Losing weight doesn't have to mean logging long hours on the treadmill. In fact, you've got our permission to cut your workout short. Don't worry, you'll still see results. Just be sure to follow these rules.

1. Don't cheat: Yes, high-intensity interval training (HIIT [1]) can burn up to 14 calories per minute, but only if you do it right — that is, you're feeling out of breath and can't talk to your workout buddy during each interval. Take this advice from an HIIT expert: if you're going for 15 or 20 minutes, make sure you perform each interval at an eight or nine on a 10-point scale. Cutting it down even more? Your intensity should be maxed out every interval. Think of it as being an 11 on a 10-point scale [2].
2. Mix it up: You can't survive on HIIT alone — overdoing it on intensity can cause an injury that can derail your efforts. Don't do more than three HIIT sessions a week [3], and be sure to mix it up with slower exercise as well. Short is good here, too: a recent study found that healthy runners who only logged a few 30-minute, slow jogs every week [4] had a lower risk of dying early than road warriors.
3. Multitask: If you're cutting your workout short, focusing on just one muscle group at a time just doesn't make sense. Make sure you're working your entire body — and raising your heart rate, too — by doing total-body moves [5] as well as explosive exercises [6] that really work your body.