Tibialis Posterior

No pain in my heel today, I am happy to report, but a slight ache elsewhere in my leg prompted me to do some web research. I had an aching muscle in the same place in each of my lower legs, and I wondered what the cause could be. Try as I might, I couldn't figure out exactly what muscle it was that was aching. It didn't seem to fit with any of the descriptions I found. There are a surprising number of muscles in the lower leg, by the way.

Eventually I tracked it down - it was a muscle called the Tibialis Posterior. This muscle is located for the most part in the middle of the lower leg, between the tibia bone and the big muscles at the back of the calf (not shown). From there, a tendon extends down and behind the Medial Malleolus, the bony lump on the inside of the ankle, and under the foot, where it joins onto one of the bones under the sole.

This muscle has three main functions. Firstly it is responsible for 'inversion' of the foot. Sit in a chair with your legs straight out in front of you and the soles of your feet pointing away from you. Now bend your right ankle so that the sole of the right foot is pointing inwards towards your left foot. The Tibialis Posterior muscle is what you just used to do that movement.

Secondly, it helps with plantarflexion, that is to say the pointing of the toes. Sit in the same position as before and point your toes away from you. The main muscle doing this movement is the big one at the back of the calf - the Gastrocnemius, but the Tibialis Posterior is assisting.

Thirdly, and most importantly from a running point of view, the Tibialis Posterior is responsible, with its antagonist, the Tibialis Anterior, for stabilising the foot. These muscles keep the foot stable and flat when running. Each time the foot is planted on the ground, your weight tries to evert the foot (the opposite of inverting it) and flatten the arch, and the Tibialis Posterior tenses and pulls back, supporting the arch and bringing the foot back into line. If you have flat feet, it is often this muscle that is underdeveloped. So the fact that mine is aching a little is a good thing - it just means it is doing the job it is supposed to be doing, and which it probably hasn't been doing for a while.