Twitch contraction properties of plantar flexor muscles in pre- and post-pubertal boys and men.

This study compared electrically evoked twitch contraction characteristics of the plantar flexor muscles in pre-pubertal (11-year-old) and post-pubertal (16-year old) boys, and young (19- to 23-year-old) men. The posterior tibial nerve was stimulated by supramaximal square-wave pulses of 1 ms duration at rest and after brief (5 s) isometric maximal voluntary contraction (MVC) of the plantar flexor muscles, i.e. during postactivation potentiation. Men had higher MVC force than boys and post-pubertal boys higher than prepubertal boys. Pre-pubertal boys had lower peak twitch forces (P(t)) at rest and when potentiated compared with post-pubertal boys and men, whereas no significant differences were found between post-pubertal boys and men. Pre-pubertal boys had higher ratios of P(t) at rest and potentiated P(t) to MVC force than post-pubertal boys and men. No age-related differences were obtained in post-activation potentiation, rest and potentiated twitch contraction and half-relaxation time, and MVC force relative to body mass. The main findings of the study were that puberty is characterized by increased muscle force-generating capacity with no change in twitch potentiation and time-course characteristics, and that twitch force-generating capacity develops in an adult-like pattern after puberty.