Altered Frontal Ankle Neuromechanics in Subjects with AI Compared to Copers and Healthy Controls

Abstract

Lateral ankle sprains often result in ankle instability (AI). However, some individuals (copers) who have a history of a sprain(s), do not exhibit residual symptoms. Defining neuromechanics of copers can help us clarify successful movement strategies to avoid AI. PURPOSE: To examine frontal-plane ankle angles, moments, and peroneus longus (PL) activation during a jump task. METHODS: 66 subjects (M=42, F=24; 22.2±2 yrs, 173.8±8 cm, 71.4±11 kg) consisted of 22 AI (77.1±15.3% FAAM ADL, 62.5±20.4% FAAM Sports, 4.1±2.8 sprains), 22 Copers (100% FAAM ADL & Sports, 2.0±1.1 sprains), and 22 healthy controls. Subjects performed 5 jumps, consisting of a max vertical jump, landing on a force plate, and transitioning immediately to a side jump, while the dependent variables were collected during stance. Functional linear models (α=.05) were used to detect mean difference between groups. If functions and corresponding effects sizes (95% confidence intervals) did not cross the zero, then significant differences existed (p<.05). RESULTS: Figure 1 shows that while copers demonstrated similar frontal ankle angles to normals, AI subjects exhibited up to 3° greater eversion compared to copers and normals (p<.05). AI subjects also demonstrated up to 0.1 Nm/kg less eversion moment relative to copers, while copers demonstrated up to 0.1 Nm/kg greater eversion moment relative to normals (p<.05). PL activation in AI subjects was 13% and 21% less than copers and normals, respectively (p<.05). CONCLUSIONS: Copers show unique neuromechanics relative to AI subjects and normals. AI subjects land with more eversion, but also exhibit less eversion moment along with less PL activation. More data are needed to determine if this strategy is associated with injury risk.