Investigation of foot landing techniques and muscle activation during single-leg drop landings : implications for non-contact anterior cruciate ligament injuries

Anterior cruciate ligament (ACL) injuries are common during sport, frequently occurring during non-contact situations, caused by the athletes’ own manoeuvres. The foot and ankle form the initial parts of the lower extremity kinetic chain during landing. Thus, foot landing positions can affect the force transmission from the ankle to the knee. Yet, many studies on ACL injuries have not focused on the ankle and this is considered a gap to the better understanding of non-contact ACL injuries. The roles of the gastrocnemius and hamstring in non-contact ACL injury risk reduction, especially during the pre-landing phase of single-leg landings are also still unclear. Therefore, investigation of foot-landing techniques and muscle activation during single-leg landings is an important area to provide new insights into non-contact ACL injury risk reduction. Four laboratory-controlled experiments were conducted in this thesis. The first three studies were conducted in a motion analysis laboratory, where kinematic and kinetic measurements were taken. Effects of varying levels of gastrocnemius activation on anterior tibial translation and the role of gastrocnemius activation on non-contact ACL injury risk reduction were investigated in the fourth and last study. A novel methodology using the ultrasound imaging, to measure anterior tibial translation under muscle activation, was incorporated into this last study. Foot landing techniques has an influence on non-contact ACL injury risks. Athletes should avoid extreme toe-out foot rotation positions during initial contact to minimize maximum knee valgus moments. Fore-foot landings are better than flat-foot landings in terms of force absorption. However, there is a proposed optimal range of ankle plantar flexion angles, that is associated with reduced non-contact ACL injury risks. Results suggest that with sufficient gastrocnemius activation and therefore joint compression, anterior tibial translation could be reduced, thereby limiting ACL injury risks. This research provided new knowledge into how foot landing techniques could be implemented to reduce non-contact ACL injury risks. It also provided a better understanding of the role of muscle activation, particularly the gastrocnemius, in non-contact ACL injury risk reduction. All these could be incorporated into future ACL injury prevention interventions and measures.Doctor of Philosophy (MAE