Fat-free mass and fat mass in active boys during adolescence

Longitudinal body composition data were examined in 24 active and 10 control boys between the ages of 12.3 and 15.3 years. The main objectives were (1) to contrast the distance and velocity curves of fat-free mass (FFM) and fat mass (FM) in active and control groups using chronological and maturity bases, and (2) to compare the timing and magnitude of peak velocities in FFM and FM in relation to those of body mass. FFM was greater in active than control boys irrespective of whether data were aligned according to chronological age (CA), peak height velocity (PHV), or peak FFM velocity. When aligned on CA there was a tendency for FM to be greater in the control group. There were definitive adolescent spurts in body mass and FFM in both active and control groups. The spurt in FFM was significantly greater in active than control boys around the time of PHV (-0.5 to +0.5 yr PHV). Fat velocities declined in the active group and increased in the control group. The pooled data showed no significant differences in the ages at which peak velocities occurred in height, body mass, FFM, or FM. It was concluded that (1) the tendency for active boys to have a larger FFM and a smaller FM is influenced by increased physical activity, and (2) the ages at PFV and PFFMV occur at the same time as the age at PBMV, and that these events coincide with the age at PHV. Am. J. Hum. Biol. 9:617-627, 1997. © 1997 Wiley-Liss, Inc.