Muscle fiber conduction velocity studied by the multi-channel surface EMG

Muscle fiber conduction velocity in single motor unit (MU) during voluntary contraction was measured by using the multi-channel surface EMG. The subjects examined were 28 normal controls (5-40 years old), four patients with myopathy and three patients with neuropathy. The tibialis anterior and the biceps brachii muscles were investigated at weak and moderate contraction levels. In normal muscles, the mean muscle fiber conduction velocity increased with muscle force (P less than 0.01). In three of four cases with myopathy, the conduction velocities were reduced compared to normal subjects (P less than 0.01), and there was little or no correlation between the conduction velocity and muscle force in myopathy. The conduction velocities were within the normal range in the muscles of patients with neuropathy. However, high-amplitude MUAPs with fast conduction velocities were detected during weak voluntary contraction in one case with neuropathy.