The anterior cruciate ligament (ACL) acts in an essential role to prevent anterior tibial displacement when experiencing jump-landing forces that are applied to the lower extremity;​ more than 100,000 injuries per year in the United States in sport activities that often require landing, deceleration-acceleration, cutting and pivoting actions have been reported. The aim of this study was to examine the nature of any lower limb coupling differences between a drop-jump and a side-step cutting actions, assess kinematic and kinetic differences between three tasks, and evaluate the effects of two landing techniques in biomechanical risk factors while performing two unanticipated tasks.

Twenty female collegiate soccer athletes from a Division I institution participated in these experiments. Participants performed two unanticipated tasks;​ sidestep cutting and pivot, combined with two landing techniques. Three-dimensional kinematics and kinetics were recorded. The coupling relations between specific kinematic and kinetic events were assessed using principal component analysis. In addition, the degree of variability between both tasks was assessed using determination of the coefficient of variation (CV). Repeated measures analyses of variance were conducted to assess differences in the kinematic and kinetic parameters between tasks and foot landing techniques (P<​0.05).

For experiment I, the results demonstrated that the highly loaded biomechanical variables were different between the movements, showing that the factors are inherently different depending on vertical versus horizontal oriented jump-landing tasks. Experiment II, the pivot task (-41.2 ± 8.8°) had lower knee flexion and increased valgus angle (-7.6 ± 10.1) than the sidestep (-53,9 ± 9.4°, and -2.9 ± 10.0°, respectively) at maximum vertical ground reaction force. For experiment III, the forefoot landing technique had significantly higher knee flexion than the rearfoot (p<​0.001), knee flexion moment (p=0.003), and knee adduction moment (p<​0.001) at initial contact. This differentiation between tasks indicates that the biomechanical movement patterns are different for each movement and that the decreased variability during the drop jump may result in different adaptability of the system. During the pivot task, the athletes presented a more erect posture and adopted strategies that may place higher loads on the knee joint and increasing the strain on the ACL.