Testing your limits brings about than just bragging rights. Lifting a heavier weight for fewer reps burns nearly twice as many calories during the two hours after your workout than lifting a lighter weight for more reps, according to research published in the journal Medicine & Science in Sports & Exercise. Feel smug in the knowledge you’re still torching calories in that 10am meeting.
The major reason HIIT works so well for dropping body fat is due to the greater calorie burn (or EPOC—excess post-exercise oxygen consumption) that's maintained after the workout is over. In other words, you burn more calories and more body fat while you're sitting around doing nothing. In addition to this increase in resting metabolism, HIIT is effective at enhancing the mechanisms in muscle cells that promote fat burning and blunt fat storage.
Here's something else most people probably don't know: Fidgeting is good for you. It's considered a nonexercise physical activity, and it's an important way to burn energy. You get more health benefits if, in addition to exercising, you are a more fidgety, more active person the rest of the day. This means gesturing while you're talking, tapping your foot, just moving around.