The effects of exercise fatigue on prefrontal and motor activations as measured by near-infrared spectroscopy.

This study aimed to examine the effects of active task-related fatigue induced by maximal exercise on human cognitive and motor systems. To achieve the goal, we measured participants' activation changes in their prefrontal and motor cortices while performing an incremental cycling task using near-infrared spectroscopy (NIRS). The participant's task was to ride a test bike to maximal exertion twice within 2 days in a low-load and a high-load condition, respectively. The behavioral data showed longer cycling time in the low-load condition than that in the high-load condition. By contrast, the NIRS data showed greater prefrontal activations in the low-load condition than that in the high-load condition. More importantly, both the prefrontal and motor activations increased significantly near maximal exertion and then decreased in the initial recovery period, and the activation changes in the left prefrontal cortex resulted in changes in the bilateral motor areas. The results directly indicate the critical role of prefrontal cortex in fatigue and suggest that NIRS is an appropriate brain-imaging tool to monitor fatigue in natural environments.