Associations between hip and knee muscle volume and lower extremity energetics during a single-leg squat in females with patellofemoral pain.

BACKGROUND: Altered lower extremity biomechanics and elevated patellofemoral joint stress are proposed mechanisms underlying patellofemoral pain (PFP). Although clinicians often associate muscle weakness with kinematic alterations in females with PFP, the relationship between muscle volume and movement strategies remains unclear. RESEARCH QUESTION: Is hip and knee muscle volume associated with lower extremity kinematics and energetics during a single-leg squat (SLS) in females with PFP? METHODS: This preliminary exploratory study included thirteen participants (age=25.8 ± 6.0 years; body mass index=26.0 ± 6.4 kg/m2) who underwent assessments of magnetic resonance imaging-derived lower extremity muscle volume (hip abductors, hip extensors, hip external rotators, and knee extensors) and three-dimensional SLS kinematics (sagittal and frontal hip, knee, and ankle joint angles) and energetics (sagittal and frontal hip, knee, and ankle joint work). Bivariate correlation analysis assessed associations between hip and knee muscle volume and SLS biomechanics. Variables demonstrating significant bivariate correlations were entered into multiple linear regression models, adjusting for pain and disability. RESULTS: Hip and knee muscle volume were not significantly associated with kinematics (p > 0.05). However, smaller muscle volume across all hip and knee muscle groups studied was (1) strongly associated with greater sagittal plane ankle joint work (r = -0.86 to -0.73; p ≤ 0.004) and (2) moderately associated with greater frontal plane hip joint work (r = -0.67 to -0.56; p ≤ 0.049). In exploratory adjusted regression analyses, these associations were observed after accounting for pain and disability (β=-0.81 to -0.45; p ≤ 0.05). SIGNIFICANCE: Hip and knee muscle volume were associated with lower extremity energetics during the SLS in females with PFP.