Blocking out an hour to break a sweat can sometimes feel downright impossible. The good news: You don't need all that time to rev your metabolism—just intensity, according to a study from the University of Capetown in South Africa.
After any workout, your body needs to replace the oxygen your muscles used during exercise—this is called an oxygen debt. And the more oxygen you owe, the harder your body has to work to recover, burning a ton of calories in the process, according to Andy Speer, winner of Men's Health Next Top Trainer and creator of The Anarchy Workout.
The athletes in the study that performed at 80 percent of their maximum effort nearly doubled their oxygen debt, the study reports. In other words, they reaped almost twice the calorie-burning benefits than people who exercised at a lower intensity.