Changes with age in monosynaptic reflexes elicited by mechanical and electrical stimulation.

Absence of the achilles tendon reflex (T) has been reported to increase with age. Other investigators have reported no age relationship. Age changes in the Hoffmann reflex (H) have been examined in only one recent investigation. It was our purpose to compare the T and H reflexes of healthy, active old (n = 20) against young (n = 20) subjects using methods which provide stimulus-response data for both T and H. We also compared the age differences of H against T to estimate fusimotor involvement in age changes. No significant age difference were found in the response:stimulus ratio for T. Amplitude of H responses were 32.7 percent smaller in the old (P less than 0.04) and M waves were smaller by 24 percent (P less than 0.025). No significant age difference was found between mechanically and electrically elicited reflexes; and, therefore, our data do not support fusimotor involvement in the age changes of monosynaptic reflexes.