A 34-year-old power lifter visits the outpatient clinic because he has difficulty walking. During physical examination it is observed that the patient has a problem unlocking the knee joint to permit flexion of the leg. Which of the following muscles is most likely damaged?,

Popliteus serves in unlocking the knee , it rotates the distal poion of the femur in a lateral direction. It also draws the lateral meniscus posteriorly, thereby protecting this cailage as the distal femoral condyle glides and rolls backward, as the knee is flexed. The Biceps Femoris is a strong flexor of the leg and laterally rotates the knee when it is in a position of flexion. The Gastronemius is a powerful plantar flexor of the foot. The Semimembranosus is involved in extending the thigh and flexing the leg at the knee joint.