Twelve- to thirteen-year-old boys are more resistant to low-frequency fatigue than young men

The aim of this study was to compare low-frequency fatigue (LFF) after 100 drop jumps in boys (age = 12.7 +/- 0.7 years, mean SD) and men (age = 25.6 +/- 1.7 years). The force-generating-capacity test (FGCT) of knee extensor muscles was performed before the exercise, as well as 3 and 20 min after the exercise. Before exercise, men were stronger than boys, but twitch time characteristics did not differ between the groups. The 20:50 Hz torque ratio was similar in boys and men as well (0.71 +/- 0.08 and 0.73 +/- 0.08, respectively). After exercise, at 20 min of recovery, the 20:50 Hz ratio was depressed to 48.9 +/- 11.6% of initial in men and 74.5 +/- 10.0% of initial in boys (p <.05). There was no significant difference between boys and men in ground-reaction forces of drop jumps when the values were normalized to body mass. It is argued that intrinsic differences in the muscle-tendon complex are responsible for less severe LFF in boys compared with men.