You don’t need to spend hours at the gym to see results — short, intense bursts might beat long, slow workouts.

Other research found that short, intense workouts burned more fat than longer, steady cardio — even when total exercise time was less. In heart patients, just 20 minutes of hard bursts improved heart fitness more than 40 minutes of slow exercise. Obese teens lost more waist fat with 30 minutes of high-intensity work than the same time spent doing slower cardio. The afterburn effect is real: intense workouts keep your body burning extra calories for up to an hour afterward, even when total energy used during exercise is the same. And yes, muscle protein synthesis does peak within the first hour after lifting weights, which includes the 30–45 minute window mentioned. None of the studies contradicted these findings.

If you’re short on time, going hard for 20 minutes might just give you more bang for your buck than dragging out a slow jog.