3D Motion Analysis of Single-leg Squat with Association to Hip Strength and Ankle Dorsiflexion

The purpose of this study was to determine if a correlation exists amongst single-leg squat (SLS) depth (defined as peak knee flexion during a SLS) using a 3D motion analysis system, hip strength, and ankle dorsiflexion range of motion (DF ROM) in a healthy population. Seventy-two participants (59.7% female, aged 22.6 + 2.79 years) met the inclusion criteria, without current lower extremity injury or previous musculoskeletal surgery. Closed-chain ankle DF ROM, hip abduction and extension strength, and a SLS task were measured. A smartphone inclinometer app (iHandy Level) was used for ankle ROM, an externally fixed handheld dynamometer for hip strength, and a single-camera 3D motion analysis device for the SLS depth. There were statistically significant, but low, positive correlations between right (R) and left (L) ankle DF ROM and the respective SLS depth (R: r = 0.223, p = 0.030; L: ρ = 0.373, p <0.001). Non-significant correlations were found between R and L hip abductor strength to the respective SLS depth and ankle DF ROM. Post-hoc analyses were conducted to determine whether exercise frequency impacted the association between SLS depth and ankle DF ROM. A statistically significant moderate positive correlation existed for individuals exercising >3x/week (R: p = 0.003; L: p <.001), but non-significant for those exercising 0-2x/week (R: p=0.279; L: p= 0.174). Findings are congruent with previous literature regarding the biomechanical influence from ankle mobility to SLS depth; however, hip strength does not appear to affect SLS depth. The methodology of this study offers a feasible, clinically applicable approach for functional movement assessment.