muscles acting on the knee and leg

quadriceps femoris

• knee extension, as in kicking a ball or rising from a chair

rectus femoris

• knee extension, as in kicking a ball or rising form a chair

• hip flexion

vastus lateralis

• knee extension 

• retention of patella on patellar surface of femur during knee movements

vastus medialis

same as vastus lateralis

vastus intermedius

knee extension

sartorius

• knee and hip flexion, as in sitting or climbing

• thigh abduction and lateral rotation

biceps femoris

• knee flexion

• hip extension

• lateral rotation of tibia on femur when knee is flexed

• lateral rotation of femur when hip is extended

• elevates trunk when rising from stooped or kneeling position

• counteracts forward bending at hips

semitendinosus

• knee flexion

• medial rotation of tibia on femur when knee is flexed

• medial rotation of femur when hip is extended 

• counteracts forward bending at hips

semimembranous

same as semitendinosus

popliteus

• medial rotation of tibia on femur

• lateral rotation of femur if tibia is fixed, to unlock knee when joint is extended and allow knee flexion