A comparison of the activation of muscles moving the patella in normal subjects and in patients with chronic patellofemoral problems

Abstract

The activation of the oblique fibres of vastus medialis, the postero-lateral fibres of vastus lateralis, and rectus femoris was studied by surface electromyography, during the force development of a maximal isometric contraction, performed near full extension (20 degrees of flexion), by 49 patients with chronic patellofemoral problems and 20 normal subjects. In the normal subjects activation of oblique portions of the vasti was in advance of force rise, during the time for 80% tension development. In the patient group, however, the activation of these lagged behind force rise. Force rise was slower in the patients even though the contraction was generally pain free. In all groups the activation of these two sections of the muscle remained approximately synchronous, suggesting that they have a reciprocal action in controlling patellar position, disruption of which might contribute to patellofemoral problems.