Even if you haven’t tried it, you’ve probably heard the buzz about high-intensity interval training, which alternates short bursts of vigorous exercise with brief periods of active recovery.
One example of a HITT workout, says Chris Kolba, a physical therapist with the Ohio State Wexner Medical Center sports medicine department in Columbus, is “alternating a sprint followed by walking for a specific time or repetition. There’s no set HIIT workout duration, but they’re typically less than 30 minutes.”
What Is HIIT?
Besides being a shorter regimen than you’d find with most continuous workouts, aerobic high-intensity interval training, or HIIT, allows you to raise your heart rate higher, and burn more calories, than you could with steady-state exercise. This can be an appealing proposition for the American adults who don’t get the Centers for Disease Control and Prevention’s recommended 150 minutes of aerobic activity per week.
“Many people feel that they don’t have enough time to work out,” notes Ivory Howard, a Washington, D.C.-based certified yoga and Pilates instructor. But HIIT workouts can be “effective bodyweight exercises that require very little time and no equipment, making these workouts accessible for more adults to workout consistently and remain active for a lifetime.”
Benefits of HITT
In addition to just plain being an efficient way to get in a workout, HIIT also confers some specific health benefits. Here are four benefits of HIIT workouts for your body and mind.
1. HIIT promotes better blood sugar regulation.
Like other forms of physical activity, HIIT can help you “lower your blood sugar naturally because it makes your body more sensitive to insulin,” Howard says. When your body is more sensitive to insulin, your risk of developing insulin resistance or Type 2 diabetes decreases.
“Physical activity causes your body to demand glucose for energy,” Howard explains, which causes your body to deliver that glucose to the muscles. “As a result, your blood sugar level drops.”
This fact was illustrated in a 2014 study in the Journal of Applied Physiology, Nutrition, and Metabolism, which found that a single HIIT session can do a better job of modulating the spike in blood sugar that typically occurs after a meal than a continuous moderate-intensity workout does among adults with excess weight.
“Your muscles are like a large sink that sucks up blood sugar after exercise: When you do HIIT – as opposed to steady-state walking, for example – you call upon more muscle fibers to do the work,” explains study lead author Jonathan Little, a professor in the School of Health and Exercise Sciences at The University of British Columbia Okanagan. “As a result, you have a larger ‘sink’ that’s hungry to suck up blood sugar after exercise.”
For the same reason, HIIT also can be beneficial for those who already have Type 2 diabetes. A 2017 study published in the European Journal of Applied Physiology found that people with Type 2 diabetes who did 12 weeks of HIIT (walking or running uphill) achieved more significant increases in their aerobic capacity, and more dramatic reductions in their hemoglobin A1C levels – an average measure of blood sugar over a three-month period – than those who did moderate-intensity continuous walking.
2. HIIT improves blood vessel function.
HIIT has also been shown to improve vascular (or blood vessel) function. A 2020 study in the American Journal of Physiology-Cell Physiology found that men with high blood pressure who engaged in HIIT training two to three times a week for six weeks showed marked improvements in blood pressure, with specific vascular benefits being noted in the lower limbs. Exercise, in general, improves blood vessel function, but the study confirmed that HIIT also provided benefits in less time than conventional exercise.
Another 2021 study that also lasted six weeks found that HIIT training offers blood pressure benefits and improved blood flow in older adults (study participants were age 65 to 85).
“As we age, endothelial dysfunction (an imbalance in the substances that make the lining of the blood vessels dilate and constrict) tends to occur and is linked to elevated blood pressure and increased risk of heart attacks,” Little explains. Adding HIIT might help offset some of these natural changes.
3. HIIT reverses age-related muscle decline.
High-intensity (aerobic) interval training also has powerful anti-aging benefits at the cellular level in skeletal muscle. Specifically, HIIT causes cells to make more proteins for their energy-producing mitochondria (the cells’ powerhouses), according to a 2017 study in the journal Cell Metabolism.
When older adults did 12 weeks of high-intensity aerobic interval training (in this case, cycling three times per week), they reaped more robust improvements in their mitochondrial function and muscle protein content than their peers who did resistance training or a combined approach.
“For aging adults, supervised high-intensity training confers the most benefits, both metabolically and at the molecular level,” says senior author Dr. K. Sreekumaran Nair, a professor of medicine at the Mayo Clinic in Rochester, Minnesota. It seems that HIIT can help slow the aging process somewhat.
Similar findings were published in 2019 in the European Journal of Sport Science. That study found that older adults who engaged in HIIT sessions three times weekly over a six-week period had favorable adaptations in skeletal muscle and more robust mitochondria.
4. HIIT can provide more enjoyment than other forms of exercise.
As challenging as they are, HIIT workouts appeal to people on a practical level, partly because they’re efficient and effective. But that’s not the only reason for their popularity.
A study 2017 PLoS One study examined the differences in people’s enjoyment, mood and perceived exertion between moderate-intensity continuous exercise and HIIT on a cycle ergometer (or, a stationary bike). The study found that 92% of participants preferred the HIIT workouts.
This may have to do with the structural differences between the two approaches. Moderate-intensity continuous exercise “requires a fixed intensity for a prolonged period of time, where the only sense of accomplishment comes at the end,” explains study co-author Todd Astorino, a professor of kinesiology at California State University–San Marcos.
By contrast, HIIT offers a sense of “accomplishment after every single HIIT effort, which may improve how exercisers perceive it.” Plus, he adds, they have a “recovery” bout to look forward to as they’re pushing hard with each high-intensity effort, which can make the protocol more pleasant.
Challenges of HIIT Workouts
However, Mike Matthews, a certified personal trainer, podcast host and founder of Legion Athletics, a sports supplement company based in Clearwater, Florida, says that to really engage with HIIT workouts requires a lot of intrinsic motivation because you have to push so hard to achieve the intensity demanded by the protocol.
“It’s all-out exertion, and after 30 or 60 seconds you’re completely gassed. Many people just don’t want to do that and they start to dread their workouts.” When that happens, you might be tempted to skip workouts or find it hard to stick with the protocol.
Matthews says he used to be “a bigger proponent of HIIT in the past than I am now” because while it can burn many calories in a short period, this approach to fitness can be hard on the body. “If you go out and run sprints, you’re going to get very sore,” he says – a situation he has personal experience with when he was doing a lot of HIIT workouts in his 20s. That soreness was getting in the way of his strength training workouts on other days. He eventually moved into more moderate cardio training exercises.
How to Get with the HIIT Program
If you’re already in the exercise habit, you don’t need to work with a trainer to do a HIIT workout. You can do it on your own while jogging, running, cycling or using a cardio machine such as the elliptical trainer or stair climber.
“It’s really just a matter of increasing the intensity of the movement till you get to that zone where you feel really challenged while you’re doing it,” says exercise physiologist Cedric Bryant, president and chief science officer at the American Council on Exercise that’s based in San Diego.
If you’re not familiar with HIIT workouts, the key to doing them safely is to start slowly and build up gradually. Bryant recommends starting with six to 10 repetitions of a 20-second high-intensity bout, followed by a one-minute recovery (doing the same activity at a more moderate intensity). Once that becomes easy, reduce the recovery interval to 40 seconds, then gradually work up to a 1-to-1 ratio of high intensity to recovery bouts (20 seconds each).
As you feel stronger, you can increase the high-intensity interval to 40 seconds, followed by a one-minute recovery, then work up to 40 seconds for each. When you’re in the high-intensity zone, your heart rate should be 80% to 95% of your maximum heart rate. (Calculate your maximum heart rate by subtracting your age from 220. Talk to your doctor about any underlying conditions you may have that impact whether it’s safe for you to work out at that level.) During the recovery portions of the exercise, your heart rate should be about 55% to 65% of maximum.
“While it’s a slower rate of progression (than many HIIT programs use), you’ll ensure you’ll stay in a pretty safe range in terms of what you can tolerate from a cardiovascular and a musculoskeletal standpoint, while still progressing,” Bryant says.
“Ramp it up by listening to your body. As your body starts to positively adapt, you’ll be able to maintain that high intensity for longer periods of time, recover more quickly and feel ready for that next rep.”
Don’t want to go it alone? Many gyms offer their own versions of HIIT training in group-class settings. Among the perks: The classes are fun, condensed and sometimes easier to bang out because of the pumping music and camaraderie. The best part? They’re usually over in 30 minutes.
Vary Your Workouts
Kolba notes that while HIIT is a good form of exercise, “it’s not the best or only way to exercise.” Consistency matters more than engaging in a specific type of exercise, and “it’s important to find an exercise routine that you enjoy and is in line with your goals. It’s also good to have variety to help maintain interest and consistency.”
He also notes that when you’re engaging in a HIIT workout, you really have to push to achieve that max effort range and get the results you’re expecting. At the same time, you need to be careful not to injure yourself. Therefore, “beginners should seek qualified instruction and start slowly, working up to near max effort level giving their bodies time to accommodate to avoid injury.”
Howard adds that when you do HIIT workouts, remember that the rest part is a key component to how it all works. “Take your rest days serious. Rest days are just as important as your workout days because they assist in healing and preventing injury.”
While HIIT is an effective workout with many benefits, “it’s not suited for everyone. Before making changes to your exercise plan, you should discuss your medical history and fitness goals with your health care providers so that you can make an informed decision about your health.”