A comparison of males and females' temporal patterning to short- and long-term heat acclimation

Abstract

The current study assessed sex differences in thermoregulatory and physiological adaptation to short-term (STHA) and long-term heat acclimation (LTHA). Sixteen (eight males; eight females) participants performed three running heat tolerance tests (RHTT), preceding HA (RHTT1), following 5 days HA (RHTT2) and 10 days HA (RHTT3). The RHTT involved 30-min running (9km/h, 2% gradient) in 40°C, 40% relative humidity. Following STHA, resting rectal temperature (Trrest) (males: -0.24±0.16°C, P≤0.001; females: -0.02±0.08°C, P=0.597), peak rectal temperature (Trpeak) (males: -0.39±0.36°C, P≤0.001; females -0.07±0.18°C, P=0.504), and peak heart rate (males: -14±12 beats/min, P≤0.001; females: -5±3 beats/min, P=0.164) reduced in males, but not females. Following STHA, sweat rate relative to body surface area (SRBSA) increased (428±269g/h/m2, P=0.029) in females, but not males (-11±286g/h/m2, P=0.029). Following LTHA, Trrest (males: -0.04±0.15°C, P=0.459; females: -0.22±0.12°C, P≤0.01) and Trpeak (males: -0.05±0.26°C, P=0.590; females: -0.41±0.24°C, P≤0.01) reduced in females, but not males. Following LTHA, SRBSA increased in males (308±346g/h/m2, P=0.029), but not females (44±373g/h/m2, P=0.733). Males and females responded to STHA; however, females required LTHA to establish thermoregulatory and cardiovascular stability. HA protocols should be designed to target sex differences in thermoregulation for optimal adaptation.