Regional vastus medialis and vastus lateralis activation in females with patellofemoral pain

INTRODUCTION:This study aimed to investigate whether regional activation patterns in the vasti muscles differ between females with and without patellofemoral pain (PFP), and whether muscle activation patterns correlate with knee extension strength.

METHODS:Thirty-six females with PFP and 20 pain-free controls performed a standardized knee flexion-extension task. The activation of vastus medialis (VM) and vastus lateralis (VL) was collected using high-density surface EMG and analyzed using principal component (PC) analysis. Spatial locations and temporal coefficients of the PC, and the percent variance they explain, were compared between groups and between the concentric and the eccentric phases of the movement. Correlations were assessed between PC features and knee extension strength.

RESULTS:The spatial weights of PC1 (general vasti activation) and PC2 (reflecting vastus-specific activation) were similar between groups (R > 0.95). Activation patterns in PFP were less complex than controls. Fewer PC features were necessary to reconstruct 90% of the signal for PFP participants in the concentric phase (P <0.05), and the difference in bias of activation to VM (concentric phase) or VL (eccentric phase) was less between phases for PFP participants (P <0.05). Smaller difference in vastus-specific activation in concentric and eccentric phases (less task specificity of VM/VL coordination) was related to greater maximal knee extension strength (P <0.05, R <-0.43).

CONCLUSION:These data suggest PFP involves a simpler control strategy of VM and VL. The inverse association between task specificity and maximal knee extension strength suggests different presentations of PFP: lower knee extension strength but VM/VL coordination task specificity comparable with controls, or knee extension strength comparable with controls but lower VM/VL coordination task specificity.