Combined effects of fatigue and decision making on female lower limb landing postures: Central and peripheral contributions to ACL injury risk

Background In spite of ongoing prevention developments, anterior cruciate ligament injury rates and the associated sex-disparity have remained, suggesting an incomplete understanding of the injury mechanism. While both fatigue and decision making are known in isolation to directly impact anterior cruciate ligament injury risk, their combined manifestations remain unknown. We thus examined the combined effects of fatigue and decision making on lower limb kinematics during sports relevant landings. Methods Twenty five female National College Athletic Association athletes had initial contact and peak stance phase 3D lower limb joint kinematics quantified during anticipated and unanticipated single (left and right) leg landings, both before and during the accumulation of fatigue. Jump direction was governed by light stimuli activated prior to and during the pre-land phase of respective anticipated and unanticipated trials. To induce fatigue, subjects performed repetitive squat (n = 5) and randomly ordered jump sequences, until squats were no longer possible. Subject-based measures of each dependent factor were then calculated across pre-fatigue trials, and for those denoting 100% and 50% fatigue, and submitted to a 3-way mixed design analysis of covariance to test for the main effects of fatigue time, decision and leg. Findings Fatigue caused significant increases in initial contact hip extension and internal rotation, and in peak stance knee abduction and internal rotation and ankle supination angles. Fatigue-induced increases in initial contact hip rotations and in peak knee abduction angle were also significantly more pronounced during unanticipated compared to anticipated landings. Interpretation The integrative effects of fatigue and decision making may represent a worst case scenario in terms of anterior cruciate ligament injury risk during dynamic single leg landings, by perpetuating substantial degradation and overload of central control mechanisms.