Effects of Stimulus Timing on the Kinetics of a Directed Jump Landing, The

Introduction: Tearing the anterior cruciate ligament (ACL) is a significant threat to athletes when an unanticipated component is present. The current research investigated the change in injury and performance kinetics when manipulating the timing of a directional stimulus through a range of 0ms to 400ms before landing. Methods: Thirteen uninjured recreational athletes jumped forward from a 30cm tall block, landing bilaterally with the dominant foot on a Bertec forceplate. Upon landing, participants either performed a vertical jump or a left/right jump at 90°, indicated by an LED panel. Stimuli were sent in one of four conditions: 1) anticipated (AN), before movement; 2) classically unanticipated (CU), moment the participant left the block; 3) timed unanticipated at 300ms (TU300) and 150ms (TU150) before landing; or 4) at landing (LA). Stimuli and timing were controlled via an Arduino Uno microcontroller. Results and Discussion: Differences in peak vertical landing force (FZLA) and peak vertical takeoff force (FZTO) were found in the lateral jump condition, LA condition resulting in a larger FZLA than the other conditions, and a smaller FZTO with stimuli presented at TU150 than AN and CU. Generally, FZTO decreased and contact time increased as available time to react decreased, negatively affecting performance. Further research on the changes of combined kinetics and kinematics is necessary before intervention programs are implemented.