Long-latency contributions to reciprocal inhibition during various levels of muscle contraction

Abstract

Reciprocal inhibition is a functional term and refers to the proportional decrease in antagonist motoneuron activity that accompanies an agonist contraction. A condition-test (C-T) H-reflex paradigm (conditioned stimulus applied to the common peroneal nerve; test reflex elicited by posterior tibial nerve stimulation) was used during: (1) rest, (2) a tonic isometric tibialis anterior (TA) contraction at 10% of its maximal voluntary contraction (MVC) and, (3) a TA contraction at 25% MVC. The purpose of the study was to assess whether or not long-latency contributions to reciprocal inhibition of soleus H-reflexes changed with increasing levels of TA contraction. C-T intervals ranged from 5 to 150 ms. Subjects (n=14) had long-latency inhibition at rest (x̄=−35.0±18.7%). This inhibition was enhanced during 10% (x̄=−46.1±17.9%; p=0.17) and 25% MVCs (x̄=−56.3±14.0%; p<0.01). Findings indicate that long-latency contributions to reciprocal inhibition of the soleus motoneuron pool are enhanced with increasing force of TA muscle contraction up to 25% MVC. These results indicate that long-latency contributions to reciprocal inhibition of soleus H-reflexes are not static but rather are task-specific and change in relation to levels of TA muscle activity.