Conduction velocity along muscle fibers in situ in healthy infants.

The muscle fibers of the biceps brachii were stimulated distally with low voltages by means of two monopolar needles in twenty-two infants aged 2 to 14 years. The electrical activity was recorded proximally by means of a SFEMG electrode. Conduction velocity of the muscle fibers (MFCV) in situ calculated with this method had a bimodal distribution in the youngest individuals of less than 4 years, and a Gaussian distribution in children aged 5 to 14 years. Propagation velocity along muscle fibers increases with children's age and is significantly slower than in adults, in good correlation with the shorter limb perimeter and with the significantly smaller fiber diameter found in muscle biopsies in infancy. The latency of the evoked potentials was linearly related with the distance between stimulating and recording points, and muscle activity and propagation velocities were the same before and after curarization, that is consistent with the reliability of the method in infancy.