During our self evaluation of the foot, we spent a lot of time talking about the three main areas of the foot: 1) the rear foot, 2) the mid foot, and 3) the forefoot. Normal foot and ankle function requires the coordinated use of all three which is what makes healing foot injuries and restoring normal function so challenging. If one part isn’t moving properly or lacks the strength/coordination to move through that mobility, then the other parts will be forced to try and compensate for that.
In the intrinsic posts, we explored the mid and forefoot in more depth by focusing on the smaller muscles in those areas. In this post, we’re going to start our discussion on the rear foot and the long tendons coming down into the foot. Before we dive into the individual muscles though, I wanted to take a few minutes to go over the rearfoot anatomy and how it moves. It’s easy to simplify things as being either “the foot” or the “ankle”, but there is A LOT of overlap between the two. For example, there are two joints responsible for the four movements at the ankle. The talocrural joint moves the foot up and down (into dorsi and plantarflexion) and the subtalar joint tilts the foot in and out (into inversion and eversion). These joints are literally stacked on top of each other in the rearfoot. If one hits the ground wrong, you can guarantee that the other will be as well.
Here’s a visual of what I mean:
Onto the muscles!
The front of the lower leg, or the shin, is made up of four extrinsic muscles. Extrinsic just means that the muscle belly is above the ankle while it’s tendon inserts below the ankle somewhere in the foot. The four muscles are: 1) the tibialis anterior (or the anterior tib), 2) the extensor digitorum longus (EDL), 3) the fibularis tertius (or peroneal tertius), and 4) the extensor hallicus longus (EHL). You may remember muscles with similar names from the intrinsic posts. Any easy way to remember the difference is look for the words brevis and longus. Brevis means intrinsic and longus means extrinsic.
#1 Tibialis Anterior (AT)
- When you look at the muscles along the shin there are essentially three options for where they can originate: strictly on the tibia, on a combination of the tibia and fibula (and the interosseus membrane that holds them together), and strictly on the fibula. The AT muscle originates strictly on the tibia.
- It then crosses over the shin itself to wrap around the medial arch, attaching to the first cuneiform and the base of the first metatarsal. This is important! If you’re someone with low arches or a super flexible foot that can pronate easily, the AT will definitely be a muscle to watch.
- The AT is responsible for moving two joints. It dorsiflexes the ankle and inverts the foot.
- While the AT does not attach directly to any of the foot intrinsics, it is connected fascially to the peroneal longus muscle. Think of it like a belt loop wrapped around your foot. Restrictions in one will 100% affect the other. That means if you’ve been battling peroneal/outer leg pain, you should be working on the anterior tib as well!
- The common pain referral area for this muscle is the purple circle pictured above. Note: see how most of that pain area is around the tendon versus up in the muscle belly?? This a good example of how working strictly on where it hurts doesn’t always help. Beating up a tendon to loosen it up won’t do much to change restrictions in the muscle itself.
- In the last post we talked about the plantar interossei. They are directly below the DI in the exact same inter-metatarsal spaces. Problems in one will definitely be present in the other. This is why they share the same pain referral areas.
- Mobility restrictions/trigger points in the AT are commonly misdiagnosed as compartment syndrome, shin splits, 1rst MTP joint dysfunction, and L5 nerve compression.
- In the video below, we’ll go over finding the AT muscle/palpating them, as well as, how to stretch it.
#2 Extensor Digitorum Longus (EDL)
- The EDL is deep to and directly lateral to the anterior tib. It originates on both the tibia and fibula and runs down the shin.
- The EDL then turns into four tendons, inserting onto the top of toes 2-4.
- This muscle is responsible for dorsiflexing the ankle and everting the foot (tilting it out). Again, this is two joints that are moving, not just one.
- Unlike the AT, the EDL does directly attach to two intrinsic muscles on the top of the foot- the dorsal interossei and the extensor digitorum brevis. Restriction in one will affect the other. Click here to review these two intrinsic muscles.
- The common pain referral area for this muscle is the purple circle pictured above.
- Mobility restrictions/trigger points in these little muscles are commonly misdiagnosed as misdiagnosed as shin splints, compartment syndrome, nerve entrapments (deep fibular nerve or L4 compression), tarsal joint dysfunction and MTP joint dysfunction.
- In the video below, we’ll go over finding EDL, as well as, how to stretch it.
#3 Fibularis/Peroneal Tertius (FT)
- Depending on the terminology used, you will hear this muscle called either the fibularis tertius or the peroneal tertius. Many people use the two interchangeably.
- In the picture above you’ll see the EDL muscle faded. This is because the FT is technically part of the EDL muscle. In fact, it is the lowest portion of that muscle. However… the FT is one of those muscles that may or may not be present. Some people have it on both sides, or just one, or not at all. Fun, right? 🙂
- The FT muscle originates strictly from the fibula and follows the EDL tendons before attaching to the 5th metatarsal. This does not impact the long EDL tendon to the 5th toe.
- This muscle is responsible for dorsiflexing the ankle and everting the foot.
- One thing to think about with this muscle is that it is part of the peroneal group. There are three muscles in total (the longus, the brevis, and the tertius). While the first two lie behind the lateral malleolus (ankle bone), this one lies in front of it. Remember that fascial loop between the AT and the peroneal longus? Problems in either of those muscles warrant checking this one out as well to make sure that it moves well.
- The common pain referral area for this muscle actually splits above the ankle into two areas (one in front of the ankle and one behind it where the other peroneal tendons are located).
- In the video below, we’ll go over finding FT, as well as, how to stretch it.
#4 Extensor Hallicus Longus (EHL)
- The EHL muscle is the most lateral of the shin muscles. It lies deep to both the AT and EDL and originates strictly on the fibula. It then crosses over the tibia/shin to insert onto the big toe.
- This muscle is responsible for extending the big toe both at the MTP and IP joints. It is also responsible for dorsiflexing the ankle and inverting the foot. That’s a lot of movements! If you’re someone who is lacking big toe mobility, this is a muscle that is likely stuck in that short position. Whether a muscle is stuck in a short or stretched out position, it still needs to be mobilized to restore function.
- Unlike the other muscles above, the EHL has no direct attachments to the other intrinisic muscles. That being said, while not attached, it does have an intrinsic muscle assisting it in moving the big toe however.
- Muscle restrictions/trigger points in this muscle are often misdiagnosed as 1rst MTP dysfunction.
- The common pain referral area for this muscle is the purple area pictured above.
Video on how to find these muscles (palpate) and stretch them:
Continue to part three (extrinsics on the inside of the lower leg) – coming soon