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.