Knee extensor fatigue developed during high-intensity exercise limits lower-limb power production

Abstract

We investigated the association between changes in vastii electromyography (EMG) and knee extensor fatigue during high-intensity cycling, and the subsequent effect on lower-limb power and intermuscular coordination during all-out cycling. On two separate days, participants completed 30-s all-out cycling or 10-min of high-intensity cycling followed by 30-s all-out cycling. EMG for gluteus maximus (GMAX), rectus femoris (RF), vastii (VAS), hamstrings (HAM) and gastrocnemius (GAS); co-activation for GMAX/RF, VAS/HAM and VAS/GAS; isometric maximal voluntary force (IMVF) and resting twitch (RT) of the knee extensors were measured. VAS EMG increases during high-intensity cycling (6% to 14%, P < 0.05) were negatively correlated (r = -0.791, P < 0.05) with knee extensor IMVF decreases (-2% to-36%, P < 0.05) following the exercise. Knee extensor IMVF decreases were positively correlated (r = 0.757, P < 0.05) with all-out cycling power reductions (0% to -27%, P < 0.05). VAS/GAS co-activation did not change (P > 0.05) during all-out cycling while VAS and GAS EMG decreased. Larger increase in VAS EMG during high-intensity cycling was associated with greater knee extensor fatigue and larger power reduction during all-out cycling. High VAS/GAS co-activation potentially limited power reduction induced by knee extensor fatigue during all-out cycling.

Fatigue and recovery measured with dynamic properties vs isometric force: effects of exercise intensity

“…Again, whether this is true following exercise at different intensities is not known. However, studies that have assessed either dynamic or isometric measures of fatigue have shown that these assessments are affected differently, according to the exercise intensity-duration relationship (Black et al, 2017;Hureau et al, 2014;Morris et al, 2012;O'Bryan et al, 2017;Thomas et al, 2016Thomas et al, , 2015. Thus, we expected changes in fatigue outcome of different amplitude after the different exercise intensities/durations.…”

Quadriceps Muscle Fatigue Reduces Extension and Flexion Power During Maximal Cycling

“…For participation in this study, six males and four females (n = 10) accustomed to regular high-intensity exercise were recruited (age: 26 ± 4 years; height: 179 ± 6 cm; mass: 74 ± 11 kg; mean ± SD). Sample size calculations using G * Power software (version 3.0.10) determined a required sample size of n = 8 based on an alpha level of 0.05, a power level of 0.95, and the assumption that the fatiguing task would lead to large reductions in maximal force of the quadriceps during knee extension IMVC and maximal cycling power (effect size f > 0.6) (Babault et al, 2006;O'Bryan et al, 2017). Participants were free from any existing cardiovascular, musculoskeletal or neuromuscular disorders.…”

“…The amplitude of these EMG signals was normalized to the peak EMG recorded during the maximal cycling effort performed at the end of the cycling warm-up during the same visit (Rouffet and Hautier, 2008;O'Bryan et al, 2014). An average EMG profile was calculated for VL and VM (VAS), while EMG profiles of the other muscles were considered separately (O'Bryan et al, 2014(O'Bryan et al, , 2017. Finally, we assessed variability in total force (F tot ) applied to the two pedals and EMG activity of the muscles across the participants by calculating variance ratios (VR) using the following equation:…”

“…During prolonged cycling exercise of maximal or nearmaximal intensity, fatigue develops for the quadriceps muscle as evidenced by reductions in isometric maximal voluntary contraction (IMVC) force. Fatigue reduced VAS and RF EMG activity and decreased knee extension power, which ultimately reduces crank power production during maximal cycling (Martin and Brown, 2009;O'Bryan et al, 2014O'Bryan et al, , 2017. However, fatigue of the other lower limb muscles is also likely to develop during intense cycling as most lower limb muscles are activated at maximal or near-maximal levels (Rouffet and Hautier, 2008;Dorel et al, 2012;O'Bryan et al, 2014;Rudsits et al, 2018).…”