Sex Difference in Regional Skin Blood Flow Perfusion and Sweat Rates during Exercise in Hot and Cool Conditions

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Background Females are reported to have lower thermosenstivity for evaporative heat loss and skin blood flow (SKbF) response to an increase in mean body temperature during exercise compared to men. However, sweat rate (SR) and SkBF are typically examined only on the forearm. It is unclear if SR and SkBF differ between sex in various body regions during exercise hyperthermia when matched for exercise heat production. Purpose This project tested the hypothesis that regional skin blood flow perfusion and sweat rates would differ between men and women exercising at matched exercise heat production. Methods Twenty‐two healthy active (7 day activity: 8620±3008 steps/day; VO 2 max: 49±10 mL/kg/min) adults (11M/11F, 22.4±4.9y, 169±7.6cm, 68.3±13kg) exercised at similar metabolic heat production (M: 7.1±1.5 W/kg, F: 6.9±1.4 W/kg; P =0.32) for 60 min (cycle ergometer) in cool (24.0±0.0□C; 14.4±3.6%R h ) and hot (42.3±0.2□C; 27.9±5.5%R h ) conditions in random order separated by at least 7 days. The change for intestinal temperature (ΔTin) and heart rate (ΔHR) utilized a factorial two‐way repeated measure analysis of variance (RMANOVA) for interaction ( In ) and main effect ( ME ) for Sex and Condition. Local skin temperature (Tsk), SKbF, and SR were measured at the chest, stomach, forearm, and shoulder regions at rest and continuously during exercise and analyzed within each condition with a factorial two‐way RMANOVA for In and ME for Time and Sex. Results Males and females had a similar increase in hot compared to cool for ΔTin (Cool: Δ0.5±0.1□C, Hot: Δ1.5±0.6□C; ME: condition; P <0.0001) and ΔHR (Cool: 58±15 b/min, Hot: 71±15 b/min; ME: Condition; P <0.01). Tsk was hotter at each site in the hot compared to cool condition but not different between sex ( ME: Condition, P ≤.0001). SkbF chest increased during exercise in both sexes ( ME : Time, P <0.0001). SkbF stomach increased during exercise in both conditions, however in the hot increased greater in females compared to males ( In : Time × Sex, P <0.002). SkBF forearm increase during exercise in both sexes; however, was attenuated in females in the hot ( In: Time × Sex, P <0.002). SkBF shoulder increased during exercise and was greater in females compared to males in the hot (ME: Sex, P <0.04) and more so in the cool ( In: Time × Sex, P <0.03). SR chest increased similar between sex in hot but was greater in cool for females ( In: Time × Sex, P <0.003). SR stomach increased less for females in the hot (ME: Sex, P <0.04) but similar to males in cool ( ME: Time, P <0.0001). SR forearm increased less in females in the hot ( In: Time × Sex, P <0.0017). SR shoulder increased similar between sex in hot and cool conditions ( ME: Time, P <0.0001). Conclusion These data indicate that sex differences exist for SkBF and SR in different body regions during exercise in hot and cool conditions. Females have elevated SkBF in the stomach and shoulder and similar in chest and forearm compared to males. SR in females are attenuated in stomach and forearm, but similar in the chest and shoulder regions compared to males.

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