The effects of aging on physiological properties of fast and slow twitch motor units in the rat gastrocnemius.
The mechanical properties of individual motor units were studied in the medial gastrocnemius of old (26-30 months) rats anesthetized with urethane and chloralose. The data were compared with results from motor units in the same muscle of middle-aged (11-14 months) rats. In the old rats there was a significant increase in mean tetanic tension for type S (slow twitch) units, whereas there was a slight decrease for type F (fast twitch) units. Twitch contraction time after maximum post-tetanic potentiation was shortened in type F units, but not in type S units. Conduction velocity of motor axons decreased in both unit types, but more marked change was found in type F units. These findings suggest the differential effects of aging on type F and type S motoneurons.
D000375:Aging; D000818:Animals; D004576:Electromyography; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction; D009132:Muscles / Q000294:innervation / Q000502:physiology*; D009929:Organ Size; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000502:physiology; D009435:Synaptic Transmission