Effects of whole-body vibration training on muscle strength and flexibility: significance of the vibration frequency

Three separate studies were carried out to test the acute, acute residual and chronic effect of whole body mechanical vibration (WBV). In the first and second study eight week WBV was used either with individually selected vibration frequency that ranged from 20 to 35Hz frequency or 30 Hz frequency for each subject. In the third study 20 Hz frequency was applied during four weeks for acute stroke patients. In the first study dynamic force was estimated by using squat jumps, countermovement jumps or 10 s rebound jumps. In the second study the flexibility of the hamstring and lower back muscle were tested during vibration, after having finished the vibration exposure, and before and after eight week vibration intervention. In addition the reactive muscle strength of the extensors in lower limbs were determined before and after eight week vibration intervention. In the third study maximum isometric force and force development, maximum eccentric force and mechanical work were determined for the affected and non-affected knee extensors.;The results of the present investigation may allow us to conclude the followings: (1) The individually selected vibration frequency based on the EMG response for WBV intervention results in greater improvement in explosive and reactive strength as compared with fixed frequencies vibration intervention; (2) The improvements in vertical jumps are greatest when movement or strength exertion is carried out with short angular displacement and when the muscle stretch is fast that occurs in rebound jumps; (3) Individualized whole-body vibration without superimposing other exercises is an effective method of acutely increasing lower back and hamstring flexibility (acute and residual effect); (4) Individualized whole-body vibration does not induce a chronic effect on hamstring flexibility; (5) The results indicates indirectly that effect of vibration frequency depends upon the physical and the neuromuscular condition of the treated muscles based on the study in patients with stroke.