Video: Muscles of the foot

What do an onion, skin, cake, and the muscles of the foot have in common? Layers -- they all have layers -- and to quote Shrek, “For your information, there's a lot more to the muscles of the foot than most people think.”

The muscles of the foot are traditionally studied in either layers or groups. The plantar muscles of the foot can be classified into four muscular layers while the dorsal and plantar muscles of the foot can be classified into four groups. Today we will explore the muscles of the foot through both of these classification systems. We'll begin with taking a look at the muscle layers of the foot before exploring the dorsal, central, medial, and lateral plantar muscle groups of the foot. Keep an eye out for some helpful study tips along the way which might help you remember all of these tricky muscles. This tutorial will just be an introduction or an overview to the muscles of the foot. For a more detailed 3D view of each muscular group, you can check out these videos.

So let's begin with taking a look at the muscles of the foot as a whole. The muscles of the foot, also known as the intrinsic muscles of the foot, originate and insert solely within the foot. These muscles mainly function to stabilize and support the arches to maintain foot structure. They also partially contribute to the movements of the foot. There are a total of 19 muscles in the foot and that doesn't even include the extrinsic muscles which have attachments in both the leg and the foot. The tendons of the extrinsic muscles of the foot can be seen traveling alongside some of the short muscles of the foot.

Muscles of the foot can generally be divided into four groups which include a dorsal group and three plantar groups -- central plantar, medial plantar, and lateral plantar groups -- or four layers. The plantar fascia which surrounds all muscles of the sole of the foot consists of three chambers, or compartments, which therefore divide the plantar muscles of the foot into central, medial, and lateral plantar groups.

The dorsal group of muscles, as its name suggests, are located on the dorsum of the foot. Muscular layers of the foot extend from superficial to deep with the most superficial muscles located in the first layer and the deepest muscles in the fourth layer. Let's begin with exploring the muscle groups of the foot.

The dorsal muscle group of the foot is composed of two muscles -- the extensor digitorum and extensor hallucis brevis muscles. Nice and easy to remember. The names of these muscles also give us a clue as to where they are headed and the action they elicit on contraction. The extensor digitorum brevis muscle inserts onto the digits while the extensor hallucis brevis muscle insert onto the hallux, or the great toe, as it is more commonly known. These muscles lie within the dorsal fascia on the dorsum of the foot and contributes to extension of the great toe and toes 2 to 5. The dorsal group of muscles of the foot are supplied by the deep fibular nerve.

Moving on, let's take a look at the plantar muscles of the foot beginning with the lateral plantar muscles. As their name suggests, the lateral plantar muscles are located on the lateral aspect of the foot. This group of muscles is made up of the abductor digiti minimi, flexor digiti minimi brevis, and opponens digiti minimi muscles. These muscles sit layered on top of each other with the abductor digiti minimi muscle being the most superficial. The lateral group of plantar muscles all act on the little toe as the digiti minimi in their name suggests.

The central muscles of the sole of the foot lie within the central compartment between the muscles of the big and little toe. It consists of layers of numerous short muscles which form the central surface of the sole of the foot. The central plantar group, from superficial to deep, is composed of the flexor digitorum brevis, quadratus plantae, lumbricals, plantar interossei, and dorsal interossei.

The medial plantar group of muscles form a bulge referred to as the ball of the great toe. This group of muscles are located within the medial compartment of the sole of the foot and attached to the hallux or great toe. Muscles of this group consist of the abductor hallucis, adductor hallucis, and flexor hallucis brevis muscles. Just remember, FLEXing ADDs ABs.

The plantar muscles of the foot are also organized into layers. The layered classification system does not include the two dorsal muscles of the foot or the opponens digiti minimi muscle. Plantar muscles of the foot can be organized into four layers. The first layer forms the most superficial layer and consists of the abductor hallucis, flexor digitorum brevis, and abductor digiti minimi muscles. This group of muscles lie immediately deep to the plantar aponeurosis on the sole of the foot. Struggling to remember which muscles belong to the first layer? ABs FLEX ABs -- abductor hallucis, flexor digitorum brevis, and abductor digiti minimi.

Peeling back the first layer reveals the second layer. The second layer of the plantar group consists of two muscle groups -- the lumbricals and the quadratus plantae. Also traveling through this layer are the tendons of the flexor digitorum longus and flexor hallucis longus muscles. The muscles of the second layer lie deep to the first layer and act on toes 2 to 5.

The third muscular layer of the plantar group consists of three muscles -- the flexor hallucis brevis, adductor hallucis, and flexor digiti minimi brevis muscles. This muscular group lies just deep to the second layer and acts at both the great and little toe. Just like the first layer, we can switch this one around and use FLEX ADD FLEX to remember the muscles of this layer -- flexor hallucis brevis, adductor hallucis, and flexor digiti minimi brevis.

The fourth layer forms the deepest muscular layer of the foot and is composed of the three plantar and four dorsal interossei. A handy way to remember the muscles of the fourth layer and the movements they elicit is 3 PAD and 4 DAB -- three plantar interossei muscles which function to adduct toes 3 to 5 and four dorsal interossei muscles that abduct toes 2 to 5. Also traveling through the fourth layer are the long tendons of the tibialis posterior muscle and the fibularis longus muscle.

Does it all seem a bit confusing? I mean, there are so many muscles. Which muscle belongs in which layer? Well, maybe this might help you to remember how many muscles are in each layer. Generally speaking, layers 1 and 3 both contain three muscles while layers 2 and 4 contain two muscles and two tendons. Now that's all left is to remember the names of each of the muscles.

And that's it! A short introduction to the classification of the muscles of the foot and a few helpful tips to make remembering these muscles a little bit easier.

Check out our more in-depth videos on the medial, lateral, and central muscles of the foot to learn about their origins, insertions, innervations, and functions using 2D illustrations and a 3D model.