Senescence and Deep Tendon Reflex: An Analysis
With increasing age, various changes occur in the human nervous system. These structural and functional changes may result in a number of neurologic signs commonly found during the examination of elderly people. Often such signs occur in the absence of any discernable neurological disease. For this reason, they are usually attributed entirely to advanced uncomplicated aging, or senescence.
Reflex testing is considered the "premier objective measure of nervous system integrity" (2:28). Moreover, it has been observed that reflex findings may change with normal aging.
A number of authors, for example, have found that a reduction or loss of the ankle jerk is a normal result of aging (2:28). Furthermore, research has suggested that the incidence of absent ankle jerks rises steadily with advancing age (1:71). One proposed explanation for the areflexia is elongation of the Achilles tendon due to shortening of the muscle (1:71).
These studies, however, have not all been in complete accord (1:71). Jenkyn and Reeves (1981) note a high degree of variation in the frequency of observed normal responses (2:29). This they attribute to factors such as different study populations, experimental methods, etc. (2:28).
DeVries et al. (1985) suggests that this variability might be caused by differences in the activity history of the subjects tested (1:71). Considerable evidence supports the hypothesis that "usage leads to increased functional efficiency of synapses and disuse to defective function" (1:71 72).
The researchers tested forty healthy subjects: ten young males, ten young females, ten old males, and ten old females (1:72). Older subjects were chosen whose physical activity history was similar to that of the younger subjects (1:72).
Each subject underwent mechanical (hammer drop) stimulation of the Achilles tendon reflex (T) and electrical stimulation of its a...