Electromyographical Analysis of and Medial-Lateral Anticipatory Postural Adjustments prior to Stepping and Single Leg Reaching in Chronic Unstable Ankles
The repetitive occurrence of multiple lateral ankle sprains within the physically active population is termed chronic ankle instability (CAI). Previous research remains limited regarding the preparatory activation of the dynamic restraints at the hip (gluteus medius-GM, adductor magnus-AM), and at the ankle, (tibialis anterior-TA, peroneus longus-PL), in individuals with CAI. Therefore, the purpose of this study was to examine lower leg preparatory electromyographic (EMG) muscular activity (EMG onset and EMG amplitude) prior to the execution of two different goal directed tasks. Additional variables such as temporal stepping parameters and center of pressure (COP) parameters were examined during the goal directed leg lifting task and reach distance during the Star Execution Balance Test (SEBT). Participants consisted of twenty-one individuals between the ages of 18 - 25 (15 females, 6 males, height = 175.96 ±8.19, mass = 75.28 ± 10.83). Participants performed a goal directed leg-lifting task in which they raised either their right or left leg as fast as possible in response to an unpredictable anticipated light stimulus. They also performed the SEBT in which they performed a single leg maximal reach in the posterior medial (PM) direction. For the goal directed leg-lifting task, EMG amplitude and EMG muscle onset of the TAst, PLst, GMst and the AMSW (st-stance, sw-swing) relative to unloading of the swing limb were examined. For the SEBT PM task, reach distance and EMG amplitude of the TAst, PLsb GMst, and AMst were recorded relative to foot touch down at maximal reach distance. The leg-lifting task revealed that no differences (p > .05) existed between limbs with respect to the preparatory muscle activity (EMG onset). No significant differences (p > .05) between sides were revealed for the temporal stepping parameters. The COP results revealed that the range of the medial-lateral COP excursion was significantly greater (p < .05) for the unstable side compared to the healthy side. The SEBT PM task revealed that all participants reached less when standing on their unstable ankle (57.09 cm ± 9.25) compared to their healthy (60.99 cm ± 8.66) and a significant side by muscle interaction {p < .05) with greater average EMG amplitude muscle activity occurring at the ankle compared to the hip when standing on the unstable side.
ETD, Repetitive occurence, Lateral ankle sprains, Charonic ankle instability, CAI, EMG onset, EMG amplitude, Goal directed tasks, Kinesiology
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