Cardiopulmonary adjustment and metabolic response to maximal and submaximal physical exercise of boys and girls at different stages of maturity

Cardiopulmonary and metabolic variables were investigated at maximal and submaximal bicycle ergometer exercises in 41 swimmers of both sexes, 8--18 years old. VO2 max and VO2 max . HR-1 were higher in boys than in girls and increased with maturity, while VO2 max. kg-1 and HVE were not influenced by this. The HV increased clearly during this growth period, the pubertal and postpubertal subjects showing 16 and 17% higher values for HV and HV . kg-1 than those reported in normal schoolchildren populations. During the submaximal exercise at 70% VO2 max the highest HR values were found in the prepubertal group, whilst the lowest were observed in the postpubertal subjects. These findings suggest that a given percentage of VO2 max as a reference unit, is more reliable than a certain HR to obtain comparable results in subjects with different ages. Blood samples were collected before, during, and after the submaximal exercise. Blood glucose and FFA did not differ in relation to the stages of maturity. During exercise, insulin decreased in prepubertal children, did not alter in pubertal adolescents, and increased in postpubertal subjects. The lactate concentration, during exercise, increased in relation to maturity. The same results were found for HGH, but no differences were found with regard to sex. Since the pattern of HGH secretion during exercise is similar to that found after arginine and insulin administration it is assumed that the same mechanism (i.e., sex hormones) triggers the HGH release.

Submaximal working capacity, heart size and body size in boys 8-18 years

Heart diameters, heart volume (HV), PWC130, VO2 at 130 heart rate, and cardiorespiratory reactions during work at 3 kgm-s-1 were obtained in 237 boys ranging in age from 8--18 years. Results indicate that heart size, PWC130, VO130, and exercise HR, VO2/HR, f and SBP change significantly with age. On the other hand, HV - kg-1 and work VO2, VE and VE/VO2 remain rather stable throughout the growth period. Correlation analysis indicates that about 85% of the observed variation in the size of the heart during growth can be accounted for by the body weight, while about 70% of the variation in light submaximal working capacity (VO130) can be explained by HV alone. Holding age, height and body weight constant by partial correlation procedures yeilds significant relationships between HV and VO130 (r = 0.461), and between HV - kg-1 and VO130 (r = 0.414). Age, height, weight and size of the heart correlated simultaneously against VO130 account for 75% of the variance in the dependent variable. It would seem important to suggest the need for study of the interactions between age, size and maturity, in addition to indicators of size and efficiency of the oxygen delivery system, and indices of muscle oxygen utilization efficiency. Such an approach will permit a more definite partitioning of the variance in submaximal aerobic capicity during growth, and would probably yeild a more conservative estimate of the relationship between the size of the heart and submaximal working capacity during growth.