Surface vs. fine-wire electrode ensemble-averaged signals during gait

Dynamic electromyography (EMG) utilizes either surface or fine-wire intramuscular electrodes. Ensemble-averaging of EMG profiles provides a convenient and commonly performed way to analyse these signals. This study was designed to evaluate the similarities of ensemble-averaged profiles of the two electrode types. We studied two muscles, the right vastus medialis (VM) and the left biceps femoris (BF), at freely-selected speeds of walking and jogging on a treadmill. Both electrodes were simultaneously attached to the subjects' legs. EMG signals were conditioned to produce linear envelopes. Pearson's correlation coefficients (r) and variance ratios (VR) were determined to assess the degree of similarity in the EMG profiles and the repeatability of the muscle activity, respectively. The ensemble-averaged signals reflect a high degree of pattern similarity as evidenced by high r values (usually greater than 0.90) for both muscles at both speeds. The low mean VRs indicate reasonable reproducibility for both electrode types; fine-wire electrodes in the BF and VM exhibit similar variability to surface electrodes. For the purpose of establishing relative profiles of activation during gait, ensemble-averaged surface and fine-wire signals are closely equivalent.