The effect of caffeine on cognitive task performance and motor fatigue
RATIONALE: In everyday life, people are usually capable of performing two tasks simultaneously. However, in a previous study we showed that during a fatiguing motor task, cognitive performance declined progressively. There is extensive literature on the (positive) effects of caffeine on cognitive and motor performance. These effects are most pronounced under suboptimal conditions, for example during fatigue. However, little is known about the effects of caffeine on cognitive performance during a fatiguing motor task. OBJECTIVE: This study was aimed to investigate whether a moderate dose of caffeine could attenuate the decline in cognitive performance during a fatiguing motor task. METHODS: The study consisted of a placebo and a caffeine (3 mg/kg) session. A total of 23 subjects completed these sessions in a semi-randomized and double-blind order. In each session, subjects performed maximal voluntary contractions of the index finger, a choice reaction time (CRT) task and a dual task consisting of a fatiguing motor task concomitantly with the same CRT task. After the fatiguing dual task, the CRT task was repeated. RESULTS: Caffeine improved cognitive task performance, in both the single and dual task, as shown by decreased reaction times together with unchanged accuracy. Cognitive performance in the dual task deteriorated with increasing fatigue. However, the decrease in cognitive performance in the beginning of the dual task, as observed in the placebo condition, was partly prevented by caffeine administration (i.e., no increase in reaction times). We found no effects of caffeine on motor parameters (absolute force, endurance time or electromyographic amplitude). CONCLUSIONS: Caffeine improved cognitive performance. This effect also extends under demanding situations, as was shown by the performance during the dual task, even during progressive motor fatigue.