Cross spectral analysis of the force and surface electromyographic signals for examining steadiness following different exercise interventions

The purpose of the present study was to compare potential changes in the force/surface EMG cross spectrum following concentric versus eccentric exercise. Twenty-six healthy, college-aged men (mean +/- SD age = 24.0 +/- 3.7 yrs) performed submaximal isometric muscle actions at 60% of the maximum voluntary contraction of the dominant (exercised) and non-dominant (non-exercised) forearm flexors before (PRE) and immediately after (POST) concentric and eccentric exercise. The concentric and eccentric exercise interventions were randomly ordered and performed on days separated by at least 48 h of rest. Both interventions required the subjects to perform six sets of ten maximal muscle actions with the dominant forearm flexors. The surface EMG signal was detected from the biceps brachii of both the dominant and non-dominant limbs during the PRE and POST submaximal contractions. The surface EMG and force signals were selected from the middle six seconds of each contraction. The signals were then analyzed for amplitude and frequency content, and the surface EMG/force cross spectrum was calculated. The total power present in the cross spectrum, as well as the cross spectrum's mean frequency (MNF) were also determined. There were distinct changes in cross spectral power that were dependent on the limb and/or exercise intervention. Cross spectral power increased following both exercise interventions, but the increase was greater for the dominant than the non-dominant limb. In addition, cross spectral MNF increased for both limbs following the concentric exercise, but decreased after the eccentric exercise. These findings indicated that the cross spectral power and MNF responses were dependent on the limb that was exercised and the type of exercise intervention that was performed.