Comparison of Muscle Activity of Thigh for Loaded and Unloaded Dynamic Squats during Whole-Body Vibration of Different Frequencies

Whole-body vibration(WBV) is a relatively new exercise modality gaining significant interest of lower limb strength,but the muscle activity characteristics of thigh during load squat and vertical vibration exercise at different vibration frequencies was unknown.Ten healthy male college students performed a series of dynamic squats(unloaded with no WBV,unloaded with WBV,loaded with no WBV,and loaded with WBV).The load was set to 30% of maximum force and WBV included 30,40,50 Hz frequencies with 2-mm amplitude.Muscle activity was recorded with surface electromyography(EMG) on the rectus femoris(RF),vastus medialis(VM),vastus lateralis(VL),biceps femoris(BF) and semitendinosus(SEM) and is reported as EMGrms(root mean square) normalized to %maximal voluntary contraction.A two-factor analysis of variance showed that vibration stimulation had significant effect on EMGrms of all the muscles(P<0.05),and loads had significant effect on EMGrms of RF,VM and VL(P<0.01).There was no significant interaction between vibration and load.After multiple comparison,it was found that exposure to WBV(50Hz) significantly increased baseline muscle activity in all muscles.In conclusion,it is suggested that WBV can increase the neuromuscular activity of the thigh muscles during dynamic squat.Loads can increase the neuromuscular activity of RF,VM and VL but cannot increase the neuromuscular activity of BF and SEM.