Effects of whole-body vibration with an unstable surface on muscle activation.

The current study examined the effects of using an unstable surface during whole-body vibration (WBV) exercise on leg and trunk muscle activity during a static semi-squat. Twenty-eight recreationally active university students completed 4 different test conditions: 1) stable surface with no WBV; 2) unstable surface with no WBV; 3) unstable surface with 30 Hz WBV low amplitude; and 4) unstable surface with 50 Hz WBV low amplitude. Surface electromyography (sEMG) was measured for the gastrocnemius medialis (GM), vastus medialis oblique (VMO), vastus lateralis (VL), rectus abdominis (RA), and multifidus (MF) muscles. Normalized to the stable condition, WBV at 30 Hz and an unstable surface increased EMG in the GM vs the unstable and stable surfaces (~35%; p<0.05). VMO EMG decreased in the unstable vs stable condition (~20%), WBV at 30 Hz and an unstable surface increased EMG vs all other conditions (~20-40%; p<0.05). MF EMG increased with WBV at 30 Hz (25%; p<0.05) vs the stable condition but not vs all other conditions. Using an unstable surface during WBV exposure increases EMG of muscles in the lower extremities and trunk suggesting the combination of an unstable surface combined with WBV may be an effective modality to further increase EMG.