EMG power spectrum shifts of biceps brachii when acting as an antagonist

EMG power spectrums of biceps brachii (BE) and triceps brachii (TB) when acting as antagonists were obtained during linearly increasing force ramp contractions. Mean BB median frequency (MF) shifted downward with increasing force levels up to 100% maximal voluntary contraction (MVC), possibly indicating a derecruitment of BB motor units. Polynomial regression between signal to noise ratios (SNRs) and MFs [r=0.94] of BB showed that at low force levels (10-40% MVC) large MF shifts are associated with a short range of small SNRs. This suggests that the initial large MF values of BB may be due to the high frequency content of heat noise and that the previously proposed derecruitment of motor units might not be solely responsible for the initial MF decrease.