"When you go out and buy a car, you know your needs quite well," says Benno Nigg, Ph.D., director of the Human Performance Laboratory at the University of Calgary. "When you buy a suit, you know your needs. When you buy a shoe, you don't."

Should you have medial arch support? Should you have hard or soft soles?

Nigg is working to establish functional characteristics and set them out in a system that would reduce shoe choices to about five standard types for each particular shoe style, such as for walking or basketball.

"You will find out by trial and error that you are a B type, for instance. The idea is that when you buy a B shoe, this shoe type should fit. So when you buy a tennis shoe, you would buy a B tennis shoe," says Nigg, a member of the Olympic Order and the International Olympic Committee Medical Commission. "There will not be more models on the market, but the existing models would be categorized functionally."

Toward that end, research is under way with 200 soldiers of the Canadian military who have chosen from seven types of shoe inserts for their boots. The seven inserts represent those that are appropriate for 95 percent of the population. A control group of soldiers is going without inserts.

After about four months, the researchers will check for injury frequency among both groups of soldiers. They will determine which volunteers used which inserts and quantify the physical characteristics of each volunteer with his or her choice of insert.

"We will have a matrix showing subject characteristic, insole characteristic, and injury frequency," Nigg says. "Then we should begin to match shoe design with physical characteristics of the wearer."

In recent years, athletic shoe manufacturers have adopted a number of design features based on research from Nigg's laboratory. Dual-density midsoles are now found in nearly all athletic shoes. These midsoles are soft on the outside and hard on the inside of the heel for a soft landing but stable support as the foot rolls over.

Athletic shoes used to prevent the front of the foot from rotating independent of the back of the foot, a natural twist that can relieve ankle stress. Many shoes now have a feature that bridges the inside of the forefoot with the outside of the rear foot and vice versa, restoring a natural mobility to the foot. The most recent concept is that of the barefoot shoe, or the "feet you wear."

"The shoes should be more like an additional shell of skin around the foot, allowing the foot to do the things it does naturally," Nigg says. It is the antithesis of the military boot or a ski boot, which anchors the foot in a block. The concept of the barefoot shoe has emerged from years of research into the biomechanics of the foot in walking and running. Only recently has a clear picture begun to emerge.

Shoe designers used to keep information about foot and shoe shape in the form of a mold, or last, on which shoes were built, rather than as physical measurements. The goal was a comfortable fit based on shape. This ignored how the shoe would function.

"The design of athletic shoes to 'fit' function and not just structure represents a major contribution of biomechanics to sports equipment design," writes Peter Cavanagh of Pennsylvania State University in Medicine and Science in Sports and Exercise.

The concept applies across the spectrum of physical ability, from athletes to the elderly and impaired, who may use all their energy just to get around and would benefit from shoes that minimize the work required for walking. In a recent study published in the Journal of Biomechanics, Darren Stefanyshyn, Ph.D., of Nigg's group looked at the metatarsophalangeal (MP) joint, the joint at the ball of the foot, to see if it contributed mechanical energy to running and sprinting.

Five male runners each went through 10 trials, and five other sprinters each went through six trials, all wearing their own running shoes. Sensors and optical cameras were used to gather data. When analyzed, the data showed that the MP joint was a large energy absorber during both running and sprinting, yet the joint did not contribute any energy at takeoff.

"Thus it appears that the MP joint is a dissipator of large amounts of energy," Stefanyshyn says. "It is possible that the incorporation of the toe spring (the raising of the forefoot of the shoe) in athletic shoes may be somewhat responsible for this energy dissipation since it forces the MP joint to remain in a flexed position during takeoff."

Conventional running shoes built with a toe spring to curve the sole are generally believed to improve the stride through the natural rocking from the heel to the front of the foot. "The results of this study may indeed suggest the opposite," Stefanyshyn concludes.

The Whitaker Foundation supports Nigg's work through a Special Opportunity Award to Calgary's graduate program in biomedical engineering.