Effect of Focal Muscle Vibration on Calf Muscle Spasticity: A Proof-of-Concept Study

Abstract

Background: Focal vibration has been studied for its ability to reduce spasticity in patients with upper motor neuron lesions, but adequate stimulation parameters remain unclear. Focal muscle vibration with adequate parameters may facilitate gait rehabilitation in patients with lower limb spasticity. Objective: To determine focal muscle vibration parameters that effectively inhibit the H-reflex of the gastrocnemius in healthy subjects. Design: A proof-of-concept exploratory study. Setting: University hospital laboratory. Subjects: Thirteen healthy volunteers. Methods: Focal muscle vibrations of 40, 80, and 120 Hz and amplitudes of 0.1, 0.3, and 0.5 mm were tested on the calf muscles of 10 healthy subjects, respectively. The H-reflex and M-response were recorded baseline, during vibration, and after vibration for each stimulation parameter. The mean vibratory inhibition index (VII) during vibration, the maximum amplitude of the H-reflex and M-response (H-max and M-max), minimal onset latency of the H-reflex, and the ratio of H-max to M-max (HMR) at each time point were measured. Results: No significant difference was found among mean VIIs at 40, 80, and 120 Hz in the healthy subjects. However, a relatively consistent reduction of H-max and HMR was observed at 80 Hz. Mean VI&apos;s at 0.3 and 0.5 mm were significantly lower than that at 0.1 mm (P < .001). Conclusion: This study suggests that focal muscle vibration may be an adjuvant therapy during gait rehabilitation in patients with calf muscle spasticity. Focal vibration at 80 Hz and 0.3 mm amplitude applied to the gastrocnemius effectively inhibits the segmental reflex pathway. A future clinical trial on this topic is warranted.