Prolonged exercise in prepubertal boys. I. Cardiovascular and metabolic adjustment.

The circulatory and metabolic changes during prolonged exercise (60 min) were studied in a group of 10 healthy prepubertal boys. The boys worked on the treadmill and on the bicycle ergometer at two levels of load, namely at oxygen uptakes of 36--39%, and 60% of the respective VO2 max for both types of exercise. The identical relative work loads represent higher metabolic rate at the treadmill exercise. The rectal temperature was higher after exercises on treadmill than on bicycle. The heart rate increase during prolonged exercise was lower in boys than in adults in both types of exercise. Better cardiovascular adjustment is suggested. The blood lactate increase was negligible in the initial phase of exercise with subsequent removal from the blood during extended exercise, which was more pronounced at the treadmill exercises. The increasing blood free glycerol concentration indicates similar fat share on energy release in children as in adults. No biological handicap could be found for prolonged exercise in children. The preference of short-time exercises in children lies probably in the psychological sphere.