Leg Muscle Activity during Whole-Body Vibration in Individuals with Chronic Stroke

Abstract

It has been previously shown that whole-body vibration (WBV) can augment muscle activity in young healthy adults. However, the EMG response of leg muscles during WBV in individuals with stroke is unknown. The objective of this study was to determine the influence of WBV on the activity of the vastus lateralis (VL) and gastrocnemius (GS) muscles during the performance of different exercises in chronic stroke patients. Forty-five chronic stroke patients were studied. Each subject was exposed to three WBV conditions of 1) no WBV, 2) low-intensity WBV protocol (peak acceleration: 0.96 unit of gravitational constant [g]), and 3) high-intensity WBV protocol (peak acceleration: 1.61g) while performing eight different static exercises involving upright standing, semisquat, deep squat, weight shifted forward, weight shifted backward, weight shifted to the side, forward lunge, and single-leg standing. Bilateral VL and GS muscle activity was recorded with surface EMG and expressed as a percentage of the EMG amplitude recorded during a maximal voluntary contraction of the respective muscles. Two-way repeated-measures ANOVA revealed that exposure to WBV (low- and high-intensity protocols) significantly increased VL and GS EMG amplitude (large effect size, partial η = 0.135-0.643, P < 0.001) on both the paretic and nonparetic sides in different exercise conditions compared with no WBV. No significant difference in EMG magnitude was found between the high- and the low-intensity WBV protocols (P > 0.05). With a few exceptions, WBV enhanced EMG activity in the paretic and nonparetic leg muscles to a similar extent in different exercise conditions. Leg muscle activity was increased significantly with the addition of WBV. Further clinical trials are needed to determine the effectiveness of different WBV protocols for strengthening leg muscles in chronic stroke patients.