Now that it’s winter, more of us are using and blogging about running on treadmills. Inevitably, well-meaning readers will remind everyone that the incline should be set at 1% in order to more closely mimic the outdoor effort. Heck, back in 1996 the National Center For Biotechnology Information disseminated a study stating just that. I must admit that I was initially a proponent of the incline, since much of what I had read seemed to support it. However, after a while, I started having more trouble with my feet, feeling plantar fasciitis-like effects and similar discomfort. Turns out that the incline may have been the culprit.
So who’s right? Incline or no incline? What’s the answer for an average runner like myself?
Researchers at the University of Brighton in the United Kingdom wondered the same thing 15 years ago, so they tested a group of trained runners on treadmills and an outdoor track, measuring their signs of exertion. "The energy cost of running outdoors is always greater than running indoors whatever the pace," says Jonathan Doust, Ph.D., one of the study's authors. "The faster you run the greater the effect."
This is most clearly seen in the tactics of races like the Tour de France, where the peloton saves energy by sharing the cost of breaking the wind. "At the slower speeds of running the effect of air resistance is much less, but still measurable," Doust says. For instance, running at a pace of 6:00/mile outdoors will add 5 percent to the total energy cost due to wind resistance. This would show up as roughly five extra beats per minute on that runner's heart rate.
The study's final verdict? At paces slower than 8 mph (7:30/mile pace), no adjustment is necessary. "The difference is so small as to be meaningless," says Doust. Between 8 mph and 11.2 mph (5:21 pace), a 1 percent treadmill grade provides the right adjustment. At higher speeds you will need at least a 2 percent grade to offset the lack of wind resistance. Don't worry if you choose to ignore your well-meaning friend's advice. You'll simply run at a slightly faster pace than you could outside with less effort. Consider it a confidence boost.