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. 2019 Feb 28;16(5):716.
doi: 10.3390/ijerph16050716.

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

Jacob F Piil  1 , Chris J Mikkelsen  2 , Nicklas Junge  3 , Nathan B Morris  4 , Lars Nybo  5
Affiliations

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

Jacob F Piil et al. Int J Environ Res Public Health. .

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.

Keywords: core temperature; heat stress; hyperthermia; mathematics; motor performance; task complexity; visuo-motor tracking.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Thermal discomfort vs. exercise time and core temperature. (A) Thermal discomfort expressed as percentage of maximal thermal discomfort (i.e., 0% representing no thermal discomfort and 100% is maximal thermal discomfort) plotted against exercise time (min), at day 0 (white dots with black line), day 14 (gray dots with gray line), and day 28 (black dots with black line) and error-bars as SEM. (B) The correlation between thermal discomfort and core temperature, at day 0 (white dots), day 14 (gray dots), and day 28 (black dots) and error-bars (SEM) symbolizing the spread. The black line is the correlation line between parameters based on all observations.
Figure 2
Figure 2
Complex motor task performance score. (A) Performance scores (expressed as the percentage of time on target) on day 0, day 14, and day 28 at baseline (black bars) and hyper (white bars) with error-bars representing SEM. (B) Individual changes (connected points representing each participant) in visuo-motor tracking (VMT) score from baseline to the hyper time-point on day 0 (before acclimation) and after day 14 and day 28 of acclimation. * significant different from Baseline, (p < 0.05).
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