Effects of local muscle vibration on plantarflexor strength and activation in individuals with chronic ankle instability: a randomized crossover trial.

BACKGROUND

Chronic ankle instability (CAI) is associated with neuromuscular impairments that increase reinjury risk. Although vibration can enhance neuromuscular function, the effects of local muscle vibration (LMV) in individuals with CAI are unknown. This study examined the immediate effects of LMV on plantarflexor strength and activation and whether stance position influences these responses.

METHODS

Twenty individuals with CAI (age, 21±2 years; 3±1 lifetime ankle sprains) participated. All participants met the inclusion criteria for CAI established by the International Ankle Consortium. Participants completed two separate sessions, each involving Pre Control, Post Control/Pre LMV, and Post LMV assessments. Maximal voluntary isometric contraction of the plantarflexor muscles during each assessment was used to calculate peak torque (PT), rate of torque development (RTD), and EMG amplitude. LMV was applied to the plantarflexor muscles in 1 of 2 randomized stance positions: 1) a mini-squat, or 2) a mini-squat with heels raised. LMV (2 g acceleration, 30 Hz frequency) was delivered in 6 sets of 60 seconds each, with 2 minutes of rest between sets. Paired t-tests evaluated pre-to-post changes in primary (PT and RTD) and secondary outcomes (EMG amplitude) following the control and LMV conditions. A two-way ANOVA compared changes between stance conditions.

RESULTS

LMV improved PT (P=0.035) and RTD (P=0.029) compared to the control condition. No significant changes were found for EMG amplitude or between stance conditions (P>0.05).

CONCLUSIONS

LMV acutely improves PT and enhances RTD across both stances, suggesting its potential as a targeted neuromuscular intervention for individuals with CAI.