What is the action of the Vastus Medialis?

• A. Flex the knee
• B. Abduct the hip
• C. Rotate the knee
• D. Extend the knee

Answer: (D)

The vastus medialis is part of the quadriceps group whose primary job is to extend the knee. When this muscle contracts, it pulls on the patellar tendon to straighten the leg at the knee joint. The vastus medialis, especially its medial fibers, also helps stabilize the patella and keep it tracking properly during extension.

Because knee extension is its main action, extending the knee is the best choice. Abducting the hip is done by the gluteal muscles, not the quadriceps. Rotating the knee isn’t a primary action of this muscle, and knee flexion is carried out mainly by the hamstrings and other flexors, not by the vastus medialis.