Knee Muscles

The knee muscles control how the knee joint and patella move. There are two main groups of muscles, the quadriceps and the hamstrings, as well as a small muscle behind the knee (popliteus).

The other muscles closely linked are the two calf muscles, which control how the ankle moves as well as the knee. 

It is vital to have both good strength and flexibility in the knee muscles.  Any tightness or weakness makes you prone to a whole host of knee problems.  Once you have finished this section, be sure to check out the knee stretches section which includes simple test to see if there is any tightness in your knee muscles and the knee strengthening exercises section.


Location: front of the thigh from the hip to the knee
Action: straighten the leg
Common activities: getting up from a chair, going upstairs
Common problems: tightness, weakness, muscle tear, tendonitis.

The quadriceps are the knee muscles found on the front of the thigh.  They work to straighten the knee

The quadriceps are a group of four muscles found in the front of the thigh and over the knee. Their primary role is to straighten the leg.

These muscles (vastus medialis, vastus intermedius, vastus lateralis and rectus femoris) all originate from the top of the femur (thigh bone) and then join together near the knee to form the quadriceps tendon. The tendon flows around the patella (kneecap) before finally attaching to the tibial tuberosity at the front of the shin bone, by which time it is known as the patellar tendon.

What Do the Quads Do?

1) Straighten the leg
2) Work most frequently in closed chain activity (meaning when the foot is fixed on the floor) e.g. getting up out of chair, walking upstairs
3) Work with the glutes (bottom muscles) and hamstrings to supply the thrusting forces of walking, running and jumping.
4) Controls the movement of the patella (kneecap)


The hamstrings are the knee muscles found on the back of the thigh.  They work to bend the knee

Location: back of the thigh from the hip to the knee
Action: bend the knee
Common activities: running, twisting the knee
Common problems: tightness, weakness, muscle tear, tendonitis

The hamstrings are made up of three muscles found in the back of the thigh. Their primary role is to bend the knee.

All three muscles (semimembranosus, semitendinosus and biceps femoris) start at the bottom of the pelvis and attach to the back of the knee.

What Do the Hamstrings Do?

1) Flex (bend) and rotate the knee
2) Help stabilise the knee by protecting the collateral and cruciate ligaments, especially when the knee twists
3) Lift the leg off the ground when walking
4) Provides the strength for propulsion e.g. running and jumping

Other Knee Muscles

There is a muscle behind the knee joint itself called popliteus which helps the knee to twist and aids stability of the knee.

The other muscles around the knee are the calf muscles (gastrocnemius and soleus) which attach just above and below the knee.  Whilst they play a small part in knee movements, they mainly control ankle movement.

Knee Muscles In-Depth

Muscles of the Lower Lim


Rectus Femoris: is the most superficial (closest to the surface), central muscle of thigh. It helps bend the knee and straighten the hip

Vastus Intermedius:
lies deep to rectus femoris. It runs down the middle of the thigh

Vastus Medialis:
wraps around femur anteromedially (front and inside part of the thigh). The main bulk of this knee muscle is in bottom part of thigh near the kneecap where it is known as VMO (Vastus Medialis Oblique)

Vastus Lateralis:
wraps itself round the femur anterolaterally (front and outside part of the leg). The main bulk of this knee muscle is at the top of the thigh


Semimembranosus: is the most superficial (closest to the surface), found on the medial (inner) side of the back of the thigh

is found underneath semimembranosus

Biceps Femoris:
is found on the lateral (outer) side of the back of the thigh. Attaches to the fibula and outside of the tibia

Can Muscle Problems Cause Pain?

Yes! Tightness or weakness in the quadricep and hamstring muscles are often part of the cause of knee pain. If there is muscle imbalance, it changes the way the forces go through the knee, and puts extra pressure on certain areas, leading to knee pain.

Knee stretches and strengthening exercises for the knee muscles help relieve knee pain in virtually every condition - click on the links to find out more.

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See Also

Anatomy overview

How can I strengthen my leg?

Test your flexibility - would stretching help you?

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