Focal vibration of quadriceps muscle enhances leg power and decreases knee joint laxity in female volleyball players

ABSTRACT Aim: This double-blind randomized controlled study aims at determining the effect of repeated muscle vibration (rMV) on explosive and reactive leg power and on knee laxity of female volleyball players. Methods Eighteen voluntary volleyball athletes, belonging to the same senior regional level team (age = 22.7 ± 3 years, height = 1, 803 ± 5 m, mass = 64 ± 4 Kg) were assigned to 3 groups (N= 6) for vibration on contracted quadriceps (VC), vibration on relaxed muscle (VR), and sham vibration (NV) respectively. Intervention consisted in 3 rMV sessions performed in 3 consecutive days. In each session, 100Hz, 300–500 μm amplitude vibratory stimuli were bilaterally delivered to the quadriceps in three consecutive 10-minutes applications. Explosive and reactive leg power and knee joint laxity were evaluated 1 day before, and 1, 30, and 240 days after intervention. Results In VC group, explosive and reactive leg power increased respectively by ~16% and ~9% at 1 day, by ~19% and ~11% at 30 days and by ~26% and ~13% at 240 days, concomitantly knee laxity decreased by ~6%, ~15% and ~18% at the same times. These changes were significantly larger than in the other groups, in which leg power increment and knee joint laxity reduction remained close to ~3%, ~5% and ~10% at 1, 30 and 240 days respectively. Conclusions Combined bilateral voluntary contraction and rMV of the quadriceps muscles is a short-lasting, non-invasive technique that can significantly and persistently improve muscle performance and knee laxity in volleyball women players.