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Discussion | Relative to healthy counterparts, physically active middle-aged and older men with well-controlled type 2 diabetes had attenuated heat-loss capacity during exercise in the heat, due primarily to impaired sweat evaporation, which exacerbated thermal (body temperature) and cardiovascular (heart rate) strain. These preliminary findings indicate that exercise heat stress may pose a health concern in patients with type 2 diabetes, especially because physical activity is recommended for diabetes management. 5 However, participants with type 2 diabetes demonstrated a greater improvement in heatloss capacity than did healthy controls after heat acclimation. A randomized clinical trial of repeated brief, supervised exercise is warranted to determine whether heat acclimation during heat exposure offsets diabetes-related thermoregulatory impairments and health complications. Study limitations include the small sample size, the inclusion of only men and patients with well-controlled diabetes, and the specific exercise and environmental conditions.

Current public health guidance designed to protect individuals against extreme heat and the ongoing COVID-19 pandemic is seemingly discordant, yet during the northern hemisphere summer, we are faced with the imminent threat of their simultaneous existence. Here we examine the environmental limits of electric fan-use in the context of the United States summer as a potential stay-at-home cooling strategy that aligns with existing efforts to mitigate the spread of SARS-COV-2.

Objectives: To examine, 1) optimal structure of break periods to mitigate physiological heat strain during rugby league play (Stage 1); and ii) effectiveness of three different cooling strategies applied during breaks (Stage 2). Design: Counter-balanced crossover design. Methods: In 37°C, 50% RH, 11 males completed six simulated 80-min (two 40-min halves) rugby league matches on a treadmill with different break structures: regular game (RG) (12-min halftime), 1-min or 3-min "quartertime" breaks halfway through each half with a 12-min halftime break (R1C and R3C), a 20-min halftime break (EH), or 1-min or 3-min quarter-time breaks with a 20-min halftime break (E1C and E3C) [Stage 1]. Nine participants completed Stage 2, which assessed the application of either ice towels (ICE), an electric fan (FAN) or a misting fan (MST) during breaks in the E3C protocol which, in Stage 1, prevailed as the optimal break structure. Results: Stage 1: Irrespective of quarter-time break duration, reductions in rectal temperature (−0.24°C ± 0.24) and heart rate (−61 ± 10 bpm) during the halftime break were greater with a 20-min compared to a 12-min break (−0.08 ± 0.13°C, p = 0.005; −55 ± −9 bpm, p = 0.021). Stage 2: End-game rises in rectal temperature were smaller (p < 0.006) in MST (1.41 ± 0.22°C), FAN (1.55 ± 0.36°C) and ICE (1.60 ± 0.21°C) than in CON (1.80 ± 0.39°C). The end-halftime heart rate was lower (p < 0.001) in ICE (89 ± 13 bpm), MST (90 ± 10 bpm) and FAN (92 ± 13 bpm) than in CON (99 ± 18 bpm). Conclusions: Combining an extended halftime period and quarter-time breaks with MST application is the optimal cooling strategy for rugby league players in hot, humid conditions.

Purpose It is often assumed that a person with a higher mean skin temperature (T sk) will sweat more during exercise. However, it has not yet been demonstrated whether T sk describes any individual variability in whole-body sweat rate (WBSR) independently of the evaporative requirement for heat balance (E req). Methods One hundred forty bouts of 2-h treadmill walking completed by a pool of 21 participants (23 ± 4 yr, 174 ± 8 cm, 76 ± 11 kg, 1.9 ± 0.2 m2) under up to nine conditions were analyzed. Trials employed varying rates of metabolic heat production (H prod; 197–813 W), and environmental conditions (15°C, 20°C, 25°C, 30°C; all 50% relative humidity), yielding a wide range of E req (86–684 W) and T sk values (26.9°C–34.4°C). Results The individual variation observed in WBSR was best described using E req (in watts; R 2 = 0.784) as a sole descriptor, relative to E req (in watts per meter squared; R 2 = 0.735), H prod (in watts; R 2 = 0.639), H prod (in watts per meter squared; R 2 = 0.584), ambient air temperature (T a) (R 2 = 0.263), and T sk (R 2 = 0.077; all, P < 0.001). A multiple stepwise linear regression included only E req (in watts; adjusted R 2 = 0.784), with T sk not significantly correlating with the residual variance (P = 0.285), independently of E req (in watts). H prod (in watts) had similar predictive strength to E req (in watts) at a fixed air temperature, explaining only 5.2% at 30°C, 4.9% at 25°C, 2.7% at 20°C, and 0.5% at 15°C (all, P < 0.001) less variance in WBSR compared with E req. However, when data from all ambient temperatures were pooled, H prod alone was a markedly worse predictor of WBSR than E req (R 2 = 0.639 vs 0.784; P < 0.001). Conclusions E req (in watts) explained approximately four-fifths of the individual variation in WBSR over a range of ambient temperatures and exercise intensities, whereas T sk did not explain any residual variance independently of E req.