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

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=180.3 +/- 5 cm, mass=64 +/- 4 kg) were assigned to three 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 gm 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 similar to 16% and similar to 9% at 1 day, by similar to 19% and similar to 11% at 30 days and by similar to 26% and similar to 13 % at 240 days, concomitantly knee laxity decreased by similar to 6%, similar to 15% and similar to 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 similar to 3%, similar to 5% and similar to 40% at 1, 30 and 240 days, respectively. Conclusion. 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.