M. Pensini – A. Martin – N. A. Maffiuletti

Introduction The modifications induced by an eccentric training can be attributed to both peripheral factors (e.g. contractile changes) and/or central factors (e.g. neural adaptations) (Colson et al. 1999). The peripheral changes could be essentially expressed by a selective adaptation of the fast twitch motor units, which are preferentially solicited during eccentric actions. The central factors were instead related to a modification of the electromyographic (EMG) activity of the agonist (Häkkinen 1983 and 1985), but also of the antagonist muscles (Carolan and Cafarelli 1992). A method used to distinguish central vs. peripheral adaptations consists of recording the mechanical and electrophysiological responses obtained under voluntary and electrical stimulation on the motor nerve. This method induces muscle contraction with no influence from central factors, therefore providing information concerning the peripheral origin of adaptations by the analysis of muscle excitation-contraction coupling and contractile kinetics. The aim of the present investigation was to study the effects of an eccentric training performed over a 4-wk period, on the plantar-flexor nervous and muscular properties. In order to differentiate the relative contribution of central and peripheral adaptations to potential torque gains, the torque and the EMG activity of agonist and antagonist muscles were recorded during maximal voluntary contractions and during electrical stimulation of the motor nerve.