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HIIT, otherwise known as high-intensity interval training, is often considered the holy grail of workouts. From burning more fat than regular cardio to boosting your metabolism, the benefits of HIIT are well known, not to mention it’s a great time investment, with most sessions lasting 30 minutes or less.
But if you’re seriously hooked on this workout trend, there’s something you need to know: HIIT could significantly up your risk for injury, depending on your fitness level.
Here's what the research says
In a new study published in the Journal of Sports Medicine and Physical Fitness, researchers analyzed data from the National Electronic Injury Surveillance System from 2007 to 2016 to estimate how many injuries are related to specific equipment (barbells, kettlebells, boxes) and exercises (burpees, lunges, push-ups) that are often used in HIIT workouts. The analysis showed that even though HIIT is great for boosting fitness and building lean muscle overall, it can also increase the chances of getting knee and ankle sprains, as well as muscle strains and rotator-cuff tears. (Watch out for these seven warning signs of overtraining.)
Over a nine-year period, there were nearly four million injuries related to HIIT equipment and workouts, according to the study's findings. The study also cites that separate data on the number of Google searches for 'HIIT workouts' revealed that the interest in the trend roughly parallels the increase in the number of injuries per year. (FYI: This isn't the first time the safety of HIIT has been called into question.)
While males aged 20 to 39 were the largest demographic to be affected by HIIT-based injuries, women weren’t far behind. In fact, about 44 percent of total injuries occurred in females, Nicole Rynecki, M.D. candidate and co-author of the study, tells Shape.
It's worth noting that the equipment and exercises the researchers studied aren't exclusive to HIIT workouts; you can safely and effectively use kettlebells and barbells and do lunges or push-ups (just to name a few) in non-HIIT workouts. Alternatively, HIIT workouts can take many different forms—as long as you're cycling between high-intensity intervals and periods of rest, you're doing HIIT. (You can do it on a treadmill, sitting on a spin bike, etc., so not all HIIT workouts may carry the same injury risk.) Plus, the researchers didn't compare the number of HIIT-related injuries to ones that have resulted from other activities, so it's unclear how risky HIIT is compared to, say, running or yoga.
But is HIIT extra risky?
The study's researchers argue that high-intensity workouts are often marketed as "one size fits all" when they most certainly are not.
“Many athletes, especially amateurs, do not have the flexibility, mobility, core strength, and muscles to perform these exercises,” said Joseph Ippolito, M.D., co-author of the study, in a press release. (Related: Is It Possible to Do Too Much HIIT? A New Study Says Yes)
This isn't the first time you've heard this sentiment: Celebrity trainer Ben Bruno has made a similar argument against burpees (a movement frequently used in HIIT classes) claiming that they’re unnecessary, especially if you're new to working out. "If you're trying to lose weight and feel better about your body, and are learning the ins and outs of exercising, you don't have any business doing burpees," he told us. "Why? Because people in this group often lack the requisite strength and mobility to do the movements correctly, which unnecessarily increases the risk of injury."
Should you stop doing HIIT?
That being said, HIIT can be functional, and researchers are definitely not saying to avoid it completely. They’re simply arguing that it’s important to improve flexibility, balance, and overall strength before challenging yourself to intense workouts like HIIT to avoid getting hurt. (See: Why It's Okay to Work Out at a Lower Intensity)
"Know your body,” says Dr. Rynecki. "Prioritize proper form, and seek appropriate guidance from fitness professionals and trainers. Depending on a participant's past medical and surgical history, consider consulting a physician prior to participation.”