Differences in Movement Preparation under Hyperthermic Conditions: Self-Initiated Versus Externally Cued Movements.

Abstract

Excessive increases in body temperature impair voluntary force production and neuromuscular function, but the underlying central mechanisms remain unclear. We investigated the effect of hyperthermia on neural activity associated with motor preparation using electroencephalographic event-related potentials (EEG-ERP). Two stimulus presentation methods were used: movement-related cortical potentials (MRCP) induced by self-initiated movement and contingent negative variation (CNV) induced by externally cued movement. The exercise intensity that elicited MRCP and CNV was set at 20% maximum voluntary contraction. Healthy young volunteers performed trials before and during whole-body heat stress on separate days. Heat stress increased esophageal temperature by 1.5°C ± 0.1°C during the MRCP trial and 1.5°C ± 0.2°C during the CNV trial. Consistent with previous studies, the results of the Go/No-go tasks showed that the hyperthermia-induced impairment of brain activity was associated with executive and inhibitory processing during heat stress in both trials. In the MRCP trial, the amplitude of Bereitschaftspotential and the negative slope remained unchanged across all electrodes. However, CNV amplitudes in the middle and late phases were significantly reduced at Cz and Pz (both phases, P < 0.005) and C4 (late phase, P < 0.05), whereas early phase amplitudes were unchanged. These findings indicate that neural activity for self-initiated movements is preserved under heat stress, whereas neural activity for externally cued movements may be inhibited due to hyperthermia-induced central fatigue, potentially involving brain regions such as the prefrontal cortex. This alteration in the central mechanisms may contribute to the attenuated exercise performance under heat stress.