MOTOR UNIT FIRINGS DURING VOLUNTARY ISOMETRIC RAMP AND BALLISTIC CONTRACTIONS IN HUMAN VASTUS MEDIALIS MUSCLE

Intra-muscular electromyographic (EMG) signals in vastus medialis muscle were decomposed into their constituent motor unit action potential trains using a specially designed quadrifilar wire electrode during voluntary isometric ramp and ballistic contractions. Five male adults participated in our experiments as subjects and performed ramp trapezoidal, ramp triangular, and ballistic contractions. By using a newly developed wire electrode, intra-muscular EMG signals were successfully decomposed into the individual motor unit action potential trains. The firing behaviors analyzed by the decomposition technique were consistent with previous studies on small muscles. This new quadrifilar wire electrode is potentially a useful tool for detecting intra-muscular electromyographic signals in large limb muscles such as the vastus medialis