Timing and Intensity of Vastus Muscle Activity During Functional Activities in Subjects With and Without Patellofemoral Pain

BACKGROUND AND PURPOSE: Differences in intensity and timing of muscle activity between the vastus medialis and vastus lateralis muscles have been hypothesized as contributing to lateral patellar tracking and patellofemoral pain (PFP). The purpose of this study was to ascertain whether there were differences in the activity of the vastus muscles that would be suggestive of patellar instability in subjects with PFP. SUBJECTS: Twenty-six subjects with PFP and 19 subjects without PFP participated in the study. METHODS: Fine-wire electromyography was used to record activity of the vastus medialis oblique, vastus medialis longus, vastus lateralis, and vastus intermedius muscles during level walking, stair climbing, and walking on ramps. Knee motion was assessed using a six-camera motion analysis system. RESULTS: No differences in onset or cessation of muscle activity was found among the vastus muscles for either group, regardless of condition. Subjects with PFP demonstrated less activity of all vastus muscles for level walking and ramp walking than did subjects without PFP. CONCLUSIONS AND DISCUSSION: These results do not support the hypothesis that timing or intensity differences between the vastus medialis and vastus lateralis muscles are associated with PFP.