Kinetics is the branch of physics that studies motion of masses in relation to the forces acting on them, and the feet are the most utilized and stressed organs of the body kinetically. Second only to our intelligence, our feet have enabled humankind to outperform other living organisms.

For feet to provide foundational support and move in closed chain, they must maintain four capabilities, efficiently. They must form a rigid, stable structure against the foundational surface. They must absorb weightbearing shock. They must become a rigid lever, giving muscle engines mechanical advantage to perform and finally, they must morph from one capability to the other, flawlessly.

In the foot, ligaments attach one or more bones to each other. They act as soft tissue binders, but must be slack to allow for motion, so that the foot can flex and move. When overstressed or overused, ligaments stretch, tear and change from elastic to plastic structures that can underperform and injure.

In addition, there are muscles whose tendons, when leveraged, function as binders to maintain support in static stance or to keep the foot rigid when in motion. Muscular leverage, when absent, leaves one or more segments of the pedal psotureweak, unstable, deformed or injured.

The Kinetics of Functional Foot Typing®

In practicing Wellness Biomechanics, there are four tests that, when performed, allow all feet to be classified into one of sixteen Functional Foot Types (FFT’s)®. This system has been documented previously^2-4.

The Pure Functional Foot Types®

To understand Functional Foot Typing kinetically, it is best to begin with the four pure FFT’s and the Rigid/Flexible Foot Type, as these profile 85% of all feet. Pure foot types have the same rearfoot and forefoot engineering. They are the Rigid/Rigid, the Stable/Stable, the Flexible/Flexible and the Flat/Flat.

Rigid/Rigid Functional Foot Type

The Rigid/Rigid FFT is like an architectural arch. The bones of this foot and its ligaments are naturally tight and bound into an arch shape and the muscles are over leveraged. This foot supports the ground well, but when morphing, shock absorbing and functioning, the Rigid/Rigid FFT lacks flexibility.

Stable/Stable Functional Foot Type

The Stable/Stable FFT represents the closest foot type to “normal”. It is supportive, morphs well and is a good mobile adaptor. It is a well functioning foot type until stressed by increased demand for efficiency or performance or when overused.

Flexible/Flexible Functional Foot Type

The Flexible/Flexible FFT is an excellent morpher and shock absorber but a weak supporter. Both pillars collapse upon stress and weightbearing. This foot fails to leverage the foot into a rigid lever.

Flat/Flat Functional Foot Type

The Flat/Flat FFT is not a good supporter, rigid lever, morpher or shock absorber. The bones of this foot type are permanently tight and flat and cannot assume an arch shape.

Rigid rearfoot / Flexible forefoot Foot Type

The Rigid rearfoot, Flexible forefoot foot type is the most prevalent and therefore important for practitioners to master. In this foot type, the rearfoot is a good supporter and rigid lever and a poor morpher and shock absorber and there is good muscular leverage. In contrast, the forefoot of this foot type is flexible and therefore a good morpher and shock absorber but depending upon this foot types ability to leverage the bones of the forefoot using muscle engine power, this foot type can range from a poor supporter and rigid lever (the bunion foot) to an almost perfect supporter and rigid lever (the ballerina) or anything in between.

To date, no orthotic is proven constructed with enough centering to the feet that they are positioning, to be successful in preventing inherited collapse and muscles must burn otherwise useful energy to position the vault optimally, reducing the energy left for function. The degenerative, pathological cascade that follows over ones lifetime in overcoming the destructive biomechanical effects of shoes, hard ground and ones lifestyle, is responsible for most of the closed chain complaints presenting for care in Podiatry.

An orthotic, in order to provide more than symptomatic relief, must act as positional centering, that places the foot in optimal functional position (OFP), so that the muscle engines can utilize their energy to perform kinetically.

Wellness Biomechanics Kinetics

This paper focuses on the extrinsic muscles and their foot type–specific properties. Intrinsic muscle function will be the subject of future discussions. In addition, the kinesiological cascade utilized for this discussion will be rearfoot to forefoot loading (The Gait Cycle) when moving forward from point A to point B. The kinetics of forefoot first loading (Barefoot Running, Sprinting, En Pointe, Eurythmy) or rearfoot, forefoot simultaneous loading (Stance or Midstance Function) and side to side movement, will be reserved for future discussions, but should not be overlooked.

In Foot Centering, once the foot is placed in OFP, muscle engines that are weak and poorly leveraged and those that are bound and contracted can be trained to provide efficient and balanced support, leverage and morphing over ones lifetime. Our goal is that Wolf’s and Davis’s Laws will compensate the bones and muscles to a place where the Foot Centering Orthotic can be reduced or removed.

Muscles must be trained to perform with power and in phase without pathological compensation, breakdown or performance issues. No foot soldier can perform well without a proper boot and Boot Camp⁵.

Human movement is a cascade of events that must occur with power and in phase. If the Triceps Surae doesn’t leverage the heel at contact, then the Peroneus Longus, Peroneus Brevis and Posterior Tibial cannot stabilize the rear pillar of the Vault of the Foot. In turn, the Peroneus Longus and Anterior Tibial cannot stabilize the forefoot pillar in Midstance and the Long Extensors and Flexors cannot fine tune forefoot stability and set the digits in a functional position in late Midstance.

Functional Foot Type-Specific Kinetics

Each of the rearfoot FFT’s and forefoot FFT’s have muscles and tendon insertions that are too weak, too strong, too tight or too loose when challenged. This means that functional foot typing provides a starting place for developing a custom training program to restore equilibrium.

The Rigid Rearfoot Types
In the Rigid Rearfoot, the calcaneal inclination angle is high and the subtalar joint axis is laterally placed. This rearfoot is a poor morpher but a good performer when it comes to leveraging the muscle engines.

The ligaments are tight, thick and strong, binding the bones firmly together. Its muscles are leveraged and contracted. A tight heel cord with functional equinus is pathognomonic but the anterior tibial, the posterior tibial and the peroneus longus are tight as well.

The Stable Rearfoot Types
In the Stable Rearfoot, the bones of the rearfoot are inverted but have enough range of motion to evert to vertical but no further. The calcaneal inclination angle is normal and the subtalar joint axis approaches normal. This foot type is both a good supporter and a good rigid lever and it morphs better than any of the other rearfoot types. The stable rearfoot is considered closest to a “normal” rearfoot type.

The ligaments in this foot type are sufficiently leveraged and strong to cement the bones firmly together but allow for healthy motion. The muscles in this foot type are both strong and leveraged. There are few if any contractures or weaknesses.

The Flexible Rearfoot Types
In the Flexible Rearfoot, the bones of the rearfoot are inverted and have range of motion large enough to evert the foot beyond vertical into an everted position and the subtalar joint axis is medially placed.

The ligaments in this foot type are stretched, weak and have suffered repetitive microtrauma. Poorly functioning Posterior Tibial, Anterior Tibial. Peroneus Longus and Peroneus Brevis muscles fail to bind the rearfoot resulting in pathological compensation, poor performance and the development of early deformity. Compensation of the Triceps produces equinus.

The Flat Rearfoot Types
In the Flat Rearfoot, the bones of the rearfoot are firmly set in an everted position in open chain and show little to no range of motion upon weightbearing. The calcaneal inclination angle is low and the subtalar joint axis is laterally placed. This foot is a poor morpher, shock absorber, stabilizer and performer when called upon to be functional.

The Rigid Forefoot Types
In the Rigid Forefoot, the bones are firmly set and show a small range of motion. They are vaulted and have little to no motion in the direction of dorsiflexion. This foot type is a poor shock absorber but a good performer when it comes to power and strength tasks.

The ligaments in this foot type are contracted, thick and strong, binding the bones together. The muscles are strongly leveraged and contracted. A tight Peroneus longus as well Extensor Hallucis Longus are most obvious with the long flexors and extensors of the digits compensated into contraction.

The Stable Forefoot Types
In the Stable Forefoot, the bones are firmly set and show a small range of motion. They Dorsiflex to vertical upon stance but no further. It is a good shock absorber, performer and morpher. This forefoot type is the closest to “normal”.

The ligaments in this foot type are average in size, thickness and tightness. The muscle engines function within a normal range and there is not much triceps compensation necessary.

The Flexible Forefoot Types
In the Flexible Forefoot, the bones lack the ability to bind the vault in place. The foot has a high range of motion and positions itself above vertical in closed chain. This foot is an excellent shock absorber but a poor supporter and rigid lever.

The ligaments in this foot type are loose and perform poorly, especially those that defend the medial dynamic arch. The muscle engines in this foot are inefficient; they are poorly leveraged and stretch with time. A tight heel cord with functional equinus is the obvious compensation and the Anterior Tibial, Posterior Tibial and the Peroneus Longus are overused.

The Flat Forefoot Types
In the Flat Forefoot, the bones are set in a flat position with the five metatarsal heads in line. The forefoot is in fixed dorsiflexion and has a small range of motion. There is virtually no forefoot vault in this type in open or closed chain. It is a poor shock absorber, morpher and rigid lever.

The ligaments in this foot type are tight, thick and strong, binding the bones firmly in a flat position. The muscles in this type are strongly leveraged and support the deformity. A tight heel cord with functional equinus is the pathognomonic but the Anterior Tibial, the Posterior Tibial and the Peroneus Brevis and Longus are tight as well.

Discussion

The goal of any practitioner of human biomechanics or kinesiology should be to offer every individual the ability to live a quality of life that maximally approaches its inherited and natal potential, in addition to being capable of overcoming the deforming forces of gravity, the hard, unyielding ground, and the hard and unyielding shoe boxes they choose to wear.

As we are living longer lives, people are looking to extend their comfort and quality of life further. Since the foot is the foundation of the posture and our connection to the underlying surface, balancing and strengthening the foot is the starting place for accomplishing this goal. Unless the foot is capable of performing its myriad of tasks at a high and efficient level, pathological compensation in the foot and posture are destined to cause predictable pain syndr`omes, deformity, degeneration and poor performance as we age.

The Centering Theory of Biomechanics evaluates and diagnoses all feet, foot type-specific. Then, with custom Foot Centrings® and a custom program of muscle engine balancing and strengthening, practitioners can target preventive, performance enhancement and treatment plans more successfully⁶.

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