<prompt> Unlocking of knee:PopliteusQuadriceps femorisSemitendinosusSemimembranosus  <response>: Ans. a PopliteusRef: BDC vol II 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 do 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 femorisAlso know Quadriceps femoris incudes: Vastus Lateralis, Vastis Medialis, Vastus Intermedius. Rectus femoris is also known as kicking muscle 