NHI Eastern Kinesiology Practice Test

The action that straightens the knee comes from the quadriceps femoris group. Located at the front of the thigh, this four‑part muscle (rectus femoris and vastus lateralis, medialis, and intermedius) pulls on the patellar tendon. When they contract, the tendon pulls the tibia forward, extending the knee joint and straightening the leg. This group is the primary knee extensor, essential for standing up, kicking, and jumping.

The other muscles don’t extend the knee: the hamstrings on the back of the thigh bend the knee; the gastrocnemius crosses the knee but mainly acts to plantarflex the foot (and may assist knee flexion in certain positions rather than extension); the iliopsoas acts to flex the hip, not the knee.