Influence of Velocity on Agonist and Antagonist Activation in Concentric Dorsiflexion Muscle Actions

Five women and 5 men performed maximal isometric and concentric dorsiflexion actions on an isokinetic dynamometer. The concentric actions were done at 10 preset velocities ranging from 0.26 to 5.23 rad∙s−1. Electromyographic (EMG) recordings were made from one agonist (tibialis anterior [TA]) and two antagonists (saleus [S], lateral gastrocnemius [LG]). The men produced greater absolute torque than the women, but there was no gender difference in the torque/body mass ratio. The shape of the torque-velocity relation was similar in men and women and approximated, but did not match, that obtained in animal preparations or in human studies using electrical stimulation. Agonist TA activation (integrated EMG/movement time) decreased with increasing velocity over the same range of velocities as torque. Antagonist S, but not LG, activation also decreased. The S/TA activation ratio was greater in men than women. In men the S/TA ratio tended to be greater than the LG/TA ratio, whereas the converse was true for women. These data indicate that velocity influences the relative activation of two antagonists in maximal dorsiflexion muscle actions, and that there is an apparent gender difference in the relative activation of two antagonists. Key words: torque-velocity relation, coactivation, electromyography