Whether you’re looking for a faster, more effective workout or just looking to shake up your routine, chances are you’ve encountered the exercise practice known as HIIT (high-intensity interval training). The concept is simple enough: short, high-intensity activity periods, followed by brief periods of low-intensity activity or rest. Several of these intervals, stacked back-to-back, form the ultra-effective workout method known as HIIT. One of the most enticing factors of HIIT-style workouts is that they pack the potential to burn more calories than traditional cardio-based workouts that are twice the length—no wonder it’s a go-to for at-home-gym-goers and personal trainers alike!
If HIIT sounds like a miracle workout, you wouldn’t be wrong. However, like anything that’s high intensity, HIIT routines take a toll on the body—and the mind—which bears the question: How often should you do HIIT workouts? More specifically: How many times a week can you do HIIT without increasing your risk of injury or counteracting its positive effects, both physically and mentally?
The answer, like so many things in fitness, is multi-pronged, but ultimately, experts suggest that you should engage in no more than a few 30–45-minute HIIT workouts each week, allowing 48 hours of rest between each workout. Remember: Approximately half of that total time will be spent on high-intensity activity, and the other half will be spent on low-intensity activity or rest. If you prefer 15-minute HIIT workouts, you could potentially work in as many as four each week.
This number is derived from a variety of factors, but perhaps most heavily stems from two widely accepted recommendations: one, that you spend only 30–40 minutes total per week with your heart rate around 85–90 percent, and two, that you allow 48 hours of rest between high-intensity workouts to optimize muscle regeneration and building.
Another factor to consider is that if you’re giving every HIIT workout all you’ve got (which you should be doing to yield maximum returns), completing a workout of the same caliber the next day shouldn’t feel feasible. If you’re wondering whether or not you’re investing enough effort during your intervals, consider that for every second of a HIIT interval, you should feel like you’re hovering at a 9 out of 10 (with 10 being the max) on a simplified effort scale.
What is HIIT?
To fully understand why HIIT is such a delicate balancing act, it’s useful to understand what HIIT is and how it impacts your body. HIIT is an exercise practice that couples maximum-effort activity with periods of idleness or low-intensity activity. The idea is to shock your body by pushing your muscles to the point of fatigue, then backing off to allow recovery time. When done right, this formula pays off, as HIIT workouts have been proven to burn more calories than traditional steady-pace cardio workouts like walking, jogging, cycling, or rowing. HIIT accelerates your heart rate and boosts your body’s ability to accommodate increased oxygen flow, thereby activating your metabolism for hours, even after your workout is done.
Why do people love HIIT?
Aside from the obvious—people love any workout that packs in maximum-calorie burn—HIIT endears itself to anyone looking for a workout that’s time-efficient. Those who aim to pull off four to six workouts a week, but don’t have the time to squeeze in an hour-long cycle session every day, can often come up with a few spare minutes to accomplish a 15-minute HIIT workout.
In addition to being time-efficient, HIIT workouts are perfect for those who don’t have a dedicated home gym or own at-home fitness equipment. The fact that HIIT workouts can easily be integrated equipment-free makes it one of the most versatile forms of exercise.
Lastly, HIIT packs a bonus that might be of little importance to those beyond top-tier athletes, but it’s actually pretty compelling when you think about it: HIIT allows you to engage in exercises that you likely couldn’t do continuously for 10 or 15 minutes—such as sprinting—by breaking them down into conquerable modules. When put together, these modules allow you to reap the benefits of a 10- or 15-minute sprint without ever having to attempt one.
Why does HIIT burn more calories than a normal workout?
While the scenario above might make it clear why a HIIT workout burns more calories than a run-of-the-mill workout, there’s also something known as the “afterburn” that aids calorie loss even after your HIIT workout has ended. Officially known as EPOC, or excess post-exercise oxygen consumption, the afterburn is the result of the body converting more oxygen to fuel at a higher metabolic rate in order to replenish your body from the breakdown that’s generated by HIIT. The amount of time in which you’ll continue to burn calories post-workout can vary, but generally, if you’re going full-throttle in every HIIT workout, EPOC can last for 24–48 hours.
Given the 48-hour benchmark, it’s easy to see why experts and personal trainers don’t endorse more than one HIIT workout every two days. Even without a workout, you’re reaping the benefits of EPOC on a daily basis without needing to induce wear and tear on your joints.
As for how many calories EPOC burns, it’s admittedly a bit of a guessing game, as everyone is different. Generally, EPOC burns between 6–15% of the total calories burned during a workout. If you knock out a 180-calorie workout, you will burn an extra 11–27 calories in the following days. While that’s not exactly a bootcamp-level calorie burn, consider the fact that it can be supplemented with a lower-impact workout to get you into your daily burn goal range.
Why is too much HIIT bad for you?
Just as you’re more likely to make a mistake when you’re working on no sleep, you’re more likely to strike an injury when you’re teetering at the brink of exhaustion. For this reason, it’s wise not to overindulge in HIIT. As mentioned before, the effectiveness of HIIT workouts primarily relies on you giving maximal effort to each and every interval, coupled with adequate rest.
This same “less-is-more” mentality shouldn’t only apply to your in-workout efforts but also to how frequently you do your workouts. When you don’t give your muscle tissue enough time to repair and grow, you increase your risk of pulls, sprains, or tears.
Don’t rule out the ill-effects of mental fatigue, either. When you work out at a high-intensity level, your body releases stress hormones like cortisol. On the one hand, cortisol can enhance your strength, improve your body’s cardiovascular system and endurance, boost your immunity, and fight inflammation, but on the other hand, doing HIIT exercise every day can result in unleashing too much cortisol, which can disrupt your mood, induce fatigue, and cause joint pain to flare up.
What should you do on days when you don’t do HIIT?
If you want to round out a HIIT exercise regimen with a roster of other exercises, try mellowing out with a low-impact routine such as resistance training, aerobics, or stretching. Yoga and pilates are both great ways to expel extra energy while keeping things relatively low-key. Steady-state cardio, such as cycling, rowing, or walking on the treadmill at a consistent pace, can also offer an effective alternative to energy-depleting HIIT circuits. It’s imperative to remember that steady-state workouts can provide the same heart health benefits and calorie burn as HIIT, just with less EPOC release.
Since HIIT is often cardio-based, some trainers are proponents of turning recovery days into strength or resistance training days. Ideally, you should hit all of your major muscle groups in the course of a week to maintain strength—twice a week to build muscle mass.
How do you get the most effective HIIT workout?
It’s crucial when you’re beginning a HIIT workout regimen to make sure that your body is prepared for high intensity. If you’re making your first foray into fitness—or the first one in awhile—ease into HIIT by queueing up a few weeks full of cardio and weight training sessions. With a progressive gameplan in motion, you can begin dropping in HIIT routines once a week to start. Not only will building a fitness foundation stave off injury, but it will ensure that you can tackle more than an interval or two, thereby making your HIIT workouts more effective from the beginning.
Another snippet of workout wisdom from the pros: Switch up your HIIT exercises, so you don’t plateau. Cycling through the same five exercises might make for an easy, no-think workout that you can put on repeat, but it doesn’t necessarily provide your body with a challenge that will reap continual total-body gains. To vary your routine, consider incorporating machines like a treadmill, bike, rower, or elliptical. Alternatively, put the gym (or home gym) on hold for a day and jump in a pool or run outside to shake things up.
What are the best HIIT exercises?
Although strength exercise can most definitely be incorporated into a HIIT format, cardio exercises may pair better with HIIT’s short circuits. Regardless of which types of exercise are being integrated, always make sure to engage in proper form and technique in order to minimize your chance of injury.
By-the-book cardio moves like tuck-ups, flutter kicks, burpees, and lunges are always fair game for a HIIT workout, but they’re by no means your only choice. If you’re averse to counting based on reps, consider sprinting on a treadmill, spinning on a stationary bike, or freestyle swimming in a pool. Treadmill sprints are actually one of the most common ways to execute a HIIT workout, but if you don’t have a treadmill, visit your local park and try sprinting on the grass or a path.
Can’t shake the desire to incorporate some strength training? If you do want to turn a HIIT session into a muscle-maker, then grab a weight, kettlebell, loop, superbands, or even a medicine ball. Unlike dumbbells, medicine balls allow you to manipulate them explosively (i.e., medicine ball slams) for the most textbook-like HIIT workout.
You can also factor in traditional weight training tools, such as a bench press. To make bench pressing more HIIT-focused, adjust your rest periods to one minute from the standard two to three minutes.
How long should a HIIT workout take?
While it’s possible to get incredibly technical, it ultimately distills down to this tried-and-true truth: If you’re noticing a dropoff in your performance, chances are it’s time to take a break. When it comes to performative exercises like running, cycling, swimming, or rowing, HIIT can dramatically improve both economy and form. However, the stipulation is that you must maintain good form throughout every interval. If your form has become less than top-notch, shift into recovery workout mode and pick it up again in a day or two.
For most—especially fitness first-timers—a dropoff in performance will happen somewhere around the 30-minute mark. As you ramp up your practice, you’ll likely be able to push into the 45-minute mark, but most professionals warn against stretching into 60 minutes or beyond unless you’re a training athlete. Keep in mind that the high-intensity portion of the workout should typically be done within 15–20 minutes.
How long should you rest between HIIT intervals?
Those who desire a more moderate workout may want to adopt a 1:2 ratio. For example, training at a maximum of 60 seconds and then resting for double the amount of time. Other options include a 1:1 ratio, 1:3 ratio, or even a 2:1 ratio, such as Tabata training. Once you have a baseline that you feel comfortable with, you can easily improvise from there.
It’s worth keeping in mind that shorter work periods don’t necessarily equate to less productive ones. Shorter work intervals allow you to maintain a higher intensity (primarily because you don’t have to maintain the work period for as long), and you want to sustain the highest level of effort possible in order to make HIIT exercises as effective as possible.
iFit HIIT classes
Ready to commit to trying HIIT? Remember: Take it slow. You can build upon HIIT intervals—there’s no pressure to knock out a 20-minute workout right away. Browse a series of iFit Trainer-curated HIIT workouts and discover one that’s just right for your gameplan, whether you’re a beginner who’s weight-focused or a pro-cardio athlete-in-training zoned in on increasing your speed.
Those who want to dig deeper into HIIT training can learn more about Tabata workouts, a subcategory of HIIT that focuses on ultra-short intervals and rest periods. No matter your goals or skill level, jump in, give it a go, and remember: It’s all about pace, not winning the race!