You May Need to Run 15% Faster on a Treadmill to Equal Running Outside

Running on a treadmill versus running outside: there really isn't a competition. It's always preferable to run somewhere rather than nowhere.

Still, treadmill running offers shelter from the elements in an air conditioned room, often with the opportunity to watch a television show or two, so it's not going out of style anytime soon.

Philosophical, weather, and convenience contentions make up most of the treadmill debate, but what about what really matters? You know, running. Do you get a better workout on a treadmill or outdoors?

In 1996, University of Brighton exercise scientists Jonathan Doust and Andrew Jones measured the energy use of nine trained male runners as they ran outdoors on a flat surface and on a treadmill. They found that running on a treadmill at consistent speeds between 6.7 and 11.1 miles per hour was less energetically demanding compared to running outside, but the disparity could be eliminated by raising the treadmill's incline to a 1% grade. The slight incline accounted for wind resistance.

Now, a team of French and Italian researchers has taken up the topic, measuring the physiological responses of fifteen college-aged males as they completed an interval training workout on both a treadmill and on a track.

Each of the subjects completed a workout in which they ran thirty seconds at a predetermined, intense speed followed by thirty seconds of rest for fifteen rounds. They repeated the workout on an outdoor track, on a treadmill at 1% grade, and on a treadmill at 1% grade and a 15% increased velocity. Indoor and outdoor workouts were performed at similar ambient temperatures with outdoor wind speeds averaging less than three miles per hour.

The researchers found that subjects exerted themselves to a greater extent on the track compared to the treadmill, despite running at the same speed.

"[High-intensity] running exercise on treadmill reduces by 6.3% the mean oxygen uptake compared to the same exercise performed outdoors," the researchers reported. "An increase in 15% of running velocity during an HIT training session performed on treadmill... appears to be a optimal solution to reach the same physiological response..."

As to why the treadmill was easier, the researchers speculated that the flimsy board of most treadmills upon which the belt runs could return elastic energy to the runner with every step, literally putting a spring in their stride.

In the end, running is a wonderful way to stay in shape whether on a treadmill or on a sidewalk. But if you're set on burning some extra calories, head outside!

Source: Panascì M, Lepers R, La Torre A, Bonato M, Assadi H. Physiological responses during intermittent running exercise differ between outdoor and treadmill running. Appl Physiol Nutr Metab. 2017 May 26. doi: 10.1139/apnm-2017-0132