The Effects of Functional Fatigue on Ground Reaction Forces of a Jump, Land, and Cut Task

Rapid acceleration, deceleration, landing and change of direction have been implicated as mechanisms of noncontact anterior cruciate ligament (ACL) injury. PURPOSE: To examine the ground reaction forces occurring to the knee during non-fatigued and fatigued jump, land and cut maneuvers in three unplanned cutting directions. METHODS: Eleven healthy, adult female collegiate soccer athletes participated in this study (age= 20.3±0.9 years; height= 167.4±4.8 cm; mass= 63.7±7.7 kg). Each subject was instructed to perform 9 jump, land, and cut maneuvers in a pre-fatigued state and fatigued state. The protocols were randomly assigned to include 3 cuts in each of the three directions. The functional fatigue protocol consisted of rapid acceleration, deceleration, and change of direction activities. A 2x2 ANOVA design was used to compare groups (fatigue state) and (leg dominance). RESULTS: Differences were noted in the medial direction during the left cut land (p=0.049). Differences in the anteriorposterior forces occurred during fatigued landing tasks for all three cutting directions (left, p=0.049; center, p=0.000; right, p=0.009), and for the center cut push off (p=0.020). Fatigue appeared to have a significant impact on the vertical push off of all three directions (left, p=0.023; center, p=0.000; right, p=0.047). CONCLUSION: Fatigue has an important impact on jump, land and cut maneuvers regardless of cutting direction. Fatigue was noted to impact the anterior-posterior direction the most during landing which is significant as the primary purpose of the ACL is to prevent anterior shear force of the tibia on the femur during motion. Fatigue may prove to be a predominant risk factor for ACL injuries. Keywordsanterior cruciate ligament, fatigue, kinetics, knee