| The purpose of this study was to determine the relationship among self-reported ankle instability symptoms and muscular onset times and amplitudes of the peroneal longus (PL), peroneal brevis (PB), tibialis anterior (TA), gluteus medius (GMed), and gluteus maximus (GMax) during a forward stepping task. Sixty-seven participants (23.8 +/- yrs 170.4 +/- cm 71.6 +/- kg) volunteered to participate. Forty-nine participants reported a history of unilateral ankle sprain. We measured ankle instability using the Ankle Joint Functional Assessment Tool (AJFAT) and by determining self-reported episodes of "giving way" (GW). We predicted these two measures of ankle instability with selected muscle activation measures obtained during a forward, diagonal stepping task. Mean amplitude of the PL, PB, TA, GMed, and GMax was evaluated during the following time intervals: (1) a 100ms linear envelope immediately prior to heel strike, (2) a 100ms linear envelope immediately following heel strike, (3) a 100ms linear envelope centered on the peak vertical ground reaction force (GRF) during loading response. Onset times of each muscle were also recorded. We predicted the AJFAT total score and self-reported GW using 8 separate stepwise linear regression analyses with five predictor variables. Predictor variables were mean amplitude of the PL, PB, TA, GMed and GMax at (1) preheel strike, (2) post-heel strike, and (3) peak vertical GRF, and lastly (4) onset time of each muscle. Alpha was set at P < 05. Three predictions were significant. A significant prediction of self-reported GW was observed with mean PL amplitude at the pre-HS interval (Step 1, r = 0.26, r2 = 0.07, Sig. F change = 0.035) and post-HS interval (Step 1, r = 0.27, r2 = 0.07, Sig. F change = 0.028). Lastly, a significant prediction of the AJFAT total score was observed with mean PB amplitude at the peak vertical GRF interval (Step 1, r = 0.29, r2 = 0.08, Sig. F change = 0.017). These findings indicate PL and PB muscle amplitude during stepping is a predictor of subjectively reported ankle instability. Specifically, increased evertor (peroneals) amplitude was related to greater self-reported instability during all time intervals evaluated. |
