During walking and running, pronation and supination normally occur in the foot. Pronation is important for optimal movement and shock absorption. During foot strike, many changes take place—the foot begins to roll inward, everting slightly, and the arch flattens. This is called pronation. It is a normal action—one that occurs in every step in every healthy foot. The purpose of this is to loosen the foot so it can adapt to the surface, especially on uneven terrain.
Following pronation, as the foot continues through its gait, supination occurs. This results in the foot turning slightly outward then changing from a flexible foot to becoming rigid so it can propel the foot and push off from the ground. During this phase the foot inverts slightly, and the arches become higher, thus enabling the foot to properly roll over the big toe.
A number of factors can disrupt a person’s normal gait. The two most common reasons are muscle imbalance and wearing stiff, over-supported shoes. Sometimes, areas above the foot, such as the pelvis or spine, can abnormally influence foot function. For example, too little or too much hip rotation can cause the foot to land in an abnormal position. In addition, injury, pain, and other problems that affect blood flow, cause inflammation, or disturb muscle function in the foot can abnormally alter the gait.
Most shoes change the gait by causing the stride length to become abnormally longer. This causes an abnormal heel strike—hitting the ground farther back on the heel. It’s especially a problem during running, as the longer stride places more shock through the foot and into the knee, and occurs despite shoe cushioning or what is commonly called a “heel crash pad.” Barefoot movement does not cause the same stress.
The notion that some people are “pronators” while others are “supinators” is a gross oversimplification that fitness magazines, shoe stores, and footwear manufacturers foist upon the public in an attempt to sell shoes. It’s mostly all marketing hype. Everyone pronates and supinates. The reason some people excessively pronate or supinate is more often from wearing over-supported shoes, which cause muscle imbalance. This is especially a problem in children whose feet need to properly develop without shoes.
More importantly, an attempt to “help” a poorly functioning foot with a particular type of shoe or orthotic insert is an example of treating symptoms; most cases of foot dysfunction are usually due to muscle imbalance. Keeping the foot in a rigid, immobile position can actually promote foot imbalance by not allowing the body to naturally correct the problem. –-by Dr. Phil Maffetone