Is reaction time altered by mental or physical exertion?

Reaction time, classically divided into premotor time and electromechanical delay (EMD), can be determinant in daily life or sport situations. While some previous studies reported a negative impact of both muscle and mental fatigue on reaction time, the respective contributions of premotor time and EMD to the changes of reaction time remains unclear. The aim of the study was, therefore, to assess the effects of both muscle and mental effort on reaction time and its components.

Thirteen subjects performed three conditions (mental effort condition, i.e., 14 min of a mathematical cognitive task; muscle effort condition, i.e., intermittent contractions of the biceps brachii; control condition, i.e., watching a documentary). Before and after each condition, reaction time, premotor time and EMD were measured during voluntary contractions of the biceps brachii. EMD was also measured during evoked contractions of the biceps brachii to separate the parts due to the onset of muscle fascicle motion and the onset of force production.

Reaction time and premotor time remained stable regardless of the condition considered (all P values > 0.05). EMD increased only after the muscle effort condition (+ 25% during voluntary contractions, no significant; + 17% during evoked contractions, P = 0.001), mainly due to an increase in the passive part of the series elastic component.

Our study showed that neither mental nor muscle effort has a negative effect on simple reaction time during voluntary contractions.