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The Effect of Cadence on the Mechanics and Energetics of Constant Power Cycling
Abstract
At a constant power output, cyclists prefer to use a higher cadence than those that minimize metabolic cost. The neuromuscular mechanism underpinning the preferred higher cadence remains unclear.
Purpose:
The aim of this study was to investigate the effect of cadence on joint level work and vastus lateralis (VL) fascicle mechanics while cycling at a constant, submaximal, power output. We hypothesized that preferred cycling cadence would enhance the power capacity of the VL muscle when compared with a more economical cadence. Furthermore, we predicted that the most economical cadence would coincide with minimal total electromyographic activity from the leg muscles.
Methods:
Metabolic cost, lower-limb kinematics, joint level work, VL fascicle mechanics, and muscle activation of the VL, rectus femoris, biceps femoris, gastrocnemius medialis, and soleus muscles were measured during cycling at a constant power output of 2.5 W·kg and cadences of 40, 60, 80, and 100 rpm. A preferred condition was also performed where cadence feedback was hidden from the participant.
Results:
Metabolic cost was lowest at 60 rpm, but the mean preferred cadence was 81 rpm. The distribution of joint work remained constant across cadences, with the majority of positive work being performed at the knee. The preferred cadence coincided with the highest VL power capacity, without a significant penalty to efficiency, based on fascicle shortening velocity.
Conclusions:
Cycling at a higher cadence is preferred to ensure that the muscle's ability to produce positive power remains high. Further investigations are required to examine what feedback mechanism could be responsible for the optimization of this motor pattern.
... CA is an important factor for cycling performance that has been widely investigated in recent years 19,20 . Although CA of ~60 rev•min −1 has been shown to minimize metabolic cost under laboratory conditions, cyclists chose a relatively higher CA during both competitions (XCC = 81.2 ...
... ± 4.7 and XCO = 77.4 ± 4.3 rev•min −1 ), as has been previously reported 19 . Nevertheless, we observed that cyclists adopted a CA higher during XCC. ...
... There is a trend of increases in CA as PO and speed increased 21 . As XCC was performed with higher PO and speed, can be that a higher CA was necessary to ensure that the muscle power capacity remains high 19 . Moreover, it is suggest that the CA selection coincides with the CA at which perception of effort is minimized or at which they are habituated 22 . ...
Different competitive environments appears to affect the physical demands during the sports competitions. Thus, the aim of this study was to report the mechanical demand and pacing behaviour of twelve male elite mountain bikers on cross-country short track (XCC) and cross-country Olympic (XCO). During both competition, total race time, speed, power output (PO) and cadence (CA) were recorded. As the race time in the XCC is shorter (21.0 ± 0.5 vs 84.0 ± 3.0 min; p<0.01), the average speed (26.6 ± 0.6 vs 17.8 ± 0.6 km/h; p<0.01), PO (365.0 ± 26.7 vs 301.0 ± 26.2 watts; p<0.01) and CA (81.2 ± 4.7 vs 77.4 ± 4.3 rev∙min⁻¹; p=0.01) were higher than the XCO. While a variable pacing was adopted during XCC, a positive profile was adopted in XCO. In addition, athletes adopted a more conservative starting pace during XCC (below average race speed) but a faster start during XCO (above average race speed). These findings demonstrated that mechanical parameters and pacing profile adopted by cyclists are different between XCC and XCO. Therefore, mountain bikers and coaches must develop specific strategy and training methods in order to obtain success in each competition.
Keywords:
Power output; Intensity; Cadence; Cross-country Olympic; Cross-country short track
... However, people do not show the same behavior when riding a bicycle, and tend to use higher cadences than the metabolically optimal one (Brisswalter et al. 2000;Alejandro Lucia, Jesus Hoyos 2000;Anthony P. Marsh and Martin 1997;Brennan et al. 2019). Apparently, other criteria besides energetic economy are at play in the self-selected pedaling rate during cycling. ...
... Several alternative factors have been proposed to influence cadence selection in cycling (Anthony P. Marsh, Martin, and Sanderson 2000;Brennan et al. 2019). For example, factors such as muscle activation (A. ...
... The ability of muscles to generate force is critically influenced by the length and velocity of muscle fibers, factors that ultimately constrain the capacity of muscles to produce power during cycling. In this context, force-length and force-velocity properties and their mechanical function during cycling under sub-maximal conditions have been reported for the vastus lateralis (VL) muscle, which is a major contributor to cycling power (Austin, Nilwik, and Herzog 2010;Muraoka et al. 2001;Brennan et al. 2018;2019). For example, Muraoka et al., (Muraoka et al. 2001) found that the timing of fascicle shortening differed from that of the muscle-tendon unit (MTU), because of interaction with the elastic tendinous tissue in series with fibers. ...
Whilst people typically chose to locomote in most economical fashion, during bicycling they will, unusually, chose cadences that are higher than metabolically optimal. Empirical measurements of the intrinsic contractile properties of the vastus lateralis (VL) muscle during submaximal cycling suggest that the cadences that people self-selected (SSC) might allow for optimal muscle fascicle shortening velocity for the production of knee extensor muscle power. It remains unclear, however, whether this is consistent across different power outputs where the SSC varies. We examined the effect of cadence and external power requirements on muscle neuromechanics and joint powers during cycling. VL fascicle shortening velocities, muscle activations and joint-specific powers were measured during cycling between 60 and 120rpm (including SSC), while participants produced 10%, 30%, and 50% of peak maximal power. VL shortening velocity increased as cadence increased but was similar across the different power outputs. Although no differences were found in the distribution of joint powers across cadence conditions, the absolute knee joint power increased with increasing crank power output. Muscle fascicle shortening velocities increased in VL at the SSC as pedal power demands increased from submaximal towards maximal cycling. A secondary analysis of muscle activation patterns showed minimized activation of VL and other muscles near the SSC at the 10% and 30% power conditions. Minimization of activation with progressively increasing fascicle shortening velocities at the SSC may be consistent with the theory that the optimum shortening velocity for maximizing power increases with intensity of exercise and recruitment of fast twitch fibers.
... The current body of literature underlines a variety of approaches when investigating physiological predictors and determinants of PPO, but does not consider recent advances in the evaluation of morphological properties such as muscle stiffness. Previous studies have analyzed fascicle lengths of vastus lateralis (VL) at different cadences in recreational cyclists (Austin and Nilwik, 2010;Brennan et al. 2018Brennan et al. ,2019. Austin and Nilwik, (2010) have used an experimental procedure with cadences at 50 and 80 RPM and at power outputs of 100 and 250 W. The findings from this study have demonstrated that a decrease in fascicle length at given pedaling rate (for 50 and 80 RPM) may reduce power production. ...
... Austin and Nilwik, (2010) have used an experimental procedure with cadences at 50 and 80 RPM and at power outputs of 100 and 250 W. The findings from this study have demonstrated that a decrease in fascicle length at given pedaling rate (for 50 and 80 RPM) may reduce power production. Brennan et al. (2018Brennan et al. ( , 2019 have found that fascicle shortening increases when cadence decreases (40-60-80-100 RPM) at 2.5 W⋅kg −1 . Concerning pennation angle, Kordi et al. (2020) have reported greater pennation angle of VL in sprinters compared with endurance cyclists. ...
Purpose
This study aimed to investigate physiological responses, muscle–tendon unit properties of the quadriceps muscle, and mechanical performance after repeated sprint cycling at optimal and 70% of optimal cadence.
Methods
Twenty recreational cyclists performed as first sprint performance cycling test and during subsequent sessions two repeated sprint cycling protocols at optimal and 70% of optimal cadence, in random order. The muscle–tendon unit outcome measures on the dominant leg included muscle thickness, fascicle length (Lf), pennation angle (θp), and stiffness for the rectus femoris (RF), vastus lateralis (VL), and vastus medialis muscle (VM) at baseline, immediately after repeated sprint cycling, and 1-h post-exercise.
Results
The results showed an increase in muscle thickness and θp in RF, VL, and VM for both cadences from baseline to immediately after exercise. The Lf decreased in RF (both cadences), while stiffness decreased in RF, VL, and VM at optimal cadence, and in VL at 70% of optimal cadence from baseline to immediately after exercise.
Conclusion
The present study revealed that the alterations in muscle characteristics were more marked after repeated sprint cycling at optimal cadence compared with a lower cadence most likely as a result of higher load on the muscle–tendon unit at optimal cadence.
... In cycling, an example of a combined use of biomechanics and neurophysiology is presented in [7]. Here, the authors have studied the effect of cadence on joint work level and vastus lateralis mechanics through a multifactorial analysis based on motion capture techniques, electromyography and using musculoskeletal digital models (i.e., OpenSim, Stanford University, USA [8]). ...
... IV and Tab. V) as well as the muscular activation data (i.e., RMS and synergy activation coefficients), the values for the biomechanical indices β, δ and are computed according to (5)- (7). The results are reported in Tab. ...
... For example, when nonseated at 70 rpm, the period of knee extension was so great (59%) that the mean knee extension velocity was actually 5.8% lower than when seated. As supported by the findings of Brennan et al. (34), the reduction in mean knee extension velocity in the nonseated (181°·s −1 ) compared with seated (192°·s −1 ) posture at 70 rpm would bring the fascicle shortening velocity of VL closer to its optimum for both efficiency and force production. Thus, it appears that riders use extra degrees of freedom afforded in the nonseated posture to increase the force-producing capabilities of knee extensor muscles. ...
... Thus, the most likely explanation is other knee flexor muscles were responsible for this increase. Another explanation is the greater mean knee flexion angle when seated compared with nonseated may have shifted the fascicle operating lengths of the knee flexors closer to optimal and hence been more favorable for generating power (34). On the whole, it appears there is a greater reliance on knee flexors to contribute power when seated, and there is a greater reliance on hip flexors to produce power when nonseated at 120 rpm. ...
Cyclists frequently use a non-seated posture when accelerating, climbing steep hills, and sprinting; yet, the biomechanical difference between seated and non-seated cycling remains unclear.
Purpose:
To test the effects of posture (seated and non-seated) and cadence (70 rpm and 120 rpm) on joint power contributions, effective mechanical advantage, and muscle activations within the leg during very-high-power output cycling.
Methods:
Fifteen male participants rode on an instrumented ergometer at 50% of their individualised instantaneous maximal power (10.74 ± 1.99 W⋅kg; above the reported threshold for seated to non-seated transition) in different postures (seated and non-seated) and at different cadences (70 rpm and 120 rpm); whilst leg muscle activity, full body motion capture, and crank radial and tangential forces were recorded. A scaled, full-body model was used to solve inverse kinematics and inverse dynamics to determine joint displacements and net joint moments. Statistical comparisons were made using repeated measure, two-way analyses of variance (posture x cadence).
Results:
There were significant main effects of posture and cadence on joint power contributions. A key finding was that the non-seated posture increased negative power at the knee, with an associated significant decrease of net power at the knee. The contribution of knee power decreased by 15% at both 70 and 120 rpm (~=0.8 W·kg) when non-seated compared to seated. Subsequently, hip power and ankle power contributions were significantly higher when non-seated compared to seated at both cadences. In both postures, knee power was 9% lower at 120 rpm compared to 70 rpm (~=0.4 W·kg).
Conclusion:
These results evidenced that the contribution of knee joint power to leg power was reduced by switching from a seated to non-seated posture during very-high-power output cycling, however the size of the reduction is cadence dependent.
... For example, when nonseated at 70 rpm, the period of knee extension was so great (59%) that the mean knee extension velocity was actually 5.8% lower than when seated. As supported by the findings of Brennan et al. (34), the reduction in mean knee extension velocity in the nonseated (181°·s −1 ) compared with seated (192°·s −1 ) posture at 70 rpm would bring the fascicle shortening velocity of VL closer to its optimum for both efficiency and force production. Thus, it appears that riders use extra degrees of freedom afforded in the nonseated posture to increase the force-producing capabilities of knee extensor muscles. ...
... Thus, the most likely explanation is other knee flexor muscles were responsible for this increase. Another explanation is the greater mean knee flexion angle when seated compared with nonseated may have shifted the fascicle operating lengths of the knee flexors closer to optimal and hence been more favorable for generating power (34). On the whole, it appears there is a greater reliance on knee flexors to contribute power when seated, and there is a greater reliance on hip flexors to produce power when nonseated at 120 rpm. ...
Riding a bicycle out of the saddle allows cyclists to generate higher peak power and improve uphill time trial performance, yet the mechanisms underpinning these performance advantages remain unclear. PURPOSE: To test the effects of posture (seated and non-seated) and cadence (70 rpm and 120 rpm) on the distribution of joint power, effective mechanical advantage and muscle activation within the lower limb during high-power output bicycling. METHODS: Fifteen male subjects rode on an instrumented ergometer at 50% of their individualised peak power (above the reported threshold for seated to non-seated transition) in different postures (seated and non-seated), and at different cadences (70 rpm and 120 rpm), whilst electromyography (EMG) from lower limb muscles, full body motion capture and crank radial and tangential forces were recorded. A scaled, full-body OpenSim™ model was used to solve inverse kinematics and inverse dynamics to determine joint motion and net joint moments. Statistical comparisons were made using a repeated measure, two-way ANOVA (posture x cadence). RESULTS: There were significant main effects of posture and cadence on the distribution of joint power within the lower limb. Subjects produced 15% less power at the knee, 10% more power at the hip and 5% more power at the ankle in the non-seated compared to seated posture. In both postures, subjects produced 9% less power at the knee, 18% more power at the hip and 9% less power at the ankle at 120 rpm compared to 70 rpm. CONCLUSION: These results provide evidence for the theory that the non-seated posture decreases mechanical requirements at the knee when bicycling at high power outputs, however this effect is cadence dependent.
... We predicted that the minimum active muscle volume would lie close to the self-selected cadence and would shift to higher cadences as power demands increased. By contrast, we expected that the cadence which minimizes predicted metabolic cost would be lower than the self-selected cadence (Brisswalter et al., 2000;Alejandro et al., 2000;Marsh and Martin, 1997;Brennan et al., 2019). ...
... The effect of the activation dependence of L 0 on estimates of force or the force-length potential is currently not considered in experimental studies on the force-length properties of human muscles. Here, the measured operating muscle fascicle length during the movement of interest is usually mapped on a single force-length curve determined at maximal activation despite the fact that the activation level is mostly submaximal during the movement (Austin et al., 2010;Bohm et al., 2019;Brennan et al., 2018;Monte et al., 2020;Nikolaidou et al., 2017;Rubenson et al., 2012). Furthermore, most common muscle models used in musculoskeletal studies and popular software systems (e.g. ...
Previous in vitro and in situ studies have reported a shift in optimal muscle fibre length for force generation (L0) towards longer length at decreasing activation levels (also referred to as length‐dependent activation), yet the relevance for in vivo human muscle contractions with a variable activation pattern remains largely unclear. By a combination of dynamometry, ultrasound and electromyography (EMG), we experimentally obtained muscle force–fascicle length curves of the human soleus at 100%, 60% and 30% EMGmax levels from 15 participants aiming to investigate activation‐dependent shifts in L0 in vivo. The results showed a significant increase in L0 of 6.5 ± 6.0% from 100% to 60% EMGmax and of 9.1 ± 7.2% from 100% to 30% EMGmax (both P < 0.001), respectively, providing evidence of a moderate in vivo activation dependence of the soleus force–length relationship. Based on the experimental results, an approximation model of an activation‐dependent force–length relationship was defined for each individual separately and for the collective data of all participants, both with sufficiently high accuracy (R² of 0.899 ± 0.056 and R² = 0.858). This individual approximation approach and the general approximation model outcome are freely accessible and may be used to integrate activation‐dependent shifts in L0 in experimental and musculoskeletal modelling studies to improve muscle force predictions. image
Key points
The phenomenon of the activation‐dependent shift in optimal muscle fibre length for force generation (length‐dependent activation) is poorly understood for human muscle in vivo dynamic contractions.
We experimentally observed a moderate shift in optimal fascicle length towards longer length at decreasing electromyographic activity levels for the human soleus muscle in vivo.
Based on the experimental results, we developed a freely accessible approximation model that allows the consideration of activation‐dependent shifts in optimal length in future experimental and musculoskeletal modelling studies to improve muscle force predictions.
... (3) In at least some locomotor tasks, we tend to choose a cadence that is suboptimum from an energetics perspective [e.g. we may transition from walking to running and vice versa despite incurring an increased energetic cost (Hreljac, 1993;Tseh et al., 2002)], which in some cases may allow the major propulsive muscles to work at shortening speeds commensurate with peak power production (e.g. in bicycling; Brennan et al., 2019), or we might choose to optimise gait stability at the expense of energetic cost (e.g. when walking downhill; Hunter, Hendrix & Dean, 2010), or choose to locomote under conditions of lower total muscle activation, and presumably sense of effort (crouched walking), rather than conditions requiring higher energetic cost (e.g. walking uphill) (McDonald et al., 2023). ...
Elastic strain energy that is stored and released from long, distal tendons such as the Achilles during locomotion allows for muscle power amplification as well as for reduction of the locomotor energy cost: as distal tendons perform mechanical work during recoil, plantar flexor muscle fibres can work over smaller length ranges, at slower shortening speeds, and at lower activation levels. Scant evidence exists that long distal tendons evolved in humans (or were retained from our more distant Hominoidea ancestors) primarily to allow high muscle-tendon power outputs, and indeed we remain relatively powerless compared to many other species. Instead, the majority of evidence suggests that such tendons evolved to reduce total locomotor energy cost. However, numerous additional, often unrecognised, advantages of long tendons may speculatively be of greater evolutionary advantage, including the reduced limb inertia afforded by shorter and lighter muscles (reducing proximal muscle force requirement), reduced energy dissipation during the foot-ground collisions, capacity to store and reuse the muscle work done to dampen the vibrations triggered by foot-ground collisions, reduced muscle heat production (and thus core temperature), and attenuation of work-induced muscle damage. Cumulatively, these effects should reduce both neuromotor fatigue and sense of locomotor effort, allowing humans to choose to move at faster speeds for longer. As these benefits are greater at faster locomotor speeds, they are consistent with the hypothesis that running gaits used by our ancestors may have exerted substantial evolutionary pressure on Achilles tendon length. The long Achilles tendon may therefore be a singular adaptation that provided numerous physiological, biomechanical, and psychological benefits and thus influenced behaviour across multiple tasks, both including and additional to locomotion. While energy cost may be a variable of interest in locomotor studies, future research should consider the broader range of factors influencing our movement capacity, including our decision to move over given distances at specific speeds, in order to understand more fully the effects of Achilles tendon function as well as changes in this function in response to physical activity, inactivity, disuse and disease, on movement performance.
... Only the two more recent studies measured cadence (CA) during XCO competition [4,5] ( Table 2). The results showed that the CA selected by the riders was higher than these reported in the laboratory tests considered most effective [10,11], mainly when time spent not pedaling was excluded. Unlike laboratory tests where the PO is constant, the XCO circuits are extremely complex, which include technical sections such as rolling over obstacles, requiring a high CA and PO variation according to the demands of each section, limiting the ability to identify an optimal cadence [12]. ...
Mountain biking (MTB) is a cycling modality performed on a variety of unpaved terrain. Although the cross-country Olympic race is the most popular cross-country (XC) format, other XC events have gained increased attention. XC-MTB has repeatedly modified its rules and race format. Moreover, bikes have been modified throughout the years in order to improve riding performance. Therefore, the aim of this review was to present the most relevant studies and discuss the main results on the XC-MTB. Limited evidence on the topic suggests that the XC-MTB events present a variation in exercise intensity, demanding cardiovascular fitness and high power output. Nonetheless, these responses and demands seem to change according to each event. The characteristics of the cyclists differ according to the performance level, suggesting that these parameters may be important to achieve superior performance in XC-MTB. Moreover, factors such as pacing and ability to perform technical sections of the circuit might influence general performance. Bicycles equipped with front and rear suspension (i.e., full suspension) and 29” wheels have been shown to be effective on the XC circuit. Lastly, strategies such as protective equipment, bike fit, resistance training and accident prevention measures can reduce the severity and the number of injuries.
... Each person rides at their own preferred cadence, so it is impossible to generalize and to find the optimal cadence for everybody. Although the results are conflicting, it would seem that the optimal cadence is around 90 rpm [33]. Furthermore, continuous cadence changes are not only influenced by physiological factors, but also by environmental ones, such as the presence of hilly terrain [34]. ...
The high rate of air pollution represents a significant threat to health across the world. At the same time, the level of sedentarism is significantly increasing. In this scenario, new active transportation strategies are needed to address both these problems and e-bikes may be the answer to this need. E-bikes represent a way to promote green sustainable transport capable of facing urban congestion and pollution problems. On the other hand, since e-bikes provide electric assistance only when the rider is pushing on the pedals, they promote a low-moderate physical activity that may enhance health and reduce sitting time. This paper suggests a prototype of a smart e-bike in its initial design stages, which is tailor-made for all users. Our e-bikes will be provided with an intelligent system capable of automatically changing the assistance level based on specific physiological and environmental parameters.
... 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 . ...
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.
... (iii) At least in some locomotor tasks, we tend to choose a cadence that is suboptimum from an energetics perspective (e.g. we may transition from walking to running and vice versa despite incurring an increased energetic cost (Hreljac, 1993;Tseh et al., 2002)), which in some cases may allow the major propulsive muscles to work at shortening speeds commensurate with peak power production (e.g. in bicycling (Brennan et al., 2018)), or we might choose to optimise gait stability at the expense of energetic cost (e.g. when walking downhill (Hunter et al., 2010)), or choose to locomote under conditions of lower total muscle activation, and presumably sense of effort (crouched walking), rather than conditions requiring higher energetic cost (e.g. walking uphill) (McDonald et al., 2022). ...
Elastic strain energy is stored and released from long, distal tendons such as the Achilles during locomotion, reducing locomotor energy cost by minimising muscle shortening distance and speed, and thus activation. However, numerous additional, often unrecognised, advantages of long tendons may speculatively be of greater evolutionary advantage, including the reduced limb inertia afforded by shorter and lighter muscles (reducing proximal muscle force requirement); reduced energy dissipation during the foot-ground collision; capacity to store and reuse the muscle work done to dampen the vibrations triggered by foot-ground collisions; and attenuation of work-induced muscle damage. Cumulatively, these effects should reduce both neuromotor fatigue and sense of locomotor effort, allowing humans to choose to move at faster speeds for longer. As these benefits are greater at faster locomotor speeds, they are consistent with the hypothesis that running gaits used by our ancestors exerted substantial evolutionary pressure on Achilles tendon length.
... Of note is that rest periods of 5 min are commonly applied in cycling studies where several consecutive bouts are performed (Brennan et al., 2019;Chavarren & Calbet, 1999;Marsh & Martin, 1998 Therefore, the purpose of the present study was to test whether history-dependent freely chosen pedalling rhythmicity occurred in a second pedalling bout, performed at a freely chosen cadence when a 5-min rest period was incorporated between that bout and an initial bout, which was performed at preset target cadence. In the case that history dependence (as it has been reported previously) indeed was averted by the incorporated rest, it could support the interpretation that a brief rest period effectively can eliminate the described phenomenon of motor behavioural history dependence. ...
Background: It was recently reported that the freely chosen cadence at the end of a bout of pedalling depended on relatively high and low preset cadences applied at the beginning of the bout. This was denoted as a phenomenon of motor behavioural history dependence. Objective: The present study aimed at expanding that recent finding by testing whether the described history dependence occurred if 5-min rest was incorporated between the initial pedalling at preset cadence and the final pedalling at freely chosen cadence.
Methods: Twenty-six participants performed three separate sequences of submaximal ergometer pedalling. In sequence A, pedalling at 50 rpm was followed by 5-min rest and pedalling at freely chosen cadence. In sequence B, pedalling at 90 rpm was followed by 5-min rest and pedalling at freely chosen cadence. In sequence C (denoted reference), the cadence was freely chosen throughout all pedalling. Behavioural (cadence), biomechanical (tangential
pedal force), and physiological (heart rate) responses were measured. Results:
Initial pedalling at 90 rpm caused the subsequent freely chosen cadence (74.5 ± 3.3 rpm) to be about 6% higher (p = 0.001) than the reference freely chosen cadence at the end of sequence C (70.8 ± 3.2 rpm). A similar difference did not occur between sequences A and C. Conclusions: These divergent findings, combined with previous reports of clear history dependence in pedalling sequences (performed similarly to here, only without incorporated rest periods),
overall suggest that the present observations reflected a borderland of
motor behavioural history dependence. Further, the 5-min incorporated rest apparently weakened the history dependence phenomenon.
... Curiously, the relationships between cycling torque and single-joint torque-generating capacities of the various muscle groups have never been investigated while considering this standing position. While the higher power during standing sprint cycling could be related to the use of athlete body mass , it was also suggested that changes in lower-limb kinematics (i.e., joint angles) could lead some muscles to operate closer to their optimal length and thus to enhance their force production (Brennan et al., 2019;. Hence, it would be interesting to determine whether more specific torque-angle configurations allowed by this standing position potentially modify the relationships observed in the seated condition. ...
This study aimed to determine the relationship between the torque-generating capacity in sprint cycling and the strength capacity of the six lower-limb muscle groups in male and female world-class sprint cyclists. Eleven female and fifteen male top-elite cyclists performed 5-s sprints at maximal power in seated and standing positions. They also performed a set of maximal voluntary ankle, knee and hip flexions and extensions to assess single-joint isometric and isokinetic torques. Isokinetic torques presented stronger correlations with cycling torque than isometric torques for both body positions, regardless of the group. In the female group, knee extension and hip flexion torques accounted for 81.2% of the variance in cycling torque, while the ability to predict cycling torque was less evident in males (i.e., 59% of variance explained by the plantarflexion torque only). The standing condition showed higher correlations than seated and a better predictive model in males (R² = 0.88). In addition to the knee extensors and flexors and hip extensors, main power producers, the strength capacity of lower-limb distal plantarflexor (and to a lesser extent dorsiflexor) muscles, as well as other non-measured qualities (e.g., the upper body), might be determinants to produce such extremely high cycling torque in males.
... 1,20,21 In addition, previous investigators have demonstrated that a pedaling rate of 80 rpm elicits observable muscle shortening velocities that were favorable for both power production as well as efficiency. 22,23 Importantly, the chainrings on the cycle ergometer was veiled such that participants were visually blinded to the condition but could sometimes perceive differences in the pedaling action. Schematic of an ellipse with eccentricity defined as the ratio of major-to-minor axes, where a is the length of the major axis and b is the length of the minor axis. ...
Pedal speed and mechanical power output account for 99% of metabolic cost during submaximal cycling. Noncircular chainrings can alter instantaneous crank angular velocity and thereby pedal speed. Reducing pedal speed during the portion of the cycle in which most power is produced could reduce metabolic cost and increase metabolic efficiency.
Purpose:
To determine the separate contributions of pedal speed and chainring shape/eccentricity to the metabolic cost of producing power and evaluate joint-specific kinematics and kinetics during submaximal cycling across 3 chainring eccentricities (CON = 1.0; LOW = 1.13; HIGH = 1.24).
Methods:
Eight cyclists performed submaximal cycling at power outputs eliciting 30%, 60%, and 90% of their individual lactate threshold at pedaling rates of 80 rpm under each chainring condition (CON80rpm; LOW80rpm; HIGH80rpm) and at pedaling rates for the CON chainring chosen to match pedal speeds of the noncircular chainrings (CON78rpm to LOW80rpm; CON75rpm to HIGH80rpm). Physiological measures, metabolic cost, and gross efficiency were determined by indirect calorimetry. Pedal and joint-specific powers were determined using pedal forces and limb kinematics.
Results:
Physiological and metabolic measures were not influenced by eccentricity and pedal speed (all Ps > .05). Angular velocities produced during knee and hip extension were lower with the HIGH80rpm condition compared with the CON80rpm condition (all Ps < .05), while angular velocity produced during ankle plantar flexion remained unchanged.
Conclusions:
Despite the noncircular chainrings imposing their eccentricity on joint angular kinematics, they did not reduce metabolic cost or increase gross efficiency. Our results suggest that noncircular chainrings neither improve nor compromise submaximal cycling performance in trained cyclists.
... A combination of the two mentioned possibilities could also have occurred. Other researchers have focused their research on characteristics of muscle mechanics and suggested that the freely chosen cadence is the one that maximises the capacity for muscle power production (Brennan et al. 2019). Still, future work has to reveal how initial cycling at relatively low and high cadences, as, in the present study, may affect the capacity for muscle power production. ...
Purpose
History dependence can refer to the fact that parts of the human physiology (e.g., one or a group of muscles, or the nervous system) as well as functional aspects of the human (e.g., motor behaviour, or performance) depend on prior muscle activation. In the present study, it was investigated whether initial cycling at relatively low and high preset target cadences affected a subsequent freely chosen cadence at the end of the same bout of submaximal ergometer cycling.
Methods
Twenty-two participants performed a single test session, which consisted of separate bouts of submaximal ergometer cycling. In one bout, cycling at 50 rpm was followed by cycling at freely chosen cadence. In another bout, cycling at 90 rpm was followed by cycling at freely chosen cadence. In yet another bout (denoted reference), the cadence was freely chosen throughout. Behavioural (cadence), biomechanical (tangential pedal force), and physiological (heart rate) responses were measured.
Results
Increased cadence resulted in decreased maximal tangential pedal force in accordance with existing knowledge. Initial cycling at 50 and 90 rpm caused freely chosen cadence to be about 5% lower and higher, respectively, than the freely chosen cadence (72.4 ± 2.4 rpm) at the end of the reference bout. These differences in cadence were not accompanied by statistically significant differences in heart rate.
Conclusion
The freely chosen cadence depended on the preset cadence applied at the beginning of the bout. This was denoted a phenomenon of motor behavioural history dependence.
Nearly a century of research has shown that humans, and other animals, tend to move in ways that minimize energy use. A growing body of evidence suggests that energetic cost is not only an outcome of our movement, but also plays a central role in continuously shaping it. This has led to an emerging research area, at the nexus between biomechanics and neuroscience, termed behavioural energetics, which is focused on understanding the mechanisms of energy optimization and how this shapes our coordination and behaviour. In this Review, we first summarize the existing evidence for and against our preferred locomotor behaviours coinciding with energy optima. Although evidence of our preference for energetically optimal gaits has existed for decades, new research is revealing its relevance across a surprising array of dynamic locomotor tasks and complex environments. We next discuss evidence that we adapt our gait toward energy optima over short timescales and in novel environments, which we view as a more stringent test that energy expenditure is optimized in real-time. This necessitates that we sense energy use, or proxies for it, on similar timescales. We therefore next provide an overview of candidate sensory mechanisms of energy expenditure. Finally, we discuss how behavioural energetics can be applied to novel wearable assistive technologies and rehabilitation paradigms, and conclude the Review by outlining what we see as the most important future challenges and opportunities in behavioural energetics.
Near-infrared spectroscopy (NIRS) provides a simple and reliable measure of skeletal muscle oxidative capacity; however, its relationship to aerobic fitness and sex are unclear. We hypothesized that NIRS-derived oxidative capacity in the vastus lateralis (VL) and medial gastrocnemius (MG) would be correlated to indices of aerobic fitness and independent of sex. Twenty-six participants (13 males, 13 females) performed ramp- and step-incremental tests to volitional exhaustion on separate days to establish maximal oxygen uptake (V̇O 2 max), peak power output (PPO), lactate threshold (LT), gas exchange threshold (GET), respiratory compensation point (RCP), and maximal fat oxidation (MFO). Data were normalized to lean body mass to account for sex-based differences in body composition. Exercise tests were preceded by duplicate measurements of NIRS-derived oxidative capacity on the VL and MG muscles (i.e., repeated arterial occlusions following a brief set of muscle contractions). Skeletal muscle oxidative capacity for the VL (mean±SD: 21.9±4.6s) and MG (22.5±6.1s) were similar but unrelated (r ² =0.03, p=0.39). Skeletal muscle oxidative capacity for the VL, but not the MG (p>0.05 for all variables), was significantly correlated with V̇O 2 max (r ² =0.24; p=0.01), PPO (r ² =0.23; p=0.01), LT (r ² =0.23; p=0.01), GET (r ² =0.23; p=0.01), and RCP (r ² =0.27; p=0.006). MFO was not correlated with VL or MG skeletal muscle oxidative capacity (p>0.05). Females (54.9±4.5mL/kg LBM/min) and males (56.0±6.2mL/kg LBM/min), matched for V̇O 2 max (p=0.62), had similar NIRS-derived oxidative capacities for VL (20.7±4.4s vs. 23.2±4.6s; p=0.18) and MG (24.4±6.8s vs. 20.5±4.8; p=0.10). Overall, NIRS-derived skeletal muscle oxidative capacity in VL is indicative of aerobic fitness and independent of sex in humans.
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.
Purpose:
Muscle fascicles-tendon interactions are the main determinant in production of high joint velocity. Currently, no study has investigated the muscle fascicles behaviour of knee extensor muscles until the highest reachable velocity (e.g., unloaded knee extension). We aimed to track the changes in vastus lateralis fascicles length during knee extensions to quantify muscle fascicles and tendinous tissues contributions to muscle-tendon unit shortening and to determine maximal muscle fascicles shortening velocity.
Methods:
Fifteen participants performed isokinetic and isoinertial knee extensions, and ultrafast ultrasound imaging was used to observe the vastus lateralis fascicles from low to very high joint velocity.
Results:
The muscle fascicles shortening velocity increased linearly with the increase in knee joint velocity up to the maximal joint velocity (mean R (2) = 0.93 ± 0.08). Muscle fascicles contribution to muscle-tendon unit shortening velocity was almost constant regardless of the condition (83 ± 23%). Using Hill's equation, the maximal velocity of knee joint and muscle fascicles was determined at 1000 ± 489°s(-1) and 5.1 ± 2.0 L0 s(-1) (47.4 ± 18.7 cm s(-1)), respectively.
Conclusions:
Contribution of muscle fascicles to the muscle-tendon unit shortening velocity was much higher for the vastus lateralis in this study compared to the gastrocnemius medialis in two previous studies. Moreover, this contribution of muscle fascicles shortening velocity was constant whatever the velocity condition, even at the highest reachable velocity. Thus, the vastus lateralis fascicles shortening velocity increases linearly with the knee joint velocity until high velocities and its behaviour strongly accorded with the classical Hill's force-velocity relationship.
Summary 1. The relationship between force and velocity of shortening and between power and velocity were examined for myotomal muscle fibre bundles from the dogfish. 2. The maximum velocity of shortening, mean value 4-8 ± 0-2 (ms" 1 half sarco- mere" 1 (±S.E.M., N = 13), was determined by the 'slack step' method (Edman, 1979) and was found to be independent of fish length. 3. The force-velocity relationship was hyperbolic, except at the high-force end where the observations were below the hyperbola fitted to the rest of the data. 4. The maximum power output was 91 ± 14 W kg" 1 wet mass (±S.E.M. , N = l)
During human locomotion lower extremity muscle-tendon units undergo cyclic length changes that were previously assumed to be representative of muscle fascicle length changes. Measurements in cats and humans have since revealed that muscle fascicle length changes can be uncoupled from those of the muscle-tendon unit. Ultrasonography is frequently used to estimate fascicle length changes during human locomotion. Fascicle length analysis requires time consuming manual methods that are prone to human error and experimenter bias. To bypass these limitations, we have developed an automatic fascicle tracking method based on the Lucas-Kanade optical flow algorithm with an affine optic flow extension. The aims of this study were to compare gastrocnemius fascicle length changes during locomotion using the automated and manual approaches and to determine the repeatability of the automated approach. Ultrasound was used to examine gastrocnemius fascicle lengths in eight participants walking at 4, 5, 6, and 7 km/h and jogging at 7 km/h on a treadmill. Ground reaction forces and three dimensional kinematics were recorded simultaneously. The level of agreement between methods and the repeatability of the automated method were quantified using the coefficient of multiple correlation (CMC). Regardless of speed, the level of agreement between methods was high, with overall CMC values of 0.90 ± 0.09 (95% CI: 0.86-0.95). Repeatability of the algorithm was also high, with an overall CMC of 0.88 ± 0.08 (95% CI: 0.79-0.96). The automated fascicle tracking method presented here is a robust, reliable, and time-efficient alternative to the manual analysis of muscle fascicle length during gait.
A fundamental feature of vertebrate muscle is that maximal force can be generated only over a limited range of lengths. It has been proposed that locomotor muscles operate over this range of lengths in order to maximize force production during movement. However, locomotor behaviours like jumping may require muscles to shorten substantially in order to generate the mechanical work necessary to propel the body. Thus, the muscles that power jumping may need to shorten to lengths where force production is submaximal. Here we use direct measurements of muscle length in vivo and muscle force-length relationships in vitro to determine the operating lengths of the plantaris muscle in bullfrogs (Rana catesbeiana) during jumping. We find that the plantaris muscle operates primarily on the descending limb of the force-length curve, resting at long initial lengths (1.3 +/- 0.06 L(o)) before shortening to muscle's optimal length (1.03 +/- 0.05 L(o)). We also compare passive force-length curves from frogs with literature values for mammalian muscle, and demonstrate that frog muscles must be stretched to much longer lengths before generating passive force. The relatively compliant passive properties of frog muscles may be a critical feature of the system, because it allows muscles to operate at long lengths and improves muscles' capacity for force production during a jump.
Skeletal muscle architecture is defined as the arrangement of fibers in a muscle and functionally defines performance capacity. Architectural values are used to model muscle-joint behavior and to make surgical decisions. The two most extensively used human lower extremity data sets consist of five total specimens of unknown size, gender, and age. Therefore, it is critically important to generate a high-fidelity human lower extremity muscle architecture data set. We disassembled 27 muscles from 21 human lower extremities to characterize muscle fiber length and physiologic cross-sectional area, which define the excursion and force-generating capacities of a muscle. Based on their architectural features, the soleus, gluteus medius, and vastus lateralis are the strongest muscles, whereas the sartorius, gracilis, and semitendinosus have the largest excursion. The plantarflexors, knee extensors, and hip adductors are the strongest muscle groups acting at each joint, whereas the hip adductors and hip extensors have the largest excursion. Contrary to previous assertions, two-joint muscles do not necessarily have longer fibers than single-joint muscles as seen by the similarity of knee flexor and extensor fiber lengths. These high-resolution data will facilitate the development of more accurate musculoskeletal models and challenge existing theories of muscle design; we believe they will aid in surgical decision making.
We have developed a model of the human lower extremity to study how surgical changes in musculoskeletal geometry and musculotendon parameters affect muscle force and its moment about the joints. The lines of action of 43 musculotendon actuators were defined based on their anatomical relationships to three-dimensional bone surface representations. A model for each actuator was formulated to compute its isometric force-length relation. The kinematics of the lower extremity were defined by modeling the hip, knee, ankle, subtalar, and metatarsophalangeal joints. Thus, the force and joint moment that each musculotendon actuator develops can be computed for any body position. The joint moments calculated with the model compare well with experimentally measured isometric joint moments. We developed a graphical interface to the model that allows the user to visualize the musculoskeletal geometry and to manipulate the model parameters to study the biomechanical consequences of orthopaedic surgical procedures. For example, tendon transfer and lengthening procedures can be simulated by adjusting the model parameters according to various surgical techniques. Results of the simulated surgeries can be analyzed quickly in terms of postsurgery muscle forces and other biomechanical variables. Just as interactive graphics have enhanced engineering design and analysis, we have found that graphics-based musculoskeletal models are effective tools for designing and analyzing surgical procedures.
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.
The power output of a muscle and its efficiency vary widely under different activation conditions. This is partially due to the complex interaction between the contractile component of a muscle and the serial elasticity. We investigated the relationship between power output and efficiency of muscle by developing a model to predict the power output and efficiency of muscles under varying activation conditions during cyclical length changes. A comparison to experimental data from two different muscle types suggests that the model can effectively predict the time course of force and mechanical energetic output of muscle for a wide range of contraction conditions, particularly during activation of the muscle. With fixed activation properties, discrepancies in the work output between the model and the experimental results were greatest at the faster and slower cycle frequencies than that for which the model was optimised. Further optimisation of the activation properties across each individual cycle frequency examined demonstrated that a change in the relationship between the concentration of the activator (Ca2+) and the activation level could account for these discrepancies. The variation in activation properties with speed provides evidence for the phenomenon of shortening deactivation, whereby at higher speeds of contraction the muscle deactivates at a faster rate. The results of this study demonstrate that predictions about the mechanics and energetics of muscle are possible when sufficient information is known about the specific muscle.
This study investigates the motor unit recruitment patterns between and within muscles of the triceps surae during cycling on a stationary ergometer at a range of pedal speeds and resistances. Muscle activity was measured from the soleus (SOL), medial gastrocnemius (MG) and lateral gastrocnemius (LG) using surface electromyography (EMG) and quantified using wavelet and principal component analysis. Muscle fascicle strain rates were quantified using ultrasonography, and the muscle-tendon unit lengths were calculated from the segmental kinematics. The EMG intensities showed that the body uses the SOL relatively more for the higher-force, lower-velocity contractions than the MG and LG. The EMG spectra showed a shift to higher frequencies at faster muscle fascicle strain rates for MG: these shifts were independent of the level of muscle activity, the locomotor load and the muscle fascicle strain. These results indicated that a selective recruitment of the faster motor units occurred within the MG muscle in response to the increasing muscle fascicle strain rates. This preferential recruitment of the faster fibres for the faster tasks indicates that in some circumstances motor unit recruitment during locomotion can match the contractile properties of the muscle fibres to the mechanical demands of the contraction.
Dynamic simulations of movement allow one to study neuromuscular coordination, analyze athletic performance, and estimate internal loading of the musculoskeletal system. Simulations can also be used to identify the sources of pathological movement and establish a scientific basis for treatment planning. We have developed a freely available, open-source software system (OpenSim) that lets users develop models of musculoskeletal structures and create dynamic simulations of a wide variety of movements. We are using this system to simulate the dynamics of individuals with pathological gait and to explore the biomechanical effects of treatments. OpenSim provides a platform on which the biomechanics community can build a library of simulations that can be exchanged, tested, analyzed, and improved through a multi-institutional collaboration. Developing software that enables a concerted effort from many investigators poses technical and sociological challenges. Meeting those challenges will accelerate the discovery of principles that govern movement control and improve treatments for individuals with movement pathologies.
The maximum force capacity of a muscle is dependent on the lengths and velocities of its contractile apparatus. Muscle-tendon unit (MTU) length changes can be estimated from joint kinematics, however contractile element length changes are more difficult to predict during dynamic contractions. The aim of this study was to compare vastus lateralis (VL) MTU and fascicle force-length and force-velocity relationships, and dynamic muscle function while cycling at a constant submaximal power output (2.5 W/kg) with different cadences. We hypothesized that manipulating cadence would not affect VL MTU shortening, but significantly affect VL fascicle shortening. Furthermore, these differences would affect the predicted force capacity of the muscle. Using an isokinetic dynamometer and B-mode ultrasound (US), we determined the force-length and force-velocity properties of the VL MTU and its fascicles. In addition, three-dimensional kinematics and kinetics of the lower limb, as well as US images of VL fascicles were collected during submaximal cycling at cadences of 40, 60, 80 and 100 RPM. Ultrasound measures revealed a significant increase in fascicle shortening as cadence decreased (84% increase across all conditions, p < 0.01), whereas there were no significant differences in MTU lengths across any of the cycling conditions (maximum of 6%). The MTU analysis resulted in greater predicted force capacity across all conditions relative to the force-velocity relationship (p < 0.01). These results reinforce the need to determine muscle mechanics in terms of separate contractile element and connective tissue length changes during isokinetic contractions as well as dynamic movements like cycling.
Ultrasonography is a useful technique to study muscle contractions in vivo, however larger muscles like vastus lateralis may be difficult to visualise with smaller, commonly used transducers. Fascicle length is often estimated using linear trigonometry to extrapolate fascicle length to regions where the fascicle is not visible. However, this approach has not been compared to measurements made with a larger field of view for dynamic muscle contractions. Here we compared two different single-transducer extrapolation methods to measure VL muscle fascicle length to a direct measurement made using two synchronised, in-series transducers. The first method used pennation angle and muscle thickness to extrapolate fascicle length outside the image (extrapolate method). The second method determined fascicle length based on the extrapolated intercept between a fascicle and the aponeurosis (intercept method). Nine participants performed maximal effort, isometric, knee extension contractions on a dynamometer at 10° increments from 50 to 100° of knee flexion. Fascicle length and torque were simultaneously recorded for offline analysis. The dual transducer method showed similar patterns of fascicle length change (overall mean coefficient of multiple correlation was 0.76 and 0.71 compared to extrapolate and intercept methods respectively), but reached different absolute lengths during the contractions. This had the effect of producing force-length curves of the same shape, but each curve was shifted in terms of absolute length. We concluded that dual transducers are beneficial for studies that examine absolute fascicle lengths, whereas either of the single transducer methods may produce similar results for normalised length changes, and repeated measures experimental designs.
Background:
Dynamic measurements of human muscle fascicle length from sequences of B-mode ultrasound images have become increasingly prevalent in biomedical research. Manual digitisation of these images is time consuming and algorithms for automating the process have been developed. Here we present a freely available software implementation of a previously validated algorithm for semi-automated tracking of muscle fascicle length in dynamic ultrasound image recordings, "UltraTrack".
Methods:
UltraTrack implements an affine extension to an optic flow algorithm to track movement of the muscle fascicle end-points throughout dynamically recorded sequences of images. The underlying algorithm has been previously described and its reliability tested, but here we present the software implementation with features for: tracking multiple fascicles in multiple muscles simultaneously; correcting temporal drift in measurements; manually adjusting tracking results; saving and re-loading of tracking results and loading a range of file formats.
Results:
Two example runs of the software are presented detailing the tracking of fascicles from several lower limb muscles during a squatting and walking activity.
Conclusion:
We have presented a software implementation of a validated fascicle-tracking algorithm and made the source code and standalone versions freely available for download.
This study investigated the influence of cycle frequency and workload on muscle coordination and the ensuing relationship with mechanical efficiency and power output of human limb movement. Eleven trained cyclists completed an array of cycle frequency (cadence)-power output conditions while excitation from 10 leg muscles and power output were recorded. Mechanical efficiency was maximized at increasing cadences for increasing power outputs and corresponded to muscle coordination and muscle fibre type recruitment that minimized both the total muscle excitation across all muscles and the ineffective pedal forces. Also, maximum efficiency was characterized by muscle coordination at the top and bottom of the pedal cycle and progressive excitation through the uniarticulate knee, hip and ankle muscles. Inefficiencies were characterized by excessive excitation of bi-articulate muscles and larger duty cycles. Power output and efficiency were limited by the duration of muscle excitation beyond a critical cadence (120-140 r.p.m.) with larger duty cycles and disproportionate increases in muscle excitation suggesting deteriorating muscle coordination and limitations of the activation-deactivation capabilities. Most muscles displayed systematic phase shifts of the muscle excitation relative to the pedal cycle that were dependent on cadence and to a lesser extent power output. Phase shifts were different for each muscle thereby altering their mechanical contribution to the pedaling action. This study shows that muscle coordination is a key determinant of mechanical efficiency and power output of limb movement across a wide range of mechanical demands and that the excitation and coordination of the muscles is limited at very high cycle frequencies.
Separate authors have reported that knee extension dominates power production during submaximal cycling (SUB(cyc)) and hip extension is the dominant action during maximal cycling (MAX(cyc)). Changes in joint-specific powers across broad ranges of net cycling powers (P(net)) within one group of cyclists have not been reported.
Our purpose was to determine the extent to which ankle, knee, and hip joint actions produced power across a range of P(net) . We hypothesized that relative knee extension power would decrease and relative knee flexion and hip extension powers would increase as P(net) increased.
Eleven cyclists performed SUB(cyc) (250, 400, 550, 700, and 850 W) and MAX(cyc) trials at 90 rpm. Joint-specific powers were calculated and averaged over complete pedal revolutions and over extension and flexion phases. Portions of the cycle spent in extension (duty cycle) were determined for the whole leg and ankle, knee, and hip joints. Relationships of relative joint-specific powers with P(net) were assessed with linear regression analyses.
Absolute ankle, knee, and hip joint-specific powers increased as P(net) increased. Relative knee extension power decreased (r(2) = 0.88, P = 0.01) and knee flexion power increased (r(2) = 0.98, P < 0.001) as P(net) increased. Relative hip extension power was constant across all P(net) . Whole-leg and ankle, knee, and hip joint duty cycle values were greater for MAX(cyc) than for SUB(cyc).
Our data demonstrate that 1) absolute ankle, knee, and hip joint-specific powers substantially increase as a function of increased P(net) , 2) hip extension was the dominant power-producing action during SUB(cyc) and MAX(cyc), 3) knee flexion power becomes relatively more important during high-intensity cycling, and 4) increased duty cycle values represent an important strategy to increase maximum power.
In humans, a large portion of the mechanical work required for walking comes from muscle-tendons crossing the ankle joint. Elastic energy storage and return in the Achilles tendon during each step enhance the efficiency of ankle muscle-tendon mechanical work far beyond what is possible for work performed by knee and hip joint muscle-tendons.
The aim of the study was to calculate the magnitude of the instantaneous muscular power output at the hip, knee and ankle joints during ergometer cycling at different work loads and speeds. Six healthy subjects pedalled a weight-braked cycle ergometer at 0, 120 and 240 W at a constant speed of 60 rpm. The subjects also pedalled at 40, 60, 80 and 100 rpm against the same resistance, giving power outputs of 80, 120, 160 and 200 W respectively. The subjects were filmed with a cine-film camera, and pedal reaction forces were recorded from a force transducer mounted in the pedal. The muscular work for the hip, knee and ankle joint muscles was calculated using a model based upon dynamic mechanics and described elsewhere. The total work during one pedal revolution significantly increased with increased work load but did not increase with increased pedalling rate at the same braking force. The relative proportions of total positive work at the hip, knee and ankle joints were also calculated. Hip and ankle extension work proportionally decreased with increased work load. Pedalling rate did not change the relative proportion of total work at the different joints.
The aim of this study was to calculate the magnitude of the instantaneous muscular power output at the hip, knee and ankle joints during ergometer cycling. Six healthy subjects pedalled a weight-braked bicycle ergometer at 120 watts (W) and 60 revolutions per minute (rpm). The subjects were filmed with a cine camera, and pedal reaction forces were recorded from a force transducer mounted in the pedal. The muscular work at the hip, knee and ankle joint was calculated using a model based upon dynamic mechanics described elsewhere. The mean peak concentric power output was, for the hip extensors, 74.4 W, hip flexors, 18.0 W, knee extensors, 110.1 W, knee flexors, 30.0 W and ankle plantar flexors, 59.4 W. At the ankle joint, energy absorption through eccentric plantar flexor action was observed, with a mean peak power of 11.4 W and negative work of 3.4 J for each limb and complete pedal revolution. The energy production relationships between the different major muscle groups were computed and the contributions to the total positive work were: hip extensors, 27%; hip flexors, 4%; knee extensors, 39%; knee flexors, 10%; and ankle plantar flexors 20%.
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.
1. The variation of isometric tetanus tension with sarcomere length in single fibres from frog striated muscle has been re‐investigated with special precautions to ensure uniformity of sarcomere length within the part of the fibre being studied.
2. In most respects the results of Ramsey & Street (1940) were confirmed, but ( a ) the peak of the curve was found to consist of a plateau between sarcomere lengths of 2·05 and 2·2 μ, ( b ) the decline of tension above this plateau is steeper than found by Ramsey & Street, and ( c ) the decline of tension below the plateau becomes suddenly steeper at a sarcomere length of about 1·67 μ.
3. Many features of this length—tension relation are simply explained on the sliding‐filament theory.
4. It is concluded that, in the plateau and at greater lengths, the tension on each thin filament is made up of equal contributions from each bridge which it overlaps on adjacent thick filaments.
5. Internal resistance to shortening is negligible in this range but becomes progressively more important with shortening below the plateau.
1. The energetic cost of work performance by mouse fast- and slow-twitch muscle was assessed by measuring the rates of thermal and mechanical energy liberation of the muscles at 21 degrees C. Thermal energy (heat) liberation was measured using a fast-responding thermopile. 2. Bundles of muscles fibres from the slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles were used. Work output was controlled by performing isovelocity shortenings during the plateau of an isometric tetanus. A range of shortening velocities, spanning the possible range, was used for each muscle. 3. During tetanic contractions, the rate of heat production from EDL muscle was 134.2 +/- 11.4 mW/g. The rate of heat production by soleus muscle was only one-fifth as great (26.8 +/- 2.7 mW/g). 4. The maximum shortening velocity (Vmax) of EDL muscles was 2.5-fold greater than that for soleus muscles and it's force-velocity relationship was less curved. Peak power output from EDL muscles was 3-fold greater than that from soleus muscle. 5. During shortening, the rate of heat output from soleus muscles increased considerably above the isometric heat rate. In contrast to soleus muscle, the rate of heat production by EDL muscle increased by only a small fraction of the isometric heat rate. The magnitude of the increases in rate was proportional to shortening velocity. 6. The total rate of energy liberation (heat rate + power) by EDL muscle, shortening at 0.95 Vmax was 1.62 +/- 0.37 times greater than the isometric heat rate. In contrast, the rate of energy liberation from soleus muscle shortening at 0.95 Vmax was 5.21 +/- 0.58 times greater than its isometric heat rate. The peak mechanical efficiency (power/total energy rate) of the both muscles was approximately 30%.
To determine the effects of cycling experience, fitness level, and power output on preferred and most economical cycling cadences: 1) the preferred cadence (PC) of 12 male cyclists, 10 male runners, and 10 less-trained male noncyclists was determined at 75, 100, 150, 200, and 250 W for cyclists and runners and 75, 100, 125, 150, and 175 W for the less-trained group; and 2) steady-state aerobic demand was determined at six cadences (50, 65, 80, 95, 110 rpm and PC) at 100, 150, and 200 W for cyclists and runners and 75, 100, and 150 W for less-trained subjects. Cyclists and runners (VO2max: 70.7 +/- 4.1 and 72.5 +/- 2.2 mL.kg-1.min-1, respectively) maintained PC between 90 and 100 rpm at all power outputs and both groups selected similar cadences at each power output. In contrast, the less-trained group (VO2max = 44.2 +/- 2.8 mL.kg-1.min-1) selected lower cadences at all common power outputs and reduced cadence from approximately 80 rpm at 75 W to 65 rpm at 175 W. The preferred cadences of all groups were significantly higher than their respective most economical cadences at all power outputs. Changes in power output had little effect on the most economical cadence, which was between 53.3 and 59.9 rpm, in all groups. It was concluded that cycling experience and minimization of aerobic demand are not critical determinants of PC in well-trained individuals. It was speculated that less-trained noncyclists, who cycled at a higher percentage of VO2max, may have selected lower PC to reduce aerobic demand.
One objective of this study was to investigate whether neuromuscular quantities were associated with preferred pedaling rate selection during submaximal steady-state cycling from a theoretical perspective using a musculoskeletal model with an optimal control analysis. Specific neuromuscular quantities of interest were the individual muscle activation, force, stress and endurance. To achieve this objective, a forward dynamic model of cycling and optimization framework were used to simulate pedaling at three different rates of 75, 90 and 105 rpm at 265 W. The pedaling simulations were produced by optimizing the individual muscle excitation timing and magnitude to reproduce experimentally collected data. The results from these pedaling simulations indicated that all neuromuscular quantities were minimized at 90 rpm when summed across muscles. In the context of endurance cycling, these results suggest that minimizing neuromuscular fatigue is an important mechanism in pedaling rate selection. A second objective was to determine whether any of these quantities could be used to predict the preferred pedaling rate. By using the quantities with the strongest quadratic trends as the performance criterion to be minimized in an optimal control analysis, these quantities were analyzed to assess whether they could be further minimized at 90 rpm and produce normal pedaling mechanics. The results showed that both the integrated muscle activation and average endurance summed across all muscles could be further minimized at 90 rpm indicating that these quantities cannot be used individually to predict preferred pedaling rates.
A group of coexcited muscles alternating with another group is a common element of motor control, including locomotor pattern generation. This study used computer simulation to investigate human pedaling with each muscle assigned at times to a group. Simulations were generated by applying patterns of muscle excitations to a musculoskeletal model that includes the dynamic properties of the muscles, the limb segments, and the crank load. Raasch et al. showed that electromyograms, pedal reaction forces, and limb and crank kinematics recorded during maximum-speed start-up pedaling could be replicated with two signals controlling the excitation of four muscle groups (1 group alternating with another to form a pair). Here a four-muscle-group control also is shown to replicate steady pedaling. However, simulations show that three signals controlling six muscle groups (i.e., 3 pairs) is much more biomechanically robust, such that a wide variety of forward and backward pedaling tasks can be executed well. We found the biomechanical functions necessary for pedaling, and how these functions can be executed by the muscle groups. Specifically, the phasing of two pairs with respect to limb extension and flexion and the transitions between extension and flexion do not change with pedaling direction. One pair of groups (uniarticular hip and knee extensors alternating with their anatomic antagonists) generates the energy required for limb and crank propulsion during limb extension and flexion, respectively. In the second pair, the ankle plantarflexors transfer the energy from the limb inertia to the crank during the latter part of limb extension and the subsequent limb extension-to-flexion transition. The dorsiflexors alternate with the plantarflexors. The phasing of the third pair (the biarticular thigh muscles) reverses with pedaling direction. In forward pedaling, the hamstring is excited during the extension-to-flexion transition and in backward pedaling during the opposite transition. In both cases hamstrings propel the crank posteriorly through the transition. Rectus femoris alternates with hamstrings and propels the crank anteriorly through the transitions. With three control signals, one for each pair of groups, different cadences (or power outputs) can be achieved by adjusting the overall excitatory drive to the pattern generating elements, and different pedaling goals (e.g., smooth, or energy-efficient pedaling; 1- or 2-legged pedaling) by adjusting the relative excitation levels among the muscle groups. These six muscle groups are suggested to be elements of a general strategy for pedaling control, which may be generally applicable to other human locomotor tasks.
Eight experienced male cyclists (C), eight well-trained male runners (R), and eight less-trained male noncyclists (LT) were tested under multiple cadence and power output conditions to determine: (1) if the cadence at which lower extremity net joint moments are minimized (cost function cadence) was associated with preferred pedaling cadence (PC), (2) if the cost function cadence increased with increases in power output, and (3) if the association is generalizable across groups differing in cycling experience and aerobic power. Net joint moments at the hip, knee, and ankle were computed from video records and pedal reaction force data using 2-D inverse dynamics. The sum of the average absolute hip, knee, and ankle joint moments defined a cost function at each power output and cadence and provided the basis for prediction of the cadence which minimized net joint moments for each subject at each power output. The cost function cadence was not statistically different from the PC at each power output in all groups. As power output increased, however, the cost function cadence increased for all three subject groups (86 rpm at 100 W, 93 rpm at 150 W, 98 rpm at 200 W, and 96 rpm at 250 W). PC showed little change (R) or a modest decline (C, LT) with increasing power output. Based upon the similarity in the mean data but different trends in the cost function cadence and PC in response to changes in power output as well as the lack of significant correlations between these two variables, it was concluded that minimiking net joint moments is a factor modestly associated with preferred cadence selection.
The objective of this work was to increase our understanding of how motor patterns are produced during movement tasks by quantifying adaptations in muscle coordination in response to altered task mechanics. We used pedaling as our movement paradigm because it is a constrained cyclical movement that allows for a controlled investigation of test conditions such as movement speed and effort. Altered task mechanics were introduced using an elliptical chainring. The kinematics of the crank were changed from a relatively constant angular velocity using a circular chainring to a widely varying angular velocity using an elliptical chainring. Kinetic, kinematic and muscle activity data were collected from eight competitive cyclists using three different chainrings--one circular and two different orientations of an elliptical chainring. We tested the hypotheses that muscle coordination patterns (EMG timing and magnitude), specifically the regions of active muscle force production, would shift towards regions in the crank cycle in which the crank angular velocity, and hence muscle contraction speeds, were favorable to produce muscle power as defined by the skeletal muscle power-velocity relationship. The results showed that our hypothesis with regards to timing was not supported. Although there were statistically significant shifts in muscle timing, the shifts were minor in absolute terms and appeared to be the result of the muscles accounting for the activation dynamics associated with muscle force development (i.e. the delay in muscle force rise and decay). But, significant changes in the magnitude of muscle EMG during regions of slow crank angular velocity for the tibialis anterior and rectus femoris were observed. Thus, the nervous system used adaptations to the muscle EMG magnitude, rather than the timing, to adapt to the altered task mechanics. The results also suggested that cyclists might work on the descending limb of the power-velocity relationship when pedaling at 90 rpm and sub-maximal power output. This finding might have important implications for preferred pedaling rate selection.
The knowledge of surface electromyography (SEMG) and the number of applications have increased considerably during the past ten years. However, most methodological developments have taken place locally, resulting in different methodologies among the different groups of users.A specific objective of the European concerted action SENIAM (surface EMG for a non-invasive assessment of muscles) was, besides creating more collaboration among the various European groups, to develop recommendations on sensors, sensor placement, signal processing and modeling. This paper will present the process and the results of the development of the recommendations for the SEMG sensors and sensor placement procedures. Execution of the SENIAM sensor tasks, in the period 1996-1999, has been handled in a number of partly parallel and partly sequential activities. A literature scan was carried out on the use of sensors and sensor placement procedures in European laboratories. In total, 144 peer-reviewed papers were scanned on the applied SEMG sensor properties and sensor placement procedures. This showed a large variability of methodology as well as a rather insufficient description. A special workshop provided an overview on the scientific and clinical knowledge of the effects of sensor properties and sensor placement procedures on the SEMG characteristics. Based on the inventory, the results of the topical workshop and generally accepted state-of-the-art knowledge, a first proposal for sensors and sensor placement procedures was defined. Besides containing a general procedure and recommendations for sensor placement, this was worked out in detail for 27 different muscles. This proposal was evaluated in several European laboratories with respect to technical and practical aspects and also sent to all members of the SENIAM club (>100 members) together with a questionnaire to obtain their comments. Based on this evaluation the final recommendations of SENIAM were made and published (SENIAM 8: European recommendations for surface electromyography, 1999), both as a booklet and as a CD-ROM. In this way a common body of knowledge has been created on SEMG sensors and sensor placement properties as well as practical guidelines for the proper use of SEMG.