Athletes Rated as Poor Single-Leg Squat Performers Display Measurable Differences in Single-Leg Squat Biomechanics Compared With Good Performers.

Lachlan E Garrick, Bryce C Alexander, Anthony G Schache, Marcus G Pandy, Kay M Crossley, Natalie J Collins

It is important to validate single-leg squat visual rating criteria used in clinical practice and research. Foot orthoses may improve single-leg squat performance in those who demonstrate biomechanics associated with increased risk of lower-limb injury. Validate visual rating criteria proposed by Crossley et al, by determining whether athletes rated as poor single-leg squat performers display different single-leg squat biomechanics than good performers; and evaluate immediate effects of foot orthoses on single-leg squat biomechanics in poor performers. Comparative cross-sectional study. University laboratory. 79 asymptomatic athletes underwent video classification of single-leg squat performance based on established visual rating criteria (overall impression, trunk posture, pelvis 'in space', hip movement, knee movement), and were rated as good (n=23), fair (n=41) or poor (n=15) performers. A subset of good (n=16) and poor (n=12) performers underwent biomechanical assessment, completing five continuous single-leg squats on their dominant limb while three-dimensional motion analysis and ground reaction force data were recorded. Poor performers repeated the task standing on prefabricated foot orthoses. Peak external knee adduction moment (KAM) and peak angles for the trunk, hip, knee and ankle. Compared to good performers, poor performers had a significantly lower peak KAM (mean difference 0.11 Nm/kg, 95% confidence interval [CI] 0.02 to 0.2 Nm/kg), higher peak hip adduction angle (-4.3°, -7.6° to -0.9°), and higher peak trunk axial rotation towards their stance limb (3.8°, 0.4° to 7.2°). Foot orthoses significantly increased the peak KAM in poor performers (-0.06 Nm/kg, -0.1 to -0.01 Nm/kg), with values approximating those observed in good performers. Findings validate Crossley et al's visual rating criteria for single-leg squat performance in asymptomatic athletes, and suggest that 'off-the-shelf' foot orthoses may be a simple intervention for poor performers to normalize the magnitude of the external KAM during single-leg squat.