The modern running shoe, with its high-tech cushioned sole, has been heavily criticized over the past few years as barefoot and "minimalist" running have gained popularity.
"Cushioned running shoes are a fraud," Chris McDougall, the author of the 2009 bestseller Born to Run, wrote on his blog last month. "They don't help, they probably hurt, and the billions of dollars that are made every year by selling and promoting them are cashing in on your pain."
Indeed, there's little evidence that shoe cushioning prevents running injuries – but it may still have a useful role, according to a new study from researchers at the University of Colorado, which found that shod runners actually consume less energy to maintain their pace than their barefoot counterparts.
Barefoot running has been touted primarily as a way to avoid running injuries, but increased efficiency is often cited as an additional benefit. The reasoning is simple: Wearing shoes forces you to carry extra weight on your feet. Studies over the years have found that for every 100 grams you add to your feet, you consume roughly 1 per cent more energy when you run. (A typical running shoe weighs about 300 grams.)
Physiologist Rodger Kram and his colleagues at the University of Colorado's Locomotion Lab set out to test this relationship rigorously for both barefoot and shod runners; the results will appear in a forthcoming issue of the journal Medicine & Science in Sports & Exercise. They measured oxygen consumption (which indicates how much energy the runners were burning) while the runners ran either barefoot or in shoes, and then added small strips of lead to the runners' feet to adjust the weight they were carrying.
As expected, adding weight to the runners' feet made them burn more energy – about 1 per cent per 100 grams added – whether they were wearing shoes or not. But surprisingly, for any given amount of weight on their feet, the runners burned 3 to 4 per cent less energy in shoes than barefoot. As a result, when all the weights were removed, running in lightweight shoes (the Nike Mayflys used in the experiment weigh just 135.6 grams in men's size 9) was still more efficient than running barefoot – the shoes somehow conferred an advantage that outweighed the disadvantage of their weight.
A possible explanation for this energy savings, Dr. Kram explains, is that you have to use your leg muscles to cushion your body from the impacts of running. If the cushioning in your shoes absorbs some of this impact energy, your muscles don't have to work as hard. Still, for most running shoes on the market these days, the benefits of cushioning are outweighed by their excess weight – only ultralight trainers like the Mayflys offer a net benefit.
The findings won't put an end to the debate about the ideal running shoe. After all, most runners would gladly sacrifice a small degree of efficiency if that earned them freedom from shin splints, plantar fasciitis and other ailments that plague the modern runner. But they do offer a plausible explanation for why shoes have been so widely adopted: They make running feel a bit easier.
For Dr. Kram, who runs on the snow- and rock-covered trails around Boulder, that leaves shoes – preferably lightweight, but still with some cushioning – as the default option.
"If I could run faster barefoot, I'd do it," he says. "As a 50-year-old runner, I need all the help I can get."
Alex Hutchinson blogs about research on exercise at sweat-science.com. His latest book is Which Comes First, Cardio or Weights?
Do running shoes cause running injuries?
Here's the trail of clues:
The number of runners at a major marathon (wearing modern running shoes) who landed on their heels; in contrast, most people who grow up without shoes land on their forefoot when they run. Source: Pete Larson et al., JSS, 2011
The number of times heel strikers on Harvard University's cross-country team were more likely to suffer repetitive-stress injuries, compared to forefoot strikers. This study of the team, between 2006 and 2011, is the first significant evidence of a link between foot-strike pattern and injury. Source: Adam Daoud et al., MSSE, 2012
The bottom line
So does this mean that all heel-strikers are more susceptible to injury? Not necessarily. The heel-strike classification includes some runners who land roughly under their centre of gravity, and others who "over-stride" and land well in front of their centre of gravity. It's these over-striders who may be the most injury-prone, suggesting that the first defence against running injuries is to ensure that your foot lands under your body – no matter what's on your feet.