A passive increase in muscle temperature enhances rapid force production and neuromuscular function in healthy adults.
OBJECTIVE
To test the effects of hot-water immersion on the rapid force production and parameters of neuromuscular function in healthy adults.


DESIGN
Cross-sectional study.


METHODS
Fifteen healthy adults (24.9±5.6 years; 178±11.4cm; 72.8±16.2kg) performed neuromuscular assessments before, after and ∼15min after either 90min of 42°C (hot) or 36°C (sham-condition) water immersion (lower body). Knee extensors rate of torque development (RTD) was measured during explosive voluntary contraction in the interval of 0-50ms (RTDV50) and 0-150ms (RTDV150) and during electrically-evoked contractions by single twitches (RTDtwitch) and low- and high-frequencies doublets (RTD20Hz and 100Hz). Rate of EMG rise (RER) was calculated for voluntary contractions and half-relaxation time (HRT) and electromechanical delay (EMD) was measured during single twitches.


RESULTS
After the hot-water immersion (when rectal and muscle temperature were elevated [↑1°C and ↑2.4°C, respectively]), RTDV50, RTD20Hz and RTD100Hz significantly increased and HRT decreased when compared to baseline and sham-condition (p<0.05). Approximately 15min after the hot-water immersion (when muscle temperature was still higher [↑1.4°C], but rectal temperature at baseline level), RTDV50 remained higher and RTDtwitch presented higher values than baseline and sham-condition. The RTD20Hz and RTD100Hz showed further increases compared to post hot-water immersion trials. HRT showed no changes compared to post water immersion, but the EMD presented lower values than baseline and sham-condition. No changes were observed for RTDV150 and RER at any moment.


CONCLUSION
Increased muscle temperature provoked by 42°C hot-water immersion increases the early phase of the RTD (<70ms) (voluntary and evoked) and decreases HRT and EMD of the knee extensors.
['Rodrigues|Patrick|P|', 'Trajano|Gabriel S|GS|', 'Wharton|Lee|L|', 'Orssatto|Lucas B R|LBR|', 'Minett|Geoffrey M|GM|']
D000328:Adult D001831:Body Temperature D003430:Cross-Sectional Studies D004576:Electromyography D019054:Evoked Potentials, Motor D006358:Hot Temperature D006801:Humans D007101:Immersion D007719:Knee Joint D009119:Muscle Contraction D009126:Muscle Relaxation D018482:Muscle, Skeletal D019415:Torque D055815:Young Adult
Heat stress Neuromuscular parameters Passive heating Rate of force development, explosive force Thermal therapy