The effect of vertical whole-body vibration on lower limb muscle activation in elderly adults : influence of vibration frequency, amplitude and exercise

Abstract

Objective: This study aimed to investigate how whole-body vibration (WBV) and exercise and their interactions influenced leg muscle activity in elderly adults. Study design: An experimental study with repeated measures design that involved a group of ambulatory, community-dwelling elderly adults (n = 30; 23 women; mean age = 61.4 ± 5.3 years). Main outcome measures Muscle activity of the vastus lateralis (VL), biceps femoris (BF), tibialis anterior (TA), and gastrocnemius (GS) was measured by surface electromyography (EMG), while participants were performing seven different exercises during 4 WBV conditions (condition 1: Frequency = 30 Hz, amplitude = 0.6 mm, intensity = 2.25 units of Earth's gravity (g); condition 2: 30 Hz, 0.9 mm, 3.40 g; condition 3: 40 Hz, 0.6 mm, 3.65 g; condition 4: 40 Hz, 0.9 mm, 5.50 g) and a no-WBV condition in a single experimental session. Results: Significantly greater muscle activity was recorded in VL (3%-148%), BF (16%-202%), and GS (19% -164%) when WBV was added to the exercises, compared with the same exercises without WBV (p ≤ 0.015). The effect of vibration intensity on EMG amplitude was exercise-dependent in VL (p = 0.002), and this effect was marginally significant in GS (p = 0.052). The EMG activity induced by the four WBV intensities was largely similar, and was the most pronounced during static erect standing and static single-leg standing. Conclusions: The EMG amplitude of majority of leg muscles tested was significantly greater during WBV exposure compared with the no-WBV condition. Low-intensity WBV can induce muscle activity as effectively as higher-intensity protocols, and may be the preferred choice for frail elderly adults.