Longitudinal changes in maximal oxygen uptake in adolescent girls and boys with different training backgrounds.

The purpose of this study was to investigate the effects of high-volume endurance training on the development of maximal oxygen uptake (VO2max ) in physically active boys and girls between the ages of 12 and 15 years, using a longitudinal design. The children participated in organized training in sports clubs for an average of 7-10 hours per week, with one group undertaking a high volume of endurance training (~7 hours per week; End boys, n = 23 and End girls, n = 17) and the other group having a primary focus on technical and tactical skill development, undertaking low volumes of endurance training (~1.6 hours per week; non-End boys, n = 29 and non-End girls, n = 9). VO2max and anthropometrics were assessed at age 12, 13, and 15. At age 12, VO2max was 58.9 (5.6), 65.5 (7.2), 56.5 (6.5), and 58.8 (7.9) mL·kg-1 ·min-1 in End girls, End boys, non-End girls, and non-End boys, respectively. Over the three years, there was no difference between the training groups in the development of VO2max independent of scaling. In boys, VO2max relative to body mass (BM) did not change from age 12 to 15, while VO2max tended to decrease relative to fat-free mass (FFM). In girls, VO2max relative to BM decreased slightly from age 12 to 15, with no changes over the years relative to FFM. The present longitudinal study suggests that in growing active children during puberty, high volumes of systematic endurance training do not have an additional effect on VO2max compared with similar volume of training mainly aiming at developing motor skills.

Longitudinal Training-related Hematological Changes in Boys and Girls from Ages 12 to 15 yr.

PURPOSE: Natural growth and maturation cause hemoglobin mass (Hbmass) and blood volume (BV) to increase during childhood and adolescence. Whether endurance training during the same period can cause further increases in these variables is not clear. Also, body composition develops differently in girls and boys during puberty, and the effect of these differences on hematological variables has not been previously studied. METHODS: Forty-two endurance athletes (End group; 24 boys) and 34 athletes from other sports (non-End group; 23 boys) were tested at ages 12, 13, and 15 yr for Hbmass, BV, plasma volume (PV), red cell volume (RCV), hematological variables, and anthropometrics. RESULTS: At age 12 yr, Hbmass and BV showed no difference between sexes and training groups in absolute values or relative to fat-free mass (FFM). Relative to FFM, Hbmass and BV averaged 11.7 (0.8) g·kg and 95 (6.8) mL·kg. Increases in FFM from ages 12 to 15 yr primarily determined the increased Hbmass and BV for both sexes with no differences between training groups. At age 15 yr, Hbmass relative to FFM was higher in boys than girls, 13.1 (0.8) g·kg and 12.1 (0.9) g·kg (P < 0.001), whereas BV relative to FFM was not significantly different between sexes and training groups at any ages, averaged 100 (6.7) mL·kg at age 15 yr. Relative to FFM, PV was higher in the End group at all ages, and RCV was, on average, lower and increased less compared with non-End group. CONCLUSION: Our results indicate that increases in Hbmass during puberty are mainly associated with increased FFM and independent of sex or volume of endurance training.However, the FFM-relative PV was higher and the FFM-relative RCV was lower in the End group compared with the non-End group.