Effects of repetitive exercise and thermal stress on human cognitive processing

Cognitive performances may improve after acute moderate exercise, but not after prolonged and/or heavy exercise. The present study aimed to investigate the effects of environmental temperature during exercise on human cognitive processing. Fifteen healthy males performed four bouts of a 15-min cycling exercise with a 10-min rest between each bout, and event-related potentials (ERPs) were recorded in five sessions during somatosensory Go/No-go paradigms (i.e., Pre, post-first exercise bout, post-second exercise bout, post-third exercise bout, and post-fourth exercise bout) in an environmental chamber with temperature controlled at 20°C (Temperate) and 35°C (Hot). Increases in external canal temperature and heart rate were greater under the 35°C condition than under the 20°C condition. Regardless of thermal conditions, reaction times (RT) and error rates were not affected by the repetition of moderate exercise, whereas the peak amplitude of the N140 component, which is mainly related to somatosensory processing, was significantly reduced with the repetition of the exercise. However the peak amplitude of P300, which is linked to cognitive processes of context updating, context closure, and event-categorization, was significantly smaller in post-third and post-fourth exercise bouts under the 35°C condition than under the 20°C condition, and this decrease was more prominent in No-go trials under the 35°C condition. These results suggest that executive function, which is based on RTs and error rates, is not affected by prolonged exercise and different thermal conditions, whereas the exercise in a hot environment impairs human cognitive processing, particularly response inhibition.