Tennis can be brutal on the body: Long-lasting heel bruises are common, as are toe injuries so severe they require surgery, like the one Serena Williams recently suffered. And the kind of knee pain that has been plaguing Rafael Nadal for years only gets worse with age. At any tennis club, most of the guys over 50 sport knee or ankle braces. Trainers and researchers are now wondering if shoes are to blame.
Injury-prone runners have been through this before. Adopting concepts from the book 'Born to Run,' which followed Tarahumaran Native Americans who run extreme distances in sandals and seem to suffer few injuries, millions of runners turned to "barefoot" or, more accurately, minimal shoes that have a low "drop" – height difference between the heel and the ball of the foot. In no time, runners grew this niche product into a $1.7 billion-a-year shoe category. Now, the U.K. footwear company VivoBarefoot expects to release a tennis-specific zero-drop shoe next year, followed by a similar approach from New Balance, to come out in 2015. "Tennis is lateral and linear," says Ken Thornby, a marketing executive for New Balance. "We are seeing how foot strike would benefit from a zero-drop shoe. We're finding the foot is more responsive."
Up until 50 years ago, most athletes wore a shoe like the Converse All Star, with a rubber sole melded to a canvas upper, creating a more modern version of moccasins or Roman sandals. Everything changed in the early 1970s as companies began to build up pricey shoe designs with the idea that more cushioning meant better-protected feet. We soon had Reebok Pumps and Nike Airs and – as many podiatrists, physical therapists, and trainers argue – more injuries. "I grew up in the era when we had All Stars, and we didn't have the injuries you see today," says Vern Gambetta, who trains professional athletes and is known as the father of functional fitness. "The more the shoe is built up, the more it sends forces up the leg that can cause injuries." Among those injuries blamed on thicker shoes are plantar fasciitis, tibial stress syndrome, Achilles tendonitis, twisted ankles, meniscus tears in the knee, and even hip and lower-back problems.
We have more than 200,000 nerve endings on the bottom of each foot, and these drive proprioception, our sense of position in space. Proprioception is what cops measure when they issue a sobriety test – it helps us to stay upright and avoid twisting an ankle when we run. The athletes with the greatest need for proprioception often wear the most minimal footwear, or sometimes none at all. These are martial artists, boxers, fencers, dancers, and gymnasts. While researchers have yet to compare the injury rates among these minimally shod athletes and basketball or tennis players, there is evidence that links decreased feedback with increased impact on the body. Researchers at University of Southern California, for example, found that in gymnastics on very soft floors – the gymnast's equivalent of a heavily padded shoe – they landed harder.
Another sport that naturally takes to minimal shoes is weightlifting. The weight-and cross-training regimen CrossFit collaborated with Reebok to create the Nano 2.0, a shoe that utilizes a wide toe bed that lets the foot spread out and stabilize the body as it's loaded with weight. Its devotees will be the first to point out that wearing this type of shoe works more muscles in the foot and lower leg, which is exactly the point: building a structure that is capable of cushioning impact to our bodies.
For other sports, it's been a slower transition. "People have been wearing shoes a long time," says Mark Verstegan, who trains professional athletes with a barefoot-style line he helped to develop for Adidas called Adipure, which includes a thin shoe with toes and a bare-bones soccer cleat. "We need to be responsible about how we introduce and transition people to restore the natural functioning of their foot," he says. Verstegan transitions many of his professional athletes – last year he trained the top four NFL draft picks – out of their traditional sport-specific shoes for strength and off-the-field cross-training. "Look at Adidas basketball shoes now, and they're the most minimalist shoe since the Converse All Star," says Darcy Norman, the director of performance innovation at Athletes' Performance, which helps professional athletes cross-train off the field. "But, of course, for game day for sports like soccer and football, you still need a cleat, so there's only so much material you can get rid of."
The minimal-shoe movement is, primarily, a reaction to the basic design of the modern sneaker, which hasn't changed much since the insistence on support and cushioning became the bedrock of its design. But it's easy to get caught up in the hype, to think of these shoes – or lack thereof – as some sort of panacea. Simply tossing on a pair from the Adipure or VivoBarefoot line is not a foolproof way to ignite your body's natural movement and keep you free from injury. "You can't just suddenly change your shoes one day and expect that all will be wonderful," says Daniel Lieberman, an evolutionary biologist at Harvard. Quickly and completely switching to minimal is a great way to strain a calf muscle or get tendinitis. We've been wearing shoes our whole lives, and adapting to a more minimalist approach takes time – months, or even years.
Lieberman is eager to point out that how you use your feet is just as important as what you wear, noting that Roger Federer wears modern tennis shoes but somehow manages to always land on the balls of his feet. Imagine the injury-prone Nadal, who spent much of the last year sidelined due to a knee injury, switching from heel striking to a more fleet-footed game like Federer's, and you get an idea of the complexity of adapting to minimalist shoes. "We would love to get our hands on Nadal," says Galahad Clark of VivoBarefoot, which makes a golf shoe along with about two dozen other varieties of minimalist shoes. "He would be a dream project. It's definitely our hypothesis that if he made the transition to barefoot [shoes], he'd have a prolonged period of injury-free tennis."