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. 2024 Jan 11:5:1274141.
doi: 10.3389/fspor.2023.1274141. eCollection 2023.

The effect of heat mitigation strategies on thermoregulation and productivity during simulated occupational work in the heat in physically active young men

Margaret C Morrissey-Basler  1   2 , Gabrielle J Brewer  1 , Travis Anderson  3   4 , William M Adams  3   4   5   6 , John S Navarro  1 , Monique Marcelino  1 , David G Martin  1 , Douglas J Casa  1
Affiliations

The effect of heat mitigation strategies on thermoregulation and productivity during simulated occupational work in the heat in physically active young men

Margaret C Morrissey-Basler et al. Front Sports Act Living. .

Abstract

Purpose: To investigate heat stress mitigation strategies on productivity and thermoregulatory responses during simulated occupational work in the heat.

Methods: Thirteen physically active men (age, 25 ± 4 years; body mass,77.8 ± 14.7 kg; VO2peak, 44.5 ± 9.2 ml·kg-1·min-1) completed five randomized-controlled trials in a hot environment (40°C, 40% relative humidity). Each trial was 4.5 h in duration to simulate an outdoor occupational shift. Thermoregulatory responses (heart rate, HR; rectal temperature, Trec; mean skin temperature, Tsk), perceptual responses (rating of perceived exertion, RPE; thermal sensation; thermal comfort; fatigue) and productivity outcomes (box lifting repetitions, time to exhaustion) were examined in the following heat mitigation strategy interventions: (1) simulated solar radiation with limited fluid intake [SUN]; (2) simulated solar radiation with no fluid restrictions [SUN + H2O]; (3) shade (no simulated solar radiation during trial) with no fluid restrictions [SHADE + H2O]; (4) shade and cooling towels during rest breaks with no fluid restrictions [COOL + H2O]; and (5) shade with cooling towels, cooling vest during activity with no fluid restrictions [COOL + VEST + H2O].

Results: [COOL + VEST + H2O] had lower Trec compared to [SUN] [p = 0.004, effect size(ES) = 1.48], [SUN + H2O] (p < 0.001, ES = -1.87), and [SHADE + H2O] (p = 0.001, ES = 1.62). Average Tsk was lower during the treadmill and box lifting activities in the [COOL + VEST + H2O] compared to [SUN] (p < 0.001, ES = 7.92), [SUN + H2O] (p < 0.001,7.96), [SHADE + H2O] (p < 0.001), and [COOL + H2O] (p < 0.001, ES = 3.01). There were performance differences during the [COOL + VEST + H2O] (p = 0.033) and [COOL + H2O] (p = 0.023) conditions compared to [SUN] during phases of the experimental trial, however, there were no differences in total box lifting repetitions between trials (p > 0.05).

Conclusion: Our results suggest that during a simulated occupational shift in a laboratory setting, additional heat mitigation strategies ([COOL + VEST + H2O] and [COOL + H2O]) reduced physiological strain and improved box lifting performance to a greater degree than [SUN]. These differences may have been attributed to a larger core to skin temperature gradient or reduction in fatigue, thermal sensation, and RPE during [COOL + H2O] and [COOL + VEST + H2O]. These data suggest that body cooling, hydration, and "shade" (removal of simulated radiant heat) as heat stress mitigation strategies should be considered as it reduces physiological strain while producing no additional harm.

Keywords: body cooling; heat stress; hydration; occupational; prevention.

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Conflict of interest statement

WA receives royalties from Springer Nature and sits on the following advisory boards; Medical and Science Advisory Board for the Korey Stringer Institute, Sport Advisory Council for the Wu Tsai Human Performance Alliance, Expert Advisory Board for Emerja Corporation, and Expert Advisory Board for My Normative. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
Experimental trials.
Figure 2
Figure 2
Experimental trial protocol. vVO2peak, velocity at peak oxygen consumption.
Figure 3
Figure 3
Box lifting Set up and protocol instructions. 1 = starting point; 2 = point 2, where participants slid the box from 1 to 2; 3 = point 3, participants slid the box down the slide from point 2 to point 3; 4 = point 4, participants bent down and picked up the box with both hands and moved it back to the starting point.
Figure 4
Figure 4
Towel placement during body cooling during rest breaks.
Figure 5
Figure 5
Rectal temperature responses during experimental trials. asignificant difference between [COOL + VEST + H2O] and [SUN + H2O]; bsignificant difference between [COOL + H2O] and [SUN + H2O]; csignificant difference between [SHADE + H2O] and [SUN + H2O]. Trec, rectal temperature; C, degrees Celsius.
Figure 6
Figure 6
Heart rate responses during experimental trials. asignificant difference between [COOL + VEST + H2O] and [SUN + H2O]; bsignificant difference between [COOL + H2O] and [SUN + H2O]; csignificant difference between [SHADE] and [SUN]; dsignificant difference between [SUN] and [COOL + VEST + H2O]; esignificant difference between [SHADE + H2O] and [COOL + H2O]; fsignificant difference between [SUN] and [COOL + VEST + H2O]; gsignificant difference between [SUN] and [SUN + H2O]; hsignificant difference between [COOL + H2O] and [SUN]; isignificant difference between [COOL + H2O] and [COOL + VEST + H2O]; k significant difference between [SUN + H2O] and [SHADE + H2O]. beats per minutes.
Figure 7
Figure 7
Box lifting productivity task. (A) Number of Box lifting Repetitions Performed Across Experimental Trials. (B) Percent Difference in Total Number of Boxes Lifted Compared to Control Condition [SUN]. asignificant difference between [COOL + VEST + H2O] and [SUN]; bsignificant difference between [COOL + H2O] and [SUN]. #, number; TEMPO, paced box lifting following a metronome; AMRAP, as many rounds as possible.
Figure 8
Figure 8
Time to exhaustion at 80% of vVO2max between experimental. asignificant difference between [COOL + H2O] and [SUN]; bsignificant difference between [COOL + H2O] and [SUN + H2O]; csignificant difference between [COOL + VEST + H2O] and [SUN]; dsignificant difference between [COOL + VEST + H2O] and [SUN + H2O]. vVO2peak, velocity at peak oxygen consumption; secs, seconds.
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