The running shoe revolution is picking up speed. And controversy.

After nearly 30 years with very little structural change to running shoes -- most trainers have had a meshy upper and thick, multidensity foam midsole with a relatively steep heel-toe ramp angle for three decades -- running shoe makers are jumping on the small but fast-moving bandwagon piloted by the fervor of Vibram FiveFingers, the New Balance 100, several models from Newton Running, Nike's line of Free shoes, and newcomers like Terra Plana and Ecco.

Starting this fall and continuing next spring, the floodgates will open with new shoe designs from nearly every major brand. While each manufacturer has its own take on the new direction in running shoes, most models are very lightweight, low to the ground and have a relatively low heel-toe drop (from 0 to 5mm or 1-4 percent). Some, although slightly higher off the ground, have new approaches to stability and more effective ways at capturing downward energy and turning it into forward propulsion.

While the 2009 bestseller Born to Run has been a catalyst, companies are reacting to the hot growth segment created by talk about barefoot and natural running mechanics, as well as research suggesting traditional shoe design is less-than-optimal for runners.

Three independent studies released last winter (from the University of Virginia, Harvard University and the Italian Olympic Committee) confirmed the notion that people run differently barefoot than they do while wearing shoes. Each also somewhat praised the benefits of barefoot running and uninhibited natural running form -- namely, having foot strikes at the midfoot, less overall impact on the body and better all-body kinematics -- while offering caveats about safety, duration and transition from heel-striking to more natural running.

"I'm glad the industry is going to go toward models with lower heels," says Jay Dicharry, MPT, director of the SPEED Clinic at the University of Virginia's Center for Endurance Sport, where one of the studies was conducted. "It's going to be tough because shoe companies want to sell shoes; they don't want to have their products look different. But now there's some movement in that direction because everybody's doing something different."

The studies didn't condone barefoot running on a full-time basis, but each suggested that the high heel-toe angle of most training shoes -- dropping anywhere from 12-23mm or 8-15 percent -- is not only counterproductive to the optimal running form of a barefoot runner as it typically puts a runner into a heel-striking gait (because the elevated heel strikes the ground earlier than a shoe with a level profile), but it also might be a big factor in common running injuries such as plantar fasciitis, shin splits and various types of knee, hip and lower back pain. Essentially, each implied there might be a better way to build running shoes.

In fact, D. Casey Kerrigan, M.D., who led the University of Virginia study that showed that traditional running shoes result in large increases in hip and knee torque, left academia to join a company developing a new cantilever midsole suspension mechanism that works in harmony with natural foot motion. It's expected to debut in the inaugural line of OESH shoes this fall.

Still, the new designs have led to heated debates about what good runner mechanics look like and how much shoe a runner needs. Both sides use "science" and experts to support claims, but in reality there's surpisingly little research about the nature and cause of most running injuries or why 50 percent of runners are injured every year.

Proponents of barefoot and natural running say heel-striking is a misplaced function of a walking gait and produces extremely destructive impact forces on feet, hips, knees and legs, while traditionalists claim midfoot/forefoot running puts more strain on the calf and Achilles tendon. Most agree, however, that a wholesale change to more minimalist footwear isn't for everyone and that even gradual changes require runners to be functionally fit, strong and efficient. "But the key isn't whether you strike at the heel or midfoot or forefoot," Dicharry says. "The key is having your footstrikes below the center of your mass and not out front of it."

Mark Cucuzzella, M.D., a 2:25 marathoner, doctor of family medicine at West Virginia University and running mechanics guru who has studied running injuries for years, agrees. He believes lightweight shoes with a level profile combined with good running mechanics can help runners avoid common overuse injuries caused from excessive forces generated by heel striking. In May, he opened Two Rivers Treads in Shepherdstown, W.V., a shop that sells only shoes geared toward natural running and walking.

"My goal as a doctor is to keep people healthy," he says. "And from my perspective, we've made zero progress in preventing and treating running injuries. We need to find better ways -- as runners, coaches, doctors and the shoe industry. And from my experience and preliminary research, there's a ton of validity to this."

While Vibram is continuing to develop new versions of FiveFingers -- such as the slightly more protective Bikila released this year -- it's also working with New Balance and Merrell to create new toeless versions that will hit stores in 2011. Terra Plana and Newton have new models for natural running on trails that will debut this fall.

"People are starting to question, 'Why are you guys using this cushioning technology?' 'Why do we have heel lifts that are so big?' 'Do we really need this and that?'" says JF Fullum, a shoe design manager at New Balance. "I think it's great for us, because we're being challenged by the outside to rethink what we're doing."