Inside the human foot
One of the first things we learn to do is walk, but how exactly do we move from heel to toe?
(Image source: Pixabay)
With every step we take, a set of biological cogs are set in motion, enabling us to get from A to B. The action of walking may seem pretty straightforward, but actually our feet are made up of a complex and unique arrangement of bones, tendons and ligaments.
Tendons are the rigid and fibrous tissues that attach muscles to a bone. In the case of moving the foot, the main tendon engaged is the Achilles tendon, which connects your calf muscle to your hindfoot bone, called the calcaneus. Ligaments are bands of elastic connective tissue that bridge the gap between bones. In order for the muscles connecting the foot to contract and relax – the basis of movement – they require stimulation from nerves that feed into the foot, like the tibial nerve.
A type of connective fibrous tissue, known as the plantar fascia, is responsible for putting the spring in your step. Spanning the length of your foot, this tissue acts as a springboard. As we lift our foot at the beginning of a step, the tissue becomes taut due to our toes lifting upwards. As the foot is returned to the ground, the tension in the tissue increases further, storing energy like a spring. That energy is released in the next step, giving our footsteps their bounce.
Heel to toe
(Image credit: Medical gallery of Blausen Medical)
This bone is connected to the lower leg’s tibia and fibula, enabling us to move from the ankle down.
The largest bone in the foot, forming the foot’s heel. The calcaneus is also vital for foot strength and balance.
Metatarsals and phalanges
The forefoot’s five metatarsal bones lead to the phalanges that make up the foot’s toes. Each toe has three phalanges, with the exception of the big toe, which only has two.
There are several joints connecting bones for flexibility, including the metatarsophalangeal joint, enabling the foot to move each toe.
The tarsal is made up of five midfoot bones to form the foot’s arch. This configuration of bones is locked in place while you stand still, and separates during a step.
This is the longest ligament and the one responsible for putting a spring in our step.
(Image source: A Marines)
In recreating the human foot, some prosthetic feet have been designed to replicate its natural physics. As the plantar fascia acts as the energy store for a biological foot, many prosthetic carbon fibre designs mimic the same function. When the wearer applies weight to the prosthetic, the carbon compresses, storing energy. When the foot is rolled to make a step, the energy is released, propelling it forward. Shock absorbers and an artificial multi-axial ankle are also incorporated to replicate the natural movement of the foot. This allows the wearer to roll the foot in the desired direction while remaining stable.
This article was originally published in How It Works issue 124, written by Scott Dutfield
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