Heat Acclimation Does Not Protect Trained Males from Hyperthermia-Induced Impairments in Complex Task Performance.

Jacob Piil,Chris Mikkelsen,Nicklas Junge,Lars Nybo,Nathan Morris

doi:10.3390/ijerph16050716

Jacob Piil, Chris Mikkelsen + Show 3 more

Open Access

https://doi.org/10.3390/ijerph16050716

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Abstract

This study evaluated if adaptation to environmental heat stress can counteract the negative effects of hyperthermia on complex motor performance. Thirteen healthy, trained males completed 28 days of heat acclimation with 1 h daily exercise exposure to environmental heat (39.4 ± 0.3 °C and 27.0 ± 1.0% relative humidity). Following comprehensive familiarization, the participants completed motor-cognitive testing before acclimation, as well as after 14 and 28 days of training in the heat. On all three occasions, the participants were tested, at baseline (after ~15 min passive heat exposure) and following exercise-induced hyperthermia which provoked an increase in core temperature of 2.8 ± 0.1 °C (similar across days). Both cognitively dominated test scores and motor performance were maintained during passive heat exposure (no reduction or difference between day 0, 14, and 28 compared to cool conditions). In contrast, complex motor task performance was significantly reduced in hyperthermic conditions by 9.4 ± 3.4% at day 0; 15.1 ± 5.0% at day 14, and 13.0 ± 4.8% at day 28 (all p < 0.05 compared to baseline but not different across days). These results let us conclude that heat acclimation cannot protect trained males from being negatively affected by hyperthermia when they perform complex tasks relying on a combination of cognitive performance and motor function.

Highlights

Environmental heat stress has profound effects on human health and performance as the additional physiological strain or hyperthermia provoked by thermal stress has a negative impact on both cognitive functions [1,2,3,4,5,6,7] and physical exercise capacity [8,9,10,11,12]
Nor longer heat acclimation seemed to be protective against the reduction in complex motor performance after exercise-induced heat stress, when the participants were exposed to uncompensable heat stress, which elevated their core temperatures, thermal comfort and sensation scores to maximal levels
The participants displayed normal physical/physiological heat acclimation responses, but the present findings indicate that this could not protect against hyperthermia-induced impairments in complex motor performance

Summary

Introduction

Environmental heat stress has profound effects on human health and performance as the additional physiological strain or hyperthermia provoked by thermal stress has a negative impact on both cognitive functions [1,2,3,4,5,6,7] and physical exercise capacity [8,9,10,11,12] This negative impact is a major societal challenge for public health, with recent meta-analyses demonstrating that occupational heat strain has implications for both health and productivity [13,14]. Many daily activities rely on fine motor skills and the ability to maintain

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