Whole body vibration (WBV) has recently emerged to develop entire muscular system rather than developing a specific area. WBV, which was newly introduced to train the muscular function in 1990s, is a new method of training widely used in various areas including sports team, rehabilitation clinic and fitness club, especially in advanced countries these days.
And, the effect of whole body vibration on the muscle strengthening, muscle activities, postural balance, gait ability, bone density and others were identified by many researchers. However, the study on the effect of whole body vibration on the adjustment of muscle strength imbalance is very insignificant. Also, a study on system development to adjust muscle strength imbalance is nonexistent.
Therefore, this study wants to prove the effect of multi-control whole body vibration providing independent exercise loads in each vibration platform on the improvement of muscle activity and muscle strength imbalance in lower extremities.

First, Ten healthy women volunteers (age 21±1.3 years, height 160±2.1 cm, weight 52±4.6 kg) were selected. Subjects performed four different squat exercises(Low Squat ; LS : Knee angle 90°, High Squat ; HS : Knee angle 120°, Heel Up & High Squat ; HU&HS Heel Up and Knee angle 120°, One Leg Squat ; OS : One leg and knee angle 120°) on a vibration platform. EMG signals four leg muscles were taken and analyzed. The exercises were performed both with 10 seconds WBV and without 10 seconds WBV. Muscle activities during WBV were compared with non-vibration stimulus. In the result, EMG signals caused by WBV were significantly higher (P<0.05) compared with non-vibration stimulus in all leg muscles and squat exercises. The increase in muscle activity caused by Whole body vibration was significantly higher (P<0.05) in LS and OS compared with HU&HS.

Second, ten (10) females aged 20 (average age 21 ± 3.0 year, average height 160 ± 4.9cm, average weight 49 ± 5.8kg) participated in this study. The subjects were consists of WBV group with more than 10% of muscle strength imbalance between the lower extremities. One (1)mm and four (4)mm of vibration intensities were applied to dominant muscle and non-dominant muscle, respectively in lower extremities for WBV group having more than 10% of muscle strength imbalance between the lower extremities; and their vibration frequency was fixed at 25Hz. All subjects were asked to perform low squat, two seconds for up and two seconds for down. This low squat was conducted: 15 times for five sets a day, three times a week for total 4 weeks. As a result, WBV group showing an average deviation of 16% before the experiment tended to decrease down to around 5%, showing improved muscle strength imbalance.

As a result of this study, the whole body vibration exercise using load deviation protocol is effective in improving leg muscle strength imbalance. Multi-control whole body vibration can be applied as a part of exercise prescription and rehabilitation program for general people, the aged or athletes having muscle strength imbalance caused by injuries in muscular skeletal system.