Key result
Short-duration whole-body immersion in 45°C water modulated neuromuscular excitability but had no additional effect on central and peripheral fatigue during a sustained 2-minute maximal voluntary contraction.
Why the study?
Whole-body hyperthermia impairs neurophysiological performance, but whether short-duration immersion in 45°C water increases or impairs neurophysiological performance without inducing hyperthermia remained unexamined.
Does brief whole-body immersion in 45°C water alter central and peripheral fatigability in healthy men?
RCT (n=15)
Open-label
Balanced random order (crossover design)
No
Does brief whole-body immersion in 45°C water alter central and peripheral fatigability in healthy men?
Brief exposure to noxious heat (45°C water immersion) modulates neuromuscular excitability but does not exacerbate central or peripheral fatigue during sustained maximal voluntary contraction.
Brief noxious heat immersion does not worsen fatigability in healthy men; leaves open effects in hyperthermic or clinical settings.
Background: Whole-body hyperthermia (WBH) has an adverse effect on the nervous system and neurophysiological performance. In the present study, we examined whether short-duration whole-body immersion in 45°C water (HWI-45°C), which produces a strong neural and temperature flux without inducing WBH, can increase or impair neurophysiological performance in humans. Methods: Fifteen men (aged 25 ± 6 years) were enrolled in this study and participated in three experiments: 1) a brief (5-min) immersion of the whole body in 37°C water (WI-37°C); 2) a brief (5-min) HWI-45°C; and 3) a control trial in a thermoneutral condition at an ambient temperature of 24°C and 60% relative humidity. Before and after the immersions, neuromuscular function (electromyographic activity, reflexes, electrically and voluntary induced torque production, voluntary muscle activation level) were tested. To provoke central inhibition, the participants performed a sustained 2-min maximal voluntary contraction (MVC). Results: Thermophysiological strain was greater after HWI-45°C than after WI-37°C. Electrophysiological modulations of motor drive transmission and peripheral modulations of muscle contractility properties in response to HWI-45°C seemed to have little effect on central activation of the exercising muscles and no effect on MVC production. Conclusion: Although exposure to acute noxious heat was effective in evoking neuromuscular excitability, the increases in core temperature (∼0.2°C) and muscle temperature (∼0.6°C) did not induce moderate or severe WBH. These changes did not seem to affect central structures; that is, there were no additional increases in central and/or peripheral fatigue during a sustained 2-min MVC.
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Eimantas et al. (2022) conducted an RCT in Healthy (n=15). Whole-body immersion in 45°C water vs. Whole-body immersion in 37°C water and thermoneutral control was evaluated on Central and peripheral fatigue during a sustained 2-min maximal voluntary contraction (MVC). Short-duration whole-body immersion in 45°C water modulated neuromuscular excitability but had no additional effect on central and peripheral fatigue during a sustained 2-minute maximal voluntary contraction.
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