Cross-trainers? Tennis shoes? Running shoes? Aerobic footwear? There seems to be a different kind of shoe for every activity on the face of the earth, and none of them are cheap, either. You are to be excused if you've been wondering whether all those different varieties really are necessary to conduct a proper workout. Here Dr. Stephen Pribut, a leading Washington, D.C., podiatrist, helps separate the facts from the fiction.

• The running shoe: This top-selling style of exercise shoe is not only a suitable choice for running, but also good for walking and other lower-impact activities that do not involve repetitive lateral motion. But if you are looking for a shoe to participate in the kind of activities that do involve a lot of repetitive lateral motion, like basketball, tennis, and squash, or activities with excessive jumping, such as aerobics - watch out. Wearing running shoes for any of these activities practically invites injury, Pribut warns, because they lack adequate support around the ankles.

• Basketball and tennis shoes: They should be judged on whether they offer good traction, good ankle support, and firm cushioning. "The extra money you spend for shoes that fit these criteria will pay off in the medical bills good shoes help you avoid," says Pribut. Some new models that boast flared soles to enhance ankle support also help to prevent the kind of ankle roll-overs that result in painful torn ligaments and sprained or broken ankles.

• The cross-trainer: A more recent addition to the athletic shoe panoply, cross-trainers are an economical alternative to purchasing different shoes for every sport. Designed for maximum versatility, cross-trainers can be worn for running, walking, racquet sports, and aerobics, as well as some indoor-court sports such as basketball and volleyball. Though cross-trainers are versatile, Pribut advises that serious runners are best off wearing real running shoes, because cross-trainers lack the sufficient amount of cushioning and ankle support required for regular jogging.

• The walking shoe: These are designed for the serious race-walker. They are a needless and expensive investment for those who jog as well as walk for exercise, though. The majority of running shoes are better for your feet than most walking shoes anyway, Pribut says, because running shoes provide more wiggle room for your toes.

• Shoes with air-cushioned soles: Air-cushioning sounds high-tech and therefore helpful, but it can cause more problems than it can prevent. Although air-cushioned athletic shoes provide helpful shock absorption, they lack a firm shank below the back of the foot, Pribut warns. A firm shank and a slight heel lift prevent the arch of the foot from dropping down too far when the foot moves. If the foot drops too far, it can cause a shift of bones and the development of a variety of podiatric deformities.

We've started a library of "Living Footnotes" for this section, and welcome your suggestions and your URLs to make it more useful. Use our customized Lycos search to linkthink your way around the web, or feel free to consult the experts about the above topic.

Living Footnotes

• Dr. Stephen Pribut's Pages on Athletic Shoes