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One of the fun things about running is that it gives one the opportunity to learn, and it seems as if this never stops. No matter how experienced you are there is always something more to learn. This observation is made relevant by several investigations into overuse injuries in runners. These studies show that experienced runners have about the same rate of overuse injuries as beginners. It is not that experienced runners never learn. Certainly some do not and constantly run, and rerun, into the same injury pattern. However, it is likely that a larger percentage cure one injury then develop and improve until they stumble into the next. This is probably because as one area gets stronger the stress load is subsequently re-applied elsewhere. Injuries, thus, tend to march along what is referred to as the “kinetic chain”. Each runner, however, tends to march to the beat of a different drummer. The specific location for an overuse injury is determined by a multitude of factors (e.g., genetics, previous injuries, training factors, etc.). This means that there is not an etched-in-stone-overuse-injury-sequence through which all runners progress (Feet first, then ankles, then shins, then knees, then … ). Thus, it is a good idea for runners to become aware of regions of the body that may become affected and learn a little about the specifics in each region. Knowledge and early warning are a runner’s best friends. In this column I periodically highlight either a specific injury or a region of the body in which overuse injuries occur or originate. This month it is, “de feet”.

Conceptually it is easy to think of the feet as an area that may become overused and injured in runners. They are, after all, the first part of the body that hits the ground. One must consider that injuries elsewhere may have their roots in the feet. Similarly, it must be pointed out that nagging foot injuries may have their cause higher up the kinetic chain.

When searching for factors that may have contributed to any running injury (i.e., not just those limited to the foot) a good starting point is the foot. The details of advanced biomechanics are beyond the scope of this article, but a discussion of a few basics is warranted. As a simplification there are three types of ‘arches’, neutral (normal), high (and/or rigid), and low (“flat feet”). In a normal running gait at footstrike the foot is in a relatively supinated position and then progresses, or rolls, through pronation during the mid-stance phase. To visualize this, open a paperback book at the midpoint and place it face down on a table. It tends to tent up with the spine elevated, supported on two “wings”. Each wing is in a supinated position relative to the spine. Now press down on the spine to flatten the book. Each wing has now moved towards a more pronated (less supinated) position. The action, from supinated to pronated, is called pronation -- and going the opposite direction is called supination. Of course when we run this happens to each foot alternatively, and obviously involves different mechanics and angles. The foot hits the ground in a relatively supinated position and then ‘rolls’ into a more pronated position by the mid-stance phase, which is the point when the foot is directly under the body and is bearing full weight.

In returning to examine different foot types it is now easier to understand why runners with high arches are referred to as “supinators” or “under pronators”. In their running gait they have decreased mobility such that there is inadequate pronation during running. These runners have a foot that doesn’t absorb shock well. This shock is transmitted to lateral (outside) structures in the foot, lower leg, and knee. An injury example is anterior (lateral) shin splints. “Overpronators” have the opposite problem. There is too much mobility and, thus, excess pronation during running. These runners end up transmitting excess force to the medial (inside) structures of the leg. An injury example here is posterior (medial) shin splints.

The right shoe for underpronators (supinators) are ones that provide extra cushioning and shock absorbing capacity. Overpronators need shoes that provide extra stability, or “motion control”. A quick and dirty method for determining individual needs is the wet footprint test. Start by placing a wet towel on concrete. Simply step onto the towel with each foot (one-two) then step forward (one-two) onto dry concrete and then step forward again. Now look at your footprints. If the only wet spots are the ball, the heel, and a sliver of the outside edge of the foot you are likely an underpronator. Conversely, if the entire footprint is filled in then you fall into the overpronator camp. There are several running shoe guides (e.g., www.roadrunnersports.com) to help you determine what shoe is right for you. Finally some runners need the extra help provided by orthotics. These customized shoe inserts may be designed to provide extra support and motion control for overpronators, or extra cushioning for underpronators.
A few other tips about running shoes. After about 250 miles shoes lose about 30 – 50% of their shock absorbing capacity. The same is true for wet shoes, which – depending upon how wet -- may take 48hrs to dry out. If you run daily you may want to consider buying two pairs and using them on alternate days. This will help prolong effective shoe life-span.


Toronto, ON Chiropodist Academy Foot and Orthotic


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