Foot Anatomy 101
Ch. 1 Ch. 2 Ch. 3 Ch. 4 Ch. 5 Ch. 6 Ch. 7 Ch. 8
Chapter 3: Foot Anatomy 101-The Foot is Designed to be Flat on the Ground
The foot is the least understood of all moving body parts because of the complex interworking between its many joints, tendons, nerves and more. What we do know is that the foot is perfectly built for its two most important functions: (1) absorbing shock and (2) propulsion. These functions are first controlled by the brain and spinal cord that receive messages from thousands of nerve endings on sole of the foot. Nerves relay vital information about the ground terrain so the body can react accordingly. When the foot's sensing system is synchronized with its moving hardware the foot becomes an unbeatable, self-sufficient and adaptable machine.
"The foot is a masterpiece of engineering"
Foot Facts
- 26 bones with 33 joints (making up one-quarter of the body's bones)
- over 100 muscles, tendons & ligaments (site of the strongest tendon in the body)
- over 200,000 nerve endings (densest concentration in entire body)
- over 250,000 sweat glands (expel 1 pint of sweat per day)
- a network of blood vessels
- gastrocnemius (large calf muscle)
- soleus (lower calf muscle)
- quadratus plantae (sole muscles)
- It is tendons that are most crucial for movement because they provide such a high amount of energy for their size, the kind of energy that can be seen by the stretching and snapping of a rubberband. The four major tendons originate below the knee and string all the way down to the foot. The later two tendons string down along the inward side of the ankle bone, wrap under the arch, and attach at the very tips of the toes.
Four Major Tendons:
- achilles tendon (strongest tendon in the body)
- posterior tibialis (supports arch)
- flexor digitorum (curls four smaller toes)
- flexor hallucis (curls big toe)
- one major ligament:
- plantar fascia (tension from heel to ball of foot)
The foot's two main mechanical functions are (1) absorbing shock and (2) propulsion. At the point of ground touchdown the foot acts as a shock absorber, soft and flexible, and then in preparation for push-off the foot turns into a rigid lever. To help us further understand the workings of these functions we use a model called the Windlass Mechanism developed in 1954 and is now commonly used in various mechanical engineering applications.
Windlass Mechanism
The foot uses the Windlass Mechanism upon landing and at push-off. The arch of the foot can imagined as a triangle. The bottom of the triangle is the all important plantar fascia ligament that serves as a high tension cable. When the toes are lifted the plantar fascia wraps around the metatarsal bones tightening its tension which lifts the foot's arch higher and higher. The further the toes are flexed back the higher the arch rises.
The raising and flattening of the arch is maybe the most important mechanism of the foot. Since the height of arch is controlled by flexing the toes, the toes play a critical role in both absorbing shock and propulsion.
During the stride cycle as the foot comes down for a landing the toes are flexed up so that the foot lands with the arch high like a shock absorber at full extension. Then as the body bears weight on the foot, the toes lower and the arch flattens dissipating shock in a controlled manner. Into the next phase of the stride the body moves forward and the heel lifts up which again flexes the toes up lifting the arch and turning it into a rigid lever. The rigid lever makes for an energy efficient and rapid push-off. Therefore, according to the Windlass Mechanism free movement of the toes and plantar fascia ligament are critical for proper shock absorption and propulsion.
Barefoot Motion
The foot has evolved to be an incredibly advanced system for movement. When in its natural state (without shoes) the foot moves in the most efficient and healthy way. It rolls, stretches, expands, and grasps the ground. The foot is so self-sufficient that it only works properly without shoes. Therefore, nothing worn on the foot can improve the foot's functions but only hinder them. For example the foot has its own built in system for absorbing shock: see the picture of the Foot's Natural Suspension System to the right.
Unshoe Fit:
- NO arch support: foot's arch needs to flatten on impact to dissipate shock.
- NO heel cushioning: heel needs to be flat & level in order to stretch achilles tendon.
- NO stability or motion control: foot uses pronation, rolling inward, to deflect shock.
- NO cramped toe box: toes splay apart upon contact softening the landing.
The foot is the model for an ideal shock absorber. Most shock absorbers work in one direction, the foot functions in three. The Windlass Mechanism explains the vertical movement of the arch but it doesn't explain the other directional planes. Pronation happens in a tilting direction and in the lateral direction the transverse arch flattens and toes splay apart.
Pronation
Pronation as a term has received a bad rap from the running shoe industry, however, it may be the most critical of all foot functions. Unfortunately, the running shoe industry has attacked "pronation" for nothing more than a marketing ploy. Pronation is the natural motion of the foot rolling or tilting inward in order to dissipate shock. It occurs at different degrees and is best seen when running or landing from a jump. The foot lands on the outside border with the ankles turned inverted. As body weight settles down on the foot, the ankles roll inward and the foot rolls inward flattening out. Pronation cannot occur with arch support, especially the support of rigid orthotics. Support simply blocks the foot from rolling inward which causes the impact force to go up the body instead of being dissipated.
Transverse Arch Flattening
The ball of the foot is made of five very mobile metatarsal bones. An arch spans across these metatarsals known as the transverse arch. The foot naturally rolls across the ball of the foot starting at the outside and rolling inward to the big toe. To initiate the roll the foot touches down on the outside at the 5th metatarsal. This 5th metatarsal is very mobile and displaces easily away from the other four metatarsals making for a soft touchdown. At this point the transverse arch begins to flatten just like a leaf spring suspension system. This flattening widens the ball of the foot by about 15%. Rarely when fitted for a shoe do you account for the extent to which the foot widens. Which is why a "snug fit" can easily result in a stress fracture of a metatarsal bone.
Toes Splay Apart
As the five metatarsals widen upon bearing-weight, the five toes splay apart. They must spread even further apart than the metatarsals, with open space between each toe. The toes are responsible for forming a stable, wide base for the upright body. A second function of the toes is sensory proprioception. Upon touching down the toes spread across the ground so they can relay critical information to the brain, describing the level of landing surface and how the body will have to adjust its lean. Contrary to popular belief, the toes are the widest part of the foot, not the ball of the foot. Unfortunately, since fashion dictates shoe design instead of foot biomechanics, shoes are designed with tapered toeboxes, narrower than the ball of the foot.
Content used with permission from Mark Cucuzzella (www.trtreads.org) and Andrew Rademacher (www.stemfootwear.com)
