cold fluid at 5 to 25 minutes (t(6) range, 2.53-3.38, P ≤ .05). Distance cycled was greater after ingestion of the cold fluid (19.26 ± 2.91 km) than after ingestion of the control fluid (18.72 ± 2.59 km; t(6) = -2.80, P = .03). Mean power output also was greater after ingestion of the cold fluid (275 ± 27 W) than the control fluid (261 ± 22 W; t(6) = -2.13, P = .05). No differences were observed for pacing, mean skin temperature, heart rate, blood lactate, thermal comfort, perceived exertion, and sweat loss (P > .05).
We demonstrated that pre-exercise ingestion of cold fluid is a simple, effective precooling method suitable for field-based application.
Context: Precooling is the pre-exercise reduction of body temperature and is an effective method of improving physiologic function and exercise performance in environmental heat. A practical and effective method of precooling suitable for application at athletic venues has not been demonstrated.
Objective: To confirm the effectiveness of pre-exercise ingestion of cold fluid without fluid ingestion during exercise on pre-exercise core temperature and to determine whether pre-exercise ingestion of cold fluid alone without continued provision of cold fluid during exercise can improve exercise performance in the heat.
Design: Randomized controlled clinical trial.
Setting: Environmental chamber at an exercise physiology laboratory that was maintained at 32°C, 60% relative humidity, and 3.2 m/s facing air velocity.
Patients or Other Participants: Seven male recreational cyclists (age = 21±1.5 years, height = 1.81±0.07 m, mass = 78.4±9.2 kg) participated.
Intervention(s): Participants ingested 900 mL of cold (2°C) or control (37°C) flavored water in 3 300-mL aliquots over 35 minutes of pre-exercise rest.
Main Outcome Measure(s): Rectal temperature and thermal comfort before exercise and distance cycled, power output, pacing, rectal temperature, mean skin temperature, heart rate, blood lactate, thermal comfort, perceived exertion, and sweat loss during exercise.
Results: During rest, a greater decrease in rectal temperature was observed with ingestion of the cold fluid (0.41±0.16°C) than the control fluid (0.17±0.17°C) over 35 to 5 minutes before exercise (t6 = -3.47, P = .01). During exercise, rectal temperature was lower after ingestion of the cold fluid at 5 to 25 minutes (t6 range, 2.53-3.38, P≤.05). Distance cycled was greater after ingestion of the cold fluid (19.26±2.91 km) than after ingestion of the control fluid (18.72±2.59 km; t6 = -2.80, P = .03). Mean power output also was greater after ingestion of the cold fluid (275±27 W) than the control fluid (261±22 W; t6 = -2.13, P = .05). No differences were observed for pacing, mean skin temperature, heart rate, blood lactate, thermal comfort, perceived exertion, and sweat loss (P > .05).
Conclusions: We demonstrated that pre-exercise ingestion of cold fluid is a simple, effective precooling method suitable for field-based application.
Ingestion of creatine (Cr) and glycerol (Gly) has been reported to be an effective method in expanding water compartments within the human body, attenuating the rise in heart rate (HR) and core temperature (Tcore) during exercise in the heat. Despite these positive effects, a substantial water retention could potentially impair endurance performance through increasing body mass (BM) and consequently impacting negatively on running economy (RE). The objective of the present study was to investigate the effects of a combined Cr and Gly supplementation on thermoregulatory and cardiovascular responses and RE during running for 30 min at speed corresponding to 60% of maximal oxygen uptake (V˙O2max) in hot and cool conditions.
Cr·H2O (11.4 g), Gly (1 g·kg-1 BM) and Glucose polymer (75 g) were administered twice daily to 15 male endurance runners during a 7-day period. Exercise trials were conducted pre- and post-supplementation at 10 and 35°C and 70% relative humidity.
BM and total body water increased by 0.90 ± 0.40 kg (P < 0.01; mean ± SD) and 0.71 ± 0.42 L (P < 0.01), respectively following supplementation. Despite the significant increase in BM, supplementation had no effect on V˙O2 and therefore RE. Both HR and Tcore were attenuated significantly after supplementation (P < 0.05, for both). Nevertheless, thermal comfort and rating of perceived exertion was not significantly different between pre- and post-supplementation. Similarly, no significant differences were found in sweat loss, serum osmolality, blood lactate and in plasma volume changes between pre- and post-supplementation.
Combining Cr and Gly is effective in reducing thermal and cardiovascular strain during exercise in the heat without negatively impacting on RE.
Carbohydrates (CHOs), branched-chain amino acids (BCAAs) and caffeine are known to improve running performance. However, no information is available on the effects of a combination of these ingredients on performance and neuromuscular function during running.
The present study was designed as a randomized double-blind cross-over placebo-controlled trial. Thirteen trained adult males completed two protocols, each including two conditions: placebo (PLA) and Sports Drink (SPD: CHOs 68.6 g.L-1, BCAAs 4 g.L-1, caffeine 75 mg.L-1). Protocol 1 consisted of an all-out 2 h treadmill run. Total distance run and glycemia were measured. In protocol 2, subjects exercised for 2 h at 95% of their lowest average speeds recorded during protocol 1 (whatever the condition). Glycemia, blood lactate concentration and neuromuscular function were determined immediately before and after exercise. Oxygen consumption (V˙O2), heart rate (HR) and rate of perceived exertion (RPE) were recorded during the exercise. Total fluids ingested were 2 L whatever the protocols and conditions.
Compared to PLA, ingestion of SPD increased running performance (p = 0.01), maintained glycemia and attenuated central fatigue (p = 0.04), an index of peripheral fatigue (p = 0.04) and RPE (p = 0.006). Maximal voluntary contraction, V˙O2, and HR did not differ between the two conditions.
This study showed that ingestion of a combination of CHOs, BCAAs and caffeine increased performance by about 2% during a 2-h treadmill run. The results of neuromuscular function were contrasted: no clear cut effects of SPD were observed.
ClinicalTrials.gov, http://www.clinicaltrials.gov, NCT00799630.
The aim of this study was to examine the influence of aerobic fitness and exercise intensity on the development of thermal and cardiovascular strain in uncompensable heat stress conditions. In three separate trials, eight aerobically trained and eight untrained subjects cycled to exhaustion at 60% (H60%) and 75% (H75%) of maximal oxygen uptake [Formula: see text] in 40°C conditions, and for 60 min at 60% [Formula: see text] in 18°C conditions (CON). Training status had no influence on time to exhaustion between trained (61 ± 10 and 31 ± 9 min) and untrained (58 ± 12 and 26 ± 10 min) subjects (H60% and H75%, respectively). Rectal temperature at exhaustion was also not significantly different between trained (39.8 ± 0.3, 39.3 ± 0.6 and 38.2 ± 0.3°C) and untrained (39.4 ± 0.5, 38.8 ± 0.5 and 38.2 ± 0.4°C) subjects, but was different between trials (H60%, H75% and CON, respectively; P < 0.01). However, because exercise was terminated on reaching the ethics approved rectal temperature limit in four trained subjects in the H60% trial and two in the H75% trial, it is speculated that increased rectal temperature may have further occurred in this cohort. Nonetheless, exhaustion occurred >96% of maximum heart rate in both cohorts and was accompanied by significant declines in stroke volume (15-26%), cardiac output (5-10%) and mean arterial pressure (9-13%) (P < 0.05). The increase in cardiovascular strain appears to represent the foremost factor precipitating fatigue during moderate and high intensity aerobic exercise in the heat in both trained and untrained subjects.
We used incorrect visual feedback of ambient and core temperature in the heat to test the hypothesis that deception would alleviate the decrement in cycling performance compared to a no deception trial. Seven males completed three 30 min cycling time trials in a randomised order on a Kingcycle ergometer. One time trial was in temperate, control conditions (CON: 21.8 ± 0.6°C; 43.3 ± 4.3%rh), the others in hot, humid conditions (HOT: 31.4 ± 0.3°C; 63.9 ± 4.5%rh). In one of the hot, humid conditions (31.6 ± 0.5°C; 65.4 ± 4.3%rh), participants were deceived (DEC) into thinking the ambient conditions were 26.0°C; 60.0%rh and their core temperature was 0.3°C lower than it really was. Compared to CON (16.63 ± 2.43 km) distance covered was lower in HOT (15.88 ± 2.75 km; P < 0.05), but DEC ameliorated this (16.74 ± 2.87 km; P < 0.05). Mean power output was greater in DEC (184.4 ± 60.4 W) than HOT (168.1 ± 54.1 W; P < 0.05) and no difference was observed between CON and DEC. Rectal temperature and iEMG of the vastus lateralis were not different, but RPE in the third minute was lower in DEC than HOT (P < 0.05). Deception improved performance in the heat by creating a lower RPE, evidence of a subtle mismatch between the subconscious expectation and conscious perception of the task demands.
This study analysed cardiopulmonary, metabolic and rating of perceived exertion (RPE) responses during exercise bouts performed below, at and above the second lactate threshold (LT2) intensity.
10 healthy men performed constant workloads to exhaustion at the first lactate threshold (LT1), LT2 and 25% of the difference between LT2 and maximal aerobic power output (TW(25%)) identified during an incremental test. The time to exhaustion (TE) was 93.8 (18.0), 44.5 (16.0) and 22.8 (10.6) min at LT1, LT2 and TW(25%), respectively (p < 0.001). Metabolic and cardiopulmonary parameters and RPE data were time normalised to the exercise bout duration. The correlation between the slope of these variables and TE was calculated.
Differences were found for respiratory exchange ratio (RER), RPE and potassium at LT1; RER, RPE, norepinephrine and potassium at LT2; and ventilation, respiratory rate (RR), RPE, lactate and potassium at TW(25%). Except for RR, no cardiopulmonary or metabolic parameter increased significantly after 50% of the exercise duration, indicating a physiological steady state. VO₂, heart rate and lactate at exhaustion in all exercise bouts were significantly lower than values reached in the maximal incremental test. The slope of most metabolic variables was not correlated to TE in LT1, LT2 and TW(25%), whereas the slope of RPE was significantly correlated to TE (r = -0.72 to -0.84; p < 0.05) for the three exercise intensities.
Contrary to traditional suggestions, exercise at LT1, LT2 and TW(25%) intensities is performed and terminated in the presence of an overall physiological steady state.
Athletes in Malaysia need to perform in a hot and humid environment due to the climatic nature of the country. Chronic supplementation of Panax ginseng (PG) (a deciduous perennial plant belonging to the Araliaceae family) enhances physical performance. As the ergogenic effect of acute supplementation of PG on endurance performance has not been explored in the Malaysian population especially in a hot and humid condition this study was taken up.
Nine heat adapted recreational runners (age: 25.4 ± 6.9 yr, body mass: 57.6 ± 8.4 kg; body height: 168.3 ± 7.6 cm) were recruited in this placebo-controlled double-blind randomized study. Subjects ingested 200 mg of PG one hour before the exercise test on treadmill at 70 per cent of their VO2max in a laboratory environment of 31° C and 70 per cent relative humidity. They drank 3 ml/kg body weight of cool water every 20 min during the exercise to prevent adverse effects of dehydration. Blood samples were drawn every 20 min for the analysis of glucose, lactate, insulin and free fatty acids. Oxygen uptake was determined every 20 min while heart rate, body and skin temperatures, and ratings of perceived exertion (RPE) were recorded every 10 min during the trials.
Endurance running time to exhaustion did not differ between PG and placebo trials. Heart rate, skin temperature, core body temperature, oxygen uptake, RPE, plasma insulin, glucose, free fatty acid and lactate levels during the endurance exercise did not show any significant differences between the trials.
We conclude that acute supplementation of 200 mg of PG did not affect the endurance running performance of the heat-adapted male recreational runners in the heat.
Athletic competition has been a source of interest to the scientific community for many years, as a surrogate of the limits of human ambulatory ability. One of the remarkable things about athletic competition is the observation that some athletes suddenly reduce their pace in the mid-portion of the race and drop back from their competitors. Alternatively, other athletes will perform great accelerations in mid-race (surges) or during the closing stages of the race (the endspurt). This observation fits well with recent evidence that muscular power output is regulated in an anticipatory way, designed to prevent unreasonably large homeostatic disturbances.
Here we demonstrate that a simple index, the product of the momentary Rating of Perceived Exertion (RPE) and the fraction of race distance remaining, the Hazard Score, defines the likelihood that athletes will change their velocity during simulated competitions; and may effectively represent the language used to allow anticipatory regulation of muscle power output.
These data support the concept that the muscular power output during high intensity exercise performance is actively regulated in an anticipatory manner that accounts for both the momentary sensations the athlete is experiencing as well as the relative amount of a competition to be completed.
This study examined the role of skin temperature on self-selected exercise intensity (i.e., power output). Eight well-trained, male cyclists completed two 60 min self-paced cycling bouts during which they completed as much work as possible. Using a liquid-perfused suit, skin temperature (T
Sk) was changed during the two trials such that T
Sk either started hot and was cooled (H to C) or started cold and was heated (C to H) throughout exercise. Pre-exercise core temperatures (T
C) and heart rates (HR) were similar between trials, while T
Sk, thermal comfort and thermal sensation were higher in H to C. The change in T
Sk was similar in magnitude during the two trials. Work completed was greatest in C to H, which was attributed to a higher initial power output. T
C was similar between trials. HR was similar until 35 min had elapsed, after which it became lower in H to C. The perception of effort increased similarly between the two trials, while thermal comfort and thermal sensation generally reflected the changes observed in T
Sk. These results indicate that upon exercise commencement T
Sk and the accompanying thermal perceptions are important inputs in the initial selection of exercise intensity.
Environmental heat stress degrades aerobic performance; however, little research has focused on performance when the selected task elicits modest elevations in core body temperature (<38.5 degrees C).
To determine the effect of environmental heat stress, with modest hyperthermia, on aerobic performance and pacing strategies.
After a 30-min cycling preload at 50% VO2peak, eight euhydrated men performed a 15-min time trial on a cycle ergometer in temperate (TEMP; 21 degrees C, 50% RH) and hot (HOT; 40 degrees C, 25% RH) environments. Core and skin temperature (Tc and Tsk, respectively) and HR were continuously monitored. Performance was assessed by the total work (kJ) completed in 15 min. Pacing was quantified by comparing the percent difference in actual work performed in each of five 3-min blocks normalized to the mean work performed per 3-min block. Pace over the final 2 min was compared with the average pace from minutes 0 to 13 for end spurt analysis.
Tc and HR rose continually throughout both time trials. Peak Tc remained modestly elevated in both environments [mean (range): HOT = 38.20 degrees C (37.97-38.42 degrees C); TEMP = 38.11 degrees C (38.07-38.24 degrees C)], whereas Tsk was higher in HOT (36.19 +/- 0.40 degrees C vs 31.14 +/- 1.14 degrees C), and final HR reached approximately 95% of age-predicted maximum in both environments. Total work performed in HOT (147.7 +/- 23.9 kJ) was approximately 17% less (P < 0.05) than TEMP (177.0 +/- 25.0 kJ). Pace was evenly maintained in TEMP, but in HOT, volunteers were unable to maintain initial pace, slowing progressively over time. A significant end spurt was produced in both environments.
During a brief aerobic exercise time trial where excessive hyperthermia is avoided, total work is significantly reduced by heat stress because of a gradual slowing of pace over time. These findings demonstrate how aerobic exercise performance degrades in hot environments without marked hyperthermia.
This study examined the independent and combined importance of aerobic fitness and body fatness on physiological tolerance and exercise time during weight-bearing exercise while wearing a semipermeable protective ensemble. Twenty-four men and women were matched for aerobic fitness and body fatness in one of four groups (4 men and 2 women in each group). Aerobic fitness was expressed per kilogram of lean body mass (LBM) to eliminate the influence of body fatness on the expression of fitness. Subjects were defined as trained (T; regularly active with a peak aerobic power of 65 ml · kg LBM ⁻¹ · min ⁻¹ ) or untrained (UT; sedentary with a peak aerobic power of 53 ml · kg LBM ⁻¹ · min ⁻¹ ) with high (High; 20%) or low (Low; 11%) body fatness. Subjects exercised until exhaustion or until rectal temperature reached 39.5°C or heart rate reached 95% of maximum. Exercise times were significantly greater in T Low (116 ± 6.5 min) compared with their matched sedentary (UT Low ; 70 ± 3.6 min) or fatness (T High ; 82 ± 3.9 min) counterparts, indicating an advantage for both a high aerobic fitness and low body fatness. However, similar effects were not evident between T High and UT High (74 ± 4.1 min) or between the UT groups (UT Low and UT High ). The major advantage attributed to a higher aerobic fitness was the ability to tolerate a higher core temperature at exhaustion (the difference being as great as 0.9°C), whereas both body fatness and rate of heat storage affected the exercise time as independent factors.
We investigated whether menstrual cycle phase would affect temperature regulation during an endurance exercise bout performed at room temperature (Ta) of 22 degrees C and 60% relative humidity. Nine eumenorrheic women [age 27.2 +/- 3.7 yr, peak O2 uptake (VO2) 2.52 +/- 0.35 l/min] performed 60 min of cycle exercise at 65% of peak VO2. Subjects were tested in both midfollicular (F) and midluteal (L) phases, although one woman did not show a rise in serum progesterone (P4) that is typically evident 1 wk after ovulation. VO2, rectal (Tre) and skin (Tsk) temperatures, heart rates (HR), and ratings of perceived exertion (RPE) were measured throughout exercise. Sweat loss (SL) was estimated from pre- and postexercise body weight differences. VO2, SL, and Tsk were not affected by menstrual cycle phase. Preexercise Tre was 0.3 degrees C higher during L than during F conditions, and this difference increased to 0.6 degrees C by the end of exercise (P less than 0.01). Compared with F, HRs during L were approximately 10 beats/min greater (P less than 0.001) at all times, whereas RPE responses were significantly greater (P less than 0.01) by 50 min of cycling. No differences in any measured values were found in the subject whose P4 was low in both test conditions. Results indicate that thermoregulation (specifically, regulation of Tre), as well as cardiovascular strain and perception of exercise, was adversely affected during the L phase.
The purpose of this study was to investigate the effects of carbohydrate substrate availability on ratings of perceived exertion (RPE) during prolonged subnuiximal running. Thirty marathon runners were recruited as subjects. A double-blind study design was used in which subjects performed an experimental trial that consisted of a 2.5-hr treadmill run at 75-80% V˙O2max. During the experimental trial, the subjects in the carbohydrate feeding group ingested a 6% glucose and fructose solution at a rate of approximately 60 g hr−1. whereas subjects in the placebo group consumed an equal volume of artificially flavored placebo. Statistical analysis of RPE. respiratory exchange ratio, fat and carbohydrate oxidation rale, and blood glucose concentrations indicated that increased carbohydrate substrate availability attenuated the intensity of exertional perceptions during the later stages of prolonged running at 75-80% VO2max in marathon runners.
The purpose of this study was to examine the effects of anticipated task duration on ratings of perceived exertion during treadmill running. Male subjects.( N = 15) completed two separate runs on a motor-driven treadmill at 85% V02 max. During one trial, subjects ran for a period of 20 minutes, while for a second trial, subjects were led to believe that they would be running for 30 minutes. In each case, the trials were terminated at the 20-minute mark. Ratings of perceived exertion, heart rates, respiratory rates, and ventilatory minute volumes were collected across each trial. Results supported the supposition that the anticipation of continued performance mediated ratings of effort expenditure. This effect was obtained only during moderate work levels and was in contrast to research examining mental fatigue.
The objective of this study was to investigate pacing strategy, perceived exertion and heart rate during a competitive run simulation. Eight recreational runners ran a 10 km distance in an outdoor 400 m track with 28-30°C temperature. Before the run they were asked to run the 10 km as faster as possible. The run velocity, the perceived exertion and the heart rate were measured each 400 m. The speed of run decreased on 19th and 20 th laps (p < 0.05). The heart rate increased significantly on 7th and 10th laps (p < 0.05) and achieved steady state afterwards, while the perceived exertion increased statistically until the 13th lap (p < 0.05). These data suggest that pacing strategy, perceived exertion and heart rate have different temporal adjustments during a competitive run. Possibly the run strategy is established before the competition simulation and has an economic aspect to the last lap. This economic effect of run strategy is determined until the half of the distance is completed by rate of perceived exertion modulation, which is a result of metabolic, context and cognitive feedbacks.
Introduction: It has been reported that perceptions of exertion are attenuated during prolonged cycle exercise. following CHO ingestion. However, no studies to date have examined the influence of such feedings on psychological affect during prolonged exercise, even though affect and perceived exertion are different constructs. Purpose: To examine the influence of regular CHO beverage ingestion on affect (pleasure-displeasure) and perceived exertion during prolonged cycle exercise. Methods: In a randomized, double-blind, counterbalanced design, nine endurance trained males cycled for 2 h at 70% VO2max on two occasions, separated by 1 wk. On each occasion, they consumed either a water placebo (PLA) or a 6.4% carbohydrate-electrolyte solution (CHO) immediately before they cycled (5 mL center dot kg(-1) body mass) and every 15 min thereafter (2 mL center dot kg(-1) body mass). Pleasure-displeasure was assessed before, during, and after the prolonged bout of cycling. Results: During exercise, reported pleasure initially improved and was subsequently maintained in the CHO trial, in contrast to a decline reported in the PLA trial. Ratings of pleasure-displeasure were more positive during recovery in the CHO trial compared with the PLA trial (P < 0.05) and the only significant increase (P < 0.05) in pleasure occurred 15 min postexercise in the CHO trial only. RPE increased (P < 0.05) over the course of the bout of cycling and was lower (P < 0.05) 75 min into exercise in the CHO trial. Immediately postexercise, plasma glucose concentration was higher in the CHO compared with the PLA trial (P < 0.05). A main effect of trial was found for plasma cortisol concentration, with higher values reported in PLA trial. Conclusion: Results suggest that CHO ingestion enhanced feelings of pleasure during and following prolonged cycling and highlighted the importance of assessing not only "what," but also "how" a person feels.
The increased use of both the treadmill and cycle ergometer for exercise testing during respirator wear has escalated the need to compare the physiological response relationships between modes. This study compared circulatory, respiratory, and metabolic responses of submaximal cycling and treadmill exercise of similar work rates in 8 males and 6 females to determine whether the two exercise modes elicited different responses. Gender differences for each exercise mode were also assessed. Subjects cycled or walked for 5 min at each of five incremental external work rates of 60, 90, 120, 150, and 180 W. Measurements of HR, VT, Fb' VE' VO2, and VC02 were obtained for each minute of exercise. Varying differences were observed in the respiratory and metabolic responses within gender groups to exercise between cycling and treadmill exercise of equal work rates with cycling eliciting greater responses at intensities of greater than 120 W. For cycling and treadmill exercise, females had significantly higher HR and Fb than males at intensities greater than 90 W, but metabolic responses were similar between gender groups. These results suggest that both exercise modes are useful for protocols evaluating the physiological effects of mask wear during low levels of physical exertion. However, treadmill exercise seems better suited for testing at higher submaximal work rates. Exercise, Males, Treadmill, Females, Cycle ergometer.
Newsholme's theory of central fatigue suggests that acute tryptophan depletion should improve endurance exercise capacity in a warm environment by reducing serotonergic activity in the brain. Eight males cycled to volitional exhaustion at 55 % [Formula: see text] peak in 30.1 ± 0.5 °C and 30 ± 7 % relative humidity on two separate occasions, after consuming either an amino acid load to deplete their circulating tryptophan concentration (TD), or a control amino acid load (CON). Blood samples were taken before ingesting the amino acids, before the start of exercise, every 15 min during exercise and at the point of exhaustion. Heart rate (HR), core (Tc) and skin (Tsk) temperatures and ratings of perceived exertion (RPE) and thermal comfort (TC) were also monitored every 10 min during exercise. Plasma tryptophan (P = 0.003) and free tryptophan (P < 0.001) concentrations, and the free tryptophan to branched-chain amino acid ratio (P = 0.004) were all lower on the TD trial than on the CON trial. There was no difference in endurance exercise capacity (TD 99.2 ± 24.4 min as compared to CON 108.4 ± 21.6 min; P = 0.088). There was a tendency for HR (P = 0.053) and Tc (P = 0.069) to be higher on the TD trials. There were no differences for any of the other parameters. Endurance cycling capacity in a warm environment is not improved by acute tryptophan depletion, suggesting tryptophan availability is not a significant factor in the development of fatigue in such situations.
Only limited research evaluates possible benefits of combined drinking and external cooling (by pouring cold water over the body) during exercise. Therefore, this study examined cold water drinking and external cooling on physiological, perceptual, and performance variables in hot, dry environments. Ten male runners completed four trials of walking 90 min at 30% VO(2max) followed by running a 5-km time trial in 33 ± 1 °C and 30 ± 4% relative humidity. Trials examined no intervention (CON), oral rehydration (OR), external cooling (EC), and oral rehydration plus external cooling (OR + EC). Investigators measured rectal temperature, skin temperatures, heart rate, thirst, thermal sensation, and ratings of perceived exertion (RPE). Oral rehydration (OR and OR + EC) significantly lowered heart rate (P < 0.001) and thirst (P < 0.001) compared with nondrinking (CON and EC) during low-intensity exercise. External cooling (EC and OR + EC) significantly reduced chest and thigh temperature (P < 0.001), thermal sensation (P < 0.001), and RPE (P = 0.041) compared with non-external cooling (CON and OR) during low-intensity exercise. Performance exhibited no differences (CON = 23.86 ± 4.57 min, OR = 22.74 ± 3.20 min, EC = 22.96 ± 3.11 min, OR + EC = 22.64 ± 3.73 min, P = 0.379). Independent of OR, pouring cold water on the body benefited skin temperature, thermal sensation, and RPE during low-intensity exercise in hot, dry conditions but failed to influence high-intensity performance.
This study investigated the effects of the menstrual cycle on prolonged exercise performance both in temperate (20°C, 45% relative humidity) and hot, humid (32°C, 60% relative humidity) conditions.
For each environmental condition, 12 recreationally active females were tested during the early follicular (day 3-6) and midluteal (day 19-25) phases, verified by measurement of estradiol and progesterone. For all four tests, thermoregulatory, cardiorespiratory, and perceptual responses were measured during 60 min of exercise at 60% of maximal oxygen consumption followed by an incremental test to exhaustion.
No differences in exercise performance between menstrual cycle phases were found during temperate conditions (n = 8) despite a higher resting and submaximal exercise core temperature (Tc) in the luteal phase. In hot, humid conditions (n = 8), however, prolonged exercise performance, as exercise time to fatigue, was significantly reduced during the luteal phase. This finding was not only accompanied by higher resting and submaximal exercise Tc but also a higher rate of increase in Tc during the luteal phase. Furthermore, submaximal exercise HR, minute ventilation, and RPE measures were higher during the luteal phase in hot, humid conditions. No significant differences were found over the menstrual cycle in heat loss responses (partitional calorimetry, sweat rate, upper arm sweat composition) and Tc at exhaustion.
In temperate conditions, no changes in prolonged exercise performance were found over the menstrual cycle, whereas in hot, humid conditions, performance was decreased during the luteal phase. The combination of both exercise and heat stress with the elevated luteal phase Tc at the onset of exercise resulted in physiological and perceptual changes and a greater thermosensitivity, which may explain the decrease in performance.
Mechanical work, mechanical power, energy consumption and mechanical efficiency were studied in constant-speed treadmill running of 5 min at seven different exercises around aerobic (AerT) and anaerobic (AnT) thresholds. The true efficiency of concentric (positive) mechanical work and gross efficiency of the whole body in seven male subjects were calculated. The total mechanical work was calculated from film through the translational, potential and rotational energy states as the sum of the changes of all the mechanical energy states in all body segments allowing energy transfer between segments and from energy state to state. The total energy consumption was measured by combining aerobic and anaerobic energy production in resting and working conditions. When the speed of the treadmill was increased from the velocity of 10 km h-1 (2.8 m s-1) to 22 km h-1 (6.1 m s-1), the concentric mechanical work per one step increased from 129 ± 45 J to 228 ± 82 J (P < 0.01). Oxygen consumption increased from 2.22 ± 0.27 l min-1 to 4.47 ± 0.24 l min-1. The amount of blood lactate increased from 0.94 ± 0.53 mmol l-1 at the lowest speed to 9.90 ± 2.89 mmol l-1 at the highest speed (P < 0.001). The true efficiency of concentric work decreased from 74 ± 14% to 56 ± 8% (P < 0.05). At the speed of the AerT, the economy of running, the vertical rise of different body segments and mechanical efficiency of positive work were high. The highest gross efficiency was found at the running speed between the AerT and AnT.
Eight endurance-trained cyclists rode as far as possible in 1 h on a stationary cycle simulator in a moderate environment (20C, 60% relative humidity, 3 ms–1 wind speed) while randomly receiving either no fluid (NF) or attempting to replace their approximate 1.71 sweat loss measured in a previous 1-h familiarisation performance ride at approximately 85% of peak oxygen uptake with artificially sweetened, coloured water (F). During F, the cyclists drank mean 1.49 (SEM 0.14)1 of which mean 0.27 (SEM 0.08)1 remained in the stomach at the end of exercise and mean 0.20 (SEM 0.05) 1 was urinated after the trial. Thus, only mean 1.02 (SEM 0.12)1 of the ingested fluid was available to replace sweat losses during the 1-h performance ride. That fluid decreased the mean average heart rate from 166 (SEM 3) to 157 (SEM 5) beatsmin–1 (P < 0.0001) and reduced the final mean serum [Na–] and osmolalities from 143 (SEM 0.6) to 139 (SEM 0.6) matom1–1(P < 0.005) and from 294 (SEM 1.7) to 290 (SEM 1.9) mosmol1–1 (P = 0.05), respectively. Fluid ingestion did not significantly attenuate rises in plasma anti-diuretic hormone and angiotensin concentrations, or decrease the approximate-15% falls in estimated plasma volume in the F and NF trials. Nor did fluid ingestion significantly affect the approximate 1.71 h–1 sweat rates, the rises in rectal temperature (from 36.6 to 38.3C) or the ratings of perceived exertion in the two trials. Ingestion of approximately 1.51 of fluid produced an uncomfortable feeling of stomach fullness and reduced the mean distance covered in 1 h from 43.1 (SEM 0.7) to 42.3 (SEM 0.6) km (P < 0.05). Thus, trying to replace more than 1.01h–1 sweat losses during high-intensity, short duration exercise in a moderate environment would not appear to induce beneficial physiological effects, and may impair exercise performance.
Initial power output declines significantly during exercise in hot conditions on attaining a rapid increase in skin temperature when exercise commences. It is unclear whether this initial reduced power is mediated consciously, through thermal perceptual cues, or is a subconscious process. The authors tested the hypothesis that improved thermal perception (feeling cooler and more comfortable) in the absence of a change in thermal state (ie, similar deep-body and skin temperatures between spray conditions) would alter pacing and 40 km cycling time trial (TT) performance.
Eleven trained participants (mean (SD): age 30 (8.1) years; height 1.78 (0.06) m; mass 76.0 (8.3) kg) completed three 40 km cycling TTs in standardised conditions (32°C, 50% RH) with thermal perception altered prior to exercise by application of cold-receptor-activating menthol spray (MENTHOL SPRAY), in contrast to a separate control spray (CONTROL SPRAY) and no spray control (CON). Thermal perception, perceived exertion, thermal responses and cycling TT performance were measured.
MENTHOL SPRAY induced feelings of coolness and improved thermal comfort before and during exercise. Skin temperature profile at the start of exercise was similar between sprays (CON-SPRAY 33.3 (1.1)°C and MENTHOL SPRAY 33.4 (0.4)°C, but different to CON 34.5 (0.5)°C), but there was no difference in the pacing strategy adopted. There was no performance benefit using MENTHOL SPRAY; cycling TT completion time for CON is 71.58 (6.21) min, for CON-SPRAY is 70.94 (6.06) min and for MENTHOL SPRAY is 71.04 (5.47) min.
The hypothesis is rejected. Thermal perception is not a primary driver of early pacing during 40 km cycling TT in hot conditions in trained participants.
Major sports championships are often scheduled in warm/dry and warm/humid environments, so it is important to be able to quantify the influence of these environmental extremes on work capacity. The aim of the present study was to examine the influence of relative humidity on endurance exercise performance in a warm environment. Eight male volunteers (mean ± SD age 26 ± 4 years; height 1.80 ± 0.03 m; body mass 72.0 ± 7.0 kg; VO(2)max 4.38 ± 0.65 l/min) performed four cycle exercise trials at 70% maximum oxygen uptake until volitional exhaustion in an environmental chamber maintained at 30.2 ± 0.2°C. Volunteers were tested under four relative humidity (rh) conditions: 24%, 40%, 60% and 80%. Core and weighted mean skin temperature, heart rate, skin blood flow, and cutaneous vascular conductance (CVC) were recorded at rest and at regular intervals during exercise. Mean (SD) time to exhaustion was 68 ± 19, 60 ± 17, 54 ± 17, and 46 ± 14 min at 24, 40, 60, and 80% rh, respectively (P < 0.001); exercise time was significantly less at 60 (P = 0.013) and 80% (P = 0.005) rh than recorded at 24% rh. There were no differences in core temperature (P = 0.480) and heart rate (P = 0.097) between trials. Core temperature at exhaustion was 39.0 ± 0.3°C at 24, 40, and 60% rh and 39.1 ± 0.3°C at 80% rh (P = 0.159). Mean skin temperature at the point of exhaustion was higher at 80% rh than at 24% rh (P < 0.001). Total sweat loss was similar between trials (P = 0.345), but sweating rate was higher at 60 and 80% rh than at 24% rh (P < 0.001). The results suggest that exercise capacity at moderate intensity in a warm environment is progressively impaired as the relative humidity increases. Early fatigue in the higher humidity trials was accompanied by a faster rate of rise in core temperature and a greater weighted mean skin temperature, with no differences in heart rate, skin blood flow or the metabolic response to exercise.
This study examined the influence of relative humidity on endurance exercise performance in a warm environment. Eight male volunteers performed four cycle exercise trials at 70% maximum oxygen uptake until volitional exhaustion in an environmental chamber maintained at 30.2 ± 0.2°C. Volunteers were tested under four relative humidity (rh) conditions: 24, 40, 60 and 80%. Core and weighted mean skin temperature, heart rate, skin blood flow, and cutaneous vascular conductance were recorded at rest and at regular intervals during exercise. Mean ± SD time to exhaustion was 68 ± 19, 60 ± 17, 54 ± 17, and 46 ± 14 min at 24, 40, 60, and 80% rh, respectively (P < 0.001); exercise time was significantly less at 60% (P = 0.013) and 80% (P = 0.005) rh than recorded at 24% rh. There were no differences in core temperature (P = 0.480) and heart rate (P = 0.097) between trials. Core temperature at exhaustion was 39.0 ± 0.3°C at 24, 40, and 60% rh and 39.1 ± 0.3°C at 80% rh (P = 0.159). Mean skin temperature at the point of exhaustion was higher at 80% rh than at 24% rh (P < 0.001). Total sweat loss was similar between trials (P = 0.345), but sweating rate was higher at 60 and 80% rh than at 24% rh (P < 0.001). The results suggest that exercise capacity at moderate intensity in a warm environment is progressively impaired as the relative humidity increases.
The purpose of this study was to examine the effect of environmental temperature on variability in power output, self-selected pacing strategies, and performance during a prolonged cycling time trial. Nine trained male cyclists randomly completed four 40 km cycling time trials in an environmental chamber at 17°C, 22°C, 27°C, and 32°C (40% RH). During the time trials, heart rate, core body temperature, and power output were recorded. The variability in power output was assessed with the use of exposure variation analysis. Mean 40 km power output was significantly lower during 32°C (309 ± 35 W) compared with 17°C (329 ± 31 W), 22°C (324 ± 34 W), and 27°C (322 ± 32 W). In addition, greater variability in power production was observed at 32°C compared with 17°C, as evidenced by a lower (P = .03) standard deviation of the exposure variation matrix (2.9 ± 0.5 vs 3.5 ± 0.4 units, respectively). Core temperature was greater (P < .05) at 32°C compared with 17°C and 22°C from 30 to 40 km, and the rate of rise in core temperature throughout the 40 km time trial was greater (P < .05) at 32°C (0.06 ± 0.04°C·km-1) compared with 17°C (0.05 ± 0.05°C·km-1). This study showed that time-trial performance is reduced under hot environmental conditions, and is associated with a shift in the composition of power output. These finding provide insight into the control of pacing strategies during exercise in the heat.
The aim of the present investigation was to examine the influence of environmental heat stress (35 degrees C) on 4-km cycling time trial performance using simulated environmental conditions and facing air velocities that closely reflect competitive situations. Nine competitive cyclists (age 34 +/- 5 years, maximal oxygen uptake 61.7 +/- 8.6 ml . kg (-1) . min (-1)) completed a simulated 4-km cycling time trial in laboratory ambient temperatures (dry bulb temperatures) of 35 degrees C and 13 degrees C (relative humidity 60 %, air velocity 5.6 m/s). Mean performance time was reduced in 35 degrees C (390.1 +/- 19.6 s) compared to 13 degrees C (382.8 +/- 18.2 s) (95 % CI of difference = 4.0 to 10.6 s; p < 0.01). This was consistent with a decline in mean power output throughout the duration of exercise in 35 degrees C compared with 13 degrees C (p < 0.01). Mean skin temperature and mean body temperatures were elevated at rest and throughout the duration of exercise in 35 degrees C (p < 0.01). A higher level of muscle temperature was also observed at the onset and cessation of exercise in 35 degrees C (p < 0.01). The rate of heat storage (35 degrees C, 413.6 +/- 130.8 W . m (-2); 13 degrees C, 153.1 +/- 112.5 W . m (-2)) representative of the entire 4-km time trial was greater in the heat (p < 0.01). When expressed per kilometre, however, difference in the rate of heat storage between conditions declined during the final kilometre of exercise (p = 0.06). We conclude that the current decrements in self-selected work-rate in the heat are mediated to some extent through afferent feedback arising from changes in heat storage at rest and during the early stages of exercise which serve to regulate the subsequent exercise intensity in attempt to preserve thermal homeostasis.
Caffeine's metabolic and performance effects have been widely reported. However, caffeine's effects on affective states during prolonged exercise are unknown. Therefore, this was examined in the present study. Following an overnight fast and in a randomised, double-blind, counterbalanced design, twelve endurance trained male cyclists performed 90 min of exercise at 70% VO(₂ max) 1h after ingesting 6 mg kg⁻¹ BM of caffeine (CAF) or placebo (PLA). Dimensions of affect and perceived exertion were assessed at regular intervals. During exercise, pleasure ratings were better maintained (F(₃,₃₈)=4.99, P < 0.05) in the CAF trial compared to the PLA trial with significantly higher ratings at 15, 30 and 75 min (all P < 0.05). Perceived exertion increased (F(₃,₃₈) = 19.86, P < 0.01) throughout exercise and values, overall, were significantly lower (F(₁,₁₁) = 9.26, P < 0.05) in the CAF trial compared to the PLA trial. Perceived arousal was elevated during exercise but did not differ between trials. Overall, the results suggest that a moderate dose of CAF ingested 1h prior to exercise maintains a more positive subjective experience during prolonged cycling. This observation may partially explain caffeine's ergogenic effects.
The present study independently evaluated temperature and thermal perception as controllers of thermoregulatory behavior in humans. This was accomplished using a self-paced exercise and heat stress model in which twelve physically active male subjects exercised at a constant subjective rating of perceived exertion (16, 'hard--very hard') while their face was thermally and non-thermally cooled, heated, or left alone (control trial). Thermal cooling and heating were achieved via forced convection, while non-thermal cooling and heating were accomplished via the topical application of menthol and capsaicin solutions. Evidence for thermoregulatory behavior was defined in terms of self-selected exercise intensity, and thus exercise work output. The results indicate that, in the absence of changes in temperature, non-thermal cooling and warming elicited thermal sensory and discomfort sensations similar to those observed during thermal cooling and warming. Furthermore, the perception of effort was maintained throughout exercise in all trials, while the initial and final exercise intensities were also similar. Thermal and non-thermal cooling resulted in the highest work output, while thermal warming the lowest. Non-thermal warming and control trials were similar. Heart rate, mean skin and core (rectal) temperatures, and whole body and local (neck) sweat rates were similar between all trials. These data indicate that changes in temperature are not a requirement for the initiation of thermoregulatory behavior in humans. Rather, thermal sensation and thermal discomfort are capable behavioral controllers.
It has been proposed that self-paced exercise in the heat is regulated by an anticipatory reduction in work rate based on the rate of heat storage. However, performance may be impaired by the development of hyperthermia and concomitant rise in cardiovascular strain increasing relative exercise intensity. This study evaluated the influence of thermal strain on cardiovascular function and power output during self-paced exercise in the heat. Eight endurance-trained cyclists performed a 40 km simulated time trial in hot (35°C) and thermoneutral conditions (20°C), while power output, mean arterial pressure, heart rate, oxygen uptake and cardiac output were measured. Time trial duration was 64.3 ± 2.8 min (242.1 W) in the hot condition and 59.8 ± 2.6 min (279.4 W) in the thermoneutral condition (P < 0.01). Power output in the heat was depressed from 20 min onwards compared with exercise in the thermoneutral condition (P < 0.05). Rectal temperature reached 39.8 ± 0.3 (hot) and 38.9 ± 0.2°C (thermoneutral; P < 0.01). From 10 min onwards, mean skin temperature was ~7.5°C higher in the heat, and skin blood flow was significantly elevated (P < 0.01). Heart rate was ~8 beats min(-1) higher throughout hot exercise, while stroke volume, cardiac output and mean arterial pressure were significantly depressed compared with the thermoneutral condition (P < 0.05). Peak oxygen uptake measured during the final kilometre of exercise at maximal effort reached 77 (hot) and 95% (thermoneutral) of pre-experimental control values (P < 0.01). We conclude that a thermoregulatory-mediated rise in cardiovascular strain is associated with reductions in sustainable power output, peak oxygen uptake and maximal power output during prolonged, intense self-paced exercise in the heat.
The aim of this two-part experiment was to investigate the effect of cooling the neck on time-trial performance in hot conditions (~30°C; 50% RH). In Study A, nine participants completed a 75-min submaximal (~60% V(O₂(max)) pre-load phase followed by a 15-min self-paced time-trial (TT) on three occasions: one with a cooling collar (CC(90)), one without a collar (NC(90)) and one with the collar uncooled (C(90)). In Study B, eight participants completed a 15-min TT twice: once with (CC(15)) and once without (NC(15)) a cooling collar. Time-trial performance was significantly improved in Study A in CC(90) (3,030 ± 485 m) compared to C(90) (2,741 ± 537 m; P = 0.008) and NC(90) (2,884 ± 571 m; P = 0.041). Fifteen-minute TT performance was unaffected by the collar in Study B (CC(15) = 3,239 ± 267 m; NC(15) = 3,180 ± 271 m; P = 0.351). The collar had no effect on rectal temperature, heart rate or RPE. There was no effect of cooling the neck on S100β, cortisol, prolactin, adrenaline, noradrenaline or dopamine concentrations in Study A. Cooling the neck via a cooling collar can improve exercise performance in a hot environment but it appears that there may be a thermal strain threshold which must be breached to gain a performance benefit from the collar.
This study examined the effects of maintaining euhydration by ingesting fluids with or without carbohydrate on subjective responses of untrained men during prolonged exercise in a hot environment. Six healthy untrained subjects completed 90 min of cycling exercises at 55% maximal oxygen consumption (V(O2max)) in a hot environment (temperature: 28(o)C, humidity: 50%) under three different experimental conditions. During the first trial, subjects did not ingest fluids during exercise (dehydration (DH) trial). In the second and third trials, subjects received mineral water (MW) and hypotonic fluid containing carbohydrate (HF), respectively, in amounts equaling their weight loss in the DH trial. At the end of exercise, the overall rating of perceived exertion (RPE-O) was lower in the MW and HF trials than in the DH trial (14.3+/-1.0 and 13.7+/-0.6 vs 17.7+/-1.0, p<0.05, respectively). RPE-cardiovascular and RPE-legs were lower at the end of exercise in the HF trial compared with the DH trial. V(O2), heart rate (HR), and rectal temperature increased during exercise in the three trials. At the end of exercise, the drift in V(O2) was lower in the MW and HF trials than in the DH trial (304+/-41 and 339+/-40 vs 458+/-33 mL, p<0.05, respectively). HR at the end of exercise in the HF trial was lower than in the DH trial (158+/-5 vs 173+/-7 bpm, p<0.05). These results suggest that maintaining euhydration during prolonged exercise in untrained men could attenuate RPE-O and that hypotonic electrolyte-carbohydrate solution could attenuate RPE-legs during exercise.
The objective of the present study was to examine ratings of perceived exertion (RPE) between adult men (n = 10) and women (n = 10) during two different modes of fatiguing exercise. Participants provided their rating of perceived exertion (6-20 scale) while performing single-leg heel raises and exercise on a rowing ergometer, during two separate experimental sessions. During the heel raise exercise, ratings of perceived exertion were reported for the exercising calf muscles, while a single undifferentiated and two differentiated ratings were obtained during the rowing exercise. Perceived exertion responses were standardized across the exercise duration between participants, via linear interpolation and power function modelling. No significant differences were observed between the sexes in number of heel raises; however, women exercised significantly (P < 0.05) longer during the rowing exercise. No significant differences were observed between the sexes for ratings of perceived exertion obtained via linear interpolation. However, power function modelling revealed greater (P < 0.05) increases for women during the heel raises. The findings of the present study suggest the presence of a subtle difference in the perceived exertion response between the sexes when modelled as a power function during single-joint exercise.
The aim of this investigation was to compare gender differences in physiologic and perceptual responses during a 1-h run at recent marathon pace and running economy at three speeds in recreational marathon runners.
In a counterbalanced design, 10 men and 10 women completed a 1-h treadmill run and a running economy test. Treadmill speed for the 1-h run ranged from 141 to 241 mmin(-1) and 134, 168, and 188 m x min(-1) for running economy. Physiologic parameters (oxygen uptake, carbon dioxide production, pulmonary ventilation, and heart rate) and perceived exertion were measured. Repeated-measures ANOVA was used to compare any gender differences (P < .05) during the 1-h run and a two-way ANOVA was used to compare running economy. With this sample, estimated marathon energy expenditure, body composition, and maximal physiologic function was reported.
With the exception of an allometric expression of VO2 (mL x min(-1) kg BW(-0.75)), similar gender physiologic and perceptual responses were found during the 1-h run. Although not significant, the females exercised at a higher percent VO2(max) (8% to 9%) during the run. Similar gender differences were also noted during the running economy tests.
Although the male runners completed a recent marathon significantly faster than the females, similar gender physiologic and perceptual responses were generally found during the 1-h treadmill run and the running economy tests.
This study investigated the effects of precooling on performance and pacing during self-paced endurance cycling in the heat and, further, the effects of cooling on contractile function as a mechanism for performance changes.
After familiarization, eight male cyclists performed two randomized 40-min time trials on a cycle ergometer in 33 degrees C. Before the time trials, participants underwent either a 20-min lower-body cold-water immersion procedure or no cooling intervention. Before and after the intervention and the time trial, voluntary force (maximal voluntary contraction (MVC)), superimposed force (SIF), evoked twitch force (peak twitch force (Pf)), muscle temperature, and blood metabolites were measured. Further, measures of core and skin temperature and HR were recorded before, during, and after cooling and time trial.
Results indicated that cycling performance was improved with precooling (198 +/- 25 vs 178 +/- 26 W for precooling and control, respectively; P = 0.05). Although core, muscle, skin, and mean body temperatures were lower in the cooling condition until the 20th minute (P < 0.05), performance did not differ until the last 10 min of the time trial, by which time no differences in physiological measures were present. Further, while MVC and SIF were reduced postexercise in both conditions, MVC, SIF, and Pf were not different between conditions preexercise or postexercise.
In conclusion, a precooling intervention improved self-paced endurance exercise; however, the improvement in performance became evident after measured physiological differences induced by precooling had dissipated. Further, the lack of difference between conditions in MVC, SIF, or Pf indicates that improvements in performance did not result from an improvement in contractile function, suggesting that improvements may result from other mechanisms such as muscle recruitment.