Endurance capacity impairment in cold air ranging from skin cooling to mild hypothermia

We tested the effects of cold air (0 degrees C) exposure on endurance capacity to different levels of cold strain ranging from skin cooling to core cooling of Delta-1.0 degrees C. Ten males completed a randomized, crossover, control study consisting of a cycling time to exhaustion (TTE) at 70% of their peak power output following: 1) 30-min of exposure to 22 degrees C thermoneutral air (TN), 2) 30-min exposure to 0 degrees C air leading to a cold shell (CS), 3) 0 degrees C air exposure causing mild hypothermia of -0.5 degrees C from baseline rectal temperature (HYPO-0.5 degrees C), and 4) 0 degrees C air exposure causing mild hypothermia of -1.0 degrees C from baseline rectal temperature (HYPO-1.0 degrees C). The latter three conditions tested TTE in 0 degrees C air. Core temperature and seven-site mean skin temperature at the start of the TTE were: TN (37.0 +/- 0.2 degrees C, 31.2 +/- 0.8 degrees C), CS (37.1 +/- 0.3 degrees C, 25.5 +/- 1.4 degrees C), HYPO-0.5 degrees C (36.6 +/- 0.4 degrees C, 22.3 +/- 2.2 degrees C), HYPO-1.0 degrees C (36.4 +/- 0.5 degrees C, 21.4 +/- 2.7 degrees C). There was a significant condition effect (P <= 0.001) for TTE, which from TN (23.75 +/- 13.75 min) to CS (16.22 +/- 10.30 min, Delta-30.9 +/- 21.5%, P = 0.055), HYPO-0.5 degrees C (8.50 +/- 5.23 min, Delta-61.4 +/- 19.7%, P <= 0.001), and HYPO-1.0 degrees C (6.50 +/- 5.60 min, Delta-71.6 +/- 16.4%, P <= 0.001). Furthermore, participants had a greater endurance capacity in CS compared with HYPO-0.5 degrees C (P = 0.046), and HYPO-1.0 degrees C (P = 0.007), with no differences between HYPO-0.5 degrees C and HYPO-1.0 degrees C (P = 1.00). Endurance capacity impairment at 70% peak power output occurs early in cold exposure with skin cooling, with significantly larger impairments with mild hypothermia up to Delta-1.0 degrees C.