The Effects of Exhaustive Exercise on Thermoregulatory Fatigue During Cold Exposure
ARMY RESEARCH INST OF ENVIRONMENTAL MEDICINE NATICK MA
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Two experiments were conducted to examine whether acute one-hour or chronic exertional fatigue 3-7 days would impair the thermoregulatory response during subsequent cold exposure thereby leading to an accentuated core temperature reduction compared to when the same individual was exposed to cold in a rested condition. In Study 1, ten men rested for 2 hours during a standardized cold air test CAT, 4.6 deg C following 2 treatments 1 60 min of cycle exercise EX at 55 VO2sub peak, and 2 passive heating HEAT. EX was performed during a 35 deg C water immersion WI and HEAT was conducted during a 38.2 deg C WI. The duration of HEAT was individually adjusted mean 53 min so that rectal temperature Tsub re was similar at the end of WI in both EX 38.2 deg C and HEAT 38.1 deg C. During CAT following EX, relative to HEAT 1 Tsub re was lower P 0.05 from min 40-120, 2 mean weighted heat flow was higher P 0.05, 3 insulation was lower P 0.05, and 4 metabolic heat production was not different. In Study 2, thirteen men 10 experimental and 3 Control subjects performed a cold-wet walk CW for up to 6 h 6 rest-work cycles, each cycle one h in duration in 5 deg C air on three occasions. One cycle of CW consisted of 10 min standing in the rain 5.4 cmhr followed by 45 min walking 1.34 ms, 5.4 ms wind. Clothing was saturated at the start of each walking period 0.75 clo vs. 1.1 clo when dry. The initial CW trial Day 0, D0 was performed afternoon with subjects rested before initiating exercise-cold exposure. During the next 7 days, 4 h of exhaustive exercise aerobic, anaerobic, resistive was performed each morning. The subsequent two CW trials were performed on the afternoon of days 3 D3 and 7 D7, 2.5 h after the cessation of fatiguing exercise. For the Control group, no exhaustive exercise was performed on any day.
- Stress Physiology