Phase plane analysis of biarticular muscles in stepping

Abstract

Analysis of biarticular muscle activity was performed from phase plane diagrams of six subjects stepping over obstacles of three different heights. A videomotion analysis system was used to record kinematic data. Surface bipolar electrodes were used to record electromyographic (EMG) data from three biarticular muscles (i.e., rectus femoris — RF, biceps femoris — BF, and semitendinosus — ST muscles). Kinematic and EMG data of the swing portion of stepping were synchronized and combined to produce phase plane diagrams. Results indicate that there is a consistent muscle activation pattern in relation to movement kinematics. However, EMG bursts vary in amplitude and duration across trials and height conditions while kinematics remain relatively stable, although scaled up across height conditions. During the flexion phase, BF burst amplitude is positively related to maximum flexion velocity and obstacle height. During the extension phase no relationship is found between BF and RF burst amplitude, maximum extension velocity and obstacle heights. During the transition phase between flexion and extension, BF and RF muscles are relatively silent. Biarticular muscles appear to act as agonists on the distal joint and as antagonist on the proximal joint independently of joint position.