<prompt> Which muscle is responsible for unlocking of knee?PopliteusQuadriceps femorisSemitendinosusSemimembranosus  <response>: Ans. A PopliteusRef: BDC, vol II pg. 155 Quadriceps femoris is the main and only extensor of knee. It produces locking action as a result of medial rotation of the femur during the last stage of extension. To reverse this lock popliteus muscle comes into action and does so by the lateral rotation of femurRemember: Lock is: Quadriceps femoris muscle and, Key is popliteus muscle.Muscles producing movements at the knee jointMovementPrincipal musclesA. Flexion Biceps femoris Semitendinosus SemimembranosusB. ExtensionQuadriceps femorisC. Medial rotation of flexed leg Popliteus Semimembranosus SemitendinosusD. Lateral rotation of flexed leg Biceps femorisExtra Mile Quadriceps femoris incudes: Rectus femoris, Vastus Lateralis, Vastis Medialis, Vastus Intermedius. Rectus femoris is also known as kicking muscle 