Thermoregulatory, Cardiovascular, And Metabolic Responses To Hot And Cold Environments In Men And Women

Abstract

Extreme environments significantly challenge human physiology, but a systematic comparison between sexes in hot and cold is lacking. PURPOSE: Investigate how extreme cold (EC) and extreme heat (EH) during rest and exercise affects men and women. METHODS: Twelve males (21.6 ± 2.3 yrs; 47.4 ± 9.3 ml/kg/min) and 12 females (22.7 ± 2.5 yrs; 45.6 ± 5.1 ml/kg/min) rested (45-min) followed by three-30 min bouts (%vVO2max) at low (1; 30%), moderate (2; 60%), and high (3; 85% & 90% interspersed with walking) intensities separated by 10-min in 0 °C and 38 °C. Rectal temperature (Trec), heart rate recovery at 30 & 60s (HRR30, HRR60), and blood lactate were assessed. RESULTS: Post-exercise Trec was ~1.1 °C higher in both sexes during EH vs EC and ~ 0.5 °C higher in men vs women in both conditions. Trec rose in females (+.14 °C) but decreased in males (-.053 °C) during EH rest (P = .026), and increased in both during EC (men: +.28 °C, women: +.10 °C). Passive cooling rates were greater in women after EH1&2 (P = .008) but rate of rise was similar. Lactate was higher in men for EH1 (~0.6 mmol/L), EH3 (~1.6 mmol/L) and EC2 (~1.3 mmol/L). Lactate was higher in EH vs EC in women (2, P = .037; 3, P = .002) and men (3, P = .030). In men, HRR30 and HRR60 were greater in EC at 85% (P = .003; P = .001), and 90% (P = .033; P = .002) vVO2max. For females, only HRR60 was greater in the cold, occurring at 60% (P = .010), 85% (P = .028), and 90% (P < .001). CONCLUSION: Extreme environments markedly influence thermoregulation, fast phase of HRR, and LA responses with distinct sex differences.