Chronic effects of different frequencies of local vibrations.

The aim of this study was to compare the chronic effects of different frequencies of mechanical vibrations, applied in the direction of the resultant muscle forces' vector addition, on the performance of the lower extremities. After performing the maximal voluntary contraction (MVC), squat jump (SJ), countermovement jump (CMJ), multiple vertical jumps and running speed tests, 55 male volunteers were distributed into 4 groups: an Isometric group, an 8-Hz group, a 26-Hz group and a Control group. After a 4-week training period, the same tests were performed. The training groups reached a significant increase of the MVC, but the increases of the 8-Hz (23.2%) and 26-Hz (22.2%) groups were higher than the Isometric group (12.1%). A significant increase was observed between SJ and CMJ values measured at the pre-test and the post-test stages in the 8-Hz (SJ=11.1%; CMJ=8.7%) and 26-Hz groups (SJ=9.6%; CMJ=7.5%). No differences were observed between 8-Hz and 26-Hz groups. The application of vibrations of 8 Hz and 26 Hz, directed to the resulting muscle forces, was able to increase the performance of the lower extremities. This kind of local vibration did not produce positive effects on multiple vertical jumps or running speed.