Investigation of quadriceps femoris function through electrical stimulation.

OBJECTIVE: Patellofemoral dysfunctions are associated with problems in the knee extensor mechanism, including specific atrophy of the distal fibers of the vastus medialis, also known as the vastus medialis oblique. Rehabilitation of the vastus medialis in patellofemoral dysfunctions has been shown to be ineffective. This limitation had stemmed from the lack of understanding of the vastus medialis' specific functions. The purpose of this project was to investigate the role of four portions of the quadriceps femoris using surface electrical stimulation. DESIGN AND SETTING: Single-group and single-test (repeated measures on muscle portions) design. All tests were performed in a university laboratory. SUBJECTS: Eight healthy university students received electrical stimulation. MEASUREMENTS: Subjects were seated with the knee at 90 degrees of flexion and the leg pushing against a strain gauge that measured the force exerted. Electrical stimulation was administered on the vastus lateralis, rectus femoris, and proximal and distal fibers of the vastus medialis to quantify the torque produced by the knee extensors. The electrical stimulation maximum intensity was adjusted to achieve specific fiber recruitment and the highest isolated contraction. Force was measured with a strain gauge placed on the anterior aspect of the distal end of the tibia. Force was recorded in two levels: force applied before the onset of electrical stimulation and force produced by the stimulation. Subjects also performed two maximum isometric knee extensions before and after electrical stimulation for normalization. RESULTS: Electrical stimulation elicited mean torques of 6.31 per thousand, 14.0 per thousand, 20.2 per thousand, and 28.0 per thousand of maximum isometric voluntary contractions of the distal and proximal fibers of the vastus medialis, the vastus lateralis, and rectus femoris, respectively. CONCLUSIONS: The distal fibers of the vastus medialis do not contribute significantly to knee extension.