Knee Muscles

Author: Chloe Wilson - BSc(Hons) Physiotherapy

The main knee muscles can be divided into two groups - the quadriceps and hamstrings. They are responsible for initiating and controlling movement of the knee and the kneecap, and they also work work with the thigh and calf muscles to control the hip and foot. 

Here we look at each of the muscles of the knee, how they work, what can go wrong and how to prevent knee muscle injuries.

Muscles work in pairs, one contracting while the other relaxes to allow for smooth, full movement of 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 how to combat that tightness, and the knee strengthening exercises section, which has loads of exercises to help you safely and effectively build up your strength.


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

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 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, aids stability of the knee and helps protect the lateral meniscus.

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.

Another group of muscles not to be overlooked with knee problems is the gluteal muscles (gluteus maximus, gluteus medius and gluteus minimus) which play an important role in the stability of the knee.

Knee Muscles In-Depth

Leg and knee muscles


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. If you want to know more about the individual muscles, use the relevant links above.

Go to Anatomy Section or Knee Pain Guide

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