The Fibularis and Tibialis Posterior Muscles: The more you Know the better.

The human body is an incredible machine. Every system is integrated, and each muscle interacts to bring both movement and balance to the rest. With that in mind, I want to look at two muscles, tibialis posterior and fibularis. We are going look at three injuries: Achilles tendon issues, shin splints, and ITB.

These two muscles balance each other out. Roll your foot inwards, and you are using tibialis posterior. Roll your foot outwards, and you use your fibularis.

Tibialis Posterior - Fibularis

Take a look at the above picture – look at the far left frame and study the pink muscle. That’s the tibialis posterior muscle. It is attached to the tibia and fibula and is the muscle that turns your foot inwards. It attaches to two bones on your foot:
1) the navicular bone – that’s the bone on the inside of your foot with a small bump on it. If you put your finger under the inside, top islet of your running shoe, you will feel the bump in the immediate vicinity. 2) It also attaches to your medial cuneiform; the bone is just forward of your navicular bone.

medial foot

This is one of the main areas that people get shin splints. Things that contribute to shin splints include a weakened tibialis posterior, a flat or high foot arch, or a foot prone to pronation. We always check what happens to this area when we fit running shoes to people.

The tibialis posterior muscle now wraps around the bottom of the foot via a band of fascia that connects on the other side with your fibularis muscle (See the third picture at the top of this article). Pull one of your calf muscles tight and look at the outside area of your lower leg. The muscle that lies on the outermost part of your leg is the fibularis.

If tight, the fibularis will pull the foot into a pronated position. You can read more about pronation here.  The fibularis attaches onto the same bony outcrop as the iliotibial band, this area is called Gerdy’s tubercle. You seldom find people with tight iliotibial bands who do not have tight fibularis muscles.

Get an imbalance in any of these two muscles and your Achilles tendon will cease to pull on a straight line this predisposing you to both calf and Achilles issues.

Some quick take home points –

  1. Make sure that both muscles are strong.
  2. Make sure that they are in balance. Sometimes you need to get a bit of myofascial release in the area.
  3. Make sure that the fibularis is released when dealing with ITB.
  4. Make sure that you are in the right running shoes. Too neutral a shoe or too corrective a shoe for your foot type, and you can allow one muscle to elongate and the opposite to shorten.
  5. Watch out for worn shoes. Put your shoes on a flat surface and look at the heel area. If the shoe slopes inward or outward, you could pick up a problem.
  6. Realise that everything in your body is connected.
  7. Give me a call if you are battling with an injury in this area and you feel I can help.


Mike Roscoe.
Mike Roscoe

About sbrsport

SBR Sport specialises in Swimming, Biking and Running. On the medical side we are able to do intensive bike setups, leg assessments and soft tissue release. Follow us on twitter - and/or facebook -
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