Effects of Vibration Frequency and Loading on Lower Limb Muscle Activation and Time-Varying Multi-Muscle Coactivation in Whole-Body Vibration Training among Recreational Runners

This study examined the effects of vibration frequency and additional loading on lower limb muscle activation and coactivation during whole-body vibration (WBV) training in recreational runners. Twenty-five male runners performed WBV training at six frequencies (0-50 Hz) under two loading conditions (no load vs. 20% body mass). Surface electromyography was used to record electromyography root mean square (EMGrms) in 11 lower limb muscles. Coactivation of six muscles was analyzed using the time-varying multi-muscle coactivation function. 1D statistical parametric mapping and two-way repeated-measures ANOVA were used to assess differences. EMGrms was significantly influenced by vibration frequency and loading. Additional loading increased activation in the gluteus maximus, quadriceps, hamstrings, and soleus (p < 0.001). Frequency effects were notable in the gluteus maximus and hamstrings, with 10-30 Hz inducing higher muscular activation than the no-vibration case (p < 0.01). Coactivation was significantly high with loading (p < 0.001), particularly during the eccentric squat phase, but frequency had no significant effect. Additional loading enhances muscle activation and coactivation, and vibration frequency primarily affects muscular activation. These findings highlight the importance of external load and frequency in optimizing WBV training for enhancing sports performance and preventing injuries in runners.