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Does Type of Unanticipated Stimulus Alter Knee Mechanics During Dynamic Tasks?

Noncontact ACL injuries occur during movements that involve sudden decelerations and changes in direction due to combined sagittal and frontal plane knee loading. Previous studies have shown altered knee mechanics when decision-making is involved, which may better simulate game-like scenarios in a lab setting. The purpose of this study was to determine how two unanticipated stimuli alter knee biomechanics during a dynamic task. Eight females and eight males, all recreationally-active, participated. Participants completed two unanticipated 45-degree cutting conditions (visual stimulus (VS); human defensive opponent (DO)). For the VS condition, a custom computer program presented one of three visual stimuli in a random order. For the DO condition, a research assistant attempted to “block” the participant’s running path with a defensive move, using the same three random-order tasks as in VS. For both conditions, participants had a reaction time range of 400-500 milliseconds. Separate 2×2 mixed-model repeated measures ANOVAs (condition×sex) were performed, with an alpha level of .05. Results showed a significant condition main effect for knee extension moments, which were greater in DO compared to VS (p=.009). Significant interactions were present for peak knee flexion angles and peak knee adduction moments. Females had greater flexion angles (p=.001) and adduction moments (p=.030) in VS compared to DO. Women had less knee flexion and more adduction moment in VS, possibly suggesting this stimulus amplifies ACL injury risk factors in females. A human defender increased sagittal plane loading in a manner that may better represent loading in game situations.
Listed In: Biomechanics, Sports Science


The Effect of a Raised Surface on Frontal Plane Knee Loading and Muscle Activation During a Sidecut in Recreational Female Softball Players

Collegiate softball has become increasingly popular since the passage of Title IX. As with any sport, injuries are a common occurrence. Interestingly, the base runner is at the highest risk of injury, and rounding the base, specifically, has resulted in approximately 187 game-day injuries. Rounding the base involves planting the right foot on a raised surface and cutting to the left, a dynamic movement often associated with noncontact ACL injuries. Frontal plane loading and unbalanced quadriceps-to-hamstring co-contraction indices (Q:H CCI) have been associated with increasing the likelihood of noncontact ACL injuries occurring. Neuromuscular abnormalities pre- and post-contact have also been suggested to increase the risk of injury. To date, no study has analyzed the effect of rounding a base on noncontact ACL injury risk factors in softball players. Nine recreationally active females completed two base conditions. The first simulated rounding a base with no base on the force platform (NB), and the second simulated rounding a base with a base on the force platform (WB). Three-dimensional motion capture, one force platform, and electromyography were utilized. Results indicated the WB condition reduced the risk of noncontact ACL injury by decreasing frontal plane loading. Movement patterns at the ankle and abnormal foot strikes may provide a better explanation for why noncontact ACL injuries occur while rounding first base. Post-contact Q:H CCI was significantly greater than pre-contact, indicating significantly greater quadriceps activity post-contact. Neuromuscular training could potentially reduce the load applied to the ACL and decrease the risk of injury.
Listed In: Biomechanics, Sports Science