biomechanics of the foot

7/27/2019 Biomechanics of the Foot

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Biomechanics

"Bio" means life or living organism. "Mechanics" isthe original discipline of physics as it applies to forceson matter. For our purposes,biomechanics is defined as the

mechanics of the human body, especially the forces of themuscles and gravity on the skeletal structure of the lowerextremity.

Foot Terminology: Anatomic terms for location of body parts andmotions are necessary for a variety of reasons. We can not simply say"outside of the toe" because not everyone will agree on which part of thetoe is the "outside." Although it may seem simple to refer to the "top ofthe foot", as soon as the foot moves or is rotated or has a deformity, thetop of the foot is no longer on top. Medical professionals need a uniform

way to describe both locations and movements.

Definitions: Anatomic Locations

Medial means towards the center line of the body.

Lateral means away from the center line of the body.

Distal means further from the body.

Proximal means closer to the body.

Anterior means the front of the body

Posterior means the back of the body

Dorsal means the top of the foot

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Plantar means the bottom of the foot

foot orientation image

Looking at the foot diagram above, the big toe is medial and the little toe

is lateral. The toes are distal to the midfoot and the midfoot is distal to theheel bone. The heel bone is proximal to the toes. The toes are alsoconsidered anterior to the midfoot and the heel sits posterior to themidfoot.

Definitions: Motions of the foot and ankle

Dorsiflexion: movement of thefoot up.

Plantarflexion: movement ofthe foot down.

Abduction: movement of thefoot away from the center line ofthe body.

Adduction: movement of thefoot towards the center line ofthe body.

Inversion: twisting movementof the foot inward.


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Eversion: twisting movement ofthe foot outward.

Supination and Pronation

Supination and pronation are a combination of the above motions. It iscommon to use supination and inversion interchangeably and pronation

and eversion interchangeably. But, supination is actually a combination ofinversion, plantarflexion and adduction. Pronation is a combination ofeversion, dorsiflexion and abduction.

Supinationis a triplanarmotioninvolving thefoot movingdown andtowards the

center of thebody.

Pronation isa triplanarmotion of

the subtalarjointinvolving thefoot movingup and awayfrom thecenter of thebody.


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To better understand supination, look at the right foot in the imagebelow. The heel rotates towards the center of the body, the big toe movestowards the center of the body, the foot flexes down and the ankle rollsout.

To better understand pronation, look at the right foot in the imagebelow. The heel rotates away the center of the body, the little toe movesaway from the center of the body, the foot flexes up slightly and the anklerolls in.


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To understand these motions while standing, try this with your own feet.Stand with your feet parallel and facing foward. Rotate your body and lookover your left shoulder, without moving your feet. Your left leg has rotated

out (external leg rotation) and your weight will be on the outside of yourleft foot. Your left foot is supinated. Your right leg has rotated in (internalleg rotation) and your weight is on the inside of your right foot. Your rightfoot is pronated.

Gait Cycle


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Contact/ Heel Strike: The beginning of the gait cycle is marked by theheel contacting the ground. This is called heel strike.

Forefoot contact: The forefoot contacts the ground, stabilizing the foot

and the body.

Midstance: When the weight of the body is directly over the foot. Theopposite foot is swinging from the rear of the body towards the front ofthe body.

Heel Off: When the heel starts to lift from the ground, the weight shiftsto the front of the foot. The opposite foot has made contact with theground.

Propulsion/ Push off: Also called toe off, this phase is the terminalstance phase of the gait cycle, which means that the foot is pushing offthe ground and will be entering the swing phase (swinging from the rearof the body to the front of the body).

During the normal gait cycle (normal walking) the feet supinate andpronate. It's important to understand that pronation is a normal motion

when walking. When the feet pronate too much, this is when peopleexperience problems like plantar fasciitis, tendonitis and painful arches.An abnormal amount of supination can cause also cause problems. Whenthe foot supinates too much people may develop tendonitis and jointproblems at the forefoot and big toe joint.

Foot Anatomy: The foot is a complex structure of 28 bones (26 mainbones and two small bones under the big toe), over 100 ligaments,multiple muscles and tendons which all work together to hold the weightof the entire body and help propel the human body. More pictures on foot

anatomy.

biomechanics of the foot

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