Measurement of muscle fiber conduction velocity in humans: techniques and applications.

Different methods of measuring human muscle fiber conduction velocity (MFCV) are outlined. A major division can be made between invasive (needle) and noninvasive [surface electromyographic (EMG)] recording techniques. The benefits and limitations associated with the different approaches are discussed. The conduction velocity of individual muscle fibers are measurable with needle recordings on routine EMG apparatus. Velocities measured with electrical stimulation of single fibers or bundle of fibers are in general lower than recordings made during voluntary contraction. With surface EMG, an average estimate of the MFCV from many fibers and motor units can be determined with computerized data analyses--both frequency and time domain approaches. The cross-correlation method is widely used to calculate the time lag between two EMGs recorded along the muscle. Using the surface EMG-based methods, MFCV can be calculated at all contraction levels. Thus, the change in sarcolemmal function during local muscle fatigue can be assessed. Physiological factors influencing the MFCV and the utility of the MFCV estimation in clinical practice are discussed. Compared to nerve conduction velocity studies, the clinical interest in MFCV has been limited.