An Examination of Patellar Tendon Reflex Pre-Motor Conduction Velocity across the Adult Lifespan

Abstract

It is known that aging is accompanied by a loss in muscle mass and motor units. However, the direct cause for the loss of motor units has not been identified. One possible mechanism could be related to changes in the sensory input motor neurons receive. Therefore, it is important to find objective measures to quantify sensory function that are sensitive to changes with aging. PURPOSE: To determine if the conduction velocity of a patellar tendon reflex is sensitive to aging. METHODS: One hundred and one volunteers participated in this study. Tendon taps were delivered to the patellar tendon of each subject while surface electromyographic (EMG) signals were recorded from the rectus femoris. The pre-motor reflex latency was calculated as the time from the onset of the hammer-strike to the onset of EMG activity. This latency (s) was adjusted for femur length (m) to instead provide a pre-motor conduction velocity (CV; m/s). The subjects were then grouped and averaged into intervals based on age as follows: 18 - 29 yrs. (n = 50), 30 - 39 (n = 10), 40 - 49 (n = 6), 50 - 59 (n = 16), 60 - 69 (n = 13) and > 70 (n = 6). Linear regression was applied across the mean age and pre-motor CV from each interval. RESULTS: Pre-motor CV was negatively related to age (r = - 0.799; p = 0.028). The resulting regression equation was y = -0.1113x + 24.216. The group averaged data as well as the line of best fit are shown in the figure below. CONCLUSION: Our findings show that the conduction velocity of a patellar tendon reflex is significantly related to age. Therefore, this variable may be useful in future studies that wish to track changes in sensory function across age.Figure