Knee Muscles

How Do The Knee Muscles Work?

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

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

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 Are Around The Knee?

The main knee muscle groups are the:

• Quadriceps: four muscles found on the front of the thigh 
• Hamstrings: three muscles found on the back of the thigh
• Calves: two muscles found on the back of the lower leg
• Glutes: three muscles that make up the buttocks
• Popliteus: small muscle found at the back of the knee

Let's have a look at each of the muscles around the knee, how they work, what activities they are important for, how they are injured and how to target them.

1. Quadriceps

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.

Quads Function

• Straighten the leg
• 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
• Work with the glutes (bottom muscles) and hamstrings to supply the thrusting forces of walking, running and jumping.
• Controls the movement of the patella (kneecap)

2. Hamstrings

The hamstrings are made up of three muscles in the back of the knee and thigh. They are the main knee flexor muscles and 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.

Hamstrings Function

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

4. Gluteal Muscles

Another group of muscles not to be overlooked with knee problems is the glutes, or buttock muscles: 

• Gluteus Maximus
• Gluteus Medius 
• Gluteus Minimus
• Piriformis

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 and would benefit from glute strengthening exercises and in some cases glute stretches as swell.

5. Popliteus

Popliteus is one of the small muscles in the back of the knee.

It is often overlooked when thinking about knee muscles but popliteus plays an important role in helping the knee to twist, as well as aiding stability of the knee and helping to protect the lateral meniscus.

Can Muscle Problems Cause Pain?

Yes, problems in the knee muscles do cause pain! Tightness or weakness in the quadriceps, hamstrings and other muscles around the knee 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 muscles are also often injured. It may be that they are overstretched and tear, or that they are overused and become inflamed.

Common injuries associated with the knee muscles include:

• Jumpers Knee
• Quads Strain
• Quads Rupture
• Quadriceps Tendonitis
• Calf Strain
• Iliotibial Band Syndrome
• Knee Bursitis
• Hamstring Tendonitis
• Hamstring Strain

How To Strengthen Knee Muscles

People often start with open chain exercises, where the foot is free rather than fixed and progress to close chain exercises where the feet are fixed to the floor and thus there is weight going through the leg as you exercise.

You can find a whole range of strengthening exercises for the knee muscles, whatever level you are at, in the knee strengthening exercises section.

How To Stretch The Knee Muscles

There is much debate on the best way to stretch muscles and in the knee stretches section, you can find out everything you need to know about the best way to stretch including how to check if your knee muscle are tight and how to stretch each of the muscles around the knee.

Knee Muscle Locations

Hamstrings

1. Semimembranosus: is the most superficial (closest to the surface), found on the medial (inner) side of the back of the thigh
   
   
2. Semitendinosus: is found underneath semimembranosus
   
   
3. Biceps Femoris: is found on the lateral (outer) side of the back of the thigh. Attaches to the fibula and outside of the tibia

Page Last Updated: 12/05/23
Next Review Due: 12/05/25

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