On-line measurement of muscle fibre conduction velocity: analysis and optimization of performance

Measurement of the average muscle fibre conduction velocity from surface electromyographic signals has important applications in the study of muscle fatigue and in ergonomics. In this paper, a two-channel hardware polarity correlator (which estimates 256 correlation coefficients per channel at a sampling rate of 18.58 kHz) and a specially designed surface electrode unit, are used to investigate various factors affecting the measurement reliability: electrode dimensions; EMG preprocessing to make the estimated correlation function more suitable for time delay measurement; and the manner in which velocity estimates, measured simultaneously from two different sections of the same muscle, are related. All the tests were performed on the biceps brachii when under medium tension; some tests involved tensions which led to muscle fatigue. Results showed that smaller electrode dimensions (i.e. smaller electrode units) and EMG preprocessing to increase its effective bandwidth, give more reliable measurements. Further, it was found that the estimated mean velocity is dependent on the location of the electrode unit on the muscle, and that at certain locations no reliable estimates can be obtained. The preliminary results obtained with muscle fatigue indicate that the estimated conduction velocity decreases, but not uniformly, across the muscle.