Exercise-induced amplitude modification of physiological action tremor of the ankle.

To determine whether exercise would affect physiological action tremor (PAT), normal male and female subjects exercised either by running or lifting weights. Surface electromyograms and acceleration recordings were analyzed using power spectral techniques to quantitate variations in amplitude and/or frequency of PAT. The results of this study show that running causes an increase in the amplitude of PAT. By having subjects run successively longer distances, a graded increase in amplitude of PAT was observed. After the subjects ran for long periods of time, PAT continued as an overt continuous oscillation. This oscillation did not greatly differ from pathological clonus. Furthermore, exercising the upper body alone by lifting weights increased the amplitude of PAT of the ankle. The results suggest that the exercise may cause alterations in the gain of the spinal reflexes which may lead to an underdamping of PAT. As the gain of the reflexes controlling PAT increases, this may lead to overt continuous oscillations, such as physiological or pathological clonus.