Quadriceps Muscle Fatigue Reduces Extension and Flexion Power During Maximal Cycling

Purpose: To investigate how quadriceps muscle fatigue affects power production over the extension and flexion phases and muscle activation during maximal cycling.Methods: Ten participants performed 10-s maximal cycling efforts without fatigue and after 120 bilateral maximal concentric contractions of the quadriceps muscles. Extension power, flexion power and electromyographic (EMG) activity were compared between maximal cycling trials. We also investigated the associations between changes in quadriceps force during isometric maximal voluntary contractions (IMVC) and power output (flexion and extension) during maximal cycling, in addition to inter-individual variability in muscle activation and pedal force profiles.Results: Quadriceps IMVC (−52 ± 21%, P = 0.002), voluntary activation (−24 ± 14%, P < 0.001) and resting twitch amplitude (−45 ± 19%, P = 0.002) were reduced following the fatiguing task, whereas vastus lateralis (P = 0.58) and vastus medialis (P = 0.15) M-wave amplitudes were unchanged. The reductions in extension power (−15 ± 8%, P < 0.001) and flexion power (−24 ± 18%, P < 0.001) recorded during maximal cycling with fatigue of the quadriceps were dissociated from the decreases in quadriceps IMVC. Peak EMG decreased across all muscles while inter-individual variability in pedal force and EMG profiles increased during maximal cycling with quadriceps fatigue.Conclusion: Quadriceps fatigue induced by voluntary contractions led to reduced activation of all lower limb muscles, increased inter-individual variability and decreased power production during maximal cycling. Interestingly, power production was further reduced over the flexion phase (24%) than the extension phase (15%), likely due to larger levels of peripheral fatigue developed in RF muscle and/or a higher contribution of the quadriceps muscle to flexion power production compared to extension power during maximal cycling.

Effects of Exercise Intensity on Pedal Force Asymmetry during Cycling

The purpose of the current investigation was to examine the effects of exercise intensity and a participant’s cycling experience on asymmetry in pedal forces during cycling. Participants were classified as cycling experienced (CE) or non-cycling experienced (NCE) based on self-reported training history. Participants completed an incremental cycling test via a cycle ergometer with inspired and expired gases, capillary blood lactate and pedaling forces collected throughout the test. Group X exercise intensity comparisons were analyzed at workloads corresponding to 2 mmol/L and 4 mmol/L for the blood lactate accumulation and peak power output, respectively. No Group X exercise intensity interactions for any variables (p > 0.05) were observed. The main effect on the exercise intensity was observed for absolute (p = 0.000, η2 = 0.836) and relative (p = 0.000, η2 = 0.752) power outputs and pedal force effectiveness (PFE) (p = 0.000, η2 = 0.728). The main effect for the group was observed for absolute (p = 0.007, η2 = 0.326) and relative (p = 0.001, η2 = 0.433) power outputs, the absolute difference between the lower limbs in power production (p = 0.047, η2 = 0.191), the peak crank torque asymmetry index (p = 0.031, η2 = 0.222) and the PFE (p = 0.014, η2 = 0.280). The exercise intensity was observed to have no impact on asymmetry in pedaling forces during cycling.

The Medial-Lateral Pedal Force Component Correlates with Q-Angle during Steady-State Cycling at Different Workloads and Cadences

Leg movement during cycling is constrained to the pedal/crank path and predominantly occurs in a sagittal plane. Medial-lateral force (FML) applied to the pedals is considered as a waste and does not contribute to the pedaling. The aim of this study was to examine the changes in FML across different cadences and workloads, and to examine the correlation with lateral knee movement (Q-angle). Twenty-two cyclists completed six trials at three workloads (2, 2.5 and 3 W/kg) and three cadences (75, 85, 95 rpm). Forces were recorded from the force pedal mounted to the left side. Absolute and normalized (to the peak total force) FML were compared across conditions and cross-correlation with Q-angle was calculated. Absolute FML was significantly different across cadences and workloads (p < 0.05) with higher absolute FML at higher cadence. There was no significant difference in normalized FML across the three cadences. There was a significant decrease in normalized FML (~10 N) at higher workloads. Statistically significant correlations were found between the FML and Q-angle (R = 0.70–0.77). The results demonstrate the link between the FML and Q-angle in healthy pain-free cyclists during stationary cycling. It has also been observed that smaller normalized magnitude of the FML is present when the force effectiveness is increased.

The brake pressure depends upon the pedal ratio

The brake disc having a factor of safety (FOS) within the range of 2 to 3 is sustainable. The disc with a FOS less than 2 or greater than 3 undergoes distortion and are less sustainable. Theoretically it has been proven using graphs and calculations that a slight variation in the pedal ratio leads to a large variation in the clamping forces and stopping distance. As per the comparisons made from the FOS and as per result from Ansys, when the pedal force is 1200N and the pedal ratios are 7.2and 4.5, the FOS are 2.1 and 2.8 respectively. Hence the disc is sustainable. When the pedal force is 1500N, and the pedal ratio is 4.5, the FOS is 2.2. Hence in this case too, the disc is sustainable. Therefore by maintaining proper pedal ratios, the length of the pedal can be made compact and with effective braking effects. This phenomenon is useful in case of racing vehicles as it reduces the effort of driver. The proper pedal design work also determines the size of master cylinder to be adopted for the vehicle.