The Adaptation of the Foot by James Earls

We are delighted to have James Earls shed some light on the foot and explain why they are not only important, but also fascinating. Taken from his book 'Born to Walk', James gives an insight into foot's function and role in movement.

Inspired? Read on for some foot investigation...

Born to walk james earls

As manual therapists, we are often taught the importance of the feet, their movements and role and the fact that they contain also one quarter of the bones in the body. More often than not though, these smelly and anaesthetically pleasing structures come with complex mechanics that are too often ignored.

We are delighted to have James Earls shed some light on the foot and explain why they are not only important, but also fascinating. Taken from his book ‘Born to Walk’, James gives an insight into foot’s function and role in movement.  Inspired? Read on for some foot investigation...

The first contact of the foot with the ground is perhaps the most important event in many movement chains. It is the first stage of “stance” phase in walking, and it will define what happens throughout the rest of the body, provided the body can accept and adapt to this impact: tensegrity in action (see figure 1).

Figure 1 born to walk

Fig 1 - When we see the body represented as a tensegrity system like this, with just the musculoskeletal elements presented (in vague approximation of reality), it is easier to comprehend how the body interacts with its environment to dissipate and produce force.

Tensegrity is the balancing act between the skeletal and myofascial systems. The tension of the myofascia should be holding each bone in some form of suspension – it is almost as if each bone has its own trampoline. It is important to remember that the skeleton does not support itself, it requires the contractile, stiffening elements of the myofascia and they also require the anchoring pints of the skeleton. It is a truly interdependent system.

The ankle complex is only the first in a series of joints that should absorb some of the shock of impact. The knee and then the hip will be the next major shock absorbers, followed by the spine. It is, therefore, the accumulation of small corrections that both spread the load of the shock and also stimulate the appropriate myofascial response. 

As we explore later in the book, this helps to distribute the forces and also initiates many energy saving mechanisms within the body’s tissues. The opening, or unlocking, of the bones of the foot is the first of many responses in a complex but yet predictable chain through the body and it is this which brings tensegrity alive and into context within our bodies.

With the foot in front of the body and the first contact coming to the heel, the ground reaction force will be angled posteriorly and superiorly, causing the ankle to plantarflex and decelerate (see fig. 2).

Figure 2 born to walk

Figure 2 - Impact with the ground leads to a quick deceleration of the foot of the swing leg, and the interaction of the forward momentum of the foot and the ground reaction force will create a strong deceleration of the calcaneus.

Some writers have described the form of the back of the foot as a flawed design, due to the greater portion of body weight being transferred through the talus, which is not fully on top of the calcaneus (see fig. 3). This design, however, is essential for the easy, economical, and shock-absorbing walking that we all aim for. On a firm surface, the calcaneus will be brought to an abrupt stop, but the body’s momentum will still be bearing down on top of it. A significant portion of the weight coming onto it is resting on a ledge of bone known as the sustentaculum talus—sometimes referred to as the “waiter’s tray”—and this arrangement creates the ability for the calcaneus to tilt under the weight descending through the talus (see fig. 3.b).

 

Figure 3 born to walk

Figure 3 - At heel strike,the position of the calcaneus will act like one end of a see-saw and force the foot into a sudden plantarflexion (A), medially tilt calcaneus—and therefore the talus and lower limb—as the talus slides down the offset sustentaculum talus (C).

The eversion of the calcaneus (approximately 5 degrees) causes the talus to also tilt medially and to rotate medially. This movement within the subtalar joint affects the joints between the talus and both the navicular and the cuboid. Because of this, the more proximal tarsal bones will rotate more quickly, which will create a relative lateral rotation in the foot’s distal joints (see fig. 4). This movement of the metatarsal bones of the foot affords them more freedom to adapt to the potentially random ground surface. This relaxation of the “form closure” (the natural support of the structure via its boney structure in a similar fashion to the “closure” given to a stone archway due to the shape of the blocks) of the foot also assists in sending the shock to the thick plantar tissues, spreading the force more widely.

Figure 4 born to walk

Figure 4 - Following heel strike, the calcaneus and talus will very quickly rotate medially.The navicular and cuboid follow more slowly and therefore create a relative lateral rotation at their joints with the talus.This unlocks the midtarsal joint and allows the midtarsals to open and adapt to the ground.

This reaction sequence happens in many different situations and with various different movements. In the forthcoming workshop (Arches and Legs, The Massage School, Exmouth, 10-12 April 2015) we will explore the many gifts the feet bring to the rest of system and why some time should be spent assessing and treating for almost every client.