The human foot is a very complex and intricate structure that has to perform many different functions often in extremely short spaces of time.
When we stand it is our primary base of support to keep us upright and stable.
When we walk or run it needs to be able to:
- Absorb our weight,
- Adapt to uneven surfaces
- Act like a spring to help us move forwards or even a different direction to avoid an obstacle.
This is achieved in part by how the arch of our foot functions which is controlled by intrinsic and extrinsic foot muscles. These muscles have been termed the “core muscle ” system of the foot.
First some foot anatomy.
The foot can be divided into what is known as the active and passive systems when it comes to how it functions.
The passive foot structures, bones and ligaments.
The passive structures are those that we have no control over and basically the bones, ligaments and other tissues that make up the ” skeleton” of the foot.
It is however a very clever piece of engineering that allows it to go from a flexible adaptable structure to a relatively stiff/rigid structure very quickly.
Due to how they are orientated to each other they form the arches of the foot, the well known longitudinal arch that runs from the back to the front of the foot. Running from left to right is the transverse arch.
These two arch structures together form a “half dome” like shape at the bottom of the foot. This half dome is maintained by the ligament system and also the active intrinsic foot muscles.It is of a perfect design for adapting to changes in load imposed on the foot when we start to move or take part in sporting / dynamic activity.
Active or Intrinsic Muscle control system
Intrinsic muscles of the foot, the foot core muscles.
The arch of the foot is controlled with muscles that stabilise it muscles that are involved in larger movements of the foot. These local stabilisers are the four layers of what are known as plantar intrinsic muscles that originate and insert on the foot. These muscles are generally smaller and not able to produce much power but are critical in stabilising the arches.
The intrinsic foot muscles are presented in their anatomic orientation within the four plantar layers and the dorsal intrinsic muscle. The numbers correspond to the muscles as follows: (1) abductor hallucis, (2) flexor digitorum brevis, (3) abductor digiti minimi, (4) quadratus plantae (note its insertion into the flexor digitorum tendon), (5) lumbricals (note their origin from the flexor digitorum longus tendon), (6) flexor digiti minimi, (7) adductor hallucis oblique (a) and transverse (b) heads, (8) flexor hallucis brevis, (9) plantar interossei, (10) dorsal interossei and (11) extensor digitorum brevis.
This is pretty similar to the idea of the lumbar spine that has deep muscle groups that help control or add “stability” to the spine and larger muscles that are meant to move it.
Extrinsic or global movement foot muscles.
The global movers are the muscles that originate in the lower leg, cross the ankle and insert on the foot. These muscles are much larger than the intrinsic muscles and are i a better position to move the foot. However they are able to assist in provdinging some stability to the arch.
Why do you need a stronger intrinsic foot muscles ?
With each footstep, the four layers of intrinsic muscles act to control how much the half dome of the foot changes shape and how controlled that change is. If they are not functioning properly then this affects;
- Rate and change of shape of the foot.
- How the mechanics of the foot function.
- Ability of the foot to absorb force.
As a result we can then develop painful foot related problems as well as potentially increase risk of ankle and lower limb injuries.
Common issues that this can contribute to are:
- Plantar fasciopathy/fascitis.
- Achillies tendinopathy.
- Shin splints.
- Tibialis posterior tendinopathy.
Training the intrinsic muscles of the foot has also been shown to improve balnce and agility as well as possibly influencing more traumatic injuries such as ankle sprains and knee ligament issues.
So how do you strengthen the intrinsic muscles of your foot ?
The simplest way is to integrate the concept of the “short foot” exercise into your current exercise or rehab regime when doing lower limb exercises or any exercise in standing.
The foot is ‘shortened’ by using the intrinsic muscles to pull the first metatarsophalangeal joint towards the calcaneus as the medial longitudinal arch is elevated. As the arch raises during this exercise, it is also referred to as ‘foot doming’.
A recent study looking at foot muscle exercises and patellofemoral or kneecap pain showed the a regime of 15 x 5 second holds 4 days a week of the short foot exercise demonstrated an improvement in pain and function in those who added it to their hip and knee strength program.
Here’s a video to take you through the technique.
It’s a relatively simple exercise once you get the hang of it and is often about training the brain at the same time.
You can do it as 5 second holds throughout the day as described in the study about knee pain or add this into any squatting, leg strength exercises or balance activity and that is a great start to getting the foot core muscles working.
Cheers Dave.
Ref: The foot core system: a new paradigm for understanding intrinsic foot muscle function, Patrick O McKeon BJSM 49 V5