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Introduction to how your biomechanics effects your lower body - by David J. Micca, DPM, FACFAS, CWS, FCCWS
The foot is a very complex structure. It is designed to adapt to varying surfaces as well as offer support and rigidity during jogging and running activities.
The foot is responsible for accepting all the rotations occurring from the hip, down to the knee, leg, and ankle. The foot must then convert these rotations and translate it into forward motion. Throughout an average day of walking, the feet must endure a force equal to several hundred tons. Weight-bearing sports, like running, put even more pressure on the feet and ankles. Most long distance running injuries are a result of abnormal biomechanics.
Biomechanics is defined as the mechanics of function.
The standard in ankle and foot biomechanics is when the foot is positioned in a neutral attitude. The neutral position is the situation that exists when the foot is stable. A neutral foot can support body weight when both feet are on the ground without the help of muscles or ligaments. In other words, the integrity of the bones and joints of the foot support the weight of the body.
When the foot is neutral there is a normal arch, which is neither too high nor too low. The heel bone (or calcaneus) is perpendicular to the floor and parallel to the lower one third of the leg. The metatarsal heads are resting on the ground and the plane of the metatarsal heads (ball of the foot) is perpendicular to the long axis of the calcaneus. When the calcaneus is straight and its posterior bisection (looking from the back of the heel) is perpendicular to the floor, a normal appearing arch exists.
The foot is considered in a “neutral” position. During gait, the foot must be in neutral position just prior to the time that the heel leaves the ground. When this does not occur, the muscles of the lower extremity work overtime in attempts to stabilize the foot. Stable propulsion is therefore unlikely and increased torque upon the leg occurs, resulting in overuse syndromes of the lower extremity.
Determining the neutral foot position.
Determining the neutral foot position is done by planting the foot on the ground and externally rotating the leg. This is accomplished by causing the patella (knee cap) to point outwards until the posterior aspect of the heel bone is perpendicular to the floor and parallel to the lower one third of the leg.
When performed properly, the arch will appear more normal. Functional foot orthotics are used to improve abnormal lower extremity function as it relates to this neutral position. Correcting abnormal locomotor function reduces recovery time and helps prevent relapse of athletic injuries.
The normal foot contacts the running surface on the outside of the heel (lateral/plantar aspect), then quickly rolls inward (everts) to adapt to uneven terrain. This inward motion causes an unlocking of the midtarsal joint and is referred to as contact phase pronation. Not all pronation is a bad thing. It is obvious that some pronation or flattening of the arch is needed for proper foot function and adaptation. During contact pronation (heel strike) the foot is relatively unstable. This allows the foot to absorb stress and act as a built-in shock absorber.
Once this is accomplished, the foot will then quickly become more rigid (resupinates) to the extent that the foot is neutral prior to lifting the heel off the ground and rigid prior to propulsion (toe off). Resupination allows the foot to become a rigid lever during propulsion. Various structural and functional abnormalities of the leg and foot can cause "prolonged" pronation. When this prolonged or abnormal pronation occurs, the foot never becomes stable during propulsion. These abnormal or protracted pronatory influences limit the ability of the foot to act as a rigid lever at toe-off and compromises forward motion. Running becomes inefficient and overuse injuries are likely to occur.
These include hip pain, runner’s knee, shin splints (enthesiopathy), stress fractures, Achilles tendinitis, heel spurs, arch fatigue, capsulitis, neuromas and compensatory structural deformity of the foot such as bunions and hammer toes.
These injuries usually begin slowly and gradually increase in severity. They may be related to a sudden increase in mileage, a change in terrain or faulty, biomechanical structure. Weight and improper shoe gear can aggravate the condition but is not usually the sole cause of overuse syndromes. General preventive measures for overuse syndromes depend upon proper training, proper conditioning, and proper biomechanical structure.