HIIT is the fitness trend that just keeps on trending—and that’s because this highly-effective (and efficient!) type of training offers all sorts of unique benefits. Not only does it blast calories while you’re doing it, but the burn keeps on going after you wrap up. Plus, you can get in a quality sweat in 20 minutes or less.
Of course, reaping the benefits of high-intensity interval training requires that you do it properly. Since HIIT is intense, doing it for too long or too often (among other mishaps) can not only keep you from seeing results but could land you with an injury.
Whether it’s already a part of your routine or you want to get started, keep an eye out for the following HIIT mistakes to make sure you’re reaping the most reward from your effort.
1. Doing HIIT for Too Long
Because HIIT is so intense, doing it for too long puts you at risk for overuse injury or pain, says sports physical therapist and trainer, Leada Malek, P.T., D.P.T., C.S.C.S., S.C.S. “Fifteen to 20 minutes seems to be the sweet spot, with the upper end being 30 minutes, including warm-up and cool-down,” Malek suggests.
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A good rule of thumb to follow: Your work intervals shouldn’t total up to more than about 15 minutes, Malek says. Remember, during HIIT you alternate between intervals of maximum effort (think sprints or 80 percent of your hardest possible effort) and recovery. Your work intervals should tire you out enough that you need those recovery intervals—and since you’re really pushing yourself during your work intervals, you don’t need an hour’s-worth of them, she says.
2. Using Weights
While you can certainly use weights for high-intensity training, they don’t quite fit the bill for true HIIT. “HIIT is a mode of cardiovascular training aimed to increase VO2 max, which is your ability to use oxygen,” Malek explains. Your muscles rely on this and need an excellent oxygen supply during HIIT to maintain high intensity, endurance, and stamina. As such, “true HIIT workouts should be done on a treadmill, rower, track, or swimming in a pool,” she says.
So, if your HIIT workout involves weights, put ‘em down. According to Malek, the added resistance of weights slows down your movement enough that you’re not able to really put in the 80-plus percent effort level required for your cardiovascular system to reap the intended results.
Wondering what this means for fitness classes that are labeled “HIIT” but last closer to an hour and involve weights? Whatever portion you’re doing on the rower, bike, or treadmill is the true HIIT, which is combined with other modes of training, such as muscular strength and endurance work, Malek notes. Just a little something to keep in mind!
3. Not Structuring Your Intervals Properly
Hate to break it to you, but if you’re doing two-minute-long “sprints” followed by 30-second jog breaks on the treadmill, you’re not actually doing HIIT. For HIIT to be effective, you need an appropriate work-to-rest ratio—and that ratio should pretty much always lean in the favor of your rest intervals, meaning that you rest for longer than you work.
Of course, you’ve got options here, with protocols ranging from a 1:2 ratio (think 30-second sprints followed by 60-second walks) all the way up to a 1:8 ratio (think 30-second sprints followed by four-minute walks). That said, some research suggests that a 1:4 ratio (that’s 30 seconds of work followed by two minutes of rest) is the sweet spot for reaping maximum benefits.
Yes, that might feel like a lot of rest—and that’s exactly the point. Don’t skimp on those structured recovery periods; they’re long for a reason! Not only does whittling down your rest intervals put you at greater risk of injury, but without them, there’s no way you’ll be able to keep pushing yourself at a high enough intensity during your work intervals to be doing true HIIT (or see results), says Malek.
4. Doing HIIT Too Often
Because HIIT is so intense, Malek recommends sticking to one to three sessions per week and spreading them out so that you have at least 48 hours of recovery in between sessions. “When you do HIIT too often, you don’t allow your body to fully recover in between sessions and risk overtraining by putting too much strain on your system, potentially leading to overuse injuries and more systemic issues,” Malek says.
If you’re new to HIIT, start with one or two sessions per week and work up to three. If you were to structure a weekly plan, you might do HIIT on Monday, Wednesday, and Saturday, low-intensity exercise or strength work on Tuesday and Thursday, and enjoy Sunday as a rest day (with perhaps a long, leisurely walk or cycle). Or, if you prefer to do your HIIT within a fitness class that also includes weights, don’t do other strength training on your non-HIIT days. Instead, consider walking or yoga, or just plain resting.
5. Overlooking Recovery
In addition to waiting at least 48 between HIIT sessions, it’s important to give your body and muscles the right fuel, care, and rest in the hours after training. “Not doing so can run you into overtraining and underfueling, which can contribute to poor immune function, sleep and mood disturbances, hormonal changes, and injuries,” Malek says. Prioritize proper nutrition throughout the rest of the day and make sure to get enough sleep (seven to nine hours, please!).
Start by refueling within 30 minutes post-HIIT with a 3:1 or 2:1 ratio of carbs-to-protein, and with macro- and micro-nutrient-dense foods, such as leafy greens, fruit, beans or legumes, and whole grains. You’ll also want to consume electrolytes (think potassium, sodium, magnesium, and calcium), which you lose through sweat during HIIT. While the carbs and proteins give your body what it needs to rebuild and make gains, replenishing those electrolytes helps you avoid nausea, cramping, and fatigue.
It’s also a good idea to pencil in 10 to 15 minutes of stretching or a bath with Epsom salts to help soothe those hard-working muscles.