Augustus, Simon and Smith, Neal (2023) Changes in lower leg kinematic frequency content during pre-ground contact and weight acceptance phases of ACL injury risk screening tasks. In: XXIX Congress of the International/Japanese Society of Biomechanics ISB/JSB2023; 30 Jul - 03 Aug 2023, Fukuoka, Japan. (Unpublished)

Abstract

INTRODUCTION Change of direction (COD) and single leg drop jump (SLDJ) tasks are often used to assess non-contact ACL injury risk. Kinematic and force data are combined in 3D motion analysis to derive biomechanical proxies of injury risk (e.g. peak knee abduction moment during weight acceptance; WA). However, the extent to which foot-ground collisions induce expansion of lower leg frequency content is unknown. Understanding these changes is important if researchers are to optimise use of contemporary low-pass filter techniques that vary the magnitude of noise reduction over different phase of a task (i.e. transition from aerial to ground contact) [e.g., 1,2]. The aim of this study was thus to assess changes in foot and shank marker frequency content during the pre-ground contact phase, WA and post-WA phases of COD and SLDJ tasks. METHODS Three-dimensional lower limb kinematics were collected from 16 recreational athletes (77 ± 12 kg, 1.76 ± 0.09 m, 26.8 ± 4.5 years) performing unanticipated COD (approach velocity = 4-5 m/s) and SLDJ (drop height = 0.3 m) tasks (250 Hz; Oqus 300, Qualysis Medical AB, Sweden). Marker trajectories from the ground contacting leg (Table 1) were exported to Matlab (R2022a, Mathworks, USA) where frequencies corresponding to 95% cumulative signal power were determined for each: pre-ground contact (peak vertical position to vGRF > 10N), WA (vGRF > 10N to first trough following the vGRF impact peak) and post-WA phases (first trough following the vGRF impact peak to vGRF < 10 N). This analysis was performed in each X (medial/lateral), Y (anterior/posterior) and Z (vertical) planes and comparisons between phases made using pairwise effect sizes (Cohen’s d; 0.2 - 0.5 small, 0.5 - 0.8 medium, > 0.8 large). RESULTS AND DISCUSSION COD and SLDJ tasks both showed large expansions in marker frequency content between pre-ground contact to WA, then reductions between WA and post-WA (d = 0.5 – 4.0; Table 1). This was likely due to the sudden deceleration of the markers after foot-ground collision. For COD, while frequencies expanded in all planes following ground contact, this was most pronounced in the vertical plane (d > 2.0) and these changes were similar irrespective of marker location. For SLDJ, frequency content was generally lower than for COD, and thus expansion and reduction was less pronounced (d = 0.3 – 3.0). This was likely due to a slower ground-contact velocity. However, like COD, the largest expansions during WA were in the vertical plane and were most evident for the foot markers (Table 1). CONCLUSIONS COD and SLDJ ACL injury risk screening tasks induce abrupt expansion and then reduction of lower leg kinematic frequency content following foot-to-ground collision. Given proxies of injury risk are often derived after transition to the higher frequencies during WA (e.g., peak knee abduction moment), researchers might consider using low-pass filter methods that vary the magnitude of noise reduction in different phases of a movement [e.g., 1,2]. The data presented here can help inform cut-off frequency selection and optimise signal-to-noise ratios when using such methods for COD and SLDJ tasks. However, it remains to be seen whether adopting such techniques would offer improvements for identifying individuals at risk from non-contact ACL injury. REFERENCES [1] Augustus S et al. J Biomech 101: 109639, 2020. [2] Davis D & Challis J. J Biomech 101: 109619, 2020

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