Food deprivation and exercise in the heat: thermoregulatory and metabolic effects.

To determine the effects of food deprivation on the physical, physiological, and metabolic responses to exercise in the heat, adult, male rats (330-360g, N = 16/group) were food-deprived for 24, 48, or 72 h. They were then exercised (9.14m X min-1) in the heat (35.5 degrees C) to hyperthermic exhaustion (Tco approximately 43 degrees C). Food deprivation had no effects on endurance, but ad lib fed controls manifested significantly (p less than 0.05) increased Tco and Tsk during the latter portion of the treadmill interval. While plasma osmolality was significantly (p less than 0.01) increased in all groups as a result of the heat/exercise contingency, hematocrit ratios were elevated (p less than 0.01) as a result of 48 and 72 h of food deprivation. Food deprivation resulted in severe hypoglycemia following exercise (p less than 0.01), and these decrements were accompanied by marked (p less than 0.01) reductions in circulating insulin levels. Prolonged food deprivation (48 and 72 h) resulted in significant (p less than 0.01) hypertriglyceridemia and hyperlactacidemia subsequent to exercise. Levels of sodium, potassium, urea nitrogen, and creatine phosphokinase were unaffected by the food deprivation intervals. We have concluded from these studies that while several thermoregulatory and metabolic responses to exercise in the heat can be significantly affected by food deprivation, short-term endurance capacity was unaltered.