Endurance Capacity Impairment in Cold Air Ranging from Skin Cooling to Mild Hypothermia

Abstract

Introduction: We tested the effects of cold air (0°C) exposure on endurance capacity to different levels of cold strain ranging from skin cooling to core cooling of ∆-1.0°C. Methods: Ten males completed cycling time-to-exhaustion (TTE) at 70% of their peak power output following: i) 30-min of exposure to 22°C thermoneutral air (TN), ii) 30-min exposure to 0°C air leading to a cold shell (CS), iii) 0°C air exposure causing mild hypothermia of -0.5°C from baseline rectal temperature (HYPO-0.5°C), and iv) 0°C air exposure causing mild hypothermia of -1.0°C from baseline rectal temperature (HYPO-1.0°C). The latter three conditions tested TTE in 0°C air. Results: Core temperature and seven-site mean skin temperature at the start of the TTE were: TN (37.0 ± 0.2°C, 31.2 ± 0.8°C), CS (37.1 ± 0.3°C, 25.5 ± 1.4°C), HYPO-0.5°C (36.6 ± 0.4°C, 22.3 ± 2.2°C), HYPO-1.0°C (36.4 ± 0.5°C, 21.4 ± 2.7°C). There was a significant condition effect (p≤0.001) for TTE, where TTE declined from TN (23.75 ± 13.75 min) to CS (16.22 ± 10.30 min, ∆-30.9 ± 21.5%, p=0.055), HYPO-0.5°C (8.50 ± 5.23 min, ∆-61.4 ± 19.7, p≤0.001), and HYPO-1.0°C (6.50 ± 5.60 min, ∆-71.6 ± 16.4%, p≤0.001). Furthermore, participants had a greater endurance capacity in CS compared to HYPO-0.5°C (p=0.046), and HYPO-1.0°C (p=0.007), with no differences between HYPO-0.5°C and HYPO-1.0°C (p=1.00). Conclusion: Endurance capacity impairment at 70% peak power output occurs early in cold exposure with skin cooling and inadequate clothing, with significantly larger impairments with mild hypothermia up to ∆-1.0°C.