Age effects on reflex and postural responses to propriomuscular inputs generated by tendon vibration.

The effects of aging on two sensorimotor levels of propriomuscular function were investigated in a young (20- to 44-year-old) and an elderly (60- to 86-year-old) population by eliciting segmental reflex and postural responses via the same muscle spindle inflow generated by applying the same pattern of tendon vibration. The latency and amplitude of the reflex responses to vibration (tonic vibration reflex) of the biceps and triceps brachii did not depend on the subjects' age. No major age-related changes were observed in the deep reflexes of the lower limbs. The postural responses to the same vibratory stimulation applied to both the soleus or the tibialis anterior muscles (vibration-induced falling) did not show any changes in latency depending on either age or the visual conditions, whereas the intensity of these responses decreased both with age and when the use of vision was possible. Our results suggest that the two levels at which the same propriomuscular messages were processed are differentially affected by aging. The lower reflex level does not undergo any noticeable impairment, whereas the higher postural control level deteriorates in the elderly, which might be partly responsible for the balance problems which tend to occur more frequently with advancing age.