Sex-specific effects of fatigue on hamstrings and quadriceps electromyography of female and male cyclists.

Previous studies have shown sex differences in muscle activation of the quadriceps and hamstrings with fatigue. However, whether these differences are present in a repeated sprint exercise (RSE) cycling task is unknown. Twenty (10 females) cyclists performed an RSE of 9 × 30 s bouts (1.5 min active rest in between) on their personal bike on a trainer, with instructions to produce as many watts as possible. Surface electromyography (EMG) of five right-side quadricep and hamstring muscles was recorded, with activation amplitude (RMS) calculated over each bout. Results show a general decrease with time, with more time-based fluctuations in females. Vastus medialis (VM; p < 0.001) and lateralis (VL; p = 0.004), biceps femoris (p = 0.013), rectus femoris (p < 0.001), and semitendinosus (p = 0.002) showed females only having time-based activation decreases over time. The VM:VL activation ratio showed females and males having different rates of increasing ratios. Results indicate sex and time-dependent quadricep and hamstring muscles activation during an RSE. Females' greater modulation may reflect increased need to stabilize the knee against stress, which if uncontrolled, could represent an injury risk. This knowledge can be used to identify needs for sex-specific injury-prevention approaches for cyclists.