Variation in neuromuscular responses during acute whole-body vibration exercise

Purpose: Leg muscle strength and power are increased after whole-body vibration (WBV) exercise. These effects may result from increased neuromuscular activation during WBV, however, previous studies of neuromuscular responses during WBV have not accounted for motion artifact. Methods: Sixteen healthy adults performed a series of static and dynamic unloaded squats with and without two different directions of WBV (rotational vibration, RV; and vertical vibration, VV, 30 Hz; 4 mm(p-p)). Activation of unilateral vastus lateralis, biceps femoris, gastrocnemius, and tibialis anterior was recorded using EMG. During RV and VV, increases in EMG relative to baseline were compared over a range of knee angles, contraction types (concentric, eccentric, isometric), and squatting types (static, dynamic). Results: After removing large, vibration-induced artifacts from EMG data using digital band-stop filters, neuromuscular activation of all four muscles increased significantly (P <= 0.05) during RV and VV. Average responses of the extensors were significantly greater during RV than VV, whereas responses of the tibialis anterior were significantly greater during VV than RV. For all four muscles, responses during static squatting were greater than or equal to responses during dynamic squatting, whereas responses during eccentric contractions were equal to or smaller than responses during concentric and isometric contractions. Neuromuscular responses of vastus lateralis, gastrocnemius, and tibialis anterior were affected by knee angle, with greatest responses at small knee angles. Conclusions: Motion artifacts should be removed from EMG data collected during WBV. We propose that neuromuscular responses during WBV may be modulated by leg muscle cocontraction as a postural control strategy and/or muscle tuning by the CNS intended to minimize soft-tissue vibration.