Control strategies of the elbow antagonist muscle pair during linearly and stepwise increasing contractions

The myoelectric signals from the biceps brachii and triceps brachii were recorded during stepwise and linearly increasing flexion and extension. The power density spectrum of each signal was determined for different force levels and the median frequency was calculated to track the average conduction velocity, which in turn reflects motor unit recruitment or de-recruitment, and thereby the control strategy of each muscle. The results suggest that muscles do change their control strategy for ramp and step contractions. The triceps as antagonist recruits motor units up to higher levels during step contractions than during ramp contractions. The biceps as antagonist de-recruits motor units up to higher force levels during ramp contractions than during step contractions.