Physical and cognitive exertion do not influence feedforward activation of the trunk muscles: a randomized crossover trial.

Fatigue arises during everyday activities, diminishes movement performance, and increases injury risk. Physical (PE) and cognitive exertion (CE) can induce similar feelings of fatigue, but it is not clear whether these also similarly affect movement performance. Therefore, this study examined the influence of PE and CE on anticipatory postural adjustments (APAs) of trunk muscles, which are feedforward mechanisms that contribute to motor control and controlled movement. Rapid arm movement tasks (RAM) were used to induce APAs of the trunk muscles prior and following three experimental conditions in 20 healthy adults: seated rest without exertion (NE), a combined isometric modified Biering-Sörensen and static abdominal curl to induce PE, and a modified incongruent Stroop colour-word task to induce CE. Fatigue was assessed using self-reported measures, and APA onset latencies of the trunk muscles with surface electromyography. Statistical analyses revealed that neither PE nor CE influence APAs of the trunk. Therefore, it is hypothesized that the influence of fatigue on movement performance might not be through altered motor control, but rather by reduced motivation. However, the possibility that fatigue might influence other mechanisms which contribute to trunk motor control, such as APA amplitude and variability, cannot be excluded and need further examination.