Electromyographic activity of vastus medialis obliquus and vastus lateralis muscles during functional activities in subjects with patellofemoral pain syndrome

Objective: The purpose of this study was to evaluate the amplitude and onset of electrical activation of the vastus medialis obliquus (VMO), vastus lateralis longus (VLL) and vastus lateralis obliquus (VLO) during functional activities in individuals with patellofemoral pain syndrome (PFPS). Methods: Twenty women participated in the study: ten in a control group and ten in the group with PFPS. The electromyographic signal of the quadriceps muscle was detected using simple active differential surface electrodes and a four-channel electromyography system, during open kinetic chain activities (using an isokinetic dynamometer) and closed kinetic chain activities (step and squat maneuvers). For the statistical analysis, Student’s t test and ANOVA with Tukey’s post-hoc method were used, with a significance level of p≤0.05. Results: The results suggested that the electrical activation of the VMO was less intense than in the VLO (p=0.04) and that there was greater delay in VMO onset (p=0.0023) in the group with PFPS, with regard to all of the functional activities evaluated. There was a significant difference between the VMO and VLO in relation to the activities of isokinetic extension at 30o/s (p=0.042) and step down with knee flexion at 75o (p=0.038) in the group with SDPF, and in the activities of rising from a bench (p=0.041), single-leg hop (p=0.046) and heel raising (p=0.004) in the control group. Conclusions: Under the experimental conditions used, this study suggests that there is an imbalance in the electric activity and abnormal recruitment patterns among the VMO, VLL and VLO muscles in individuals with PFPS, with greater delay and lower amplitude of activation of the VMO in this group.