Author(s): PANG, J., PEELING, P., LANDERS, G.J., WALLMAN, K., PÉRIARD, J., CHONG, E., PESCH, T., GIRARD, O., Institution: UNIVERSITY OF WESTERN AUSTRALIA, Country: AUSTRALIA, Abstract-ID: 2334

INTRODUCTION:
Although heat-related strain during intermittent exercise is well documented, direct comparisons between contrasting environments (i.e., hot-dry (HD) and warm-humid (WH) environments), especially between sexes, remain limited. This study compared thermal, cardiovascular, and perceptual responses of male and female athletes during intermittent running under temperate (TEM), HD, and WH conditions.
METHODS:
Twenty-six intermittent-sport athletes (13 males, 13 females) completed three trials, each comprising two 30-min halves (first (H1) and second (H2) half) of high-intensity intermittent treadmill running in TEM (19.9 ± 0.4°C, 55.6 ± 1.5% RH, WBGT: 16.0 ± 0.5°C), HD (40.1 ± 0.4°C, 24.4 ± 1.5% RH, WBGT: 29.0 ± 0.5°C), and WH (31.3 ± 0.4°C, 80.3 ± 1.5% RH, WBGT: 29.3 ± 0.5°C). Exercise intensity was matched between sexes by prescribing running velocities across six zones as a percentage of individual peak sprint velocity. Gastrointestinal temperature (Tgi), skin temperature (Tsk), heart rate (HR), rating of perceived exertion (RPE), whole-body sweat rate (WBSR), and total distance were measured. Water was provided ad libitum, and participants rested in the laboratory before H2.
RESULTS:
Mean HR, WBSR, RPE, Tsk, and Tgi in H2 were higher in HD and WH compared with TEM (P≤0.004). Physiological and perceptual responses were largely similar between HD and WH (P≥0.280); however, HD elicited higher Tsk (P<0.001) and WBSR (P≤0.004), with an increase in mean HR from H1 to H2 (P=0.048). Although males covered a greater total distance than females (1775 m [1282, 2269]; P<0.001), physiological and perceptual responses did not differ by sex (P≥0.541). A sex × condition interaction was observed for WBSR (P=0.001), with greater values in males than females under HD and WH conditions (P<0.001). A sex × time interaction was observed for mean Tgi (P = 0.048), indicating a differential temporal response between sexes; however, no significant effects were detected at individual time points (P≥0.974). Increases in sweat rate (P<0.001) and HR (P≤0.009) were observed in H2 (compared to H1) for both HD and WH. Despite significant interaction for Tgi (P≤0.048) and RPE (P<0.001), no differences between halves were detected within conditions or sexes (P≥0.078). Similarly, females displayed similar mean Tsk across halves in all conditions (P≥0.835). In contrast, mean Tsk for males did not differ between halves in TEM (P=0.995) but was lower in H2 than H1 in both HD and WH (P≤0.009).
CONCLUSION:
When matched for WBGT, high-intensity intermittent treadmill running elicited comparable thermal, cardiovascular and perceptual strain across HD and WH in both sexes. However, HD still imposed greater thermal and cardiovascular strain than WH, as reflected by the higher Tsk, HR, and WBSR, despite comparable Tgi responses. The absence of cumulative heat strain across halves was likely attributable to heat dissipation during recovery in the cooler laboratory environment between the halves.