Maximal and minimal motor nerve conduction velocities determined by a collision method: correlation with axonal conduction velocity of type-identified motor units.

Maximal and minimal motor nerve conduction velocities of the medial gastrocnemius (MG) muscle nerve were measured by a new collision method in 20 rats of 8-9 weeks of age; the rate of tension increase produced by the muscle was also recorded. Single motor unit analysis in the other 20 rats obtained axonal conduction velocity and contractile properties of type-identified MG motor units. Comparison of the data from these experiments revealed that the maximal and minimal motor nerve conduction velocities obtained by this collision method were most likely to be the axonal conduction velocity of fast-twitch and slow-twitch motor units, respectively. Therefore, these motor nerve conduction velocities in man may also be used as functional parameters of human fast-twitch and slow-twitch motor units, respectively.