A group of 7 healthy males was studied after maximal exercise and during and after prolonged exercise of two types (approximately at 40 and 67% of their VO2 max). Hematocrit, plasma proteins concentration, and hemoglobin were followed. Relative changes of plasma volume and total content of plasma protein were calculated from hematocrit changes. The mean corpuscular hemoglobin concentration was obtained by dividing hemoglobin by hematocrit. After maximal exercise, hemoconcentration with concomitant decrease of plasma volume (-13.0%) was found, with a corresponding increase in protein concentration (+12.9%) and without any protein content changes. Later normalisation at the 30th min of the recovery phase was shown. During prolonged submaximal exercise (67% of VO2 max) the changes in hemoconcentration, plasma volume (-7.1%), and plasma protein concentration (+6.9%) reached the highest changes in the first 15 min of exercise, and no decrease in protein content was observed. After them the spontanious tendency to the normalisation was found. No changes were registered in prolonged mild exercise (40% of VO2 max). The ratio of hemoglobin to hematocrit remained unchanged during and after all types of exercise.
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.
A group of 10 prepubertal boys was studied during prolonged exercise (60 min) on bicycle ergometer and on treadmill at two levels of work load (appr. 40% and 60% VO2 max). The hematocrit, serum proteins, Cl- and K+ were followed, and from the blood hematocrit changes the plasma volume changes were calculated. At the exercises of lower intensity of both types a slight hemodilution was found (appr. +5% increase in plasma volume), at higher intensity practically no changes could be demonstrated. These findings are supported by the values of serum protein concentration, where no increase was found, and by the fact that at the lower work loads a rather decreasing trend was found for this blood constituent. These findings are at variance with those in adults under similar conditions. The authors suggest that different changes of plasma volume during exercise in boys than in adults could be related to the disparate lactate production and fate in these age groups.
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