Author(s): KUEHNE, M., SANIN, C., MOHR, M., Institution: UNIVERSITY OF INNSBRUCK, Country: AUSTRIA, Abstract-ID: 1864

INTRODUCTION:
In evasion sports, ruptures of the Anterior Cruciate Ligament (ACL) frequently occur with minimal opponent contact within the first 50 ms after the initial contact (IC) of change of direction (COD) movements [1]. One influencing factor for the observed movement pattern is whether or not the athlete was planning the sidestep in advance. Although previous research has suggested more injury-prone movements in unplanned CODs, conflicting results and interpretations exist, e.g. regarding knee flexion [2]. The disagreement may stem from little information available in the COD kinematics of a single point in time (such as IC). We aimed to provide further insight into the anticipation effect on CODs regarding ACL injury risk by investigating the joint angle progression after IC during multiple CODs in an on-field setting mimicking real game scenarios.
METHODS:
Twenty male soccer players performed 12 maximum-speed COD sequences in a setup of 6 COD options (45°, 90°, 135°; L, R) on artificial turf. For half of the trials, participants knew the running direction in advance (planned). The other half were unplanned trials, in which participants received their direction cue during the run-up. IMU sensors (Noraxon Ultium Motion) were placed on 8 body parts and joint angles were estimated by the corresponding software (Noraxon myoMotion). Using linear mixed effect models (factors anticipation and COD angle), the change in angle from IC to IC+50 ms was examined for knee flexion and abduction, ankle flexion, hip abduction and flexion, trunk flexion, lateral lean and rotation and as pelvis orientation (alpha = 0.05).
RESULTS:
A significant main effect of anticipation was found for knee flexion, revealing a larger flexion movement in the planned (M = 13.3) compared to the unplanned condition (M = 10.7, p = 0.002). Significant interaction effects (COD angle x anticipation) highlighted angle-dependent differences of planned vs. unplanned CODs for trunk rotation (p = 0.004) and hip flexion (p = 0.001). Main effects of COD angle were found for all joint angles except knee abduction.
CONCLUSION:
In planned CODs, a larger knee flexion movement in the initial contact phase may enable a safer absorption of initial momentum compared to unplanned CODs, possibly reducing ACL injury risk [1]. Sagittal plane ankle and hip movements were comparatively small for both conditions, especially at sharper COD angles. This suggests a low contribution of hip and ankle and a high contribution of the knee to energy absorption during CODs. While for some variables the observation of a single posture (e.g. at IC) might be sufficient for risk assessment, analyzing the change in joint angles in the critical first 50 ms of contact can help to gain more insight into the movement strategies that may prevent or provoke ACL injuries.
[1] Boden & Sheehan, J Orthopaed Res, 2022
[2] Brown & Hume, Sports Med, 2014