Knee Muscles

Written By: Chloe Wilson, BSc(Hons) Physiotherapy
Reviewed by: KPE Medical Review Board

Knee Muscles: Find out everything you need to know about the muscles that control the knee, how to keep them in good shape and how they can go wrong.

Our knee muscles are responsible for initiating and controlling movement of the knee and the kneecap.

They also work work with the various buttock, thigh and calf muscles to help control the hip and foot. 

When we think about knee muscles, the ones that usually spring to mind are the quadriceps, found on the front of the thigh, and the hamstrings, found at the back of the thigh. 

How Do The Knee Muscles Work?

The hamstrings and quadriceps work together, one contracting (agonist) while the other relaxes (antagonist) to allow the knee to bend and straighten.

There are also other muscles that work with the quads and the hamstrings, that are just as important to help protect the knee, most notably the glutes and calf muscles.

Knee muscles need to have both good strength and flexibility. Any tightness or weakness makes you prone to a whole host of knee problems. 

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.


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

Location: The quads are found on the front of the thigh from the hip to the knee

Action: Their main action is to straighten the knee, but they also help bend the hip

Common Activities: Getting up from a chair, going upstairs, walking & running

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.

The four muscles, vastus medialis, vastus intermedius, vastus lateralis and rectus femoris, each originate from the top of the femur (thigh bone).

They pass down the front of the thigh and then join together near the knee to form the quadriceps tendon.

The quads 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: The hamstrings are found on the back of the thigh from the hip to the knee

Action: Their main action is to bend the knee, but they also help to extend the hip

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.

Each of the three hamstrings muscles, semimembranosus, semitendinosus and biceps femoris, originate from the bottom of the pelvis, travel down the back of the thigh 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.

Calf Muscles

Calf Muscles

Just below the knee on the back of the shin are the calf muscles, soleus and gastrocnemius.

The calf muscles mainly control foot and ankle movement but the do also play a small part in knee movements.

Weakness in the calf muscles can often lead to knee pain too. 

Gluteal Muscles

Another group of muscles not to be overlooked with knee problems is the glutes, or buttock muscles, gluteus maximus, gluteus medius and gluteus minimus.

The glutes play a very important role in the stability of the knee and in my experience, almost everyone suffering from ongoing knee pain has weak glutes.

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.

  1. Knee Pain Guide
  2.  ›
  3. Knee Anatomy
  4.  ›
  5. Knee Muscles

Page Last Updated: 11/10/18
Next Review Due: 11/10/20

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