BACKGROUND: Vibration training can affect strength improvement. However, the role of the vibration frequency, in terms of knee muscle strength, is unclear. OBJECTIVE: To evaluate the effect of vibration training with the same amplitude and different frequencies on the isokinetic muscle strength of the knee in juvenile football players. METHODS: Juvenile football players were divided into four groups: low frequency (n= 13, 25 Hz), medium frequency (n= 14, 40 Hz), high frequency (n= 14, 50 Hz), and control (n= 13). The frequency groups completed 12 weeks of weight-free vibration training (three times/week) with the same amplitude (3 mm) but different frequency. RESULTS: Compared with baseline, the peak extension torque of the knee at 60°/s and 240°/s increased by 8.4% and 12.9%, respectively, in the medium-frequency group, and by 8.9% and 15.5%, respectively, in the high-frequency group. The extensor endurance (the ability of joint muscle groups to maintain a force output over time) of the knee in the high-frequency group increased by 4.3%. At 12 weeks, the high-frequency group had greater knee extensor endurance than the low- and medium-frequency groups. CONCLUSION: In juvenile football players, weight-free vibration training at 40 Hz and 50 Hz improves peak torque of the knee extensors at 60°/s and 240°/s, while training at 50 Hz improves endurance of the knee extensors.
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