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

Heart diameters, heart volume (HV), PWC ₁₃₀, \(\dot V\) O₂ 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, PWC ₁₃₀, \(\dot V\) O₁₃₀, and exercise HR, \(\dot V\) O₂/HR, \(\dot f\) and SBP change significantly with age. On the other hand, HV·kg⁻¹ and work \(\dot V\) O₂, \(\dot V\) _E and \(\dot V\) _E/ \(\dot V\) O₂ 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 body weight, while about 70% of the variation in light submaximal working capacity ( \(\dot V\) O₁₃₀) can be explained by HV alone. Holding age, height and body weight constant by partial correlation procedures yields significant relationships between HV and \(\dot V\) O₁₃₀ (r = 0.461), and between HV·kg⁻¹ and \(\dot V\) O₁₃₀ (r = 0.414). Age, height, weight and size of the heart correlated simultaneously against \(\dot V\) O₁₃₀ 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 capacity during growth, and would probably yield a more conservative estimate of the relationship between the size of the heart and submaximal working capacity during growth.