The Effect of Exercise on the Biomechanical Determinants of Knee Energy Absorption during Single-leg Jump-cuts

Graduation date: 2015Anterior cruciate ligament injuries are common in a wide variety of sports and most frequently occur during activities requiring rapid deceleration such as landing and cutting. Deceleration of the body's center of mass during movement results primarily from eccentric muscle contraction. This type of contraction serves to absorb energy from the whole-body system with the magnitude of energy absorbed directly related to the internal joint moment and the joint angular velocity. There is substantial evidence to demonstrate that following exercise females land with lesser knee flexion which may increase their risk for ACL injury. However, it is not known whether this change in knee position is a compensatory mechanism to overcome a reduction in quadriceps moment producing capacity that occurs during sustained exercise. It is possible that a more extended knee position is used after exercise in order to allow for greater knee flexion angular velocity so that the magnitude of knee energy absorption (EA) during landing can be maintained. Therefore, the purpose of this study was to: 1) evaluate the influence of exercise on the magnitude of knee EA during a single-leg jump-cut and, and 2) identify whether exercise influences the individual\ud biomechanical determinants (internal knee moment and knee angular velocity) of knee EA. Forty recreationally active females performed single-leg jump-cuts before and after a standardized 30-minute exercise protocol. From recorded motion capture and ground reaction force data, the magnitude of knee EA, mean internal knee extension moment, and mean knee flexion angular velocity during the initial 100 milliseconds of landing were calculated. Despite no change in knee flexion angle at initial contact, females landed with 10% lesser knee EA following the exercise protocol. The lesser EA was the result of a 14% reduction in mean internal knee extension moment coupled with an 8% reduction in mean knee flexion angular velocity post-exercise. The results suggest that females utilized a stiffer landing strategy with lesser knee EA after sustained exercise. While the magnitude of the EA reduction observed during the single-leg jump-cut is probably not clinically meaningful, it is likely that the adoption of a stiffer landing strategy following exercise during more demanding movement tasks might result in increased loading of static structures and greater lower extremity injury risk