Vibratory facilitation of strength in fatigued muscle

OBJECTIVE: To assess the effects of tendon vibration on isometric torque and electromyographic activity of fatigued muscles. DESIGN: Subjects performed a 30-trial isometric (2-s maximal effort contractions alternating with 6-s rest periods) elbow extensor fatigue series. Three additional trials with the same work-to-rest ratio were then performed in which the triceps extensor tendon was subjected to a 60-Hz, 1-mm vibration during the rest intervals. SETTING: A biomechanics research laboratory. PARTICIPANTS: Thirteen healthy women without history of upper-extremity injury or neurologic disorder. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Elbow extension torque was measured with a load cell. Triceps and biceps brachii muscle activity was measured with surface electromyography electrodes. RESULTS: Elbow extension torque increased 10% (2 Nm) during the stimulation trials relative to the control trials (P<.05). The associated increase in mean peak-to-peak electromyographic amplitude was 47 % (103 microV) for the triceps brachii and 38% (33 microV) for the biceps brachii (all P<.05). The electromyographic frequency measures failed to reach the.05 probability level of significance. CONCLUSIONS: Elbow extension torque and triceps electromyographic activity were facilitated by tendon vibration of fatigued triceps in healthy subjects. This finding supports the use of proprioceptive feedback to facilitate voluntary muscle contractions.