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

Ten healthy male college students performed a series of dynamic squats(loaded with no WBV and loaded with WBV).The load was set to 30% of maximum force and WBV included 25、30、35、40、45、50 Hz frequencies with 2-mm amplitude.Muscle activity was recorded with surface electromyography(EMG) on the tibialis anterior(TA) and gastrocnemius(GC) and was 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(P0.05),and loads had significant effect on EMGrms of GC(P0.01).There was no significant interaction between vibration and load.After multiple comparisons,it was found that exposure to WBV(45Hz) significantly increased baseline muscle activity in all muscles.In conclusion,it is suggested that WBV can increase the neuromuscular activity of the calf muscles during dynamic squat.Loads can increase the neuromuscular activity of GC,but can not increase the neuromuscular activity of TA.