Study Design: Experimental, within-subject repeated measures. Objective: To determine electromyographic (EMG) activity of the hip and the trunk muscles during the Star Excursion Balance Test (SEBT) performance in 8 reach directions. Background: Dynamic balance (DB) is a measure of core stability. Deficits in DB have been related to injuries in athletic populations. The SEBT is suggested to measure DB by assessing the functional strength of core muscles and lower extremity muscles. Methods: Surface EMG data was collected in 22 healthy adults for the erector spinae (ES), external oblique (EOB), and rectus abdominis (RA) bilaterally, and gluteus medius (GMED) and gluteus maximus (GMAX) muscles of the stance leg. A 2 way repeated measures ANOVA was used to determine the interaction between percentage maximal voluntary isometric contraction and reach directions. The %MVIC for each muscle was compared across 8 reach directions using the Sidak post hoc test. Alpha level was set a-priori at 0.05. Results: Significant differences were observed for all 8 muscles across reach directions of the SEBT. Highest EMG activity was found for the tested muscles in the following reach directions ipsilateral EOB: anterolateral, contralateral EOB: medial, ipsilateral RA: anterior, contralateral RA: anteromedial, ipsilateral ES: posterolateral, contralateral RA: anteromedial, ipsilateral ES: posterolateral, contralateral ES: posteromedial, GMAX: posterior, and GMED: medial direction. Conclusion: Trunk and hip muscle activation is direction dependent during the SEBT. The EMG activity during the 8 reach directions of the SEBT can be used to either evaluate functional strength or to rehabilitate the trrunk and the hip muscles.
