Author(s): SHORTER, K., LATSINOS, E., LAKE, J., BENSON, A., Institution: SWINBURNE UNIVERSITY OF TECHNOLOGY, Country: AUSTRALIA, Abstract-ID: 1930

INTRODUCTION:
Quantifying barbell motion during the back squat is a valid and reliable approach to monitor training performance[1]. When contrasted with force-velocity metrics obtained via integration of vertical ground reaction force (vGRF) from a force plate, the bar trajectory demonstrates a strong positive correlation in the vertical plane[2]. Whilst movement of the centre of pressure (COP), the point of application of the vGRF in the horizontal plane, is reflective of stability[3], there is a paucity of research considering the insight horizontal plane motion of the bar may afford. This study evaluated the similarity between the bar and COP to quantify horizontal plane motion during the back squat.
METHODS:
Ten participants (age = 31.0 ± 10.1 years; mass = 82.7 ± 12.2 kg; height = 173.5 ± 7.82 cm; 1RM = 116.98 ± 18.32 kg) completed 3 sets of 8 full-depth back squat repetitions at 80%1RM emphasising maximal intent and velocity[1]. COP was derived from a Kistler 9281EA force plate sampling at 1000Hz synchronised to 8 Oqus 300 Qualisys cameras at 100Hz to quantify motion of the bar trajectory, defined as the midpoint between markers positioned on the bar ends. A 10Hz lowpass filter was applied to the bar trajectory with a bandpass filter applied to the COP within Visual3D. The concentric phase of each repetition[4] was extracted for analysis within Python 3.12, with horizontal plane motion defined by the range in the anterior/posterior (AP-Range) and medial/lateral (ML-Range) directions. Procrustes analysis[5] using Scipy.spatial assessed the similarity of horizontal plane motion between the bar and COP trajectories. Procrustes analysis applies an optimised transformation to minimise the distance between datasets with the associated dissimilarity measure implying the degree of similarity (0) or dissimilarity (1). Following exclusion of outliers (mean ± 3SD), statistical analysis was undertaken using descriptive statistics and Student’s t-tests (p=0.05) using Scipy.stats.
RESULTS:
From 234 back squat repetitions analysed, significant (p<0.001) differences with small-medium (AP-Range: bar = 8.87 ± 3.15cm, COP = 7.92 ± 2.57cm; d=0.337) and large effect (ML-Range: bar = 1.83 ± 0.97cm, COP = 6.52 ± 2.85cm; d= -1.816) were identified. Bar and COP trajectories had a dissimilarity score of 0.54 ± 0.24.
CONCLUSION:
Horizontal plane motion was significantly different for both AP-Range and ML-Range with Procrustes analysis establishing a lack of similarity between the bar and COP trajectories during the concentric phase of the back squat. Whilst the practical suitability of vertical plane motion of the bar to monitor training performance during the back squat is accepted [1], further research is required to elucidate horizontal plane contributions with results identifying that such motion should not be considered reflective of the COP or therefore stability during a back squat.

1.Thompson et al (2020) 2.Rahmani et al (2000) 3.Kohn et al (2021) 4.McMahon et al. (2018) 5.Krzanowski, W (2000)