Plasma volume and intravascular protein masses in trained boys and fit young men.

Plasma volumes and intravascular protein masses were measured in eight well-trained boys (VO2 max = 59.6 +/- 6.5 ml/kg body wt) aged 13-15 yr and compared with two groups of adult athletes aged 17-20 yr (VO2 max = 61.8 +/- 3.4 ml/kg body wt) and 24-30 yr (VO2 max = 63.3 +/- 4.1 ml/kg body wt), respectively. The trained boys had larger plasma volumes and increased intravascular masses of albumin and hepatogenic globulins as compared with values available for children with normal physical activity. There was no significant difference between the boys and the adults concerning maximal oxygen uptake, plasma volume, albumin, immunoglobins, and haptoglobin, when allowance was made for differences in body dimensions; probably due to the young age, however, the boys had considerably higher relative alpha2-macroglobulin and transferrin masses. Endurance training apparently elicits the same response of the plasma protein system regardless of age, at least after pubertal age has been attained. The overall effect of these changes implies an increase of the water binding capacity of the plasma