BLUNTING THE RISE IN BODY-TEMPERATURE REDUCES MUSCLE GLYCOGENOLYSIS DURING EXERCISE IN HUMANS

To examine the effect of blunting the rise in body temperature on exer cise metabolism, seven endurance-trained men cycled for 40 min at 65 % of maximal oxygen consumption (V over dot(O2,max)) in an environmenta l chamber at either 20 degrees C and 20 % relative humidity (RH) (T-20 ) or 3 degrees C and similar to 50 % RH (T-3). The trials were conduct ed in random order at least 1 week apart. Mean oxygen comsumption (V o ver dot(O2)) during exercise was not different when comparing the two trials. In contrast, the mean respiratory exchange ratio (RER) was low er (P < 0.05) at T-20 compared with T-3. Heart rate, rectal temperatur e and plasma catecholamines were higher (P < 0.05) during exercise at T-20 compared with T-3, as was post-exercise muscle temperature (P < 0 .01). Muscle and blood lactate and blood glucose concentrations were n ot significantly different when comparing T-20 with T-3. Net muscle gl ycogen utilization was greater (P < 0.05) at T-20 compared with T-3. T hese results suggest that glycogenolysis in contracting skeletal muscl e is reduced during exercise when the rise in body core temperature is attenuated. These changes in carbohydrate metabolism appear to be inf luenced by alterations in muscle temperature and/or sympatho-adrenal a ctivity.