Experts weigh in on whether the criticisms of America's favorite workout are legit.

By Julia Malacoff
December 04, 2017
Photo: Getty Images/Neustockimages

Each year, the American College of Sports Medicine (ASCM) surveys fitness professionals to find out what they think is next in the workout world. This year, high-intensity interval training (HIIT) took the number-one spot on the list of major workout trends for 2018. This was pretty much news to no one, since HIIT has ranked near the top of the list since 2014. Still, the fact that it's finally taking the top slot means it's probably here to stay. (Yay boot camp!)

There are tons of great reasons that HIIT has become the most popular workout in America. It's been shown to slow down aging at the cellular level. It burns tons of calories and boosts your metabolism. It's also super efficient. Research has shown you can make faster cardiovascular progress with shorter, more intense workouts than you can with longer, less intense ones. Plus, you can do it from the comfort of your own home with little to no equipment required. There's just one important drawback to the trend that ACSM was careful to highlight in their press release about the list: HIIT carries an increased risk of injury compared to lower-intensity workouts.

That's a pretty big deal, mainly because as exercise trends grow bigger, more people inevitably try them. And a lot of people are doing HIIT at home. "Even though some aspects of HIIT have been around for a long time, its emergence into mainstream exercise routines is still new," explains Aaron Hackett, D.P.T., a doctor of physical therapy and corporate wellness consultant. "There's always caution with new trends."

That's because the time when exercisers are most likely to get hurt is when they're trying something new, especially if they are newer to exercise overall. But it's important to note that the majority of the concern about injury is related to "untrained" individuals, aka exercise newbies. "The primary fears expressed by other physical therapists and fitness professionals specific to HIIT recently seem to focus on people with little or no experience in exercise or training just jumping into it without being prepared," Hackett says.

But are there really more injuries from HIIT than from other types of workouts? Laura Miranda, D.P.T., a doctor of physical therapy and trainer, says she absolutely has seen a rise in HIIT-related injuries over the past few years. Of course, it's important to acknowledge that most sports-related injuries are not due to just one thing, but rather a buildup of a combination of factors over time, according to Miranda.

Here, four of the main factors that experts say you should watch out for when it comes to HIIT:

Inadequate Warm-Up or Preparation

Most people sit at a desk for eight to 10 hours per day and hit up the gym before or after work. Jumping right into an intense workout-without an adequate warm-up that includes activation of the muscle groups that oppose the "chair posture" we're so accustomed to-can set exercisers up for injuries, Miranda says. Because HIIT is so convenient and popular, people often want to try it when they're new to (or just getting back to) exercise. "Undertrained individuals who are just getting back into fitness should acclimatize themselves first to a baseline level of both cardio and strength training prior to jumping into HIIT," Miranda says. "Failure to do so can increase the chance of injury."

Bad Programming and Instruction

Unfortunately, not all coaches and trainers are created equal. "A major part of this concern is the variation in education and training of personal trainers and coaches that lead these workouts," Hackett says. "In as little as a weekend, I could take a course and become a 'certified' coach." Of course, there are plenty of amazing, qualified trainers out there, but one of the downsides of not having a solid background in fitness is accidentally planning workouts (aka "programming") in a way that's likely to lead to injury. "HIIT is classified by near-maximal intervals, mixed with lower-intensity intervals," Miranda notes. A mistake in programming would be not leaving enough time for rest during the workout, which can make injury way more likely, or focusing too much on primary muscle groups without paying any attention to the smaller muscles that stabilize you.

Improper Form

"This is the mother of all reasons why people get injured," Miranda says, and it's especially true of newer exercisers. "The inexperienced will not focus on proper form and technique first, which results in injuries that could have been avoided," Hackett explains. What's more, while form issues can happen with any type of workout, the nature of HIIT makes it more likely. "These new HIIT workouts often focus on speed and numbers, which takes emphasis away from doing something properly first."

More experienced exercisers aren't immune to this concern, mainly because of the way HIIT workouts are structured. "Certain HIIT workouts don't typically offer a regression of the exercise or movement pattern once the participant's form has broken down," Miranda says. In other words, there are no options provided for when your body starts to get tired but the workout requires you to keep moving. "The person is then forced to then continue with the same load or exercise, cranking out the remainder reps with sloppy form in this extremely fatigued state, thus setting the stage for injury." (Fear not, we've got you covered with just that: Try These Modifications When You're Tired AF In Your HIIT Class)

Not Prioritizing Recovery

It can be tempting to hit your boot-camp class five times a week. But if the class you're taking is truly a HIIT workout, this isn't allowing for nearly enough time to rest and recover. Lana Titus, master instructor at Burn 60-a HIIT-dedicated studio-recommends students work out there three to four times per week max. That's because the risk of overtraining is real. To get benefits from your training, you also need to spend time doing restorative activities. Miranda suggests yoga, foam rolling, and flexibility work, along with paying attention to the quality of your nutrition and sleep.


So where does all of this leave us? Basically, it's not just the type of workout that contributes to an injury, but rather the "perfect storm" of factors that causes a person's body to give out. While injuries are more likely to happen when you're doing HIIT than when you're slowly jogging on a treadmill, that's not completely due to the method of exercise itself. It's related to how prepared people are for HIIT and the quality of instruction they're given.

In spite of the risks, there are still *so many* benefits to high-intensity exercise, and research even shows that exercise is more fun when it's harder.

With that in mind, here's how to stay safe during HIIT workouts, especially if you're newer to them.

If you're working out at home:

One of the best things about HIIT is that you don't need to be in a gym to do it. But experts caution that if you haven't tried a move before, you should go over it with a trainer or instructor first. Plenty of people do even basic moves like push-ups and jumping jacks wrong, Hackett says. "Form is even more important when you're adding equipment." That means if you're incorporating dumbbells, barbells, kettlebells, or any other type of weights into your at-home workouts, it's a good idea to check your form with an expert first.

If you're working out in a class:

Here, you have the advantage of a teacher or trainer who ideally will be keeping an eye on you. Titus highlights the importance of seeking out a trainer or instructor who is experienced and can make sure you're doing the moves correctly. And if you're new to HIIT, "always let the instructor know so she can keep an eye on your form," she says.

Still, it's important to go with your gut if something doesn't feel right. "Remember to listen to your own body and go at whatever speed and intensity are comfortable," Miranda says. "It's easy to get caught up in the excitement and competitive nature of these types of classes, but don't be a hero. No rep/time/PR is worth getting injured. After all, zero training can happen if you're injured and out on the sidelines."

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