SURFACE EMG ANALYSIS A DURING VERTICAL JUMP WHILE A SEMI-RIGID ANKLE BRACE

Abstract

PURPOSE The purpose of this study was to evaluate muscle activity while wearing a semi-rigid ankle brace during a vertical jump in persons with functional ankle instability. METHODS Twelve subjects (6 stable ankles 22.0 ± 0.37 yrs; BMI = 25.1 ± 1.20 kg m2; 6 unstable ankles 22.0 ± 1.20 yrs; BMI = 28.1 ± 1.98 kg m2) volunteered to participate in the study. Ankle instability was determined by subject history as well as talar tilt and anterior drawer tests. Both stable (controls) and unstable ankle (US) subjects were asked to perform three vertical jump trials on two successive days. US group were randomly assigned into braced (B) and unbraced (UB) conditions for each day. The brace worn for the US group was a semi-rigid brace (Sure Step® Custom). Surface electromyography (SEMG) activity of seven muscles-semitendinosus, biceps femoris, vastus lateralis, vastus oblique, peroneus longus, tibialis anterior, and lateral gastrocnemius were simultaneously recorded during the jump. For each jump, the SEMG data were divided and normalized to each respective maximal voluntary isometric muscle contraction, and then averaged for all subjects across the three trials in each condition. RESULTS The controls were able to jump higher than UB subjects (F = 7.99, p < 0.05), however, there were no differences in jump height when the subjects were braced. There were also no significant differences in SEMG activity in any of the seven muscles between B and UB conditions. CONCLUSION The UB subjects were not able to jump as high as the controls, however, when braced there were no differences between groups. In addition, it appears that the brace does not limit or alter muscle activity in either the PREP or LAND phases of the vertical jump.