(25) PREDICTORS OF FATIGUE INDUCED ANTERIOR CRUCIATE LIGAMENT INJURY RISK FACTORS IN RECREATIONALLY ACTIVE FEMALES

Abstract Details: Anterior cruciate ligament (ACL) injuries occur when excessive loads are placed on the ligament. The injury most commonly arises when an anterior tibial load is combined with valgus motion. Compared to males, females tend to have greater knee valgus, and higher rates of ACL injuries.

Purpose: The purpose of this study was to determine specific variables related to increased knee valgus during a fatiguing drop jump protocol.

Methods: Ten recreationally active females (24.33 ± 5.81 years, 167.33 ± 4.93 cm, 70.90 ± 10.43 kg) completed a fatiguing drop jump protocol where continuous drop jumps were performed every 20 seconds until the participants could no longer achieve 80% of the averaged jump height of their initial five jumps. The height of the drop jump was individually set to 90% of the participant’s maximal countermovement jump height. All drop jumps were performed on dual force platforms to obtain ground reaction force (GRF). Pre-and-post relative peak GRF was calculated during landing, while knee joint laxity and ACL size were quantified using a knee arthrometer and ultrasound, respectively. Kinetic data were averaged across the initial five drop jumps (pre fatigue) and the last five drop jumps (post fatigue). Muscle cross sectional area (CSA) and quality (echo intensity [EI]) of the quadriceps and hamstrings were measured pre fatigue.

Results: Fatigue significantly increased knee valgus (pre: -5.943 ± 2.260°; post: -6.684 ± 2.254°). Out of the 11 dependent variables, three significantly predicted the observed increase in knee valgus when fatigued (Table 1) and explains 98.4% of variance. Specifically, the model suggests peak GRF (R² = 0.720, p = 0.012), hamstring EI (ΔR² = 0.177, p < 0.001), and ACL size post fatigue (ΔR² = 0.087, p = 0.003) predicts the increase in knee valgus.

Conclusions: Fatigue induced increases in knee valgus are predicted by greater relative peak ground reaction force, decreased hamstring muscle quality, and decreased ACL size. PRACTICAL APPLICATIONS: To reduce ACL injury risk, strength and conditioning practitioners should focus on decreasing peak ground reaction forces during landing movements. Additionally, proper hamstring training should be emphasized to improve muscle quality and size of the surrounding ligaments.

Acknowledgements: None