Growth trends of dynamic strength in adolescent boys. A 2-year follow-up survey

The present study aims to investigate the growth trends of dynamic torque during adolescence through a 2-year follow-up survey.

Concentric torque during elbow flexions and knee extensions at 3 constant velocities (1.05, 3.14, and 5.24 rad x sec(-1)) were determined year-by-year, i.e., 3 times (T1, T2, and T3), using an isokinetic dynamometer in 10 boys aged 12.7 to 13.5 years at the start of the study. In addition, the muscle thickness at the anterior sites of the upper arm and thigh were measured using a brightness mode ultrasound apparatus. For the two motions, torque output at 1.05 rad x sec-1 increased significantly year by year, but those at 3.14 and 5.24 rad x sec-1 did not show significant changes between T2 and T3.

The muscle thickness showed significant differences between T1 and T3 for the anterior upper arm and between T3 and either T1 or T2 for the anterior thigh. In both motions, the ratio of torque output at 1.05 rad x sec-1 to the product of muscle thickness squared and height was significantly higher in T2 and T3 than in T1. The corresponding ratios in elbow flexions at 3.14 and 5.24 rad x sec-1 were also significantly higher in T2 compared to T1, but those in the knee extensions did not show significant effects of age.

These results indicate that, for adolescent boys, 1) the age-related changes in dynamic torque at high velocity contractions differ from those at slow velocity contractions, and 2) the growth rate of dynamic torque at slow velocity contractions exceeds that of muscle size in the earlier stage of adolescence.