Antagonist muscle activity during stretching: a paradox re-assessed

The purpose of this investigation was to examine and compare the simultaneous electromyographic activity from surface and implanted wire electrodes of an antagonist pair of muscles during a reversal stretching technique. Previous studies reported increased electromyographic activity of a muscle being stretched during antagonist muscle activation. Five male subjects performed a stretching method which consisted of active plantarflexion, followed by active dorsiflexion. Adjacent surface and implanted wire electrodes were applied to the soleus and tibialis anterior muscles. Comparison of the surface electrode recordings showed apparent cocontraction during dorsiflexion. However, no activity was observed on the soleus wire electrode trace during the dorsiflexion phase of the stretching method. Power spectral analysis showed a significant (P less than 0.001) frequency shift between plantarflexion (91.9 V2.Hz-1) and dorsiflexion (66.1 V2.Hz-1) from the surface electrode recordings. Cross-correlation between tibialis anterior and surface soleus activity during dorsiflexion provided strong evidence that the apparent electromyographic soleus signal originated in the tibialis anterior muscle with an average of 8.7 ms delay of the surface soleus signal. Although not generalizable to other studies, it was concluded that in this study the tracings from the surface electrodes, which gave the appearance of co-contraction between antagonist muscles, were actually cross-talk between the electrodes. The rationale for antagonist contraction during stretching in order to inhibit contraction of the muscle being stretched is supported with this evidence and is consistent with those studies which show greater range of motion gains using the reversal technique.