Pedal Rate Research Articles

Exercise efficiency is reduced by mitochondrial uncoupling in the elderly

A reduction in exercise efficiency accompanies ageing in humans. Here we evaluated the impact of changes in the contractile-coupling and mitochondrial-coupling efficiencies on the reduction in exercise efficiency in the elderly. Nine adult (mean, 38.8 years old) and 40 elderly subjects (mean, 68.8 years old) performed a cycle ergometer test to measure O2 uptake and leg power output up to the aerobic limit ( ). Reduced leg power output per unit O2 uptake was reflected in a drop in delta efficiency (εD) from 0.27 ± 0.01 (mean ± SEM) in adults to 0.22 ± 0.01 in the elderly group. Similar declines with age were apparent for both the leg power output at and the ATP generation capacity (ATPmax) determined in vivo using (31)P magnetic resonance spectroscopy. These similar declines resulted in unchanged contractile-coupling efficiency values (εC) in the adult (0.50 ± 0.05) versus the elderly group (0.58 ± 0.04) and agreed with independent measures of muscle contractile-coupling efficiency in human quadriceps (0.5). The mitochondrial-coupling efficiency calculated from the ratio of delta to contractile-coupling efficiencies in the adults (εD/εC = 0.58 ± 0.08) corresponded to values for well-coupled mitochondria (0.6); however, εD/εC was significantly lower in the elderly subjects (0.44 ± 0.03). Conversion of ATPmax per mitochondrial volume (ATPmax/Vv[mt,f]) reported in these groups into thermodynamic units confirmed this drop in mitochondrial-coupling efficiency from 0.57 ± 0.08 in adults to 0.41 ± 0.03 in elderly subjects. Thus, two independent methods revealed that reduced mitochondrial-coupling efficiency was a key part of the drop in exercise efficiency in these elderly subjects and may be an important part of the loss of exercise performance with age.

Variability in Cadence During Forced Cycling Predicts Motor Improvement in Individuals With Parkinson's Disease

Variability in severity and progression of Parkinson's disease symptoms makes it challenging to design therapy interventions that provide maximal benefit. Previous studies showed that forced cycling, at greater pedaling rates, results in greater improvements in motor function than voluntary cycling. The precise mechanism for differences in function following exercise is unknown. We examined the complexity of biomechanical and physiological features of forced and voluntary cycling and correlated these features to improvements in motor function as measured by the Unified Parkinson's Disease Rating Scale (UPDRS). Heart rate, cadence, and power were analyzed using entropy signal processing techniques. Pattern variability in heart rate and power were greater in the voluntary group when compared to forced group. In contrast, variability in cadence was higher during forced cycling. UPDRS Motor III scores predicted from the pattern variability data were highly correlated to measured scores in the forced group. This study shows how time series analysis methods of biomechanical and physiological parameters of exercise can be used to predict improvements in motor function. This knowledge will be important in the development of optimal exercise-based rehabilitation programs for Parkinson's disease.

Sound Stabilizes Locomotor-Respiratory Coupling and Reduces Energy Cost

A natural synchronization between locomotor and respiratory systems is known to exist for various species and various forms of locomotion. This Locomotor-Respiratory Coupling (LRC) is fundamental for the energy transfer between the two subsystems during long duration exercise and originates from mechanical and neurological interactions. Different methodologies have been used to compute LRC, giving rise to various and often diverging results in terms of synchronization, (de-)stabilization via information, and associated energy cost. In this article, the theory of nonlinear-coupled oscillators was adopted to characterize LRC, through the model of the sine circle map, and tested it in the context of cycling. Our specific focus was the sound-induced stabilization of LRC and its associated change in energy consumption. In our experimental study, participants were instructed during a cycling exercise to synchronize either their respiration or their pedaling rate with an external auditory stimulus whose rhythm corresponded to their individual preferential breathing or cycling frequencies. Results showed a significant reduction in energy expenditure with auditory stimulation, accompanied by a stabilization of LRC. The sound-induced effect was asymmetrical, with a better stabilizing influence of the metronome on the locomotor system than on the respiratory system. A modification of the respiratory frequency was indeed observed when participants cycled in synchrony with the tone, leading to a transition toward more stable frequency ratios as predicted by the sine circle map. In addition to the classical mechanical and neurological origins of LRC, here we demonstrated using the sine circle map model that information plays an important modulatory role of the synchronization, and has global energetic consequences.

Sacrificing economy to improve running performance—a reality in the ultramarathon?

ultramarathons have become increasingly popular in recent years. Although complex tactical and psychological-motivational factors play important roles in performance ([Fig. 1][1]), running velocity sustained over a prolonged time is directly proportional to maximal sustainable Vo2 and inversely

Influence of musculo-tendinous stiffness of the plantar ankle flexor muscles upon maximal power output on a cycle ergometre

The importance of maximal voluntary torque (T (MVC)), maximal rate of torque development (MRTD) and musculo-tendinous stiffness of the triceps surae for maximal power output on a cycle ergometre (Pmax) was studied in 21 healthy subjects by studying the relationships between maximal cycling power related to body mass (Pmax BM(-1)) with T (MVC), MRTD and different indices of musculo-tendinous stiffness of the ankle flexor. Pmax BM(-1) was calculated from the data of an all-out force-velocity test on a Monark cycle ergometre. T (MVC) and MRTD were measured on a specific ankle ergometre. Musculo-tendinous stiffness was estimated by means of quick releases at 20, 40, 60 and 80% T (MVC) on the same ankle ergometre. Pmax BM(-1) was significantly and positively correlated with MRTD related to body mass but the positive correlation between Pmax BM(-1) and T (MVC) did not reach the significance level (0.05). Pmax BM(-1) was significantly and positively correlated with the estimation of stiffness at 40% T (MVC) (S(0.4)), but not with stiffness at 20, 60 and 80% T (MVC). The results of the present study suggest that maximal power output during cycling is significantly correlated with the level of musculo-tendinous stiffness which corresponds to torque range around peak torque at optimal pedal rate. However, the low coefficient of determination (r2 = 0.203) between Pmax BM(-1) and S (0.4) BM(-1) suggested that Pmax BM(-1) largely depended on other factors than the musculo-tendinous stiffness of the only plantar flexors.

The Effect of Movement Rate and Complexity on Functional Magnetic Resonance Signal Change During Pedaling

We used functional magnetic resonance imaging (fMRI) to record human brain activity during slow (30 RPM), fast (60 RPM), passive (30 RPM), and variable rate pedaling. Ten healthy adults participated. After identifying regions of interest, the intensity and volume of brain activation in each region was calculated and compared across conditions (p < .05). Results showed that the primary sensory and motor cortices (S1, M1), supplementary motor area (SMA), and cerebellum (Cb) were active during pedaling. The intensity of activity in these areas increased with increasing pedaling rate and complexity. The Cb was the only brain region that showed significantly lower activity during passive as compared with active pedaling. We conclude that M1, S1, SMA, and Cb have a role in modifying continuous, bilateral, multijoint lower extremity movements. Much of this brain activity may be driven by sensory signals from the moving limbs.

Muscle damage slows oxygen uptake kinetics during moderate-intensity exercise performed at high pedal rate

This study aimed to investigate the dependence of oxygen uptake (VO₂) kinetics on pedal cadence during moderate-intensity exercise following exercise-induced muscle damage (EIMD). Twenty untrained males were randomly assigned to a 50 revolution per minute (rpm) (age, 23.3 ± 1.8 years; VO₂(max), 38.9 ± 2.8 mL·kg⁻¹·min⁻¹) or 100 rpm group (age, 24.4 ± 3.5 years, VO₂(max), 42.9 ± 4.3 mL·kg⁻¹·min⁻¹). Participants completed "step" tests to moderate-intensity exercise from an unloaded baseline on a cycle ergometer before (baseline) and at 24 and 48 h after muscle-damaging exercise (10 sets of 10 eccentric contractions performed on an isokinetic dynamometer with a 2-min rest between each set). Pedal cadence was kept constant throughout each cycling trial (50 or 100 rpm). There were no changes in phase II pulmonary VO₂ kinetics following EIMD for the 50 rpm group (baseline = 35 ± 4 s; 24 h = 35 ± 7 s; and 48 h = 36 ± 9 s). However, the phase II VO₂ was significantly greater at 24 h (59 ± 27 s) compared with baseline (39 ± 6 s) and 48 h (40 ± 9 s) for the 100 rpm group. It is concluded that the effects of EIMD on phase II VO₂ kinetics during moderate-intensity cycling exercise is dependent on pedal cadence. The slower VO₂ kinetics after muscle damage suggests that type II fibers are involved during transition to moderate-intensity exercise at high pedal cadence.

Estimation of the anaerobic threshold from the data on lung ventilation and heart rate variability

The goal of the study was to develop methods for estimating the anaerobic threshold from the rate of lung ventilation and heart rate variability during bicycle ergometer and treadmill tests with a stepwise increasing load. At the first stage, the method of estimation of the anaerobic threshold from lung ventilation data was developed. Forty-nine skilled ski racers participated in the experiment. They performed a treadmill ski-walking test with poles, with the slope gradually increasing from 0 to 25 degrees at a rate of one degree per minute. At the second stage, we developed a method for determining the anaerobic threshold from heart rate data. Eighty-six athletes of different sports specialties performed pedaling on a Monarch bicycle ergometer until exhaustion. The initial power was 25 W; the power increased by 25 W every 2 min. The pedaling rate remained constant (75 rpm). The lung ventilation, as well as oxygen consumption and carbon dioxide exhalation parameters, were measured using a COSMED K4 gas analyzer. Arterial blood was sampled from an earlobe or a finger; the blood lactate concentration was determined using an Akusport instrument. The RR intervals were recorded using a Polar s810i heart rate monitor. The results showed that the onset of ventilation anaerobic threshold (VAnT) determined by the graphical method coincided with the moment when blood lactate accumulated to 3.8 ± 0.1 mM in the treadmill test and 4.1 ± 0.6 mM in the bicycle ergometer test. The oxygen consumption at the VAnT level was found to be related to the variance of RR intervals (SD 1). The following regression equation was derived: VO2 AnT = 0.35 + 0.01SD 1 W + 0.0016SD 1 HR + 0.106SD 1 (ms), l/min; (R = 0.98, function estimation error, 0.26 l/min, p < 0.001), where W (W) is power, HR is heart rate (bpm), and SD 1 is the variance of RR intervals (ms) at the moment of recording of the heart rate threshold.

Effect of Crank Length on Joint-Specific Power during Maximal Cycling

Previous investigators have suggested that crank length has little effect on overall short-term maximal cycling power once the effects of pedal speed and pedaling rate are accounted for. Although overall maximal power may be unaffected by crank length, it is possible that similar overall power might be produced with different combinations of joint-specific powers. Knowing the effects of crank length on joint-specific power production during maximal cycling may have practical implications with respect to avoiding or delaying fatigue during high-intensity exercise. The purpose of this study was to determine the effect of changes in crank length on joint-specific powers during short-term maximal cycling. Fifteen trained cyclists performed maximal isokinetic cycling trials using crank lengths of 150, 165, 170, 175, and 190 mm. At each crank length, participants performed maximal trials at pedaling rates optimized for maximum power and at a constant pedaling rate of 120 rpm. Using pedal forces and limb kinematics, joint-specific powers were calculated via inverse dynamics and normalized to overall pedal power. ANOVAs revealed that crank length had no significant effect on relative joint-specific powers at the hip, knee, or ankle joints (P > 0.05) when pedaling rate was optimized. When pedaling rate was constant, crank length had a small but significant effect on hip and knee joint power (150 vs 190 mm only) (P < 0.05). These data demonstrate that crank length does not affect relative joint-specific power once the effects of pedaling rate and pedal speed are accounted for. Our results thereby substantiate previous findings that crank length per se is not an important determinant of maximum cycling power production.

Effects of Two Different Half-Squat Training Programs on Fatigue During Repeated Cycling Sprints in Soccer Players

This study compared the effects of two different half-squat training programs on the repeated-sprint ability of soccer players during the preseason. Twenty male professional soccer players were divided into 2 groups: One group (S-group) performed 4 sets of 5 repetitions with 90% of their 1-repetition maximum (1RM), and the other group (H-group) performed 4 sets of 12 repetitions with 70% of 1RM, 3 times per week for 6 weeks, in addition to their common preseason training program. Repeated-sprint ability was assessed before and after training by 10 × 6-second cycle ergometer sprints separated by 24 seconds of passive recovery. Maximal half-squat strength increased significantly in both groups (p < 0.01), but this increase was significantly greater in the S-group compared with the H-group (17.3 ± 1.9 vs. 11.0 ± 1.9%, p < 0.05). Lean leg volume (LLV) increased only in the H-group. Total work over the 10 sprints improved in both groups after training, but this increase was significantly greater in the second half (8.9 ± 2.6%) compared with the first half of the sprint test (3.2 ± 1.7%) only in the S-group. Mean power output (MPO) expressed per liter of LLV was better maintained during the last 6 sprints posttraining only in the S-group, whereas there was no change in MPO per LLV in the H-group over the 10 sprints. These results suggest that resistance training with high loads is superior to a moderate-load program, because it increases strength without a change in muscle mass and also results in a greater improvement in repeated sprint ability. Therefore, resistance training with high loads may be preferable when the aim is to improve maximal strength and fatigue during sprinting in professional soccer players.

The distribution of blood flow in the carotid and vertebral arteries during dynamic exercise in humans

The mechanism underlying the plateau or relative decrease in cerebral blood flow (CBF) during maximal incremental dynamic exercise remains unclear. We hypothesized that cerebral perfusion is limited during high-intensity dynamic exercise due to a redistribution of carotid artery blood flow. To identify the distribution of blood flow among the arteries supplying the head and brain, we evaluated common carotid artery (CCA), internal carotid artery (ICA), external carotid artery (ECA) and vertebral artery (VA) blood flow during dynamic exercise using Doppler ultrasound. Ten subjects performed graded cycling exercise in a semi-supine position at 40, 60 and 80% of peak oxygen uptake (VO2 peak) for 5 min at each workload. The ICA blood flow increased by 23.0 ± 4.6% (mean ± SE) from rest to exercise at 60% (VO2 peak). However, at 80% (VO2 peak), ICA blood flow returned towards near resting levels (9.6 ± 4.7% vs. rest). In contrast, ECA, CCA and VA blood flow increased proportionally with workload. The change in ICA blood flow during graded exercise was correlated with end-tidal partial pressure of CO2 (r = 0.72). The change in ICA blood flow from 60% (VO2 peak) to 80% (VO2 peak) was negatively correlated with the change in ECA blood flow (r = −0.77). Moreover, there was a significant correlation between forehead cutaneous vascular conductance and ECA blood flow during exercise (r = 0.79). These results suggest that during high-intensity dynamic exercise the plateau or decrease in ICA blood flow is partly due to a large increase in ECA blood flow, which is selectively increased to prioritize thermoregulation.

Effects of Seat Tube Angle Manipulation on Cardiorespiratory Response and Frontal Area in Female Cyclists

Anecdotal and photographic evidence suggests that female cyclists and triathletes exhibit markedly more upright body positions than their male counterparts when riding in an aerodynamic position, which may, in turn, lead to a decreased performance outcome. Manipulating seat tube angle is a potential mechanism for improving the aerodynamic position in competitive cyclists. PURPOSE: Therefore, the purpose of this study was to investigate the cardiorespiratory and metabolic responses and frontal area when the position on the aerodynamic bicycle was manipulated in trained female cyclists and triathletes. METHODS: The study sample (n = 25) consisted of eight cyclists and 17 triathletes (age = 41.8±10.8 yrs; ht = 167.5±6.4 cm; body mass = 62.3±7.5 kg; body fat = 17.7±3.9%; VO2max = 51.7±9.3 ml·kg-1·min-1). Subjects performed three, 15-minute trials at seat tube angles of 73°, 82°, and self-selected (mean = 76°) at a workload corresponding to 65% of VO2 max and a pedaling rate of 90 rpms. The tests were performed on an adjustable stationary ergometer equipped with forward facing aerodynamic handlebars, and the position for each subject was adjusted to maintain the hip angle across all positions. Oxygen uptake (VO2), minute ventilation (VE), heart rate (HR), blood lactate (LA), rating of perceived exertion (RPE), and frontal area were recorded for each position. RESULTS: VO2 and %VO2max were significantly lower in the 82° position compared to the 73° and self-selected positions (32.9, 34.5 and 33.9 ml·kg-1·min-1; 64.2%, 67.3%, and 65.9%, respectively; p < 0.05). VE was significantly lower at 82° compared to 73° (55.1 and 57.3 L·min-1; p < 0.05). There were no significant differences for HR, RPE, or LA between positions. Frontal area was significantly lower at 82° compared to the 73° and self-selected positions (2424, 2532, 2526 cm2, respectively; p < 0.05). CONCLUSION: In this group of women, the 82° position (i.e., steepest seat tube angle) was the most economical position for oxygen uptake and ventilation, suggesting that during steady state cycling a steep seat tube angle may be the most beneficial position for cardiorespiratory responses and reduced frontal area. This study demonstrated that female cyclists can achieve aggressive aerodynamic positions without compromising cardiorespiratory performance.

The effect of pedal rate on pulmonary O2 uptake kinetics during very heavy intensity exercise in trained and untrained teenage boys

This study tested the hypothesis that the VO2 kinetic response would be slowed in untrained (UT) but not trained (T) teenage participants whilst cycling at 115 rev min(-1) compared to 50 rev min(-1). Eight UT and seven T boys completed two square-wave transitions to very heavy-intensity exercise pedalling at 50 rev min(-1) and 115 rev min(-1). In UT at the higher pedal rate, the phase II VO2 was significantly (P < 0.01) slower (50 rev min(-1): 32 ± 5 vs. 115 rev min(-1): 42 ± 11 s) and the relative VO2 slow component was significantly (P < 0.01) elevated (50 rev min(-1): 10 ± 3 vs. 115 rev min(-1): 16 ± 5%). The phase II VO2 (50 rev min(-1): 26 ± 4 vs. 115 rev min(-1): 22 ± 6s) and relative VO2 slow component (50 rev min(-1): 14 ± 5 vs. 115 rev min(-1): 17 ± 3%) were unaltered by pedal rate in T (P > 0.05). These data are consistent with the notion that VO2 kinetics are influenced by muscle fibre recruitment in youth but this effect is attenuated in endurance trained teenage boys.

Pedal power for occupational activities: Effect of power output and pedalling rate on physiological responses

Because of the socio-economical conditions of farmers in developing countries including India, human muscle power is going to contribute energy requirements for performing many farm activities for the next two decades. Pedalling is the most efficient way of utilising power from human muscles. Pedal power enables a person to drive devices at the same or higher rate as that achieved by hand cranking, but with far less effort and fatigue. However, the use of pedal power for occupational work such as stationary farm operations has got scant attention in the past. Keeping these points into consideration a study was planned to optimise power output and pedalling rate for stationary farm operations. Physiological responses of 12 male subjects were studied on a computerised bicycle ergometer at five levels of power output (30–90 W) and seven levels of pedalling rates (30–90 rev min −1). Analysis of data indicated that physiological responses were significantly affected with power output as well as pedalling rate. Increase in physiological responses (heart rate and oxygen consumption rate) over rest (delta values) were significantly higher when pedalling frequency was 30 rev min −1 and above 50 rev min −1. There was no significant difference between physiological responses at 40 and 50 rev min −1. Physiological responses increased linearly with power output and were significantly different at different power outputs. The delta values of physiological responses at 60 W power output and 50 rev min −1 pedalling rate (ΔHR = 40 beats min −1 and ΔVO 2 = 0.56 l min −1) were within acceptable limits for continuous pedalling work. From the results of the study it was concluded that for daylong pedalling work the power output from an Indian agricultural worker should be limited to 60 W and pedalling rate should be 50 rev min −1. Relevance to industry The optimal power output and pedalling rate may be used for the ergonomic design of a dynapod or any pedalling device for efficient utilization of human muscle power with reduced drudgery and fatigue.

Is soy milk a better recovery aid compared to semi-skimmed milk after exercise? does it increase time to exhaustion in trained cyclists?

IntroductionMilk has been proven to be a popular recovery drink for trained cyclists to achieve high profile results because milk contains carbohydrates and protein. On the other hand, research has...

Stabilizing the Locomotor-Respiratory Coupling Using a Metronome to Save Energy

The Locomotor-Respiratory Coupling (LRC) is often evidenced by phase- or frequency-locking patterns. The model of the sine circle map is used here to characterize LRC. Several studies have suggested that a sound emitted by an external metronome can stabilize the LRC. Participants in our task were asked during a cycling exercise to synchronize either their respiration or their pedaling rate with an external auditory stimulus corresponding to their preferred respiratory and pedaling frequencies respectively. Our results showed a significant reduction in energy expenditure when participants breathed in sync with the auditory stimulation, but not accompanied by a change in the stabilization of LRC. A large within- as well as between-participants LRC variability, together with the spontaneous adoption of the most stable pace, contributes to explain this result.

Effect of Posture on Muscle Activity and Oxygen Uptake in Cycle Ergometer

This study evaluated the effects of saddle height on the muscle activity and oxygen uptake during bicycling. The subjects were 20 young adult volunteers. Muscle activity and oxygen uptake were measured with the two saddle heights (maximum knee extension of 180o and 120 o ) and at two power outputs (70 and 100 watts, respectively.) The pedaling rate was 40 rpm. The exercise time was 1 minute and the resting time between each condition was 3 minutes. The raw electromyogram activity was measured for 1 minute and was converted to a root mean square value. Oxygen uptake was measured during exercise using the mixing chamber mode. The activities of two flexors (the medial hamstring and medial head of gastrocnemius) increased at the high saddle height and the activities of four extensors (rectus femoris, vastus medialis, vastus lateralis, and tibialis anterior) increased at the low saddle height. The oxygen uptake at the low saddle height was significantly higher than that at the high saddle height. The oxygen uptake positively correlated with the muscle activities of the knee extensors. The muscle activity and oxygen uptake were significantly affected by the postures (saddle heights) in cycle ergometer. The postures should be considered in the exercise test and prescription.

Effect of “Pose” cycling on efficiency and pedaling mechanics

The purpose of this study was to determine the effect of "Pose" cycling (a combination of specific bicycle setup and pedaling technique) on metabolic efficiency and pedaling mechanics. Eighteen recreational cyclists were tested for efficiency and pedaling mechanics during steady-state cycling (90% gas-exchange threshold) using two different bicycle setups (preferred and "Pose") and three different pedaling rates (70, 90 and 110 rpm). Nine of the participants underwent a coaching intervention (4 × 1 h) consisting of drills based on the "Pose" instruction manual. The remaining nine participants did not receive an intervention. All participants were tested before and after the intervention period. Analyses of variance were performed to test the independent effects of the "Pose"-specific bicycle setup and pedaling technique on gross efficiency and pedaling mechanics. The "Pose"-specific bicycle setup resulted in increased gross efficiency at each pedaling rate compared to the participants' preferred bicycle position (P < 0.05). This increase in efficiency was accompanied by a significant increase in trunk frontal area (P < 0.05). The coaching intervention resulted in decreased gross efficiency at 110 rpm (P < 0.05); at this pedaling rate the intervention resulted in a slight increase in the non-muscular contribution to pedal power in the experimental group and a decrease in the control group. The combination of changed bicycle setup and pedaling technique had no effect on gross efficiency and only small effects on pedaling mechanics. Our findings add to a growing body of literature that short-term interventions in pedaling technique can change pedaling mechanics but do not improve efficiency during steady-state cycling.

Interpretation of crank torque during an all-out cycling exercise at high pedal rate

The use of cycle ergometers with strain gauges bonded on to the cranks enables the evaluation of strength, velocity and power. However, the torque measured at the end of downstroke is higher at high velocity than at medium velocity in contradiction with the force–velocity relationship. Kinematic data were collected with a camera during sprints on a Lode ergometer with strain gauges. Leg mechanical energy (E Leg) and its derivative (dE Leg/dt) were calculated from the sum of the kinetic and potential energies. The opposition of P ext (output at crank level) and dE Leg/dt before bottom dead centre suggested a transformation of E Leg into external work, explaining the higher torque at the end of downstroke at peak velocity. Another explanation is that the leg muscles worked on different parts of their torque–angle relationships as the phase between knee and ankle angles was different at low and high cycling frequencies. Musculo-skeletal net power output (algebraic sum of P ext and dE Leg/dt) indicated that musculo-skeletal structures participated in the upward movement, whereas P ext was negative.

Fatigue during Maximal Sprint Cycling

Maximal cycling power has been reported to decrease more rapidly when performed with increased pedaling rates. Increasing pedaling rate imposes two constraints on the neuromuscular system: 1) decreased time for muscle excitation and relaxation and 2) increased muscle shortening velocity. Using two crank lengths allows the effects of time and shortening velocity to be evaluated separately. We conducted this investigation to determine whether the time available for excitation and relaxation or the muscle shortening velocity was mainly responsible for the increased rate of fatigue previously observed with increased pedaling rates and to evaluate the influence of other possible fatiguing constraints. Seven trained cyclists performed 30-s maximal isokinetic cycling trials using two crank lengths: 120 and 220 mm. Pedaling rate was optimized for maximum power for each crank length: 135 rpm for the 120-mm cranks (1.7 m x s(-1) pedal speed) and 109 rpm for the 220-mm cranks (2.5 m x s(-1) pedal speed). Power was recorded with an SRM power meter. Crank length did not affect peak power: 999 +/- 276 W for the 120-mm crank versus 1001 +/- 289 W for the 220-mm crank. Fatigue index was greater (58.6% +/- 3.7% vs 52.4% +/- 4.8%, P < 0.01), and total work was less (20.0 +/- 1.8 vs 21.4 +/- 2.0 kJ, P < 0.01) with the higher pedaling rate-shorter crank condition. Regression analyses indicated that the power for the two conditions was most highly related to cumulative work (r2 = 0.94) and to cumulative cycles (r2 = 0.99). These results support previous findings and confirm that pedaling rate, rather than pedal speed, was the main factor influencing fatigue. Our novel result was that power decreased by a similar increment with each crank revolution for the two conditions, indicating that each maximal muscular contraction induced a similar amount of fatigue.