Physiological considerations in training young athletes.

Healthy children evidence smaller values of cardiorespiratory function than adults, but these are in proportion to the smaller body size. At birth, the distribution of muscle fibres and the activity of enzymes in muscle are different from in adults, but these differences disappear at about age 6. On the other hand, muscle fibre thickness increases from birth to about 18 years of age and this is concurrent with increases in muscular strength. The increase in maximal oxygen consumption (VO2max) that accompanies growth and maturation in the human has been attributed in the main to appreciating muscle mass. During exercise, heart rate and cardiac output increase in the child as in the adult, but the heart rate in the child is greater and the stroke volume smaller. Furthermore, the arteriovenous difference in oxygen is greater in the exercising child than in the adult. Children also evidence a diminished blood pressure response to exercise. It seems that control of ventilation at exercise is the same in children as in adults, but exercise ventilation has been reported to be less efficient in the child. The young are less capable of regulating core temperature at exercise than adults and are more readily dehydrated. Very limited data suggest that muscle energy substrate storage and utilisation in children are such that they are less capable of anaerobic metabolism than adults. Generally, children respond to aerobic training as do adults, but such training in the first decade of life has been reported to have negligible effects. Blood lipid levels in children seem to be favourably influenced by persistent endurance activity. Ventilatory efficiency of children at exercise is augmented by aerobic training. Maximal values of ventilation and breathing frequency are increased in children and youth by endurance training. Conflicting data exist regarding the influence of training upon the child's vital capacity. Pulmonary diffusion capacity in well trained children has been seen to be greater than in untrained youngsters and many workers have reported increased VO2max as an outcome of endurance training. Limited data indicate that the nature of training may alter muscle fibre distribution in youthful athletes, and that muscle fibre hypertrophy can be induced in the young by means of strength and power training.(ABSTRACT TRUNCATED AT 400 WORDS)