Physiological properties of two antagonist human muscle groups.

The physiological features of two antagonistic muscle groups, the dorsiflexors (DF) and plantarflexors (PF) of the ankle, have been compared in 46 healthy subjects (31 men and 15 women) aged 19-65 years. The DF muscles, of which tibialis anterior (TA) was studied most thoroughly, had relatively small twitches, with moderately fast contraction and relaxation phases, and had marked post-activation potentiation; they were susceptible to fatigue during isometric exercise. The PF muscles had comparatively large twitches, with slow contraction and relaxation phases, and poor post-activation potentiation; they were more resistant to fatigue. Women differed from men in having smaller TA twitches and slower PF twitches; PF twitches were also slower in older subjects. The marked differences in physiological properties between DF and PF muscles contrasted with relatively modest histochemical differences found by ourselves and others.