Inhibitory Effects of Prolonged Vibratory Stimulus on the Maximal Voluntary Contraction Force and Muscle Activity of the Triceps Brachii: An Experimental Study.

ABSTRACT

OBJECTIVE: The purpose of this study was to quantify the effects of prolonged vibratory stimulus on the maximal voluntary contraction (MVC) force and muscle activity of the triceps brachii and to clarify the effective stimulus time. METHODS: Twenty-five healthy volunteers with a mean age of 21.4 years participated. A vibratory stimulus at 86 Hz was applied to the triceps brachii tendon for 5 and 10 minutes. Before and after these stimuli, the elbow extension MVC force was measured using a handheld dynamometer. Muscle activities of the lateral, long, and medial heads of the triceps brachii were also recorded by surface electromyography. RESULTS: The median MVC force significantly decreased to 82.7% after 5 minutes of vibratory stimulus and to 83.3% after 10 minutes of vibratory stimulus (P < .001). The median percentage of integrated electromyography of the triceps also significantly decreased to 78.2 (lateral head), 83.8 (long head), and 81.5 (medial head) after 5 minutes of vibratory stimulus and to 77.7, 81.4, and 77.2, respectively, after 10 minutes of vibratory stimulus (P < .001). There were no differences in the decrease in the MVC force and median percentage of integrated electromyography between 5 and 10 minutes of vibratory stimulus (P > .05). CONCLUSION: Prolonged vibratory stimulus (5 minutes) to the triceps brachii tendon appeared to have an inhibitory effect on MVC force and muscle activity. The present results suggest that prolonged vibratory stimulus could be an effective treatment capable of reducing muscle tonus of the triceps brachii.