To investigate the effects of joint position and effort level of antagonist contraction on reciprocal inhibition, experiments with 15 healthy volunteers were performed to compare the changes of standardized soleus H reflex during dorsiflexion contraction (0%, 25%, 50%, 75% maximal voluntary contraction [MVC] associated with different ankle positions (plantarflexion 20°, neutral, and dorsi-flexion 20°). The results indicated that a decrease of the soleus H response was dependent on the level of prefibial contraction, but a significant interaction of ankle position and pretibial contraction was noted (p ≤ .05). Post hoc analysis suggested that progressive H-amplitude decrement as the pretibial contraction increased was especially significant in the plantar-flexed position, but not in the dorsiflexed position. In contrast to H-reflex amplitude, standardized intrasubject variances of the H amplitude (Hvar/Hmean) significantly increased with pretibial dorsiflexion (p < .05), but neither with the ankle position nor interaction effect (p > .05). These findings suggest that progressive reciprocal inhibition was position relevant pertaining to joint stability as well as force variability.
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