Article

Muscle fiber type effects on energetically optimal cadences in cycling

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Abstract

Fast-twitch (FT) and slow-twitch (ST) muscle fibers vary in their mechanical and energetic properties, and it has been suggested that muscle fiber type distribution influences energy expenditure and the energetically optimal cadence during pedaling. However, it is challenging to experimentally isolate the effects of muscle fiber type on pedaling energetics. In the present study, a modeling and computer simulation approach was used to test the dependence of muscle energy expenditure on pedaling rate during submaximal cycling. Simulations were generated using a musculoskeletal model at cadences from 40 to 120 rev min(-1), and the dynamic and energetic properties of the model muscles were scaled to represent a range of muscle fiber types. Energy expenditure and the energetically optimal cadence were found to be higher in a model with more FT fibers than a model with more ST fibers, consistent with predictions from the experimental literature. At the muscle level, mechanical efficiency was lower in the model with a greater proportion of FT fibers, but peaked at a higher cadence than in the ST model. Regardless of fiber type distribution, mechanical efficiency was low at 40 rev min(-1), increased to a broad plateau between 60 and 100 rev min(-1) , and decreased substantially at 120 rev min(-1). In conclusion, muscle fiber type distribution was confirmed as an important determinant of the energetics of pedaling.

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... Although the active muscle volume has been typically quantified by combining measures of joint torque with morphological data from human cadavers (Kipp et al., 2018;Biewener et al., 2004), such estimates often ignore muscle dynamics (e.g., muscle length and velocity) which contribute to activation requirements. An alternative approach is to use musculoskeletal simulations (Delp et al., 1990;Arnold et al., 2013) to predict muscle forces and activations required of all muscles required to achieve cycling mechanics (Umberger et al.,2006;Lai, et al., 2017;Lai et al., 2021). Musculoskeletal simulations can be used to determine the instantaneous active muscle volume (across all muscles) and also estimations of local muscle energy consumption (Umberger, 2010;Umberger et al., 2006). ...
... An alternative approach is to use musculoskeletal simulations (Delp et al., 1990;Arnold et al., 2013) to predict muscle forces and activations required of all muscles required to achieve cycling mechanics (Umberger et al.,2006;Lai, et al., 2017;Lai et al., 2021). Musculoskeletal simulations can be used to determine the instantaneous active muscle volume (across all muscles) and also estimations of local muscle energy consumption (Umberger, 2010;Umberger et al., 2006). Although such models still require validation under a range of conditions (Park et al.,2022), including the sparse mechanical conditions achievable during cycling, this approach could help to elucidate whether metabolic cost and active muscle volume differ. ...
... Furthermore, the metabolic cost minima was considerably lower than the SSC across power conditions. We suspect that the mismatch between minimizing summed active muscle volume and metabolic rate was due to the additional cost of muscle shortening at high rates with increased cadence (Barclay and Curtin, 2023;Fenn, 1924;Umberger et al., 2006). The summed average active muscle volume likely acts as a signal of the demand placed on motor units and muscle fibers, rather than a proxy of energy expenditure. ...
... Consequently, the effect of maintaining pre-limb loss muscle strength on the metabolic cost of walking post-limb loss is unknown. Optimal control simulations can be useful in such situations where obtaining data from live humans is impractical or impossible [14] and in situations where multiple objectives are relevant in the control problem, e.g. metabolic cost, gait deviations, symmetry, balance, joint loading, etc. [15]. ...
... Uniform distributions for muscle moment arm lengths, maximum isometric forces, fast-twitch fiber fractions, and unloaded series elastic component lengths were defined centered on the original value with a width of ±10%, and new sets of parameter values were drawn randomly from these distributions to define a sample of 25 subjects. These particular parameters were used to define subjects because model results can be particularly sensitive to their values [14,28,29]. The 10% distribution width is a reasonable estimate of the variance between human subjects in these parameters [30]. ...
... where 0 i(t) 1 is a control variable analogous to a motor current, a(t) is the motor activation, τ max = 500 Nm is the maximum torque, and k = 400 Nm/rad. The motor activation rate constants c 1 = 5 s -1 and c 2 = 30 s -1 produced smooth motor torque while allowing very fast activation dynamics, analogous to a 100% fast-twitch muscle [14,37]. The maximum torque was set simply to allow the prosthesis to produce a realistic range of torques for walking. ...
Article
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Recent studies on relatively young and fit individuals with limb loss suggest that maintaining muscle strength after limb loss may mitigate the high metabolic cost of walking typically seen in the larger general limb loss population. However, these data are cross-sectional and the muscle strength prior to limb loss is unknown, and it is therefore difficult to draw causal inferences on changes in strength and gait energetics. Here we used musculoskeletal modeling and optimal control simulations to perform a longitudinal study (25 virtual “subjects”) of the metabolic cost of walking pre- and post-limb loss (unilateral transtibial). Simulations of walking were first performed pre-limb loss on a model with two intact biological legs, then post-limb loss on a model with a unilateral transtibial prosthesis, with a cost function that minimized the weighted sum of gait deviations plus metabolic cost. Metabolic costs were compared pre- vs. post-limb loss, with systematic modifications to the muscle strength and prosthesis type (passive, powered) in the post-limb loss model. The metabolic cost prior to limb loss was 3.44±0.13 J/m/kg. After limb loss, with a passive prosthesis the metabolic cost did not increase above the pre-limb loss cost if pre-limb loss muscle strength was maintained (mean -0.6%, p = 0.17, d = 0.17). With 10% strength loss the metabolic cost with the passive prosthesis increased (mean +5.9%, p < 0.001, d = 1.61). With a powered prosthesis, the metabolic cost was at or below the pre-limb loss cost for all subjects with strength losses of 10% and 20%, but increased for all subjects with strength loss of 30% (mean +5.9%, p < 0.001, d = 1.59). The results suggest that maintaining muscle strength may prevent an increase in the metabolic cost of walking following unilateral transtibial limb loss, and that a gait with minimal deviations can be achieved when muscle strength is sufficiently high, even when using a passive prosthesis.
... The distribution of the muscle fibers can influence the cycling performance in terms of VO2 response, which can be quantified by Effmet. This distribution, in the muscles, is quite heterogeneous, and the percentage of ST and FT fibers heavily influences the indexes assessing the performance, as confirmed also by quantitative models (Coyle et al., 1992; Umberger et al., 2006). ...
... These two quantities are influenced from, and mutually connected to, several factors, even different in nature, that have not been yet completely investigated, and whose cross-effects are still far from being fully understood. Among these factors it is worth citing the following: muscle fibers distribution (Staron and Pette, 1986; Coyle et al., 1991, 1992; Ahlquist et al., 1992; Hansen et al., 2002; Umberger et al., 2006; Hansen and Sjøgaard, 2007), pedaling cadence (Chavarren and Calbet, 1999; Neptune and Herzog, 1999; Neptune and Hull, 1999; MacIntosh et al., 2000; Lucía et al., 2001; Hansen et al., 2002; Umberger et al., 2006; Bieuzen et al., 2007; Hansen and Sjøgaard, 2007; Mornieux et al., 2008; Abbiss et al., 2009; Ettema et al., 2009; Vercruyssen and Brisswalter, 2010; Leirdal and Ettema, 2011), biomechanical characteristics (Davis and Hull, 1981; Coyle et al., 1991; Neptune and Herzog, 2000; Bibbo et al., 2006; Cannon et al., 2007; Korff et al., 2007, 2011; Sarre and Lepers, 2007; Van Sickle and Hull, 2007; Mornieux et al., 2008, 2010; Carpes et al., 2010; Wakeling et al., 2010; Theurel et al., 2012; Romanov, 2008), ergogenic factors, which include dietary supplements and psychological strategies (Morgan, 1973; Morgan et al., 1973; Foster et al., 1994; Morgan, 1985; Dietary Supplement Health, 1994; Ulmer, 1996; Garcin et al., 1998; Berger et al., 1999; Raglin, 2001; Williamson et al., 2001; Albertus et al., 2005; Williams, 2004, 2005; MacRae and Mefferd, 2006; Tucker et al., 2006; Bishop, 2010; Waterhouse et al., 2010) and, last but not least, muscular fatigue (MFat) (Coast and Welch, 1985; Neptune and Hull, 1999; Lepers et al., 2002; Abbiss and Laursen, 2005; Theurel and Leperd, 2008; Bini et al., 2010; Theurel et al., 2012). ...
... In particular, the correlation between MHC-I and GE is positive when subjects pedal at preset pedal rates, and becomes negative when a freely PC is chosen (Chavarren and Calbet, 1999; Hansen et al., 2002; Zameziati et al., 2006). Musculoskeletal models and computer simulations confirmed those experimental values (Seabury et al., 1977; Coast and Welch, 1985; Neptune and Hull, 1999; Umberger et al., 2003, 2006). It has also been reported that a low PC (around 50 rpm), for the same metabolic cost, causes augmented muscular forces when compared to higher PCs (Ahlquist et al., 1992). ...
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Finding an optimum for the cycling performance is not a trivial matter, since the literature shows the presence of many controversial aspects. In order to quantify different levels of performance, several indexes have been defined and used in many studies, reflecting variations in physiological and biomechanical factors. In particular, indexes such as Gross Efficiency (GE), Net Efficiency (NE) and Delta Efficiency (DE) have been referred to changes in metabolic efficiency (EffMet), while the Indexes of Effectiveness (IE), defined over the complete crank revolution or over part of it, have been referred to variations in mechanical effectiveness (EffMech). All these indicators quantify the variations of different factors [i.e., muscle fibers type distribution, pedaling cadence, setup of the bicycle frame, muscular fatigue (MFat), environmental variables, ergogenic aids, psychological traits (PsychTr)], which, moreover, show high mutual correlation. In the attempt of assessing cycling performance, most studies in the literature keep all these factors separated. This may bring to misleading results, leaving unanswered the question of how to improve cycling performance. This work provides an overview on the studies involving indexes and factors usually related to performance monitoring and assessment in cycling. In particular, in order to clarify all those aspects, the mutual interactions among these factors are highlighted, in view of a global performance assessment. Moreover, a proposal is presented advocating for a model-based approach that considers all factors mentioned in the survey, including the mutual interaction effects, for the definition of an objective function E representing the overall effectiveness of a training program in terms of both EffMet and EffMech.
... Before running the simulation, the 123 MTU's muscle-tendon parameters such as the lengths of optimal fiber and tendon slack were 124 scaled morphometrically using an optimization technique (Modenese et al. 2016), without altering 125 the muscle-tendon dimension of the scaled Lai model (Figure 1). An energetic probe was included 126 in the model (Umberger 2010;Umberger, Gerritsen, and Martin 2006) to estimate energetic 127 demand (metabolic rate) in each condition. The muscle energetics model considered the effect of 128 muscle mass, the ratio of muscle slow-twitch fibers, and the muscle fiber velocity. ...
... CC-BY-NC-ND 4.0 International license available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made Umberger, Gerritsen, and Martin 2006). We also speculate that while energy costs may be lower 267 at lower cadences, the requirement to activate more could contribute to a form of fatigue 268 (peripheral or central) that could limit overall cycling performance over time. ...
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This study used musculoskeletal modelling to explore the relationship between cycling conditions (power output and cadence) and muscle activation and metabolic power. We hypothesized that the cadence that minimized the simulated average active muscle volume would be higher than that which minimized the simulated metabolic power. We validated the simulation by comparing predicted muscle activation and fascicle velocities from select muscles with experimental records of electromyography and ultrasound images. We found strong correlations for averaged muscle activations and moderate to good correlations for fascicle dynamics. These correlations tended to weaken when analyzed at the individual participant level. Our study revealed a curvilinear relationship between average active muscle volume and cadence, with the minimum active volume being aligned to the self-selected cadence. The simulated metabolic power was consistent with previous results and was minimized at lower cadences than that which minimized active muscle volume across power outputs. Whilst there are some limitations to the musculoskeletal modelling approach, the findings suggest that minimizing active muscle volume may be a more important factor than minimizing metabolic power for self-selected cycling cadence preferences. Further research is warranted to explore the potential of an active muscle volume based objective function for control schemes across a wider range of cycling conditions.
... The question remains what causes the increase in pVO 2 . Umberger et al. [28] showed, using computer simulation, that during constant load cycling, lower limb muscles only increased their energy expenditure substantially at high cadences (i.e. at 120 rpm). Our results indicate that this also applies to oxygenation, saturation and mVO 2 at high cadence, with the non-uniform effect of cadence visible only at the highest cadences. ...
... Our results indicate that this also applies to oxygenation, saturation and mVO 2 at high cadence, with the non-uniform effect of cadence visible only at the highest cadences. The increase in TA mVO 2 contributes to the increase in pVO 2 that occurs following increasing cadence in addition to the energy expenditure increase associated with non-lower limb muscle action [28]. The increase in HHb and decrease in StO 2 with increasing cadence would be expected to increase mVO 2 . ...
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The purpose of the present study was to investigate the effect of cadence on joint specific power and cycling kinematics in the ankle joint in addition to muscle oxygenation and muscle VO2 in the gastrocnemius and tibialis anterior. Thirteen cyclists cycled at a cadence of 60, 70, 80, 90, 100 and 110 rpm at a constant external work rate of 160.1 ± 21.3 W. Increasing cadence led to a decrease in ankle power in the dorsal flexion phase and to an increase in ankle joint angular velocity above 80 rpm. In addition, increasing cadence increased deoxygenation and desaturation for both the gastrocnemius and tibialis anterior muscles. Muscle VO2 increased following increased cadence but only in the tibialis anterior and only at cadences above 80 rpm, thus coinciding with the increase in ankle joint angular velocity. There was no effect of cadence in the gastrocnemius. This study demonstrates that high cadences lead to increased mVO2 in the TA muscles that cannot be explained by power in the dorsal flexion phase.
... Its physiological basis is less clear, but could be related to motor performance, as movement uncertainty increases with force magnitude (due to signal-dependent noise, [38]). Another interpretation is that the exponent describes a metabolic cost, because greater force entails recruitment of less efficient motor units within a muscle [43,88]. But even though the physiological explanation may be unclear, optimization studies often require a force-squared or similar term, without which the optimum may call for unrealistically high force application (or bang bang control, [82]). ...
... This cost is intended to qualitatively model a physiological cost of force production or force fluctuation [23,24,55]. While various detailed models of low level muscle energetics have been proposed and used to analyze walking [55,65,88], we use simplified models of both locomotion dynamics and muscle energetics. These simplifications allow us to investigate various aspects of force cost and their potential effects on gait, independent of the particulars of a high dimensional model. ...
Article
Although humans normally walk with both stability and energy economy, either feature may be challenging for persons with disabilities. For example, in patients with lower-limb amputation, falling is pervasive, and may lead to activity avoidance. Similarly, energy expenditure is higher than for healthy subjects and may deter patients from walking, reducing mobility. A better understanding of the fundamental principles of stability and economy could lead to better prostheses that increase quality of life for patients. When designing a mechanism to assist or mimic human gait, such as orthoses or walking robots, the stability and economy of the resulting gait should be considered. To further our understanding of these fundamental principles of gait, I explore a lesser known balance mechanism, foot heading, as well as the role of muscle force production costs in gait. To investigate the stabilizing role of foot heading, I first characterize a method of measuring natural human gait variability outside of lab environments using foot mounted inertial sensors. Accuracy is found comparable to motion capture, while allowing capture of gait in natural environments. Then, using both a simple model of walking, and a variability analysis of human walking, I present evidence that humans stabilize gait laterally by altering foot heading step-to-step. I then consider the metabolic cost of force production in human locomotion. First, an optimization study of a simple model of locomotion shows that force fluctuation costs have a stronger role in determining gait than force amplitude costs. I then illustrate the connection between force fluctuation and a cost for calcium pumping in muscles using a simple muscle model. Finally, a human subject experiment altering force fluctuation in walking demonstrates the higher metabolic cost of fluctuating forces. While human locomotion is a complex activity involving many muscles, sensory systems, and neural circuitry, we can use basic mechanical models to study underlying principles of gait. A better understanding of stability and economy could have applications to many fields involving locomotion, such as the diagnosis of fall-risk in elderly subjects, the development of rehabilitation techniques, the design of prostheses, and the creation of robust and practical walking machines.
... Individual effort during cycling exercise is comprised of many factors including individual (external) effort to move the bicycle flywheel, as well as internal variables such as muscle fiber contraction speed and fiber type (Umberger et al., 2006). VO 2 and VCO 2 were therefore matched as surrogates of effort between tests to measure cumulative effort performed by the participant during exercise. ...
... There is a plateau of energy expenditure for both fibre types between 60 and 100 r min −1 , which suggests that the range of sinusoidal pedaling cadence we selected was an optimal range. However, mean pedaling cadence (75 r min −1 ) may have increased oxygen consumption due to decreased mechanical efficiency in the group of runners (Umberger et al., 2006). Changes in efficiency may have increased the intercept of the ramp test modeling of the ventilation-oxygen consumption slope used to calculate predicted ventilation. ...
Article
Human experimentation investigating the contribution of limb movement frequency in determining the fast exercise drive to breathe has produced controversial findings. To evaluate the role of limb movement frequency in determining the fast exercise drive to breathe, endurance runners and recreationally-active controls performed two sinusoidal exercise protocols on a cycle ergometer. One protocol was performed at constant workload with sinusoidal pedaling cadence, and a second with sinusoidal workload at constant cadence. Metabolic rate (Vo2) increases and means were matched between these two experiments. The ventilatory response was significantly faster when limb movement speed was varied, compared to when pedal loading was varied (18.49 ± 15.6 s vs. 50.5 ± 14.5 s, p<0.05). Ventilation response amplitudes were significantly higher during pedal cadence variation versus pedal loading variation (3.99 ± 0.25 vs. 2.58 ± 0.17 L/min, p<0.05). Similar findings were obtained for endurance athletes, with significantly attenuated ventilation responses to exercise versus control subjects. We conclude that fast changes in limb movement frequency are a potent stimulus for ventilation at submaximal workloads, and that this response is susceptible to attenuation through training.
... Evidence shows that during trek competitions world top sprinters attain maximum power output at pedalling rate near 129±9 rpm (Dorel et al., 2005; Gardner et al., 2007). The effectual or optimal cadence depends on cycling experiences (Coast & Welch, 1985; Marsh & Martin, 1995), muscle fibre type distribution in lower limb muscles (Ahlquist et al. 1992; Hansen et al., 2002; Umberger et al., 2006), bicycle crank length (Martin & Spirduso, 2001), cyclists age and power level (Rannama et al., 2012), but there is substantial lack of information regarding relationship between effectual cadence and strength variables of lower limb muscles. ...
... It was found that effectual cadence value had no significant relations with neither absolute and relative peak torque values, but had significant relationship with strength maintaining rate in hip extensors between velocities 60°/s and 180°/s (P-max, r=0.65 and P-10s, r=0.54, p<0.05). Assuming that greatest torque at high velocities is related to fast twitch fibres and the number of fibres in series (Wickiewicz et al., 1984) and that cycling cadence is related also with muscle fiber architecture (Ahlquist et al., 1992; Hansen et al., 2002; Umberger et al., 2006) we can suppose that muscle architecture of main hip extensor muscles is determining the effectual cadence value. ...
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The ability to produce maximal short term power plays important role in success and tactical economy in competitive road cycling. There are no current studies relating the isokinetic strength parameters of lover limb muscles to sprinting power in high level competitive cyclists. The purpose of this study was to characterise lower body muscles strength among high level cyclists and examine the relationship between isokinetic muscle strength and cycling sprinting power. Power output of 17 high level road cyclists (age 20.5±3.8 yrs., mass 180.8±5.7 cm, height 74.3±7.0 kg) was measured with the help of isokinetic test on a Cyclus2 Ergometer. Also isokinetic strength of ankle plantar flexors, ankle dorsal flexors, knee and hip extensors and flexors were measured with Humac NORM isokinetic dynamometer in angular speeds 60, 180 and 240°/s. The hip extensors were the strongest muscle group in all measured velocities, followed by knee extersors and hip flexors, the weakest muscle group was ankle dorsi flexors. Hip extensors torque at 180°/s was strongly correlated (r=0.9 between absolute values and r=0.74 between relative to body weight values) with short term cycling power while other muscle group demonstrated weaker relationship. Relative strength of hip flexors and ankle dorsi flexors did not show meaningful relationship with sprinting power after correction with riders body weight. In conclusion, the strongest muscle group in road cyclists are hip extensors, sprinting power has strongest correlation with hip extensors strength at angular speed of 180°/s, relationship between sprinting power and strength of hip flexors was statistically insignificant
... Alternatives are to integrate the muscle force or activation, or the joint torque, raised to the second (or higher) power [11,12], which tends to promote sharing of force between muscles (e.g., [13]). The relation to physiology is less clear, but could be associated with recruitment of less efficient motor units within a muscle as overall force increases [14,15]. High forces might also be costly in terms of motor performance rather than economy, for example due to "signal-dependent noise" that increases movement uncertainty with force [16]. ...
... This cost is intended to approximately model a number of costs previously proposed in the literature, albeit in simplified form. Although detailed models of low level muscle energetics have been proposed [15,28,29], simple models might be helpful for conceptual exploration of the trade-offs governing locomotion. The simplifications allow investigation of various aspects of force cost and their potential effects on gait, independent of the particulars of a more complex model. ...
Article
Full-text available
Simple optimization models show that bipedal locomotion may largely be governed by the mechanical work performed by the legs, minimization of which can automatically discover walking and running gaits. Work minimization can reproduce broad aspects of human ground reaction forces, such as a double-peaked profile for walking and a single peak for running, but the predicted peaks are unrealistically high and impulsive compared to the much smoother forces produced by humans. The smoothness might be explained better by a cost for the force rather than work produced by the legs, but it is unclear what features of force might be most relevant. We therefore tested a generalized force cost that can penalize force amplitude or its n-th time derivative, raised to the p-th power (or p-norm), across a variety of combinations for n and p. A simple model shows that this generalized force cost only produces smoother, human-like forces if it penalizes the rate rather than amplitude of force production, and only in combination with a work cost. Such a combined objective reproduces the characteristic profiles of human walking (R2 = 0.96) and running (R2 = 0.92), more so than minimization of either work or force amplitude alone (R2 = -0.79 and R2 = 0.22, respectively, for walking). Humans might find it preferable to avoid rapid force production, which may be mechanically and physiologically costly.
... The quadriceps muscle involvement is greatest from 60-90°, and the gluteus maximus muscle involvement greatest from 70-150° (Asplund and St Pierre, 2004; Lopes and McCormack, 2006). The hamstrings muscle group becomes active in sweeping the pedal up to the 270° position (Umberger, Gerritsen, and Martin, 2006). ...
... The hamstrings muscles exhibit peak activity late in the downstroke when the hip extensor and knee flexor moments coincide, and they effectively couple these joint motions together via the guide-wire effect(Burke, 2003). The hamstrings are predominantly active in the upward movement of the pedal, from 150-270°(Umberger, Gerritsen, and Martin, 2006). As cycling is repetitive in nature, restrictions in range of movement may occur(Burke, 2003). ...
... correlation with cadence at maximum power output effort (Hansen et al., 2002). This leads to the findings of Umberger et al. (2006) who declare that the fundamental muscle properties determining the energetic of pedaling, rather than experience or training history. In contrast, Coast and Welch (1985) have suggested that during training cyclists adapt to become more efficient at pedaling, often with the adoption of a relatively high cadence. ...
... It appears that effectual cadence depends more on maturation and physiological condition (strong positive correlation between effectual cadence and maximal power value, r=0.55, p<0.01), than a regular cycling with higher cadence. These results confirm assumption that a fundamental muscle properties are determining the energetic of pedaling more than experience or training history (Umberger et al., 2006; Hansen et al., 2002; Hintzy et al., 1999). ...
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Rannama I, Port K, Bazanov B. Does limited gear ratio driven higher training cadence in junior cycling reflect in maximum effort sprint?. J. Hum. Sport Exerc. Vol. 7, No. Proc1, pp. S85-S90, 2012. Maximum gears for youth category riders are limited. As a result, youth category riders are regularly compelled to ride in a high cadence regime. The aim of this study was to investigate if regular work at high cadence regime due to limited transmission in youth category riders reflects in effectual cadence at the point of maximal power generation during the 10 second sprint effort. 24 junior and youth national team cyclist's average maximal peak power at various cadence regimes was registered on Cyclus-2 ergometer using cyclists own bikes. Effectual cadence at the point of maximal power generation (group average 113.9±10.6 rpm) is similar to the values of professional road cyclist during the last 200m sprinting to finish where 10 second average cadence is 109.9±5.3 rpm and highest average cadence is 117.6±6.1 rpm. The premise that regular work at high cadence regime due to limited transmission in youth category riders reflects in effectual cadence at the point of maximal power generation during the 10 second sprint effort was not corroborated.
... In this regard, variations in ME are related to those in muscle fiber types. Specifically, a high proportion of type I fibers has been associated with a higher ME (Horowitz et al. 1994;Layec et al. 2011;Pleguezuelos et al. 2021;Umberger et al. 2006), which may be related to mitochondrial content (Hesselink Russell et al. 2002;Schrauwen et al. 1999). Perry et al. (2008) investigated vO 2 peak and skeletal muscle capacity variations following a 6-week highintensity interval training program in untrained subjects and showed that this type of training induced an increase of 9% in vO 2 peak and 18-29% increase in maximal activity or content of several key mitochondrial enzymes suggesting substantial oxidative metabolic adaptations. ...
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The aim of this study was to assess the association between net mechanical efficiency (NME) and body composition and glycemic profile, in middle-aged (38.3 ± 14.3 years) participants from the Quebec Family Study (QFS). Analyses were completed on a sample of 605 participants (271 males and 334 females) who performed a submaximal exercise test on an ergometer consisting of three consecutive 6-min workloads at increasing intensity during which respiratory gas exchange was assessed. The calculation of NME [power output/ (vO2-vO2seated before exercise)] was based on the values of the last 3 min of the first workload at a targeted power output of 30 W. Correlations between NME and dependent variables were computed separately in males and females. Associations between NME and body composition and glucose–insulin variables were assessed by comparing groups of subjects categorized in sex-specific tertiles of NME after adjustments for age. Significant negative correlations were observed between NME and body composition and glycemic profile in both sexes. Comparison across tertiles showed that individuals with high NME displayed more favorable adiposity and glycemic profiles. These differences remained significant after further adjustments for participation in vigorous physical activity, cardiorespiratory fitness, and mean exercise respiratory exchange ratio whereas most differences in glucose–insulin variables became non-significant after further adjustment for percent body fat. QFS familial data indicate that the heritability of NME reaches about 30%. In conclusion, the results of this study show that beyond aerobic fitness and physical activity-participation, mechanical efficiency is an additional activity-related variable that is independently associated with variations in body composition and glycemic profile.
... Although in our study, only the RSH-Mask group obtained an increase in mean power (+ 37%, Δ = 2%), power can be maintained with the RSHTent but not increased with RSHMask [34]. Increased power output is related to the ability to recruit more fast contractile (FT) fibres, and FT is known to be essential for power output as intensity increases [35]. Some recent evidence [36] demonstrated that RSH training significantly increased the number of maximal cycling sprints, although mean power output remained unchanged compared to equivalent normoxic training. ...
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This study aimed to evaluate the effect of repeated sprint in hypoxia (RSH) training in mask vs. tent system on the physiological parameters associated with the cyclist’s performance. Sixteen well-trained cyclists (VO2max 66 ± 5.9 mL/kg/min) participated in a randomised and two parallel groups design. Participants were assigned to different hypoxia methods [RSHMask (n = 8) vs RSHTent (n = 8)]. The sprint number and power output were measured during a repeated sprint test to failure before and after the effect of eight sessions of RSH. In addition, the following physiological parameters were evaluated: oxygen consumption (VO2), heart rate (HR), arterial oxygen saturation (SpO2), muscle oxygen saturation (SmO2), lactate and core temperature (CoreT°). Linear mixed models were used for repeated measures (p value < 0.05), and the effect size (ES) between groups was reported. An inter-individual analysis of participants was also reported. There was an increase in sprint numbers in both groups (ES = 0.167, p = 0.023) and an increase in power output (∑w) in the RSHMask group (ES = 0.095, p = 0.038). The RSHMask group showed improvement in VO2 recovery (ES = 0.096, p = 0.031) and SmO2 desaturation % (ES = 0.112, p = 0.042) compared to the RSHTent group. Likewise, 50% of the participants in RSHTent showed adaptations to withstand higher T°Core (+ 0.45°), and eight participants showed lactate decreases between 2.9 and 3.1 mmol/L (−24%) after RSH in both groups. Generally, RSH improves the cyclist’s performance, whether the mask or tent method is used. However, RSHTent has the advantage of causing adaptations in T°Core, whilst RSHMask improves anaerobic performance in the oxygenation of peripheral muscles.
... Previous studies showed an optimal energy cadence around 60 rpm and a freely cycling cadence around 90 rpm (29,37). However, more recent studies recognized that optimal energy cadence and freely cycling cadence often overlap during high-intensity performance (39) and that maximal energy efficiency, with the optimal muscle recruitment and lower VȮ 2 , is between 80 and 100 rpm (25). This study demonstrated similar values for minimum cadence at Posttraining for the K6 group (96.0 6 6.7 rpm). ...
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Ambrosini, L, Presta, V, Vitale, M, Menegatti, E, Guarnieri, A, Bianchi, V, De Munari, I, Condello, G, and Gobbi, G. A higher kick frequency swimming training program optimizes swim-to-cycle transition in triathlon. J Strength Cond Res XX(X): 000–000, 2023—The purpose of this study was to evaluate the effect of an 8-week swimming training program on biomechanical and physiological responses during a swim-to-cycle simulation. Fifteen triathletes were randomly allocated to 3 groups: a 6-beat-kick group (K6), a 4-beat-kick group (K4), and a control group (CG). Biomechanical and physiological parameters were evaluated during a 400-m swim and a 10-minute cycle segment before (Pretraining) and after (Posttraining) the program. A lower stroke frequency ( p = 0.004) and a higher stroke length ( p = 0.002) was found in K6 compared with CG at Posttraining. A reduction in the K6 emerged between Pretraining and Posttraining during cycling for heart rate ( p = 0.005), V̇O 2 ( p = 0.014), and energy expenditure ( p = 0.008). A positive association emerged between swim kick index and cycling cadence in the K6 group. The improvement in stroke frequency and length observed in the K6 group could be explained as an improvement in swimming technique. Similarly, the reduction in energy expenditure during cycling at Posttraining for the K6 group suggests an improvement in the working economy. Triathlon coaches and athletes should consider the inclusion of high swim kick into their training programs to enhance swim and cycling performance, which can ultimately lead to an improvement in the swim-to-cycle transition and the overall triathlon performance.
... Thus, appropriate activation of the slow muscle fibres during exercise is essential. Previous studies have reported a relationship between sports aptitude and training effects and muscle fibre composition [15][16][17][18][19] but there are no reports on its relationship with muscle fibre in archery-related exercise. The development of training that activates slow muscle fibers is desired by many archers. ...
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Background In archery training, side bridges are performed in a posture similar to archery shooting for training the muscles around the shoulder joint and the shoulder girdle of the pusher. Aim The purpose of this study was to determine whether a low-tremor side-bridge exercise for 4 weeks improves bow tremor during archery movements. Methods Participants were 20 male college students. First, we measured the tremor during side bridges performed with trunk inclinations of 25°, 40°, 55°, and 70° using an accelerometer attached to the elbow joint and identified low-tremor side bridges. The participants were then randomly divided into intervention and non-intervention groups, and the low-tremor side bridges were performed for 4 weeks. Results The effect of the intervention was determined by measuring the total tremor value using an accelerometer attached to the bow and changes in the median power frequency (MdPF) of the middle deltoid, upper trapezius, and lower trapezius. This intervention reduced the bow tremor and the median power frequency of the middle deltoid (p < 0.05). Conclusions The findings suggested that the tremor during the archery sighting phase could be reduced by performing side bridges with a specific trunk angle for a certain period of time. This intervention was also shown to reduce the intermediate frequency of the middle deltoid. The reduced tremor can shorten the sighting phase, which can facilitate injury prevention.
... min −1 ) (Fuentes et al. 2013). As the rate of metabolic energy expenditure is increased at a given power output at higher pedalling cadences (Umberger et al. 2006;Brennan et al. 2019), it is possible the higher cadences achieved during laboratory trials may be necessary to fully deplete work above MMSS in the initial period of a 3MT, and therefore for end-test power to produce a valid estimate of the MMSS. This may explain why other studies have reported lower end-test power output during laboratory-based 3MTs performed at higher than preferred cadences (Wright et al. 2019), and that critical power is greater when cycling at 60 vs.100 revs . ...
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Purpose: The three-minute all-out test (3MT), when performed on a laboratory ergometer in a linear mode, can be used to estimate the heavy-severe-intensity transition, or maximum metabolic steady state (MMSS), using the end-test power output. As the 3MT only requires accurate measurement of power output and time, it is possible the 3MT could be used in remote settings using personal equipment without supervision for quantification of MMSS. Methods: The aim of the present investigation was to determine the reliability and validity of remotely performed 3MTs (3MTR) for estimation of MMSS. Accordingly, 53 trained cyclists and triathletes were recruited to perform one familiarisation and two experimental 3MTR trials to determine its reliability. A sub-group (N = 10) was recruited to perform three-to-five 30 min laboratory-based constant-work rate trials following completion of one familiarisation and two experimental 3MTR trials. Expired gases were collected throughout constant-work rate trials and blood lactate concentration was measured at 10 and 30 min to determine the highest power output at which steady-state [Formula: see text] (MMSS-[Formula: see text]) and blood lactate (MMSS-[La-]) were achieved. Results: The 3MTR end-test power (EPremote) was reliable (coefficient of variation, 4.5% [95% confidence limits, 3.7, 5.5%]), but overestimated MMSS (EPremote, 283 ± 51 W; MMSS-[Formula: see text], 241 ± 46 W, P = 0.0003; MMSS-[La-], 237 ± 47 W, P = 0.0003). This may have been due to failure to deplete the finite work capacity above MMSS during the 3MTR. Conclusion: These results suggest that the 3MTR should not be used to estimate MMSS in endurance-trained cyclists.
... Di↵erent muscles contain di↵erent relative proportions of the two main fibre types and as such exhibit di↵erent force-producing and fatigue-resistance properties. Therefore, when modelling real musculotendons, it is important to parameterise the musculotendon models so that they are representative of their counterpart muscles' properties [108,318,319]. ...
Thesis
Applications of biomechanical predictive simulation are wide ranging, with the technique used to provide insights into movement disorders, sports performance, and injury prevention. However, current software provision has limitations. Users are restricted from leveraging state-of-the-art methods and algorithms. Alternatively, they are required to develop bespoke implementations of direct collocation, or laboriously manually link multiple software packages. In order to address these limitations, this research aims to develop and critically evaluate a software suite that enables both expert and non-expert users to construct and solve predictive simulation optimal control problems (OCPs) involving musculoskeletal models. Solving OCPs is a critical part of predictive simulation. Algorithms for transcription, scaling, mesh refinement, and derivative generation are presented, along with their implementations in an open-source software package for numerically solving OCPs, Pycollo. Benchmarking of Pycollo against an industry-standard commercial software package, GPOPS-II, by solving five known OCPs from the literature demonstrates comparable convergence and computational performance, with Pycollo requiring fewer mesh iterations and sparser discretisation meshes to meet defined error tolerances in four out of five cases. Biomechanical predictive simulations also require the ability to derive multibody dynamics and implement musculotendon models. Furthermore, these need to be formulated in a way suitable for OCPs. Two software packages, Pynamics and Pyomechanics, which formulate multibody dynamics and musculoskeletal OCPs respectively, are presented. Comparison of explicit and implicit formulations of multibody dynamics shows that solution accuracies, solve times, convergence rates, and discretisation errors are improved when implicit dynamics are used. Similarly, comparison of multiple musculotendon formulations and their numerical sensitivity finds that implicit musculotendon equations offer the best numerical properties for OCPs and should be preferred. Testing of solution sensitivity to the sigmoidal smoothing coefficient in continuous activation dynamics suggests a value of 100 should be preferred over the previously published recommendation of 10.
... However, these models enable researchers to calculate biomechanical variables that cannot be measured directly or require undesired invasive methods. In addition, these models can be used to simulate human movement to understand how the elements of the musculoskeletal system interact to produce movement (Anderson and Pandy, 2001;Neptune et al., 2001;Neptune et al., 2004;Umberger, 2010;Umberger et al., 2006;Zajac et al., 2002Zajac et al., , 2003, to identify which elements affect movement disorders (Hu and Blemker, 2015;Jansen et al., 2014;Silverman and Neptune, 2012), and to evaluate potential treatments (Arnold and Delp, 2005;Fey et al., 2012;Grabke et al., 2019;LaPre et al., 2014;Mansouri et al., 2016). ...
Thesis
People with a unilateral transtibial amputation (TTA) complete functional tasks asymmetrically, using compensatory strategies to accommodate for the lost ankle muscle function. These strategies may contribute the greater intact limb joint pain, low-back pain, and greater risk of falling commonly reported in this population. Prosthetists attempt to reduce asymmetries during the prosthetic alignment process. However, this process, which focuses on straight-line walking, may not capture the effect of prosthetic alignment on other functional tasks. The purpose of this dissertation was to determine how people with TTA maintain dynamic balance during turning and seat transfers and to quantify the effects of prosthetic alignment during seat transfers. The first aim was to determine how balance regulation during turning is affected by the side the prosthesis is on and quantify how people with TTA maintain dynamic balance during a 90-degree turn. Participants with TTA had greater range of whole-body angular momentum when turning with the prosthesis on the inside compared to outside of the turn. There were altered head/trunk and legs interactions between turns and groups. The observed differences when turning with the prosthesis on the inside of a turn may suggest people with TTA have a greater risk of balance loss during turning. The second aim was to quantify the effect of prosthetic alignment on dynamic balance during functional tasks. We compared the range and number of adjustments of whole-body angular momentum during walking, sit-to-stand, stand-to-sit, sit-to-walk, and walk-to-sit between different alignments. Sit-to-stand was the only task where alignment significantly affected angular momentum, although differences in magnitudes were small. Participants with TTA had less balance control compared to non-amputees, across alignments. These results suggest that acute changes in prosthetic alignment likely do not affect balance control during seat transfers. The third aim was to determine the effects of anterior-posterior alignment shifts on movement strategies during sit-to-stand. We compared 3D ground reaction force impulses, sagittal-plane knee moments, anterior/posterior center of pressure position, and 3D trunk range of motion between alignments. The posterior alignment reduced braking impulse asymmetry and axial trunk range of motion compared to other alignments. These results suggest that prosthetic alignment may affect the movement strategies used during sit-to-stand which may have implications for asymmetric and altered movement patterns found in people with TTA. The fourth aim was to determine the effect of prosthetic alignment on hip and low-back joint contact forces during sit-to-stand in people with a unilateral transtibial amputation. Using a musculoskeletal simulation framework, there were no differences in hip and L4-L5 joint contact forces between alignments. Participants with TTA had a greater peak hip joint contact force on the intact side hip compared to the amputated side across all alignments. This result may have important implications as greater cumulative intact hip loading throughout daily life may increase the risk of hip joint pain and degeneration in people with TTA. Together, these studies support the idea that even highly functional individuals with a lower limb amputation have decreased balance control and altered joint loading across a range of functional tasks. Results from these studies also suggest that people with TTA develop compensatory strategies in response to acute changes in prosthetic alignment do not affect balance or joint loading during seat transfers. Future work should explore whether these findings extend to long-term changes in alignment or to lower functioning individuals.
... While there is some overhead associated with using finite differences, OpenSim provides an easy to use environment for musculoskeletal modeling with a robust API that facilitates implementation of the DC method [13]. Moreover, the quality of solutions obtained with the OpenSim-MATLAB interface on relatively coarse temporal grids were similar to the results on finer grids, and can be obtained in much less time than is required for the more common direct shooting methods that have been used for simulating pedaling [6,15,41]. ...
Article
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The direct collocation (DC) method has shown low computational costs in solving optimization problems in human movements, but it has rarely been used for solving optimal control pedaling problems. Thus, the aim of this study was to develop a DC framework for optimal control simulation of human pedaling within the OpenSim modeling environment. A planar bicycle-rider model was developed in OpenSim. The DC method was formulated in MATLAB to solve an optimal control pedaling problem using a data tracking approach. Using the developed DC framework, the optimal control pedaling problem was successfully solved in 24 minutes to ten hours with different objective function weightings and number of nodes from two different initial conditions. The optimal solutions for equal objective function weightings were successful in terms of tracking, with the model simulated pedal angles and pedal forces within ±1 standard deviation of the experimental data. With these weightings, muscle tendon unit (MTU) excitation patterns generally matched with burst timings and shapes observed in the experimental EMG data. Tracking quality and MTU excitation patterns were changed little by selection of node density above 31, and the optimal solution quality was not affected by initial guess used. The proposed DC framework could easily be turned into a predictive simulation with other objective functions such as fastest pedaling rate. This flexible and computationally efficient framework should facilitate the use of optimal control methods to study the biomechanics, energetics, and control of human pedaling.
... with an almost equivalent meaning. As such, it is possible to uncover results pertaining to cycling efficiency (Hansen et al., 2002;Korff et al., 2007), muscular efficiency (Neptune and Herzog., 1999;Zameziati et al., 2006;Carpes, Diefenthaeler et al., 2010), mechanical efficiency (Umberger et al., 2006; and mechanical effectiveness (Zameziati et al., 2006;Korff et al., 2007;Mornieux et al., 2010), all of which are related to alterations in cycling 'performance'. ...
Thesis
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Optimisation of movement strategies during cycling is an area which has gathered a lot of attention over the past decade. Resolutions to augment performance have involved manipulations of bicycle mechanics, including chainring geometries. Elliptical chainrings are proposed to provide a greater effective diameter during the downstroke, manipulating mechanical leverage and resulting in greater power production during this period. A review of the literature indicates that there is a pervasive gap in our understanding of how the theoretical underpinnings of elliptical chainrings might be translated to practical use. Despite reasonable theory of how these chainrings might enforce a variation in crank angular velocity and consequently alter force production, performance-based analyses have struggled to present evidence of this. The purpose of this thesis was to provide a novel approach to this problem by combining experimental data with musculoskeletal modelling and evaluating how elliptical chainrings might influence crank reactive forces, joint kinematics, muscle-tendon unit behaviour and muscle activation. One main study was proposed to execute this analysis, and an anatomically constrained model was subsequently used to determine the joint kinematics and muscle-tendon unit behaviour. Bespoke elliptical chainrings were designed for this study and as such, different levels of chainring eccentricity (i.e. ratio of major to minor axis) and positioning against the crank were presented whilst controlling the influence of other variables known to affect the neuromuscular system such as cadence and load. Findings presented in this thesis makes a new and major contribution in our understanding of the neuromusculoskeletal adaptations which occur when using elliptical chainrings, showing alterations in crank reaction force, muscle-tendon unit velocities, joint kinematics and muscle excitation over a range of cadences and loads, and provides direction for where the future of this research might be best applied. Keywords: Elliptical chainrings; Cycling; Musculoskeletal modelling; Principal Component Analysis; Electromyography
... >80 rpm) may change muscle contraction dynamics due to higher ankle joint angular velocities (Skovereng, Ettema, and Van Beekvelt 2017), which may partly explain the higher _ V O 2 , HR and RPE. Alternatively, or perhaps additionally, higher cadences may necessitate greater contributions of type II muscle fibres due to higher contraction velocities required at a given intensity (Sargeant 1994;Umberger, Gerritsen, and Martin 2006). Higher mechanical outputs from the muscle are achievable via increased muscle fibre recruitment, whereby the type II muscle fibres are less efficient and less fatigue resistant, therefore necessitating a proportionately higher _ V O 2 compared to type I muscle fibres (Pringle et al. 2003;Sargeant 1994). ...
Article
Whole-body vibration training is useful for eliciting additional training benefits, but whether vibration-based cycle ergometry would elicit similar benefits has been largely unexplored. Thirteen participants were recruited to investigate differences in vibration (VB) cycle ergometry compared to non-vibration (NV) cycle ergometry with regards to oxygen uptake (V̇O 2) kinetics, rating of perceived exertion (RPE), heart rate (HR), jumping height, and isokinetic knee joint torque at different intensities and cadences. Meaningful ergometer differences (in favour of VB) were evident for maximal steady state V̇O 2 HR and RPE, but not for the phase II V̇O 2 time constant. No meaningful changes were observed for jumping height or isokinetic knee joint torque. The noteworthy increases in V̇O 2, RPE and HR when using VB ergometry, specifically at higher cadences, and independent of intensity domain, may be linked to changes in muscle fiber recruitment or muscle activation. Practitioner Summary: Traditional vibration training has purported various beneficial effects, but whether such effects transferred to cycling ergometry was under-researched. Vibration-based cycle ergometry may be a viable method of additionally stressing the cardiovascular system at the same relative intensity compared to non-vibration cycling.
... The upper body is generally accepted as having a greater proportion of fast-twitch fibers when compared to the lower body [39,40]. Interestingly, the energetically optimal cadence has been reported to be higher in a model with more fast-twitch fibers than a model with more slow-twitch fibers [41], consistent with predictions from the literature [42][43][44]. This would partially explain why higher cadences displayed worse gross efficiency values in the current study. ...
Article
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Background: Due to the importance of energy efficiency and economy in endurance performance, it is important to know the influence of different paddling cadences on these variables in the stand-up paddleboarding (SUP). The purpose of this study was to determine the effect of paddling at different cadences on the energy efficiency, economy, and physiological variables of international SUP race competitors. Methods: Ten male paddlers (age 28.8 ± 11.0 years; height 175.4 ± 5.1 m; body mass 74.2 ± 9.4 kg) participating in international tests carried out two test sessions. In the first one, an incremental exercise test was conducted to assess maximal oxygen uptake and peak power output (PPO). On the second day, they underwent 3 trials of 8 min each at 75% of PPO reached in the first test session. Three cadences were carried out in different trials randomly assigned between 45–55 and 65 strokes-min−1 (spm). Heart rate (HR), blood lactate, perceived sense of exertion (RPE), gross efficiency, economy, and oxygen uptake (VO2) were measured in the middle (4-min) and the end (8-min) of each trial. Results: Economy (45.3 ± 5.7 KJ·l−1 at 45 spm vs. 38.1 ± 5.3 KJ·l−1 at 65 spm; p = 0.010) and gross efficiency (13.4 ± 2.3% at 45 spm vs. 11.0 ± 1.6% at 65 spm; p = 0.012) was higher during de 45 spm condition than 65 spm in the 8-min. Respiratory exchange ratio (RER) presented a lower value at 4-min than at 8-min in 55 spm (4-min, 0.950 ± 0.065 vs. 8-min, 0.964 ± 0.053) and 65 spm cadences (4-min, 0.951 ± 0.030 vs. 8-min, 0.992 ± 0.047; p < 0.05). VO2, HR, lactate, and RPE were lower (p < 0.05) at 45 spm (VO2, 34.4 ± 6.0 mL·kg−1·min−1; HR, 161.2 ± 16.4 beats·min−1; lactate, 3.5 ± 1.0 mmol·l−1; RPE, 6.0 ± 2.1) than at 55 spm (VO2, 38.6 ± 5.2 mL·kg−1·min−1; HR, 168.1 ± 15.1 beats·min−1; lactate, 4.2 ± 1.2 mmol·l−1; RPE, 6.9 ± 1.4) and 65 spm (VO2, 38.7 ± 5.9 mL·kg−1·min−1; HR, 170.7 ± 13.0 beats·min−1; 5.3 ± 1.8 mmol·l−1; RPE, 7.6 ± 1.4) at 8-min. Moreover, lactate and RPE at 65 spm was greater than 55 spm (p < 0.05) at 8-min. Conclusion: International male SUP paddlers were most efficient and economical when paddling at 45 spm vs. 55 or 65 spm, confirmed by lower RPE values, which may likely translate to faster paddling speed and greater endurance.
... However, physiological parameters regularly measured in the laboratory could help this selection [1,4,6]. The prediction of the performance is possible from several parameters such as the maximum power normalised to body weight (> 5.5 W/kg), the distribution of quadriceps muscle fibers from biopsy and the blood lactate concentration collected during maximal exercise [7][8][9]. These parameters are not easy to measure, are expensive and require time. ...
Article
Objectives To take part in a Grand Tour, the selection of the cyclists is not easy despite a link between isokinetic knee muscle strength and sprinting power. This study aimed to measure knee muscle strength among professional cyclists and to explore the difference in lower limb force between the rouleur/sprinter and the puncher/climber cycling tactic profiles. Materials and methods Thirty nine professional cyclists, who participated in at least one Grand Tour, were assessed at knee level with an isokinetic dynamometer. The relative peak torques normalised to the body mass at the 60, 180 and 240°/s angular speeds and the Limb Symmetry Index, were assessed. Four parameters of the Fatigue testing were studied: total work/kg of extensors and flexors, Fatigue slopes, breakpoint and angle. Results All knee extensors isokinetic parameters, excepted extensor LSI, were different between the 2 groups. The best prediction to identify rouleurs/sprinters was found with 2 parameters: knee extensors strength at 240°/s (Odd-ratios: 1440; P = 0.03) and extensors fatigue slope (ORs: 2.57; P = 0.02). The Receiver Operating Characteristic curves areas were respectively 0.851 and 0.840. Conclusion Isokinetic knee extensors strength and fatigue slope of rouleurs/sprinters are different from those of climbers/punchers. Isokinetic knee extensor's force could represent a new tool to select rouleurs/sprinters for a Grand Tour.
... Sacchetti et al. (2010) reported average preferred cadences of 80-85 rpm for their older participants at power outputs of 75-125 W. Gross efficiency for their older adults was highest at or near 60 rpm. These cadences also closely approximate the most economical and preferred cadences, respectively, reported for younger adults (Marsh & Martin, 1993, 1995Umberger, Gerritsen, & Martin, 2006). Pilot testing of these power output-cadence conditions revealed that these conditions were challenging and yet achievable for recreationally active older men. ...
Article
It is unknown if higher antagonist muscle co-activation is a factor contributing to higher energy cost of cycling in older adults. We determined how age, power output, and cadence affect metabolic cost and lower extremity antagonist muscle co-activation during submaximal cycling. Thirteen young and 12 older male cyclists completed 6-minute trials at four power output-cadence conditions (75W-60rpm, 75W-90rpm, 125W-60rpm, and 125W-90rpm) while electromyography (EMG) and oxygen consumption were measured. Knee and ankle co-activation indices were calculated using vastus lateralis, biceps femoris, gastrocnemius, and tibialis anterior EMG data. Net rate of energy cost of cycling was higher in older compared to young cyclists at 125W (p=0.002) and at 90rpm (p=0.026). No age-related differences were observed in the magnitude or duration of co-activation about the knee or ankle (p>0.05). Our results indicated knee and ankle co-activation is not a substantive factor contributing to higher energy cost of cycling in older adults.
... Soleus was involved in generating initial propulsive force during cycling. Moreover, Umberger, Gerritsen, and Martin (2006) reported the greatest percentage of fast twitch fiber type in anterior thigh muscles (60e75%) and the lowest in soleus (35%). Although the effects of EIMD on repeated sprint performance are unknown. ...
Article
Objective: To determine the effect of short-term cold-water immersion (CWI) on muscle pain sensitivity after maximal anaerobic power training in track cyclists. Design: Repeated measures. Setting: University Laboratory. Participants: 12 elite sprint track cyclists (age 24,75 ± 4,23 years). Main outcome measures: PPT measurements were made on dominant lower extremity (right) in 20 reference points, including anterior thigh muscles, posterior thigh muscles and posterior cuff muscles. PPT levels were measured: 1) before workout, 2) immediately after workout, but before CWI 3) 1 h after CWI and 4) 12 h after CWI. Mean PPT values for each muscle group per participant were calculated for further statistical analysis. Results: The average PPT for anterior thigh muscles decreased significantly after effort (p ¼ 0.001) and increased significantly 1 h after CWI (p ¼ 0.048). In posterior thigh muscles PPT decreased significantly after effort (p ¼ 0.014) and increased significantly 1 h and 12 h after CWI (p ¼ 0.045 and p ¼ 0.25 respectively). However, in posterior cuff muscles PPT decreased only after effort (p ¼ 0.001). Conclusions: Short-term repeated sprint exercise appears to affect PPT in track cyclists. This study have reported that CWI in 5 �C for 5 min have had a beneficial effect in minimizing PPT 1 h post repeated maximal sprint training.
... The large variation in body-mass-normalized _ V O 2peak found in the current study, ranging from 66.9 to 80.8 mlÁkg -1 Ámin -1 , may result in gross efficiency being a less important performance measure for XC skiing among elite NC athletes compared to XC skiers with more homogenous _ V O 2peak levels. Also the lack of association between cycle length and XC performance may be related to the heterogeneous study group; for example in cycling, variation in muscle fiber type distribution has been found impact the energetically optimal cadence [31]. However, as we do not have muscle biopsy of these athletes, this is something future studies need to investigate. ...
Article
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Background Nordic combined (NC) is an Olympic winter-sport performed as a ski jumping (SJ) event followed by a cross-country (XC) pursuit race employing the skating style. Purpose To elucidate the associations between sport-specific laboratory capacities and SJ, XC skiing, and overall NC performance in a world-cup NC event. Methods Twelve international world-cup NC athletes from 8 nations performed laboratory testing one day prior to participating in a world-cup NC event. Squat jumps and SJ imitations (IMIT) were performed on a three-dimensional force plate, whereas XC skiing-specific physiological characteristics were obtained from roller ski skating tests on a treadmill and an all-out double poling (DP) test. Finally, body composition was measured. Laboratory capacities were correlated against performance in SJ, 10-km XC skiing, and overall NC in the world-cup event. Multiple regression analysis was used to determine the best suited laboratory variables for predicting performance. Results Vertical IMIT velocity together with body-mass provided the best prediction for SJ performance (r² = 0.70, p<0.01), while body-mass-normalized V˙O2peak and DP power provided the best prediction for XC performance (r² = 0.68, p<0.05). Body-mass-normalized V˙O2peak was the only significant correlate with overall NC performance (r² = 0.43, p<0.05) in this competition. Conclusion Overall, the concurrent development of V˙O2peak, upper-body power, and SJ-specific vertical jump capacity while minimizing body-mass within the BMI limit set by FIS should be considered in the seasonal training of NC athletes.
... Part of the increase in pVO 2 has been reported to originate in areas other than the legs (e.g., stabilization of the upper body). Umberger et al. (2006) showed increased pVO 2 as cadence increased, but the energy expenditure of the leg muscles did not increase until cadence exceeded 100 rpm. This is in accordance with the results of the present study. ...
Data
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Previous publication from the same experiment. (PDF)
... Soleus was involved in generating initial propulsive force during cycling. Moreover, Umberger, Gerritsen, and Martin (2006) reported the greatest percentage of fast twitch fiber type in anterior thigh muscles (60e75%) and the lowest in soleus (35%). Although the effects of EIMD on repeated sprint performance are unknown. ...
Article
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In the literature, the exercise capacity of cyclists is typically assessed using incremental and endurance exercise tests. The aim of the present study was to confirm whether peak oxygen uptake (V̇O2peak) attained in a sprint interval testing protocol correlates with cycling performance, and whether it corresponds to maximal oxygen uptake (V̇O2max) determined by an incremental testing protocol. A sample of 28 trained mountain bike cyclists executed 3 performance tests: (i) incremental testing protocol (ITP) in which the participant cycled to volitional exhaustion, (ii) sprint interval testing protocol (SITP) composed of four 30 s maximal intensity cycling bouts interspersed with 90 s recovery periods, (iii) competition in a simulated mountain biking race. Oxygen uptake, pulmonary ventilation, work, and power output were measured during the ITP and SITP with postexercise blood lactate and hydrogen ion concentrations collected. Race times were recorded. No significant inter-individual differences were observed in regards to any of the ITP-associated variables. However, 9 individuals presented significantly increased oxygen uptake, pulmonary ventilation, and work output in the SITP compared with the remaining cyclists. In addition, in this group of 9 cyclists, oxygen uptake in SITP was significantly higher than in ITP. After the simulated race, this group of 9 cyclists achieved significantly better competition times (99.5 ± 5.2 min) than the other cyclists (110.5 ± 6.7 min). We conclude that mountain bike cyclists who demonstrate higher peak oxygen uptake in a sprint interval testing protocol than maximal oxygen uptake attained in an incremental testing protocol demonstrate superior competitive performance.
... Not only the workload but also pedaling cadence affects the physiological demand (Faria, Sjøjaard, & Bonde-Petersen, 1982;Jameson & Ring, 2000;Lepers, Millet, Maffiuletti, Hausswirth, & Brisswalter, 2001;Montenegro et al., 2011;Woolford et al., 1999). Pedaling cadence has a nonlinear effect on physiological states due to changes in mechanical and metabolic efficiency (Faria et al., 1982;Umberger, Gerritsen, & Martin, 2006;Woolford et al., 1999). Studies have shown that cycling at 50 to 60 r/min produces higher muscle tension, electromyographic activity, and torque than cycling at 90 to 100 r/min, with effect sizes ranging from 1.1 to 3.1 (Bertucci, Grappe, Girard, Betik, & Rouillon, 2005;Lo¨llgen, Graham, & Sjogaard, 1980;Lucia et al., 2004). ...
Article
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Pleasure plays a key role in exercise behavior. However, the influence of cycling cadence needs to be elucidated. Here, we verified the effects of cycling cadence on affect, perceived exertion (ratings of perceived exertion), and physiological responses. In three sessions, 15 men performed a maximal cycling incremental test followed by two 30-min constant workload (50% of peak power) bouts at 60 and 100 r/min. The pleasure was higher when participants cycled at 60 r/min, whereas ratings of perceived exertion, heart rate, and oxygen uptake were lower (p < .05). Additionally, the rate of decrease in pleasure and increase in ratings of perceived exertion was less steep at 60 r/min (p < .01). Cycling at 60 r/min is more pleasant, and the perceived effort and physiological demand are lower than at 100 r/min.
... Detailed musculoskeletal models combined with dynamic simulations can be used to study the relationship between muscle coordination and resulting movements. Although standing balance is of critical importance in many activities of daily living, there has been little effort in developing detailed musculoskeletal models and simulations of balance control compared to other whole-body motor activities such as walking (Anderson and Pandy, 2003;Liu et al., 2008;Neptune et al., 2008;Thelen and Anderson, 2006;Winby et al., 2009), running (Dorn et al., 2012;Hamner et al., 2010;Sasaki and Neptune, 2006), jumping (Anderson and Pandy, 1999;Bobbert and van Soest, 2001;Pandy and Zajac, 1991;Spagele et al., 1999), and cycling (Neptune and Hull, 1998;Raasch et al., 1997;Umberger et al., 2006). ...
Article
Although standing balance is important in many daily activities, there has been little effort in developing detailed musculoskeletal models and simulations of balance control compared to other whole-body motor activities. Our objective was to develop a musculoskeletal model of human balance that can be used to predict movement patterns in reactive balance control. Similar to prior studies using torque-driven models, we investigated how movement patterns during a reactive balance response are affected by high-level task goals (e.g., reducing center-of-mass movement, maintaining vertical trunk orientation, and minimizing effort). We generated 23 forward dynamics simulations where optimal muscle excitations were found using cost functions with different weights on minimizing these high-level goals. Variations in hip and ankle angles observed experimentally (peak hip flexion = 7.9-53.1°, peak dorsiflexion = 0.5–4.7°) could be predicted by varying the priority of these high-level goals. More specifically, minimizing center-of-mass motion produced a hip strategy (peak hip flexion and ankle dorsiflexion angles of 45.5° and 2.3°, respectively) and the response shifted towards an ankle strategy as the priority to keep the trunk vertical was increased (peak hip and ankle angles of 13.7° and 8.5°, respectively), We also found that increasing the priority to minimize muscle stress always favors a hip strategy. These results are similar to those from sagittal-plane torque-driven models. Our muscle-actuated model facilitates the investigation of neuromechanical interactions governing reactive balance control to predict muscle activity and movement patterns based on interactions between neuromechanical elements such as spinal reflexes, muscle short-range stiffness, and task-level sensorimotor feedback.
... Part of the increase in pVO 2 has been reported to originate in areas other than the legs (e.g., stabilization of the upper body). Umberger et al. (2006) showed increased pVO 2 as cadence increased, but the energy expenditure of the leg muscles did not increase until cadence exceeded 100 rpm. This is in accordance with the results of the present study. ...
Article
Full-text available
Purpose: The present study investigates the effect of cadence on joint specific power and oxygenation and local muscle oxygen consumption in the vastus lateralis and vastus medialis in addition to the relationship between joint specific power and local muscle oxygen consumption (mVO2). Methods: Seventeen recreationally active cyclists performed 6 stages of constant load cycling using cadences of 60, 70, 80, 90, 100 and 110 rpm. Joint specific power was calculated using inverse dynamics and mVO2 and oxygenation were measured using near-infrared spectroscopy. Results: Increasing cadence led to increased knee joint power and decreased hip joint power while the ankle joint was unaffected. Increasing cadence also led to an increased deoxygenation in both the vastus lateralis and vastus medialis. Vastus lateralis mVO2 increased when cadence was increased. No effect of cadence was found for vastus medialis mVO2. Conclusion: This study demonstrates a different effect of cadence on the mVO2 of the vastus lateralis and vastus medialis. The combined mVO2 of the vastus lateralis and medialis showed a linear increase with increasing knee joint specific power, demonstrating that the muscles combined related to power generated over the joint.
... Given that an actual paradox is considered, it indicates that coincidence of freely chosen and energetically optimal pedalling frequency should be expected. And actually it has, somewhat surprisingly, been indicated occasionally in the literature that humans choose to pedal in a particular way (e.g. at a particular frequency) with the purpose of minimizing the rate of energy turnover (Sparrow & Newell 1998, Umberger et al. 2006, Sparrow et al. 2007) despite the considerable amount of contrasting evidence referred to in the beginning of this paragraph. ...
Thesis
Acta Physiol, Volume 214, Issue Supplement S702, pages 1–18 The thesis can be downloaded from the Acta Physiol homepage Summary: The overall purpose of the present dissertation was to contribute to the understanding of voluntary human rhythmic leg movement behaviour and control. This was achieved by applying pedalling as a movement model and exposing healthy and recreationally active individuals as well as trained cyclists to for example cardiopulmonary and mechanical loading, fatiguing exercise, and heavy strength training. As a part of the background, the effect of pedalling frequency on diverse relevant biomechanical, physiological, and psychophysiological variables as well as on performance was initially explored. Freely chosen pedalling frequency is considerably higher than the energetically optimal pedalling frequency. This has been shown by others and was confirmed in the present work. As a result, pedal force is relatively low while rates of VO2 and energy turnover are relatively high during freely chosen pedalling as compared to a condition where a lower and more efficient pedalling frequency is imposed. The freely chosen pedalling frequency was in the present work, and by others, found to most likely be less advantageous than the lower energetically optimal pedalling frequency with respect to performance during intensive cycling following prolonged submaximal cycling. This stimulates the motivation to understand the behaviour and control of the freely chosen pedalling frequency during cycling. Freely chosen pedalling frequency was in the present work shown to be highly individual. In addition, the pedalling frequency was shown to be steady in a longitudinal perspective across 12 weeks. Further, it was shown to be unaffected by both fatiguing hip extension exercise and hip flexion exercise as well as by increased loading on the cardiopulmonary system at constant mechanical loading, and vice versa. Based on this, the freely chosen pedalling frequency is considered to be characterised as a highly individual, steady, and robust innate voluntary motor rhythm under primary influence of central pattern generators. The last part of the characterisation is largely based on, and supported by, work of other researchers in the field. Despite the robustness of the freely chosen pedalling frequency, it may be affected by some particular factors. As an example from the present work, freely chosen pedalling frequency during treadmill cycling increased by on average 15 to 17 rpm when power output was increased from a value corresponding to 86% and up to 165% of Wmax. This phenomenon is supported by other studies. As another example from the present work, freely chosen pedalling frequency decreased by on average 9 to 14 rpm following heavy strength training that involved both hip extension and hip flexion. Further, the present work suggested that the latter phenomenon occurred within the first week of training and was caused by in particular the hip extension strength training rather than the hip flexion strength training. The fast response to the strength training indicated that neural adaptations presumably caused the observed changes in movement behaviour. The internal organisation of the central pattern generator is by some other researchers in the field considered to be functionally separated into two components, in which, one is responsible for movement frequency and another is responsible for movement pattern. For the present dissertation, the freely chosen pedalling frequency was considered to reflect the rhythmic movement frequency of the voluntary rhythmic leg movement of pedalling. The tangential pedal force profile was considered to reflect the rhythmic movement pattern. The present work showed that fatiguing hip flexion exercise in healthy and recreationally active individuals modified the tangential pedal force profile during cycling at a pre-set target pedalling frequency in a way that the minimum tangential pedal force became more negative, the maximum tangential pedal force increased, and the phase with negative tangential pedal force increased. In other words, the legs were “actively lifted” to a lesser extent in the upstroke phase. Fatiguing hip extension exercise did not have that effect. And none of the fatiguing exercises affected the freely chosen pedalling frequency. The present work furthermore showed that the primary effect of hip extension strength training was that it decreased the freely chosen pedalling frequency. An interpretation of this could be that the hip extension strength training, in particular, influenced the output from the component of the central pattern generator that may be responsible for rhythmic movement frequency.
... Thus, the results of the present study suggest that developing subjectspecific models that include activationdeactivation dynamics based on individual fiber types (e.g. Umberger et al., 2006) can better match chainring shapes to individual cyclists. ...
... 12 We have recently set up an experimental setup to study bicycle pedaling and how pedaling rate correlates with other biological and physical markers such as heart rate, force on the pedal, etc. In this paper we review the basic ideas with an aim toward examining by way of simulations what timefrequency methods are appropriate for the study of nonstationary biomechanical signals, such as bicycle pedaling rate 1,3,8,9,[14][15][16][17][18][19][20][21][22][23] ...
Article
We discuss the application of time-frequency analysis to biomechanical-type signals, and in particular to signals that would be encountered in the study of rotation rates of bicycle pedaling. We simulate a number of such signals and study how well they are represented by various time-frequency methods. We show that time-frequency representations track very well the instantaneous frequency even when there are very fast changes. In addition, we do a correlation analysis between time-series whose instantaneous frequency is changing and show that the traditional correlation coeficient is insuffcient to characterize the correlations. We instead show that the correlation coeficient should be evaluated directly from the instantaneous frequencies of the time series, which can be easily estimated from their time-frequency distributions.
... A cadência de pedalada pode ser entendida como os diferentes ritmos de pedalada imprimidos pelos praticantes. É uma variável que influencia a eficiência mecânica, os níveis de lactato sangüíneo, a freqüência cardíaca (FC) e o consumo de oxigênio do indivíduo (CANDOTTI et al., 2007; FARIA et al., 1982; LUCIA et al., 2004; UMBERGER et al., 2006; WOOLFORD et al., 1999). Pelo fato de influenciar o desempenho e a diversas respostas fisiológicas frente ao esforço para uma dada potência (BELLI & HINTZY, 2002; LEPERS et al., 2001), a cadência de pedalada tem se tornado um dos fatores relevantes na estruturação de um treino de ciclismo para induzir uma variação da intensidade de esforço (DIAS et al., 2007). ...
Article
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It is known that pedaling cadence affects the mechanical efficiency, the levels of blood lactate, heart rate (HR), oxygen consumption. However, information about how pedaling cadence influences the rating of perceived exertion (RPE) is still scarce. Thus, the purpose of this study was to compare the responses of maximum power, HR and RPE achieved during maximal incremental tests (ITmax), 50 and 100 rpm, with 15W/min up to voluntary exhaustion. The sample (n = 7) comprised physically active individuals (20.4 ± 2.2 years, 73.1 ± 8.3 kg and 176.8 ± 4.6 cm). Were performed two ITmax in cycle ergometer, with cadences of 50 and 100 rpm, performed in random order (minimum of 48 hours between tests). The results showed that RPE was higher in tests with cadence of 100 rpm, but at the end of the test, the RPE did not presented differences between the cadences. Likewise, no significant difference was found in maximal HR (50rpm: 183±7,81bpm vs. 100rpm: 185,6±8,1bpm). Already in submaximal intensities, the HR was higher in the test at 100 rpm. Can conclude that the RPE and HR are influenced by the PC, is higher according to the increase in cadence. This demonstrates the applicability of the use of RPE for monitoring the intensity of effort in exercise programs performed in cycle.
Article
Older adults walk using their hips relatively more and their ankles relatively less than young adults. This “distal-to-proximal redistribution” in leg joint mechanics is thought to drive the age-related increase in metabolic rate during walking. However, many morphological differences between hip and ankle joints make it difficult to predict how – or if – the distal-to-proximal redistribution affects metabolic rate during walking. To address this uncertainty, we compared the metabolic rate of participants while they repeatedly produced isolated hip and ankle moment cycles on a dynamometer following biofeedback. Overall, participants produced greater joint moments at their ankle vs. hip (p=0.004) and correspondingly activated their largest ankle extensor muscle more than their largest hip extensor muscle (p=0.046). Cycle average muscle activation across other hip and ankle extensors was nondifferent (all p=0.080–0.848). Despite producing greater joint moments using slightly more relative muscle activation at the ankle, participants expended more net metabolic power while producing moments at the hip (p=0.002). Therefore, producing joint extension moments at the hip requires more metabolic energy than that at the ankle. Our results support the notion that the distal-to-proximal redistribution of joint mechanics contribute to greater metabolic rate during walking in older vs. young adults.
Article
This paper introduces a new lower-limb rehabilitation machine that meets the rehabilitation needs of hemiplegic patients. First, a left–right independent rotary pedal mechanism was selected to facilitate rehabilitation and adapt to the user’s physical condition. Then, a half model of the lower-limb rehabilitation machine is designed and manufactured with ergonomics in mind. As analytical tools, we combine non-negative matrix factorization and non-negative double singular value decomposition to calculate muscle synergy of the walking muscle surface electromyography (sEMG) signal, and use cosine similarity to evaluate the similarity between walking and pedaling activities. By comparing the results of the walking and pedaling experiments, the effectiveness of pedaling in gait rehabilitation is revealed. To further improve the similarity between walking and pedaling, double integration of the sEMG signal is introduced, and the relationship between load input and rotation angle is described for the first time using Fourier series. The results of the experiment confirmed that more than half of the 10 subjects performed pedaling exercises similar to walking using Fourier series loading compared to pedaling exercises with normal constant loading. This loading parameter may have the potential to improve rehabilitation efficiency for many subjects compared to the usual exercise.
Thesis
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In high impact human activities, much of the impact shock wave is dissipated through internal body structures, preventing excessive accelerations from reaching vital organs. Mechanisms responsible for this attenuation, including lower limb joint compression and spinal compression have been neglected in existing whole-body simulation models. Accelerometer data on one male subject during drop landings and drop jumps from four heights revealed that peak resultant acceleration tended to decrease with increasing height in the body. Power spectra contained two major components, corresponding to the active voluntary movement (2 Hz – 14 Hz) and the impact shock wave (16 Hz – 26 Hz). Transfer functions demonstrated progressive attenuation from the MTP joint towards the C6 vertebra within the 16 Hz – 26 Hz component. This observed attenuation within the spine and lower-limb joint structures was considered within a rigid body, nine-segment planar torque-driven computer simulation model of drop jumping. Joints at the ankle, knee, hip, shoulder, and mid-trunk were modelled as non-linear spring-dampers. Wobbling masses were included at the shank, thigh, and trunk, with subject-specific biarticular torque generators for ankle plantar flexion, and knee and hip flexion and extension. The overall root mean square difference in kinetic and kinematic time-histories between the model and experimental drop jump performance was 3.7%, including ground reaction force root mean square differences of 5.1%. All viscoelastic displacements were within realistic bounds determined experimentally or from the literature. For an equivalent rigid model representative of traditional frictionless pin joint simulation models but with realistic wobbling mass and foot-ground compliance, the overall kinetic and kinematic difference was 11.0%, including ground reaction force root mean square differences of 12.1%. Thus, the incorporation of viscoelastic elements at key joints enables accurate replication of experimentally recorded ground reaction forces within realistic whole-body kinematics and removes the previous need for excessively compliant wobbling masses and/or foot-ground interfaces. This is also necessary in cases where shock wave transmission within the simulation model must be non-instantaneous.
Article
Purpose: The physiological consequences of freely chosen cadence (FCC) during cycling remains poorly understood. We sought to determine the effect of cadence on the respiratory and hemodynamic response to cycling exercise. Methods: Eleven cyclists (10M:1F; age=27±6yr; V[Combining Dot Above]O2max=60.8±3.7ml·kg·min) completed four, 6-min constant-load cycling trials at 10% below their previously determined gas exchange threshold (i.e., 63±5% peak power) while pedaling at 60, 90, and 120rpm, and a FCC (94.3±6.9rpm), in randomized order. Standard cardiorespiratory parameters were measured and an esophageal electrode balloon catheter was used to assess electromyography of the diaphragm (EMGdi) and the work of breathing (Wb). Leg blood flow index (BFI) was determined on four muscles using near-infrared spectroscopy (NIRS) with indocyanine green dye injections. Results: Oxygen uptake (V[Combining Dot Above]O2) increased as a function of increasing cadence (all pairwise comparisons, p<0.05). EMGdi and Wb were significantly greater at 120rpm compared to all other conditions (all p<0.01). Vastus medialis and semitendinosus BFI were significantly greater at 120rpm compared to 60 rpm and 90 rpm (all p<0.05). Gastrocnemius BFI was higher at 120 rpm compared to all other cadences (all p<0.01). No difference in BFI was found in the vastus lateralis (p=0.06). BFI was significantly correlated with the increase in V[Combining Dot Above]O2 with increasing cadence in the medial gastrocnemius (p<0.001) and approached significance in the vastus lateralis (p=0.09), vastus medialis (p=0.06), and semitendinosus (p=0.09). There was no effect of cadence on Borg 0-10 breathing or leg discomfort ratings (p>0.05). Conclusions: High cadence cycling at submaximal exercise intensities is metabolically inefficient and increases EMGdi, Wb, and leg muscle blood flow relative to slower cadences.
Article
The purpose of this study was to identify one or more performance-based criteria that may be used to generate predictive optimal control simulations of submaximal pedaling. Two-legged pedaling simulations were generated based on minimizing muscle activation, muscle stress, metabolic energy, time derivative of muscle force, and minimizing metabolic energy while pedaling smoothly. The simulations based on minimizing muscle activation and muscle stress most closely matched experimental pedaling data, with the activation criterion better matching experimental muscle activation timing. We conclude that predictive simulations of submaximal pedaling may be generated using a cost function based on minimizing muscle activation.
Thesis
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L’objectif de cette thèse est d’étudier l’évolution des performances sportives au cours de l’èreolympique et tenter d’en interpréter les influences physiologiques, technologiques, génétiqueset environnementales.La modélisation mathématique des performances sportives quantifiables montre desévolutions similaires dans toutes les épreuves : elles suivent une loi de progression multiexponentiellepar séries scandée par les événements historiques. Cette vision intégratricepermet la découverte d’un phénomène limitant commun à toutes les disciplines, lesperformances ne peuvent pas continuer à progresser continuellement, certaines ayant déjàcessé de croître. Ces limites observées dans le domaine sportif sont un indicateur des limitesphysiologiques de l’organisme humain.Les principaux facteurs qui permettraient de nouvelles améliorations des performances sontles innovations technologiques.Les prédispositions génétiques des athlètes et leur phénotype qui résulte d’interactions entreleurs gènes et l’environnement leur permettent d’accomplir ces performances sportivesmaximales. La majorité des records du monde a été battue pas les athlètes de nations quicomptent parmi les grandes puissances mondiales, fournissant un environnementgéographique, économique et sociopolitique, favorisant l’épanouissement sportif. Le sport estun indicateur du développement économique et politique d’un pays.Les résultats de cette thèse analysant un nombre important de données apportent une nouvellevision sur nos capacités de progression : les performances physiologiques humaines nes’accroissent pas de manière linéaire.
Article
Subject-specific torque-driven models have ignored biarticular effects at the hip. The aim of this study was to establish the contribution of monoarticular hip flexors and hip extensors to total hip flexor and total hip extensor joint torques for an individual and to investigate whether torque-driven simulation models should consider incorporating biarticular effects at the hip joint. Maximum voluntary isometric and isovelocity hip flexion and hip extension joint torques were measured for a single participant together with surface electromyography. Single-joint and two-joint representations were fitted to the collected torque data and used to determine the maximum voluntary joint torque capacity. When comparing two-joint and single-joint representations, the single-joint representation had the capacity to produce larger maximum voluntary hip flexion torque (larger by around 9% of maximum torque) and smaller maximum voluntary hip extension torque (smaller by around 33% of maximum torque) with the knee extended. Considering the range of kinematics found for jumping movements, the single-joint hip flexors had the capacity to produce around 10% additional torque, while the single joint hip extensors had about 70% of the capacity of the two-joint representation. Two-joint representations may overcome an over-simplification of single-joint representations by accounting for biarticular effects, while building on the strength of determining subject-specific parameters from measurements on the participant.
Article
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Purpose Pure predictive dynamics aims at predicting the set of driving inputs in the absence of any a priori data and can be applied in movement science to generate biomechanical variables in many different what-if scenarios. The objective of this research was to solve the problem of the predictive dynamics of sub-maximal cycling by means of an optimal control computational algorithm that makes use of an indirect method. Methods To this, a 2D two-legged seven bodies three degrees of freedom model of the lower limbs of a cyclist has been developed and validated against the average behaviour of eight well-trained cyclists pedalling at different sub-maximal intensities (100, 220, 300 W) at constant cadence (90 rpm). Experimental data adopted in model validation consists of the hip, knee, ankle joint centre and crank kinematics and the right/left crank torques. Results It has been found that the model can replicate the major features of pedalling biomechanics and the ability of a cyclist to deliver a larger torque if a larger power output is required and the cadence is kept constant. The reported mismatches with experimental data get smaller as the power output increases. Conclusions It is suggested that: (1) an optimal control based on an indirect method approach can provide a solution to the predictive dynamics of sub-maximal cycling, (2) predictive dynamics adapts accordingly to real data for changes in power output.
Article
The purpose of this study was to consider whether it is necessary for biarticular effects to be accounted for in subjectspecific representations of maximal voluntary knee extension and knee flexion torques. Isovelocity and isometric knee torques were measured on a single participant at three different hip angles using a Contrex MJ dynamometer. Maximal voluntary torque was represented by a 19-parameter two-joint function of knee and hip joint angles and angular velocities with the parameters determined by minimizing a weighted rms difference between measured torques and the two-joint function. The weighted rms difference between the two-joint function and the measured knee flexion torques was 14 Nm or 9% of maximum torque, while for knee extension the difference was 26 Nm or 9% of maximum torque. The two-joint representation was shown to be more accurate than an existing single-joint representation for torques measured at hip angles other than those used to derive the single-joint function parameter values. The differences between the traditionally used single-joint representation and the measured knee flexion and knee extension torques were largest for the most extended hip joint angle (15 and 18% of maximum torque, respectively), while the corresponding differences for the two-joint function were 9% and 8% of maximum torque. It is concluded that a two-joint function can account for changes in knee flexion and knee extension joint torques due to both monoarticular and biarticular muscles over a range of both hip and knee angles, and this has the potential to improve the biofidelity of whole-body subject-specific torque-driven simulation models.
Conference Paper
In the context of human movement, efficiency is defined as the ratio of mechanical energy output (work) to metabolic energy input [1,2]. It is straightforward to determine whole-body efficiency in a task such as pedaling a bicycle ergometer. In this case, work is computed from the ergometer load and pedaling cadence, and metabolic energy is determined from pulmonary gas exchange. It is also relatively straightforward to determine the efficiency of contraction in isolated muscle preparations, where the work done is easily measured, and energy input can be inferred from heat production or oxygen consumption. However, our understanding of the efficiency of muscle function during locomotion, and how this contributes to organismal efficiency, is incomplete [1]. The ability to determine efficiency of individual muscles as they perform work in vivo would greatly enhance our understating in this area. Experimental measurement of both work and metabolic energy consumption in muscles during dynamic activities is currently limited to isolated applications in non-human animals [3]. Similar data could be obtained using computational modeling and simulation techniques, provided that estimates could be obtained for both muscle work and muscle metabolic energy consumption. This non-invasive approach would open the door to investigations in humans as well as other species. Therefore, the primary purpose of this study was to determine efficiency at both the organismal and muscular levels for bicycle pedaling, using a musculoskeletal modeling approach. A secondary purpose was to identify factors that account for between-muscle differences in efficiency.
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The purpose of this study was to clarify the reason for the difference in the preferred cadence between cyclists and noncyclists. Male cyclists and noncyclists were evaluated in terms of pedal force, neuromuscular activity for lower extremities, and oxygen consumption among the cadence manipulation (45, 60, 75, 90, and 105 rpm) during pedaling at 150 and 200 W. Noncyclists having the same levels of aerobic and anaerobic capacity as cyclists were chosen from athletes of different sports to avoid any confounding effect from similar kinetic properties of cyclists for lower extremities (i.e., high speed contraction and high repetitions in prolonged exercise) on both pedaling performance and preferred cadence. The peak pedal force significantly decreased with increasing of cadence in both groups, and the value for noncyclists was significantly higher than that for cyclists at each cadence despite the same power output. The normalized iEMG for vastus lateralis and vastus medialis muscles increased in noncyclists with rising cadence; however, cyclists did not show such a significant increase of the normalized iEMG for the muscles. On the other hand, the normalized iEMG for biceps femoris muscle showed a significant increase in cyclists while there was no increase for noncyclists. Oxygen consumption for cyclists was significantly lower than that for noncyclists at 105 rpm for 150 W work and at 75, 90, and 105 rpm for 200 W work. We conclude that cyclists have a certain pedaling skill regarding the positive utilization for knee flexors up to the higher cadences, which would contribute to a decrease in peak pedal force and which would alleviate muscle activity for the knee extensors. We speculated that pedaling skills that decrease muscle stress influence the preferred cadence selection, contributing to recruitment of ST muscle fibers with fatigue resistance and high mechanical efficiency despite increased oxygen consumption caused by increased repetitions of leg movements.
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Muscle samples were obtained from the gastrocnemius of 17 female and 23 male track athletes, 10 untrained women, and 11 untrained men. Portions of the specimen were analyzed for total phosphorylase, lactic dehydrogenase (LDH), and succinate dehydrogenase (SDH) activities. Sections of the muscle were stained for myosin adenosine triphosphatase, NADH2 tetrazolium reductase, and alpha-glycerophosphate dehydrogenase. Maximal oxygen uptake (VO2max) was measured on a treadmill for 23 of the volunteers (6 female athletes, 11 male athletes, 10 untrained women, and 6 untrained men). These measurements confirm earlier reports which suggest that the athlete's preference for strength, speed, and/or endurance events is in part a matter of genetic endowment. Aside from differences in fiber composition and enzymes among middle-distance runners, the only distinction between the sexes was the larger fiber areas of the male athletes. SDH activity was found to correlate 0.79 with VO2max, while muscle LDH appeared to be a function of muscle fiber composition. While sprint- and endurance-trained athletes are characterized by distinct fiber compositions and enzyme activities, participants in strength events (e.g., shot-put) have relatively low muscle enzyme activities and a variety of fiber compositions.
Article
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The purpose of this investigation was to relate muscle fiber composition to the isokinetic measure of peak torque production through a range of leg extension velocities. Twenty-one males were biopsied from the vastus lateralis muscle to determine their percent distribution of slow twitch (%ST) and fast twitch (%FT) muscle fibers as identified through myofibrillar adenosine triphosphatase activity. All subjects showed a decline in peak torque with increasing velocities. Subjects with predominantly FT fibers were able to generate 11, 16, 23 and 47 percent greater relative peak torque than could predominantly ST subjects at lever arm velocities of 115, 200, 287 and 400 degrees/second respectively. Likewise the correlation between relative torque production and % FT were significant (p less than .05) and increased from r = 0.44 to r = 0.75 as velocity increased from 115 to 400 degrees/second respectively. These data suggest that muscle fiber composition becomes increasingly more related to power performance as the velocity of movement increases.
Article
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In a comparison of traditional and theoretical exercise efficiency calculations male subjects were studied during steady-rate cycle ergometer exercises of "0," 200, 400, 600, and 800 kgm/min while pedaling at 40, 60, 80, and 100 rpm. Gross (no base-line correction), net (resting metabolism as base-line correction), work (unloading cycling as base-line correction), and delta (measurable work rate as base-line correction) efficiencies were computed. The result that gross (range 7.5-20.4%) and net (9.8-24.1%) efficiencies increased with increments in work rate was considered to be an artifact of calculation. A LINEAR OR SLIGHTLY EXPONENTIAL RELATIONSHIP BETWEEN CALORIC OUTPUT AND WORK RATE DICTATES EITHER CONSTANT OR DECREASING EFFICIENCY WITH INCREMENTS IN WORK. The delta efficiency (24.4-34.0%) definition produced this result. Due to the difficulty in obtaining 0 work equivalents, the work efficiency definition proved difficult to apply. All definitions yielded the result of decreasing efficiency with increments in speed. Since the theoretical-thermodynamic computation (assuming mitochondrial P/O = 3.0 and delta G = -11.0 kcal/mol for ATP) holds only for CHO, the traditional mode of computation (based upon VO2 and R) was judged to be superior since R less than 1.0. Assuming a constant phosphorylative-coupling efficiency of 60%, the mechanical contraction-coupling efficiency appears to vary between 41 and 57%.
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The effects of three different cadences and five different work rates on Gross (GE) and Delta Efficiency (DE) during cycle ergometry were studied. Fifteen well-trained cyclists exercised for 30 minutes at 60, 80, or 100 RPM on three different occasions. On each occasion, the load was increased every five minutes and corresponded to approximately 50, 60, 70, 80 and 90% of VO2max. During the last three minutes of each stage, steady-state energy expenditure was calculated while work rate was recorded. In addition, the oxygen cost of unloaded cycling (CUC) was also measured. GE was calculated as the ratio of work rate to the rate of energy expenditure, whereas DE was calculated as the reciprocal of the slope of this relationship at work rates between 50 and 90% of VO2max. The CUC corresponded to 0.66 +/- 0.03 l/min, 0.77 +/- 0.04 l/min and 1.04 +/- 0.04 l/min at 60 RPM, 80 RPM and 100 RPM, respectively (p less than 0.01 for all comparisons). GE was similar at all cadences when cycling at 80 and 90% VO2max. DE increased with increasing rpm and corresponded to 20.6 +/- 0.4%, 21.8 +/- 0.6%, and 23.8 +/- 0.4% at 60 RPM, 80 RPM and 100 RPM, respectively (p less than 0.01 for all comparisons). Therefore, when trained cyclists exercise intensely (80-90% VO2max), GE is similar at cadences of 60, 80 and 100 RPM, despite the significant increase in the CUC. Thus, it is possible that delta efficiency increases with increasing cadence.
Article
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A design is presented for a bicycle pedal dynamometer that measures both normal and tangential forces (i.e. driving forces). Mechanical decoupling is used to reduce the cross-sensitivity of the dynamometer to loads doing no work to propel the bicycle. This obviates the need to measure all six loads for accurate data reduction. A compact strain ring is the transducer element, and a monolithic design eliminates mechanical hysteresis between the strain ring and the dynamometer frame. The angular orientation of the dynamometer with respect to the crank arm is determined with a continuous-rotation potentiometer. Design criteria and design implementation are discussed, sample data are presented, and the performance of the dynamometer is evaluated.
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The mechanical efficiency of mouse fast- and slow-twitch muscle was determined during contractions involving sinusoidal length changes. Measurements were made of muscle length, force production and initial heat output from bundles of muscle fibres in vitro at 31 degrees C. Power output was calculated as the product of the net work output per sinusoidal length cycle and the cycle frequency. The initial mechanical efficiency was defined as power output/(rate of initial heat production+power output). Both power output and rate of initial heat production were averaged over a full cycle of length change. The amplitude of length changes was +/- 5% of muscle length. Stimulus phase and duration were adjusted to maximise net work output at each cycle frequency used. The maximum initial mechanical efficiency of slow-twitch soleus muscle was 0.52 +/- 0.01 (mean +/- 1 S.E.M. N = 4) and occurred at a cycle frequency of 3 Hz. Efficiency was not significantly different from this at cycle frequencies of 1.5-4 Hz, but was significantly lower at cycle frequencies of 0.5 and 1 Hz. The maximum efficiency of fast-twitch extensor digitorum longus muscle was 0.34 +/- 0.03 (N = 4) and was relatively constant (0.32-0.34) over a broad range of frequencies (4-12 Hz). A comparison of these results with those from previous studies of the mechanical efficiency of mammalian muscles indicates that efficiency depends markedly on contraction protocol.
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To determine whether power-velocity relationships obtained on a nonisokinetic cycle ergometer could be related to muscle fibre type composition, ten healthy specifically trained subjects (eight men and two women) performed brief periods of maximal cycling on a friction loaded cycle ergometer. Frictional force and flywheel velocity were recorded at a sampling frequency of 200 Hz. Power output was computed as the product of velocity and inertial plus frictional forces. Force, velocity and power were averaged over each down stroke. Muscle fibre content was determined by biopsy of the vastus lateralis muscle. Maximal down stroke power [14.36 (SD 2.37)W.kg-1] and velocity at maximal power [120 (SD 8) rpm] were in accordance with previous results obtained on an isokinetic cycle ergometer. The proportion of fast twitch fibres expressed in terms of cross sectional area was related to optimal velocity (r = 0.88, P < 0.001), to squat jump performance (r = 0.78, P < 0.01) and tended to be related to maximal power expressed per kilogram of body mass (r = 0.60, P = 0.06). Squat jump performance was also related to cycling maximal power. expressed per kilogram of body mass (r = 0.87, P < 0.01) and to optimal velocity (r = 0.86, P < 0.01). All these data suggest that the nonisokinetic cycle ergometer is a good tool with which to evaluate the relative contribution of type II fibres to maximal power output. Furthermore, the strong correlation obtained demonstrated that optimal velocity, when related to training status, would appear to be the most accurate parameter to explore the fibre composition of the knee extensor muscle.
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The aim of this study was to compare optimal pedalling velocities during maximal (OVM) and submaximal (OVSM) cycling in human, subjects with different training backgrounds. A group of 22 subjects [6 explosive (EX), 6 endurance (EN) and 10 non-specialised subjects] sprint cycled on a friction-loaded ergometer four maximal sprints lasting 6 s each followed by five 3-min periods of steady-state cycling at 150 W with pedalling frequencies varying from 40 to 120 rpm. The OVM and OVSM were defined as the velocities corresponding to the maximal power production and the lowest oxygen consumption, respectively. A significant linear relationship (r 2 = 0.52, P < 0.001) was found between individual OVM [mean 123.1 (SD 11.2) rpm] and OVSM [mean 57.0 (SD 4.9) rpm, P < 0.001] values, suggesting that the same functional properties of leg extensor muscles influence both OVM and OVSM. Since EX was greater than EN in both OVM and OVSM (134.3 compared to 110.9 rpm and 60.8 compared to 54.0 rpm, P < 0.01 and P < 0.05, respectively) it could be hypothesised that the distribution of muscle fibre type plays an important role in optimising both maximal and submaximal cycling performance.
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The objectives of this study were twofold. The first was to develop a forward dynamic model of cycling and an optimization framework to simulate pedaling during submaximal steady-state cycling conditions. The second was to use the model and framework to identify the kinetic, kinematic, and muscle timing quantities that should be included in a performance criterion to reproduce natural pedaling mechanics best during these pedaling conditions. To make this identification, kinetic and kinematic data were collected from 6 subjects who pedaled at 90 rpm and 225 W. Intersegmental joint moments were computed using an inverse dynamics technique and the muscle excitation onset and offset were taken from electromyographic (EMG) data collected previously (Neptune et al., 1997). Average cycles and their standard deviations for the various quantities were used to describe normal pedaling mechanics. The model of the bicycle-rider system was driven by 15 muscle actuators per leg. The optimization framework determined both the timing and magnitude of the muscle excitations to simulate pedaling at 90 rpm and 225 W. Using the model and optimization framework, seven performance criteria were evaluated. The criterion that included all of the kinematic and kinetic quantities combined with the EMG timing was the most successful in replicating the experimental data. The close agreement between the simulation results and the experimentally collected kinetic, kinematic, and EMG data gives confidence in the model to investigate individual muscle coordination during submaximal steady-state pedaling conditions from a theoretical perspective, which to date has only been performed experimentally.
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In this chapter fundamental energetic properties of skeletal muscles as elucidated from isolated muscle preparations are described. Implications of these intrinsic properties for the energetic characterization of different fiber types and for the understanding of locomotion have been considered. Emphasis was placed on the myriad of physical and chemical techniques that can be employed to understand muscle energetics and on the interrelationship of results from different techniques. The anaerobic initial processes which liberate energy during contraction and relaxation are discussed in detail. The high-energy phosphate (approximately P) utilized during contraction and relaxation can be distributed between actomyosin ATPase or cross-bridge cycling (70%) and the Ca2+ ATPase of the sacroplasmic reticulum (30%). Muscle shortening increases the rate of approximately P hydrolysis, and stretching a muscle during contraction suppresses the rate of approximately P hydrolysis. The economy of an isometric contraction is defined as the ratio of isometric mechanical response to energetic cost and is shown to be a fundamental intrinsic parameter describing muscle energetics. Economy of contraction varies across the animal kingdom by over three orders of magnitude and is different in different mammalian fiber types. In mammalian skeletal muscles differences in economy of contraction can be attributed mainly to differences in the specific actomyosin and Ca2+ ATPase of muscles. Furthermore, there is an inverse relationship between economy of contraction and maximum velocity of muscle shortening (Vmax) and maximum power output. This is a fundamental relationship. Muscles cannot be economical at developing and maintaining force and also exhibit rapid shortening. Interestingly, there appears to be a subtle system of unknown nature that modulates the Vmax and economy of contraction. Efficiency of a work-producing contraction is defined and contrasted to the economy of contraction. Unlike economy, maximum efficiency of work production varies little across the animal kingdom. There are difficulties associated with the measurement of maximum efficiency of contraction, and it has yet to be determined unequivocally if the maximum efficiency of contraction varies in different fiber types. The intrinsic properties of force per cross-sectional area, economy, and Vmax determine the basic energetic properties of skeletal muscles. Nonetheless, the mechanics and energetics of skeletal muscles in the body are profoundly influenced by muscle architecture, attachment of muscles to the skeleton, and motor unit organization.(ABSTRACT TRUNCATED AT 400 WORDS)
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This experiment was designed to estimate the optimum pedal rates at various power outputs on the cycle ergometer. Five trained bicycle racers performed five progressive maximal tests on the ergometer. Each rode at pedal rates of 40, 60, 80, 100, and 120 rev X min-1. Oxygen uptake and heart rate were determined from each test and plotted against pedal rate for power outputs of 100, 150, 200, 250, and 300 W. Both VO2 and heart rate differed significantly among pedal rates at equivalent power outputs, the variation following a parabolic curve. The low point in the curve was taken as the optimal pedal rate; i.e., the pedal rate which elicited the lowest heart rate or VO2 for a given power output. When the optimum was plotted against power output the variation was linear. These results indicate that an optimum pedal rate exists in this group of cyclists. This optimum pedal rate increases with power output, and when our study is compared to studies in which elite racers, or non-racers were used, the optimum seems to increase with the skill of the rider.
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The variability of fiber type distributions between different regions of the same human muscle is believed to be small, based on the sampling of between two and four sites. The objective of the present investigation was to determine the variability of slow-twitch (ST) and fast-twitch (FT) fiber distributions using a more extensive sampling technique than those previously employed. The soleus, biceps, triceps, and vastus lateralis muscles were excised from each of four young men who had died suddenly. Between 13 and 17 sites were sampled from each of the muscles; 3 transverse areas were then examined within each sample. Fiber type distributions were determined from photographs of sections stained for myofibrillar adenosine triphosphatase at pH 10.3, 10.0, or 4.3. The numbers of fibers counted in the four muscles ranged between a mean of 13,660 and a mean of 21,601. The variability in fiber type distributions observed between sites and areas within a site were statistically greater (P less than 0.01) than could be expected from muscles whose fiber type distributions are equally distributed throughout the muscle. It was concluded that sampling between 3 and 5 sites in the different muscles was necessary to reduce the between-site standard deviation to 5%.
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The aim of this investigation was to study how the known dependence of working efficiency on pedaling frequency is influenced by the work load as well as by physical fitness. Oxygen uptake, CO2 output, ventilation, heart rate, and lactate concentration in capillary blood from the ear-lobe were determined at varying combinations of work loads and pedaling rates in road-racing cyclists and medical students. Respiratory exchange ratio, consumption of energy, gross efficiency, net efficiency, and delta efficiency (Δ work rate/Δ metabolic rate) were calculated. All parameters showed a nonlinear dependence on pedaling frequency. The lowest oxygen uptake and the highest efficiency shifted to higher frequencies with increasing work load. Delta efficiency increased with rising pedaling frequency. Differences of V̇O2 and efficiencies between trained and untrained subjects were only small. Most effects can be explained by variations in leg movement frequency and recruitment of muscle fibers. There is evidence that racing cyclists chose pedaling rates yielding optimal efficiency at any load.
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The relationship between maximum isometric strength and muscle fiber type composition was examined in seven endurance and eight power trained athletes. Knee extension strength and ankle extension strength was assessed on 10 separate days and muscle biopsies were taken from the vastus lateralis and gastrocnemius muscles. The percent composition of slow twitch (ST) fibers and fast twitch (FT) fibers was determined from the biopsy samples. Correlation between maximal knee extension strength and percent ST fibers of the vastus lateralis was found to be 0.80 (n = 8,p less than 0.05) for the power group and 0.63 (n = 7,N.S.) for the endurance group. Corresponding correlation coefficients for the relationship between ankle extension strength and gastrocnemius percent ST fibers were -0.94 (p less than 0.01) and -0.19 (N.S.), respectively. The results suggest that the relationship to be expected between muscle fiber type composition and maximum isometric strength may well depend upon the muscle group under study as well as the type of athlete in terms of specific training adaptations.
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This investigation was undertaken to determine the effect of pedal frequency on submaximal exercise responses. Seven well-trained competitive cyclists were studied riding their road-racing bicycles on a motor-driven treadmill at 80% of maximum O2 consumption (VO2 max) using different gear ratios. Cyclists were also studied during a series of unloaded trials to assess the effects of varying rates of limb movements independent of external work load. Heart rate (HR) increased, whereas net HR (after subtracting the HR during unloaded cycling) decreased with increasing pedal frequency during loaded cycling. Expiratory flow (VE), O2 consumption (VO2), blood lactate, net VO2 (after subtracting the VO2 of unloaded cycling), and net VE (after subtracting the VE during unloaded cycling) were quadratically related to pedal frequency. The quadratic relationships evident after corrections were made for the additional work needed to move the legs more frequently may be explained at the lower pedaling rates by a less uniform pattern of blood flow caused by increasing the force requirement per pedal stroke and, at the higher pedal frequencies, by the recruitment of additional musculature to stabilize the trunk. The average of preferred frequency for the group, which was also the most economical pedaling rate judged by most of the variables was 91 rpm, although the preferred pedaling rate for each subject ranged from 72 to 102 rpm.
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Fibre composition in the vastus lateralis muscle, leg blood flow, oxygen uptake and respiratory exchange ratio were determined in 12 healthy male volunteers during submaximal exercise (50% of V02 max). The percentage of slow-twitch fibres varied from 26 to 66. Mean leg blood flow during exercise was 4.68 +/- 0.191.min-1. The blood flow and respiratory exchange ratio correlated positively to the percentage of slow-twitch fibres in the vastus muscles. No correlation was found between the muscle fibre composition and either oxygen uptake heart rate or mechanical efficiency. The results with a dependence of muscle blood flow and carbon dioxide release to muscle fibre composition support the view that the arrangement of the vascular bed and blood supply differ between fast-twitch and slow-twitch muscle fibres in humans.