Quantification of peripherally induced reciprocal activation during voluntary muscle contraction

A new method was developed to compare patterns of coactivation and reciprocal activation of antagonistic muscles during different experimental conditions. Pure coactivation was defined as a muscle activity pattern where there was never a difference between the slope of the agonist EMG record and the slope of the antagonist EMG record. The degree of reciprocal activation was defined as being proportional to the average absolute value of the difference between these two slope values. Use of this method for the comparison of muscle activity patterns during isometric contractions and unexpected movements showed that peripheral input related to agonist unloading and antagonist stretch significantly increased reciprocal activity.