The acute effects of local muscle vibration frequency on peak torque, rate of torque development, and EMG activity

Purpose: Vibratory stimuli enhance muscle activity and may be used for rehabilitation and performance enhancement. Efficacy of vibration varies with the frequency of stimulation, but the optimal frequency is unclear. The purpose of this study was to examine the effects of 30 Hz and 60 Hz local muscle vibration (LMV) on quadriceps function. Methods: Twenty healthy volunteers (age = 20.4 +/- 1.4 years, mass = 68.1 +/- 11.0 kg, height = 170.1 +/- 8.8 cm, males = 9) participated. Isometric knee extensor peak torque (PT), rate of torque development (RTD), and electromyography (EMG) of the quadriceps were assessed followed by one of the three LMV treatments (30 Hz, 60 Hz, control) applied under voluntary contraction, and again immediately, 5, 15, and 30 min post-treatment in three counterbalanced sessions. Dependent variables were analyzed using condition by time repeated-measures ANOVA. Results: The condition x time interaction was significant for EMG amplitude (p = 0.001), but not for PT (p = 0.324) or RTD (p = 0.425). The increase in EMG amplitude following 30 Hz LMV was significantly greater than 60 Hz LMV and control. Conclusions: These findings suggest that 30 Hz LMV may elicit an improvement in quadriceps activation and could be used to treat quadriceps dysfunction resulting from knee pathologies. (C) 2014 Elsevier Ltd. All rights reserved.