H. Peterson, A. Halstead, L. Kleiner, B. Miller, A. Strickland, E. Hollingsworth, C.J. Wutzke

Gonzaga University, Spokane, WA

Anterior cruciate ligament (ACL) tears are a leading knee injury in athletes, often occurring when fatigued. Fatigue increases risk for injury as control of lower limbs is compromised and may lead to biomechanical disadvantages at the knee as adductors and abductors reduce load in the medial lateral compartment of the knee. Single-leg drop tests assess knee stability and strength during plyometric movements and are common in rehab settings post ACL tear. A drop test onto a force plate allows for analysis of ground reaction forces (GRF) to determine magnitude of forces and loading patterns during a landing. PURPOSE: To determine the influence of the frontal plane hip exercise on GRFs during a single leg drop test in unimpaired young adults. METHODS: Participants (n=11) completed two sessions that included single leg drops from a 20 cm tall box onto a force plate. Participants exercised dominant limb hip abductors and adductors separately during individual sessions using an isokinetic dynamometer. Hip adductors and abductors were isometrically activated maximally until torque output was less than 50% of individual peak torque. Once torque was less than 50%, three single-leg drop tests were completed. Participants returned within 10 days for second session. Components of vertical ground reaction force including acceptance slope, absorption slope, balance slope, and mediolateral force range were calculated. Data was analyzed using a repeated measures ANOVA to determine influence due to exercise and between muscles. RESULTS: Abductors demonstrated greater mediolateral range (PRE: 194.9±40.6N, POST: 185.4±83.3N) compared to adductors (PRE:150.1±63.8N, POST: 136.7±51.8N, p=0.006). Adductor absorption slope magnitude increased post exercise (PRE: -7191±2258.1N, POST: -8353±3476.2N) while abductor absorption slope magnitude decreased post exercise (PRE: -8210±2845.80N, Post: -7173±3667.10N, p=0.020). Peak vertical force of the hip adductors increased after exercise (PRE: 2301±649.9N, POST: 2413±673.7N) while peak vertical force of abductors decreased after exercise (PRE: -2512.3±625.4N, POST: -2241.4±711.4N, p=0.014). CONCLUSION: Hip adductors contribute to absorption of vertical GRF moreso than hip abductors although abductors may influence mediolateral stability.

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