Motor unit control strategies of knee antagonist muscles during constant force and linearly increasing isometric contractions

The motor unit control strategies of the quadriceps and hamstrings muscles were studied during two different types of isometric contraction (step-wise and ramp increasing) by means of the EMG power density spectrum median frequency. It was found that each muscle has different motor unit control strategies when acting as agonist and antagonist. In the agonist muscle, ramp type contractions resulted in recruitment up to 60% of the maximal voluntary force, whereas step type contractions showed evidence of median frequency increase up to 50% of maximum. Antagonist recruitment was found up to a higher force level in extension tasks. It was concluded that the role of each muscle and the particular type of task have an influence on the control strategy employed