Adidas 1 and Nike Free 5.0, two newfangled sneaker concepts, could hardly be more dissimilar. With a motor implanted below the arch, Adidas 1 constantly tightens and loosens itself to create a custom fit. A company official, with a straight face, calls it the "world's first intelligent shoe." It may also be the world's first $250 sneaker.

Nike Free, at the slightly more bearable price of $80, is built around an ultra-flexible sole, scored deeply from heel to toe, to mimic barefoot walking or running. Why pay for what is, essentially, an anti-shoe? Because navigating in it strengthens the foot, of course. "It's a weight room for your feet," says Nike engineer Tobie Hatfield.

Parents across the country are hoarse from trying to talk their kids out of buying eye-catching, gizmo-filled sneakers and into purchasing a pair of sturdy, no-frills cross-trainers. But it may be of no use. As the fevered back-to-school shopping binge begins, the country's top shoemakers are talking, perhaps more than ever, about technology, the innovations in shoe design that somehow create buzz every year or so.

Pumps (yes, they're back). Sensors. Shocks. (Or Shox, as Nike calls them.) Or ClimaCool, which Adidas says channels air through the sneaker to cool the foot.

The sci-fi-sounding bells and whistles are fueling a $15 billion athletic footwear industry that now cranks out a shoe for every activity, sport, season and lifestyle. Reebok's Zan Chi Yoga/Pilates slip-ons, for example, help you "find your inner 'chi,' " according to the company. In case you missed the cultural memo, the age of the all-purpose sneaker is over -- tossed out with the all-purpose handbag.

In 2004, consumers spent $237 million just on aerobic shoes (lightweight materials to prevent foot fatigue), $234 million on skateboarding shoes (thin soles to control the board) and $43 million on cheerleading shoes (finger notches to be grabbed during stunts), according to National Sporting Goods Association. Then there are the big categories: $3.5 billion on walking shoes (rigid fronts to protect toes), $1.9 billion on running shoes (thick soles to absorb impact) and $877 million on basketball shoes (high-tops to prevent ankle injuries).

This, in an industry that grew out of a slapdash foot cover constructed from leather and grass. As we learned from the Neolithic corpse found in 1991, man had created a snow-proof shoe sturdy enough to roam the Alps by around 3300 B.C. Rubber soles, a technological innovation of the 1800s, gave birth to the modern athletic shoe. Keds became the first mass-marketed "sneaker" -- a term coined circa 1917 by an advertising executive who noticed that rubber soles allowed people to sneak around unheard.

"When manufacturers come out with a new shoe, technology is where they begin," says Dan Kasen, manager of information services at the National Sporting Goods Association. "It is a critical consideration."

Take the proposed merger of Adidas-Salomon AG and Reebok International Ltd., both of which trail behind sneaker king Nike Inc.

When executives from both companies described the merger in a recent conference call, the word "technology" kept creeping into the conversation. "Adidas is a technology-driven company," said chief executive Herbert Hainer. At the same time, he said, Reebok has successfully fused "sports, entertainment and technology."

But what do the foot doctors, who presumably see patients after they've picked the wrong shoe, think about all of this technology? By and large, they think it confuses consumers. In interviews, several podiatrists offered roughly the same set of guidelines for sneaker buying: The shoe must have a strong sole and mid-sole (the thick area above the sole) to absorb the impact of everyday walking or running, a rigid heel counter (which curves around the heel) to keep the foot stable and a toe box that is big enough and high enough to prevent chafing.

"For the average person, buying any reputable shoe that adheres to these rules is perfect," says Harold Glickman, chief of podiatric surgery at Sibley Memorial Hospital in Washington and president of the American Podiatric Medical Association.

Of course, those criteria are meaningless when fashion comes into play. Who can sell a junior high school student on a stable toe box when he's surrounded by Reebok G Units, endorsed by Allen Iverson, and Nike Air Force Operates, worn by Carlos Boozer? And would the hipsters care if their vintage Adidas Boston Supers didn't offer the proper cushioning?

Still, the podiatrists try.

The APMA puts its "seal of acceptance" on a wide range of sneakers, each submitted by the manufacturer and tested by independent podiatrists. Ten styles of Reeboks made the cut, most of them designed for walking. Nike does not submit shoes, Glickman says -- perhaps because an endorsement from the APMA is less potent than one from Serena Williams or Kobe Bryant.

Stephen M. Pribut, a local podiatrist and president of the Rockville-based American Academy of Podiatric Sports Medicine, knows how to sort out the good, the bad and the mediocre. To demonstrate, he goes to a local specialty footwear store, Fleet Feet, in Adams Morgan.

He grabs an armful off a display wall -- Adidas Supernova Control, the Brooks Beast, Asics Gel Evolution and Nike Free -- and dissects each. Pribut believes that sport-specific shoes are not a bad idea. Tennis and basketball, he points out, require side-to-side motion, and therefore side-to-side stability. "You don't want to wear a tennis shoe for walking. It is not as well designed for straight-ahead movement," he says.

Pribut favors the Brooks Addiction Walker, which has a strong heel counter, plenty of cushioning and a rigid structure. "For a lot of people, this might be too much shoe," he says. "But it's the ultimate motion control for a walker."

The Nike Free is a different matter. "It deserves that surgeon general box on cigarette packs -- 'This could be dangerous to your foot health,' " he says. "It allows the shoe to do whatever it wants to do. Feet need guidance."

Hatfield, the Nike engineer, says the Free is not designed to "replace any other shoe. We've said all along that Nike Free is a tool" for strengthening the feet, he says, adding that consumers must ease into it over time. "You might wear it two, three days a week. When you get back into your other shoes, you can push yourself that much harder."

Still, Nike has put its marketing muscle behind the Free. The sneaker has its own Web site, whose introduction seems to suggest that the Free will turn a pickup game of basketball or a run around the track into a back-to-Eden, barefoot experience. "In the beginning there was the foot. And that was good. That's why we designed a shoe that lets the foot run free. On any surface."

Adidas 1 has its own Web site, too. The company says the shoe, which it introduced first for runners, helps customize footwear in a world where body weights and foot shapes can vary widely. Two people might buy the same running shoe -- size 9, perhaps -- but one weighs 120 pounds, and the other 200. "Before now, you could never change cushioning," says Christian DiBenedetto, who helped develop the Adidas 1.

Now you can. A cable, attached to the sneaker's cushioning and running underneath the arch, works with a microprocessor and electric motor to adjust the fit with every step. (A battery must be periodically replaced.) Adidas 1's value for the non-runner is less clear. "Is it going to do them any harm? Absolutely not," DiBenedetto says.

Reebok, meanwhile, has resuscitated the pump, but this time there is no need to squeeze the tongue of the shoe. With the Pump 2.0, an air-filled chamber automatically takes on the contour of the foot after five to 10 steps. (The pump places enough pressure against the foot that laces are unnecessary.) Another version, called the Pump Wrapshear, lets buyers turn off the pump, should they tire of all that customization.

For the serious athletes of the world, however, the quest for the right shoe is endless. Donald Wilson, a competitive runner in the region, owns 30 pairs of sneakers -- a few Nikes, a few Adidas, a few Pumas -- each with its own function. Some are for running 5K races, others for marathons. One pair is designated for running on trails; another for running on concrete.

His rule of thumb: When a sneaker costs more than $100 "you are usually looking at too many bells and whistles."

Pribut, the podiatrist, has even simpler advice for sneaker buying: "If you've never had a problem with your feet, don't change."

When it comes to the latest technology, career athletic footwear salesmen seem to have the same reservations as podiatrists. "A lot of the technology is sold to people who don't have a clue how it works," says Shawn Fenty, who works at the Adams Morgan Fleet Feet store. He points to pair of Nike Shox, whose spring-like sole, the company says, distributes energy "so that your legs feel less fatigued over time."

"People come in and want to know what's going on here that's not happening in their shoe," he says. The answer? "Nothing," he says. Still, he continues, the genius of designing a shoe for a narrow athletic niche is that it tends to have the widest appeal.

Sneaker designers don't deny that. Many of their most elaborate concepts are created with a hard-charging athlete in mind -- in some cases, they recommend them only for those athletes. But they are thrilled when those shoes become hits in the mass market, and they make no apologies for the bells and whistles lost on the lazy consumer.

Reebok's senior vice president of research and development, Gene McCarthy, compares such buyers to SUV drivers who never take their cars off-road: "Most running shoes are never run in."