Ahh, HIIT. It’s the workout every body brags about doing, day in and day out, because they have #bodygoals that they’re here to, err, hit. But guess what? HIIT, or high-intensity interval training, wasn’t meant to be done every day. And if you’re able to actually bust out that level of intensity seven days per week (or even five or six days), you’re likely doing it wrong. I know, it’s not what you want to hear. But when HIIT workouts were first developed, these super-quick, seven- to 10-minute routines were sent into the universe so that you could perform your chosen form of cardio at maximum effort, says Joey Thurman, certified personal trainer and author of 365 Health and Fitness Hacks That Could Save Your Life. “The idea is to elevate your heart rate for a brief period, followed by resting for a given period,” he explains. “You can train in a 1:1 work-to-rest ratio (sprint for 30 seconds, rest for 30), a 1:2 ratio (sprint for 30 seconds, rest for 1 minute), a 1:3 ratio (sprint for 30 seconds, rest for 1.5 minutes), and so forth.” The key, he says, is to go at your maximum effort during the sprints. A lot of studies that show the benefits of extremely intense, short bouts of exercise are a result of those working at their give-it-all-you-got effort, says Dalton Wong, certified personal trainer and author of The Feel Good Plan: Happier, Healthier, and Slimmer in 15 Minutes a Day. “True HIIT is like sprinting, and it should make you feel like your gas tank is completely empty,” he says. So if you’re doing a 30-second sprint during a HIIT interval, you shouldn’t be able to get to second 31 without wanting to collapse. Which means: If you’re able to go for even one second longer—or pencil in another HIIT session tomorrow—you probably didn’t go hard enough. We hate to be so blunt, but that’s the truth. Most people aren’t used to pushing themselves as hard as necessary for HIIT, especially a HIIT workout that’s as short as 7 or 10 minutes, because it’s extremely uncomfortable.Oh yeah, they exist—it’s why HIIT workouts are so enticing. We all want the fastest, most efficient way to get in shape so we can do other awesome things with our lives. So the idea of being able to work out for such a short amount of time and get results, rather than slogging away on the treadmill for hours, sounds like a no-brainer. The first benefit everyone talks about is, of course, the fat burning. “Research shows that intervals can repair your metabolism by reducing inflammation, forcing the body to improve its ability to use and burn energy,” says Thurman.