The Concurrent Validity and Reliability of Single Leg Squat Among Physically Active Females with and without Dynamic Knee Valgus

Background The single leg squat (SLS) motion imitates various maneuvers in sports. It is commonly used as a functional test for the lower limb. SLS with two-dimensional (2-D) video analysis is regularly performed in the clinical setting to assess dynamic knee valgus (DKV). However, 2-D video analysis may not be able to demonstrate the same level of accuracy as three-dimensional (3-D) motion analysis. Purpose This study aimed to determine the within- and between-day reliability as well as the concurrent validity of 2-D and 3-D motion analysis of lower limb kinematics during 45 degrees and 60 degrees SLS among physically active females with and without DKV. Study Design Cross-sectional study Methods A total of 34 physically active females (17 individuals with excessive DKV and 17 without DKV) participated in the study. Their DKV was determined based on the cut-off values of knee frontal plane projection angle during drop landing. Their lower limb kinematics during SLS at 45 degrees and 60 degrees knee flexion were captured simultaneously by digital cameras (2-D motion capture) and infrared cameras (3-D motion capture). Intraclass Correlation Coefficient (ICC) was used as an indicator for within- and between-day reliability tests of both groups. Bland-Altman Plot and Pearson correlation were used to examine the validity of 2-D and 3-D motion capture methods in evaluating knee valgus angle. Results Two-dimensional knee FPPA and 3-D knee angle measured during 45 degrees and 60 degrees SLS in normal and excessive DKV groups showed moderate to excellent within-day and between-day reliability (ICC= 0.50). The current study showed that the 2-D knee frontal plane projection angle (FPPA) during 45 degrees SLS were valid for the non-dominant leg in both groups. Additionally, the 2-D knee FPPA during 60 degrees SLS were valid for non-dominant leg in excessive DKV group and dominant leg in normal group. Conclusion Two-dimensional knee FPPA during 45 degrees and 60 degrees SLS also showed high within-and between-day reliability for both groups. The validity of 2-D knee FPPA during SLS depends on the squat depth, stance leg, and presence of DKV.