A COMPARISON OF THE ACTIVATION OF MUSCLES MOVING THE PATELLA IN NORMAL SUBJECTS AND IN PATIENTS WITH CHRONIC PATELLOFEMORAL PROBLEMS

The activation of the oblique fibres of vastus medialis, the postero-l ateral fibres of vastus lateralis, and rectus femoris was studied by s urface electromyography, during the force development of a maximal iso metric contraction, performed near full extension (20 degrees of flexi on), by 49 patients with chronic patellofemoral problems and 20 normal subjects. In the normal subjects activation of oblique portions of th e vasti was in advance of force rise, during the time for 80% tension development. In the patient group, however, the activation of these la gged behind force rise. Force rise was slower in the patients even tho ugh the contraction was generally pain free. In all groups the activat ion of these two sections of the muscle remained approximately synchro nous, suggesting that they have a reciprocal action in controlling pat ellar position, disruption of which might contribute to patellofemoral problems.