AGE EFFECTS ON REFLEX AND POSTURAL RESPONSES TO PROPRIOMUSCULAR INPUTS GENERATED BY TENDON VIBRATION

The effects of aging on two sensorimotor levels of propriomuscular fun ction were investigated in a young (20- to 44-year-old) and an elderly (60- to 86-year-old) population by eliciting segmental reflex and pos tural responses via the same muscle spindle inflow generated by applyi ng the same pattern of tendon vibration. The latency and amplitude of the reflex responses to vibration (tonic vibration reflex) of the bice ps and triceps brachii did not depend olt the subjects' age. No major age-related changes were observed ill the deep reflexes of the lower l imbs. The postural responses to the same vibratory stimulation applied to both the soleus or the tibialis anterior muscles (vibration-induce d falling) did not show any changes in latency depending on either age or the visual conditions, whereas the intensity of these responses de creased both with age and when the use of vision was possible. Our res ults suggest that the two levels at which the same propriomuscular mes sages were processed are differentially affected by aging. The lower r eflex level does not undergo any noticeable impairment, whereas the hi gher postural control level deteriorates in the elderly, which might b e partly responsible for the balance problems which tend to occur more frequently with advancing age.