Foot intrinsics & intrinsic foot muscles
It is a commonly known “fun fact” that the bones of the feet make up roughly 25% of the total bones in the body. What is not as commonly understood is the complexity of the role the foot plays in the overall function of the body and the importance of the muscles that control the foot. A well functioning foot can adapt shape and both generate and dissipate force depending on the demands placed on it. Just think of a foot walking barefoot on pebbles compared to sprinting at top speed compared to dancing en pointe. The muscles of the foot make all these different activities possible.
When we discuss the muscles of the foot, they are often separated into two groups – intrinsic and extrinsic muscles. Intrinsic means the muscles originate and insert in the foot, while extrinsic means the muscle starts outside the foot (eg somewhere along the shin) but inserts in the foot (think along the lines of your calf muscles). The intrinsic muscles are often somewhat forgotten, but their importance in injury prevention is continuing to emerge in the research.
The intrinsic muscles of the foot are divided into layers. On the bottom (plantar surface) of your foot they are in 4 layers (listed below in order of most superficial to deepest)
- Plantarfascia (thick fascia that is influenced by the muscles that insert into it)
- Abductor hallucis, abductor digiti minimi, flexor digitorum brevis
- Adductor hallucis, flexor hallucis brevis, flexor digiti minimi
- Plantar interossei
On the top of foot is extensor hallucis brevis, extensor digitorum brevis and the dorsal interossei
Together these muscles control the arch of the foot, help modulate the foot and create the stiffness in the foot that is vital to forward propulsion in walking. Reduced strength and even muscle bulk of the intrinsic foot muscles has been implicated in a number of conditions in the foot and lower leg.
Below are some exercises that specifically target the intrinsic foot muscles. Even if you are injury free they are fun to try out!
Short foot exercise (doming) – sitting down and keeping the toes flat (ie not curling under), “shorten” the foot by drawing up the arch of the foot
Toe spread – try to separate your toes away from one another
Big toe extension – keeping your smaller toes flat on the floor, lift just the big toe up
Small toe extension – keeping your big toe flat on the floor, lift up toes 2-5
If you have a foot injury or are interested in learning more
about intrinsic foot muscles, chat to your physio!