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Athletes Rated as Poor Single-Leg Squat Performers Display Measurable Differences in Single-Leg Squat Biomechanics
Context:
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.
Objective:
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.
Design:
Comparative cross-sectional study.
Setting:
University laboratory.
Participants:
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, and knee movement), and were rated as good (n = 23), fair (n = 41), or poor (n = 15) performers.
Intervention:
A subset of good (n = 16) and poor (n = 12) performers underwent biomechanical assessment, completing 5 continuous single-leg squats on their dominant limb while 3-dimensional motion analysis and ground reaction force data were recorded. Poor performers repeated the task standing on prefabricated foot orthoses.
Main Outcome Measures:
Peak external knee adduction moment (KAM) and peak angles for the trunk, hip, knee, and ankle.
Results:
Compared with good performers, poor performers had a significantly lower peak KAM (mean difference = 0.11 Nm/kg, 95% confidence interval = 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 toward 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.
Conclusions:
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.
