Among professional and amateur runners alike, there’s always been this internal debate about which of the two is better: running indoor on a treadmill or outside in the open.

Credit: Runners Connect

Some prefer the treadmill because it’s convenient to jog in the same gym where you can do other workouts. It’s also nifty to know you can use the treadmill anytime of the day no matter how freezing it is outside or whether it’s raining cats and dogs or not.

Running outside, of course, is the oldest exercise routine in the book. It’s free, accessible, and hardly boring – especially if you have a nice track around nature or even in an inspiring city neighborhood like the harbor.

There are subjective pros and cons to both kinds of runs which will differ from person to person. Ultimately, though, there is also a clear objective factor that can differentiate the two – something many people would care to know, more so if losing weight is a priority. Specifically, how much energy you consume while running outside or on a moving band or how hard you’re working out.

More than two decades ago, in 1996, British researchers from the University of Brighton set out to measure how much energy nine male runners expended while running outside on a flat surface versus on a treadmill. Their conclusion what that running on a treadmill at a constant speed anywhere from 6.7 to 11.1 miles per hour was less demanding than running outside at the same speed. The two kind of jogs, however, could be equivalated if the treadmill incline is raised to a 1% grade, a slight incline which accounts for wind resistance outdoors.

Most recently, French and Italian researchers revisited the topic. They measured the physiological response of 15 healthy college-aged men as they performed interval training workout on either a treadmill or on a track.

Each participant had to run at an intense speed for 30 seconds followed by 30 seconds of rest for 15 rounds. The workouts were performed for three scenarios:

• outdoor track
• on a treadmill at 1% grade
• on a treadmill at 1% grade and 15% more velocity.

Indoor or outdoor, the researchers were careful to measure performance at the same ambient temperature and during low winds averaging no more than three miles per hour.

Despite essentially running at the same speed, outdoor runners burned more energy than the treadmill runners.

“[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…”

Researchers reckon treadmill belts return some elastic energy as the runner makes every step which could explain why it’s less physically demanding than running outside at the same velocity. At the end of the day, it’s a matter of personal preference which of the two kinds of runs you enjoy more. It’s good to know, however, that running outside is the easiest way to burn energy.

Scientific Reference: 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