Postural sway and electromyography (EMG) muscle activation of the lower body on surfaces with varying stability

Abstract

The purpose of this study was to quantify muscle activation and body sway on a series of unstable surfaces. Surface electrodes were used to obtain muscle activation data from the tibialis anterior, gastrocnemius, gluteus medius, and gluteus maximus while body sway data (mean amplitude of A-P Sway, mean amplitude of M-L Sway, and Sway Index) was obtained using a force platform. Theraband stability trainers were used to provide a series of unstable surfaces. A total of fifteen participants (five females, ten males) volunteered in this study. It was determined that muscle activation increased as surfaces increased in instability. For example, peak tibialis anterior muscle activation when standing on the platform (one leg) was 34.5 %MVC while that for standing on the black surface was 64.9 %MVC. It was also determined that as body sway increased, muscle activation of the lower body increased as well. Several standing conditions (i.e. standing on one leg versus two legs, leaning in a particular direction) were also studied and it was determined that certain conditions significantly affect muscle activation as well as postural sway. This study provides objective muscle activity and postural sway data previously void in the literature which can be applied to a rehabilitation, health, or ergonomic setting.