The Correlation Between Single Leg Squat and Rear Step-down Frontal Plane Knee Motion

The single leg squat (SLS) is a transitional movement assessment used to identify lower extremity movement dysfunction. Poor performance on this assessment may indicate a lack of frontal plane stabilization due to impaired neuromuscular control. Increased knee valgus during the SLS may be linked with increased risk of lower extremity injury. The rear step-down (RSD) movement is similar and may be an alternative screen for individuals that are unable to perform the SLS. PURPOSE: The purpose of this study was to determine the correlation between SLS performance and RSD performance in collegiate aged, female athletes from sports with a high percentage of ACL tears. METHODS: Eleven college aged, female athletes were recruited and granted informed consent for this IRB approved study. Reflective markers were placed at the ASIS, medial and lateral femoral epicondyles, and medial and lateral malleoli. Digital video was collected in the frontal and sagittal planes using Vicon Vue cameras (Vicon Motion Systems, UK) sampling at 60 Hz while subjects performed three trials each of the SLS and step-up/step-down exercise bilaterally. Step height was based on participant height. 2-D kinematics for the SLS and RSD were analyzed using Kinovea software to compute frontal plane projection angle (FPPA) of the knee. FPPA was determined by placing the fulcrum between the epicondyle markers, with the proximal segment aligned with the ASIS, and the distal segment aligned between the malleoli markers. The FPPA was measured as the peak valgus position that was observed during each movement and then averaged across the three trials. SPSS 27 (IBM SPSS Statistics, USA) was used to calculate a Pearson correlation coefficient to determine the relationship between peak FPPA during SLS and RSD respectively. RESULTS: There was a moderate, positive correlation between SLS and RSD performance (r = .32, n = 22) however, the correlation was not significant (p = .15). There was no significant difference (p = .14) between the SLS (-17.9 ± 11.5o) and RSD (-14.2 ± 7.3o), with negative numbers indicating movement toward valgus. CONCLUSION: Performance on the SLS and RSD do not appear to be correlated in this population. Based on these findings, it is not appropriate for a clinician to substitute the RSD for the SLS to determine knee valgus in an athletic female population.