Which way do your ankles curve?

gait irregularities such as excessive pronation can cause many problems over the long term. If left uncorrected, over-pronation turns the lower leg inward, which pulls the knee, hip and even the spine out of alignment. And there is evidence that under-pronators, who can develop an externally rotated tibia, are even more prone to injury. In any case, frequent ankle sprains, painful arches, posterior tibial tendinitis, Achilles tendinitis, plantar fasciitis and stress fractures can result from either condition.

To help runners make determinations about foot type, and consequently to ensure an informed shoe choice, it helps to discuss what occurs during a gait irregularity and the practical ways to identify one.

For anyone trying to understand and correct a gait irregularity, confusion can result when we talk about over-pronation as the "excessive inward roll of the foot." Does "inward roll" refer to a foot whose lateral (outer) side lands first (and rolls off it), or does the medial (inner) side land first--as in a gait that favors the inner edge?

During landing (strike phase), everyone more or less hits the ground on the outside of the foot. This can occur at midfoot, more toward the toes, or toward the heel (midfoot is ideal landing form). The phase of the running gait where we determine if a runner is an over-pronator is midstance, when the foot's contact with the ground is greatest.

In a particular runner, the best way to discover what occurs at midstance is to look at pushoff. Over-pronators push off to the inside of the big toe; under-pronators push off to the outside of it; people without gait problems push off through the big toe. Under-pronation is sometimes referred to as "supination," but this term can add confusion because "pronation" and "supination" are naturally-occurring foot positions during running, and different from the qualities of excessive weight-bearing on one or the other edge of the foot at midstance. Vague vocabulary can make it seem like pronation and supination are always problematic. In fact, only when these processes are extreme do they cause problems. When we speak of pronation, we usually mean over-pronation in the context of gait problems.

Skin condition can provide clues as well. Calluses on the medial side of the big toe joint can occur when a runner over-pronates. The same is true for the inner side of the ball of the foot.

"Pronation" really refers to the natural compression of the foot arch just after the strike phase of running. This helps attenuate shock. As the arch flattens, weight is transferred to the inside aspect of the sole. The tibia (shin bone) is internally rotated during this phase. Physiological factors can cause the foot to enter the pronated phase of your gait too early, or stay in it too long. By contrast, at strike phase the foot is naturally supinated, meaning more weight is on the outside aspect of the sole. The tibia is externally rotated during this phase.

A common misconception is that the story of the foot is written on the shoe's sole, but it is not the case that an old running shoe will definitively tell you your gait type. Many times, the ways in which the sole of the shoe wears down can be misleading. Video gait analysis is the ideal means of telling whether a runner has a gait irregularity. But you can get a very good idea by looking at someone in a standing position.

To determine your gait type, stand barefoot and have someone observe the shape of your ankles from behind. If they unnaturally curve inward, you are almost certainly an over-pronator. The result of this curvature is that you stand with too much weight on the inner aspect of the foot. For someone who over-pronates, the Achilles tendon will run straight down the right leg and then, most times, suddenly curve into an open parenthesis shape at the right heel. The medial aspects of both ankles will appear more prominent than the lateral sides. Conversely, if a runner has an under-pronated gait (another term for this is "cavus" foot type), the lateral aspects of the ankles will usually protrude more, resulting in a closed parenthesis shape at the right heel.

The angle at which your sole lands has much to do with whether you excessively pronate or supinate. This is why physicians often refer to pronation as the "unlocking" of the subtalar joint in the ankle. This is the joint that controls side-to-side motion of the ankle, and is crucial for surface adaptation. Barefoot walking, then, can be an even more effective way to quickly assess an over-/under-pronator than a simple standing observation. Orthotic devices can counteract an undesirable slant. Heel cups, however, offer very little, if any, control.

Runners essentially move from supination to pronation to supination again from landing to pushoff. If you don't move from pronation to supination at pushoff, you over-pronate. In this case, look for running shoes with extra medial support and/or "motion control," which reduces internal tibial rotation. These runners may have flat, weak, overly flexible arches.

Supination causes the outside edge of the bottom of your foot to bear the majority of the load, and can be thought of as the "locking" of the subtalar joint in preparation for a strong pushoff. If the lateral aspect of your foot lands first, you may under-pronate--but not necessarily; recall supination is the natural landing position. Severe under-pronators often have a history of repeated ankle sprains. Under-pronators need greater flexibility in their arches and should avoid shoes that offer rigid support in the midfoot. They may benefit from shoes with a thinner midsole.

In an extreme situation, orthopedic surgery for either problem looms as an option. If you suspect a gait irregularity, visit a podiatrist who frequently treats runners. It's obviously never a good idea to leave diagnosis to you or your loved ones. But hopefully this practical overview of what these terms mean and how to preliminarily recognize problems will help you understand them and better discuss them with a health care professional.

(Textbook of Running Medicine, 2001, McGraw-Hill pp. 51-56, 590-592; www.sportsinjuryclinic.net; www.ourfootdoctor.com; www.footsmart.com; www.foot.com; www.time-to-run.com)