What Burns More Kilojoules: Running Inside Or Outside?
By Locke Hughes; Photography by Freepik
Hot outdoor runs may *feel* more exhausting, but here’s what science says.
Plenty of people pick running as their go-to cardio workout to burn calories and shed fat. And for good reason—all you need is a pair of sneakers, and you can do it anytime, anywhere! Running also offers a host of benefits for your body beyond torching cals—it can help lower stress, reduce your risk of heart disease, and strengthen joints, just to name a few.
That said, if you are focusing on losing weight, you may have pondered: Do certain running conditions give you more bang for your buck? Say you’re running outside on a hot summer day, for example. It certainly may feel like you’re burning way more kilojoules than you’d burn on an indoor treadmill run (cue pounding heart and dripping sweat). But are you actually?
On a physiological level, yes! “You probably burn about 3 to 7 percent more kilojoules running outside than on a treadmill,” says Dr. John Porcari, director of the Clinical Exercise Physiology program at the University of Wisconsin, LaCrosse. When you’re on a treadmill, the moving belt helps propel you as you run, and you’re not dealing with wind resistance, he explains.
It also depends on your speed: If you’re at a jogging pace, you’re likely burning about 3 percent more kilojoules outside, while running at a faster pace burns up to 7 percent more, Porcari says. You can thank the changing incline levels, wind resistance, and variances in your speed for that extra boost.
A final factor that increases your kilojoule burn: Getting back to homeostasis, or a normal body temperature, takes more effort from your body on hot days. “Because your body has to pump more blood to the skin and dissipate the heat you’ve built up, you’re burning slightly more kilojoules after a run on a hot day than you would on a cooler day,” Porcari explains. But only about 1 to 5 percent more.
Now for the bad news: Running outdoors on hot days isn’t a magic bullet for weight loss. The higher kilojoule burn may be negligible compared to the risks of forcing yourself to run during brutal heat, such as dehydration and overheating, Porcari says.
Running on hot days also increases your rate of perceived exertion (RPE), which means you may feel fatigued more quickly than you would on a treadmill. And while some may see that as a sign your body is working hard, consider this: Not being able to complete your full workout isn’t going to help with your weight-loss efforts.
A better idea? When temps are soaring, add five minutes or so to your indoor run and bump up the incline slightly, Porcari suggests. has proven that a 1 percent incline on a treadmill equals the extra effort that running outside takes. And if you’re looking to truly boost your kilojoule burn, switch up the super-sweaty slog with speed and incline intervals. “Intervals are a great way to increase kilojoule expenditure, challenge your body, and mobilise fat stores,” says Anita Mirchandani, a certified trainer.
In the long run, those small amounts of extra kilojoules burned won’t lead to big changes on the scale. If you do see your weight drop dramatically post-run, you can probably thank depleted fluid levels and lost water weight, says Mirchandani. That’s why it’s important to replenish electrolytes and minerals when exercising in warmer temperatures.
Finally, remember: To achieve lasting weight loss, don’t be fooled into eating more than you burned off. “We always think we burn more kilojoules than we actually do,” Mirchandani says. Post-workout, focus on a combo of lean protein and whole grains to help you refuel and feel satiated, she suggests, and stay hydrated since adequate water intake does aid in long-term weight loss.
Looking for more? Here are 6 kilojoule-busting moves that’ll make you a better runner.
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