Altered Knee Neuromechanics during a Jump Task in AI Subjects Compared to Copers and Normals

Abstract

Ankle sprains often lead to ankle instability (AI). Copers are individuals who have sprained their ankles but have no residual symptoms. A comparison between copers and AI subjects can help clarify problematic movement neuromechanics in AI. PURPOSE: To examine sagittal and frontal knee angles, moments, and vastus lateralis (VL) activation during a max 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 dependent variables were collected during stance. Functional linear models (α=.05) were used to detect mean difference between groups. If functions and associated effects sizes (95% confidence intervals) did not cross the zero, significant differences existed (p<.05). RESULTS: : Figure 1 shows that copers exhibited similar neuromechanics to AI in frontal knee angles and moments, but AI showed 5° more knee flexion, which could be related to 0.6 Nm/kg more knee extension moment and 23% more VL activation during 0-25% of stance (p<.05). Copers exhibited similar neuromechanics to normals in sagittal knee angles and VL activation (p<.05). CONCLUSIONS: Copers demonstrate unique neuromechanics similar to normals at times (sagittal-plane variables), and similar to AI at others (frontal-plane variables). AI subjects utilize a knee flexion dominant strategy with more VL activation and knee extension moments in a potential attempt to land safely, but ankle and hip motion may play a major role in altered knee neuromechanics.