Bilateral asymmetries of lower extremity strength have been reported in the literature and their existence may influence performance and increase injury risk. Although functional movement screen (FMS) deep squat (DS) scoring criteria does not include lateral weight shift, previous reports have demonstrated weight distribution asymmetry in both adolescent soccer players and active, adult participants. Lateral weight shifts are often observed in FMS DS, however, no previous report has determined the ability to validly and reliably observe this characteristic.
PURPOSE: To determine if lateral weight shift could be reliably rated when compared to bilateral vertical ground reaction forces (vGRF) during FMS DS.
METHODS: Thirty-seven active subjects (19 F, 18 M, 20.8 ± 1.4 yrs) granted informed consent and performed three FMS DS trials on two force plates (1200 Hz) while video (30 Hz) captured frontal, sagittal plane views. A Matlab script processed vGRF data with a lowpass filter and computed limb symmetry index (LSI) during the descent phase and full squat position. Two sports medicine professionals independently viewed videos and rated asymmetry using a novel, web-based sliding scale scoring rubric. Raters scored trials from 0-100 in interval increments of 1 with 50 representing a symmetric DS. Scores were averaged across trials and intraclass correlations (ICCs) were performed to determine inter-rater reliability. Receiver operator characteristics (ROC) curves determined cut-off scores that maximized sensitivity and specificity of determining substantial weight shifts (>10%, >15%).
RESULTS: Subjects demonstrated average LSI of 9.8 ± 6.9% with eighteen subjects demonstrating LSI > 10%. Raters were able to determine correct shift direction (L, R) in 57.7% of all subjects and 68.1% for those with average LSI > 10%. Inter-rater reliability was poor (ICC=0.41, 95% CI=-0.07, 0.69). All ROC curve areas were < 0.61 indicating the scoring rubric failed to accurately diagnose LSI > 10% or >15%.
CONCLUSIONS: Although active, adult subjects demonstrated lateral weight shift during FMS DS, raters weren’t able to reliably observe this shift even in severe cases. Clinicians should demonstrate caution when prescribing interventions based on visual observance of lateral weight shift during the FMS DS.