The muscle contents of high-energy phosphates and their derivatives [ATP, ADP, AMP, creatine phosphate (CrP), and creatine], glycogen, some glycolytic intermediates, pyruvate, and lactate were compared in 11 dogs performing prolonged heavy exercise until exhaustion (at ambient temperature 20.0 +/- 1.0 degrees C) without and with trunk cooling using ice packs. Without cooling, dogs were able to run for 57 +/- 8 min, and their rectal (Tre) and muscle (Tm) temperatures increased to 41.8 +/- 0.2 and 43.0 +/- 0.2 degrees C, respectively. Compared with noncooling, duration of exercise with cooling was longer by approximately 45% while Tre and Tm at the time corresponding to the end of exercise without cooling were lower by 1.1 +/- 0.2 and 1.2 +/- 0.2 degrees C, respectively. The muscle contents of high-energy phosphates (ATP + CrP) decreased less, the rate of glycogen depletion was lower, and the increases in the contents of AMP, pyruvate, and lactate as well as in the muscle-to-blood lactate ratio were smaller. The muscle content of lactate was positively correlated with Tm. The data indicate that with higher body temperature equilibrium between high-energy phosphate breakdown and resynthesis was shifted to the lower values of ATP and CrP and glycolysis was accelerated. The results suggest that hyperthermia developing during prolonged muscular work exerts an adverse effect on muscle metabolism that may be relevant to limitation of endurance.

No abstract

Six healthy men were studied under normal conditions and after dehydration caused by sweating produced 1) in a sauna at 80 C, 2) by hard muscular work at 18 C, and 3) by mild exercise at room temperature 38 C. The dehydration period lasted for 2.5@#X2013;3.5 hr. Sweat was collected in impermeable plastic bags around the forearm. Body weight, Evans blue space, and apparent inulin space were determined before and about 90 min after the dehydration period. The average decrease in body weight was 3.1 (4.1%), 3.1, and 3.5 kg for 1, 2, and 3, respectively. The reduction in apparent inulin space was 1.4, 0.2 and 1.3 liters, respectively. The decrease in Evans blue space paralleled the reduction in apparent inulin space. In the three conditions no significant differences were found in calculated total loss of electrolytes. Water liberated from combustion of fat and carbohydrates plus water previously stored with glycogen can account for up to 1.1 liters of the intracellular water loss during the hard exercise (2). The additional water loss from the cells is discussed in light of electrolyte shifts. dehydration; intracellular fluid; extracellular fluid; plasma volume Submitted on January 20, 1964