Pronation is the normal movement the foot makes to absorb the impact from walking or running. It occurs once the heel strikes the ground and the foot disperses the impact, stretching and flattening the arch as the foot rolls inward. Supination is the opposite motion of pronation. The foot supinates, or rolls on its outer edge, to help with stability as we walk or run. A reasonable amount of pronation is necessary for the foot to function properly. However, when the foot arch remains flat and the foot rolls inward too much one may have excessive pronation or overpronation. This medical condition can result from continually straining the feet and wearing footwear that lacks sufficient foot arch support.
There is a relationship between biomechanics and injury that is specific to each body part. Overall though, poor mechanics will either increase the landing forces acting on the body or increase the work to be done by the muscles. Both increase the stress, which, depending on the individual and the amount of running can become excessive and cause injury.
Because pronation is a twisting of the foot, all of the muscles and tendons which run from the leg and ankle into the foot will be twisted. In over-pronation, resulting laxity of the soft tissue structures of the foot and loosened joints cause the bones of the feet shift. When this occurs, the muscles which attach to these bones must also shift, or twist, in order to attach to these bones. The strongest and most important muscles that attach to our foot bones come from our lower leg. So, as these muscles course down the leg and across the ankle, they must twist to maintain their proper attachments in the foot. Injuries due to poor biomechanics and twisting of these muscles due to over-pronation include: shin splints, Achilles Tendonitis, generalized tendonitis, fatigue, muscle aches and pains, cramps, ankle sprains, and loss of muscular efficiency (reducing walking and running speed and endurance). Foot problems due to over-pronation include: bunions, heel spurs, plantar fasciitis, fallen and painful arches, hammer toes, and calluses.
People who overpronate have flat feet or collapsed arches. You can tell whether you overpronate by wetting your feet and standing on a dry, flat surface. If your footprint looks complete, you probably overpronate. Another way to determine whether you have this condition is to simply look at your feet when you stand. If there is no arch on the innermost part of your sole, and it touches the floor, you likely overpronate. The only way to truly know for sure, however, is to be properly diagnosed by a foot and ankle specialist.
Non Surgical Treatment
Over-pronation and the problems that go with it are treated with shoe inserts called arch supports or orthotics. You can buy orthotics at a pharmacy or athletic shoe store or they can be custom made. Make sure the arch supports are firm. If you can easily bend them in half, they may be too flexible.
Wear supportive shoes. If we're talking runners you're going to fall in the camp of needing 'motion control' shoes or shoes built for 'moderate' or 'severe' pronators. There are many good brands of shoes out there. Don't just wear these running, the more often the better. Make slow changes. Sudden changes in your training will aggravate your feet more than typical. Make sure you slowly increase your running/walking distance, speed and even how often you go per week. Strengthen your feet. As part of your running/walking warm up or just as part of a nightly routine try a few simple exercises to strengthen your feet, start with just ten of each and slowly add more sets and intensity. Stand facing a mirror and practice raising your arch higher off the ground without lifting your toes. Sit with a towel under your feet, scrunch your toes and try to pull the towel in under your feet. Sitting again with feet on the ground lift your heels as high as you can, then raise and lower on to toe tips.