Mental fatigue impairs cycling endurance performance and perception of effort, but not muscle activation
Mental fatigue is induced by prolonged engagement in cognitively demanding tasks and impairs endurance performance. The neuropsychophysiological mechanisms underlying this decreased performance remain unclear, with suggestion that mental fatigue may disrupt motor command and consequently muscle activation. We aimed to test this hypothesis in a repeated cross-over design study in which 18 participants completed two experimental sessions involving a time-to-task failure cycling test at 80% of peak power output. Each cycling task was preceded by 1h of a prolonged Stroop task (Stroop condition) or a neutral control task (Control condition). Mental fatigue was assessed using a visual analog scale anchored with "not fatigued at all" and "extremely fatigued. Perception of effort and surface electromyography from ten lower-limb muscles of the right leg were recorded at regular intervals during cycling. Mental fatigue was higher in the Stroop compared to the Control condition (p = .002). Endurance cycling time was shorter in the Stroop than in the Control condition (887 {+/-} 284 s vs. 999 {+/-} 379 s, respectively; -111 {+/-} 160 s, p = .009). No significant differences in electromyography parameters were observed between Stroop and Control conditions, for any muscle (p > .05). Perception of effort was higher in the Stroop condition from the onset of the cycling task (p = .006), and the rate of increase in perception of effort was significantly higher in the Stroop than Control condition (p = .031). Our findings do not support the hypothesis that mental fatigue alters motor control or increases central motor command, as no changes in muscle activation were detected. Conversely, our results reinforce the notion that prolonged cognitive engagement impairs endurance performance primarily through an increased perception of effort. Future research should consider combining surface electromyography with more sensitive neurophysiological techniques to investigate potential subtle changes in motor drive during dynamic, whole-body tasks under mental fatigue.