Prior heat stress effects fatigue recovery of the elbow flexor muscles

: Long‐lasting alterations in hormones, neurotransmitters, and stress proteins after hyperthermia may be responsible for the impairment in motor performance during muscle fatigue. Methods : Subjects ( n = 25) performed a maximal intermittent fatigue task of elbow flexion after sitting in either 73° or 26°C to examine the effects of prior heat stress on fatigue mechanisms. Results : The heat stress increased the tympanic and rectal temperatures by 2.3° and 0.82°C, respectively, but there was full recovery prior to the fatigue task. Although prior heat stress had no effects on fatigue‐related changes in volitional torque, electromyographic (EMG) activity, torque relaxation rate, motor evoked potential (MEP) size, and silent period (SP) duration, prior heat stress acutely increased the pre‐fatigue relaxation rate and chronically prevented long‐duration fatigue ( P < 0.05). Conclusions : These findings indicate that prior passive heat stress alone does not alter voluntary activation during fatigue, but prior heat stress and exercise produce longer‐term protection against long‐duration fatigue. Muscle Nerve 44: 115–125, 2011