High-intensity interval training, or HIIT for short, was named one of the top fitness trends in the world for 2020, based on an annual survey by the American College of Sports Medicine. This super hard, super-effective style of training isn’t just the “it” workout of the moment—of the 14 years ACSM has been conducting this survey, HIIT ranked in the top five for seven consecutive years.
Why? Because it works, and it works fast. Whether you’re coming straight off the couch, training for a marathon, or even if you race for a living, HIIT training is good for your health and makes you fitter and faster.
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What Exactly Is HIIT?
HIIT sounds very scientific, but it’s really very simple. It’s comprised of short, hard bouts of cardio exercise—anywhere from 10 seconds to five minutes in length—broken up by brief recovery periods.
How hard is hard? That depends on the interval length, but the key is to go as hard as you can for the duration of the effort. So if you’re doing Tabatas (20 seconds of effort, followed by 10 seconds of recovery), you’re running full throttle for 20 seconds. If you’re doing longer, 3- to 5-minute intervals, you’re working in your VO2 max zone, or about 95 percent of your max heart rate (or a 9 on a scale of 1 to 10) for the duration of the interval.
How much recovery you take between intervals depends on your goals. Short intervals are usually paired with equally short or even shorter recovery periods so your body can adapt to repeated maximal efforts. And because your heart rate stays elevated during the recovery periods, your aerobic energy system gets a training benefit, as well. In other cases, such as high-intensity sprints, you want each effort to be done at max, so you need to let your body fully recover for four or five minutes between bouts.
What Are the Benefits of HIIT?
New studies on the benefits of HIIT make the news on a regular basis. Take, for example, this one from the November 2018 issue of the American Journal of Physiology-Regulatory, Integrative and Comparative Physiology. Researchers found that just two minutes of sprint interval training (in this case, four 30-second max-effort sprints followed by four and a half minutes of recovery for a total of 20 minutes) improved mitochondrial function—when your cells can change fuel to energy quickly, a benchmark for good health and exercise performance—just as well as 30 minutes of moderate exercise in a group of active men and women. In other words, busting out two minutes of really hard running can give you the same fitness benefits as slogging through 30 minutes at a steady, moderate pace.
So it’s no surprise HIIT training is outstanding for your cardiovascular system. Research shows, depending on how fit you are when you begin, HIIT can boost your VO2 max (how much oxygen you can use) up to 46 percent in 24 weeks; increase your stroke volume (how much blood your heart pumps out per beat) by 10 percent after eight weeks of training, and significantly lower your resting heart rate.
It also makes your body a furnace of a fat burner. HIIT jacks up production of your body’s growth hormones that help you maintain muscle and burn fat for hours after you’re done, and it lowers insulin resistance for better blood sugar control.
And it does more than benefit your body. HIIT is also good for your mind. Research shows that high-intensity workouts improve cognitive function and increase levels of brain-derived neurotrophic factor (BDNF). BDNF is essential for learning, memory, and mood regulation, and your brain uses it to repair and maintain brain cells. Also, this study shows that in older adults, HIIT can enhance cognitive flexibility.
The best part is that it provides all of these benefits as well as—and in some cases better than—traditional longer bouts of moderate cardio exercise in far less time.
What HIIT Means for You
Most of us already run a lot because as endurance athletes, that’s our thing. But even if you’re already fit, you can still reap measurable benefits from adding HIIT to your training regimen, says exercise physiology professor and endurance coach Paul Laursen, Ph.D., author of The Science and Application of High-Intensity Interval Training (HIIT), and contributor to HIITscience.com.
For runners who like to go long, HIIT can be part of a smart base-building strategy. “Your base comes down to your mitochondrial capacity,” Laursen says. “Longer, lower-intensity exercise increases the number of mitochondria in your cells, which is why people perform long, steady endurance exercise to build base. But high-intensity training makes those mitochondria more powerful,” he says, noting that research also shows that high-intensity exercise performed regularly can stimulate the production of mitochondria, as well.
“Our research found that when well-trained cyclists performed two interval sessions a week for three to six weeks, their VO2 max, peak aerobic power output, and endurance performance improved by 2 to 4 percent,” he says.
Plus, recent research out of Australia suggests that doing your HIIT workouts in the evening won’t mess with your shuteye—and it may even curb your appetite after a session.
More on HIIT
How To Do HIIT
Laursen says you’ve got three main weapons to choose from in the HIIT arsenal: Long intervals like the VO2 intervals that range from one to four minutes; short intervals done at about 120 percent VO2 max that can last from 10 to 60 seconds with equal recovery periods; and sprint intervals, which are done “all out” and can be either very short (three to eight seconds) or longer (20 to 30 seconds).
You can take the shotgun approach and rotate through all three each week. Or choose the format that best works your weak spot. “If you fade out during longer efforts, do longer HIIT training intervals.” he says. But if you need to sharpen your short-distance power—like the finish kick at the end of a race—do sprints.
For general endurance benefits, interval durations ranging between 30 seconds to five minutes at a very hard intensity build your aerobic system while also recruiting some fast twitch sprint fibers, which makes your power-producing fibers more fatigue-resistant over time, Laursen says.
“Performing three to six of these efforts, allowing one to two minutes of recovery between, can have impressive effects,” he says.
You can perform running HIIT intervals, or you can do them when you cross train to get a metabolic boost while giving your body a break from your usual activity, Laursen says. “This works well for runners and team sport athletes who occasionally need to reduce their impact while nursing a little injury or niggle,” he says. “They can do a HIIT session on the bike to maintain their cardiovascular load, while lessening the impact on their neuromuscular system.”
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HIIT Workouts
To help you get started, follow along with Runner’s World+ Coach Jess Movold in the video above (detailed below), or try any of these high-intensity interval run workouts below.
At Home
You don’t need any fancy equipment to get a killer HIIT workout in. Try this bodyweight HIIT burner by performing a proper warmup and cooldown before and after.
- Air Squat - 30 reps
- Straight-Leg Sit-Up - 20 reps
- Push-Up - 10 reps
- Repeat 5 times through and rest as needed between sets
In the Gym
If you’ve got a set of weights or dumbbells lying around or at the gym, then you can progress to this HIIT circuit with resistance. It’s a 20-minute total body workout that’s perfect for your strength training days. Perform each exercise for 40seconds on, 20 seconds off.
- Squat to Overhead Press
- Dumbbell Renegade Row
- Reverse Lunge to Biceps Curl
- Burpee
- Repeat 5 times through
On the Road
Bored with your usual routine? Switch up your next run with this reverse pyramid HIIT workout. Warm up with an easy jog and dynamic drills, perform the workout below, and then cool down.
- Run hard for 3 minutes
- Recover for 3 minutes
- Run hard for 2 minutes
- Recover for 2 minutes
- Run hard for 1 minute
- Recover for 1 minute
- Take 2 minutes of rest or walk, and repeat the entire set 1 to 2 more times
On the Track
High-intensity track sessions move the muscles through the full range of motion, improving elasticity and enhancing coordination between your nervous system and muscles. With time, you’ll develop a more efficient stride at all your paces, says Joe McConkey, M.S., an exercise physiologist and coach at the Boston Running Center.
- Perform a proper warmup of easy jogging and dynamic drills.
- Begin with two 100-meter accelerations that include 40 meters at top speed, with 2 to 3 minutes of walking or jogging between.
- Build to 6 x 150 meters hard, including 80 meters at top speed, with 3 to 4 minutes jogging or walking rest.
- Over time, increase the number of repeats to 10, lengthen reps to 300 meters (running nearly the entire distance at top speed), or reduce the rest interval to 1 minute.
On the Trails
It adds to the challenge, but running fast over softer, less-groomed terrain like bridle paths, trails, or grass can increase agility and athleticism—or your ability to run with the “precise amount of power, speed, and coordination needed for efficient movement,” McConkey says. Because of the terrain and potential strain on your leg muscles, ease into off-road workouts if you’re used to running on flat surfaces, and always be careful not to trip.
- Perform a proper warmup of easy jogging and dynamic drills.
- Do five 30-second pickups at a moderate intensity during an easy 20-minute run.
- Build up to ten 60-second, near-all-out bursts during a 40-minute run.
- From there, progress to running 5 cycles alternating 30 seconds of all-out running with 90 seconds jogging, then to 10 cycles alternating 1 minute easy with 1 minute super hard.
On the Hills
Inclines are a great venue for super fast speedwork. Compared with a flat surface, hills reduce the impact on your legs and limit your range of motion, thereby lowering the risk of strains and pulls. Plus, hill repeats build muscle power, which helps you run more efficiently on level ground, says McConkey.
- Perform a proper warmup of easy jogging and dynamic drills.
- On an incline, start with three 30-second moderate repeats and walk down the hill for recovery.
- When this becomes comfortable, progress to 4 x 1-minute, near all-out efforts with a downhill jog and an additional 30 to 60 seconds jogging or walking rest.
- Over time, add additional reps, extend effort length up to two minutes, and aim for steeper hills, says McConkey.
How Often Should You Do HIIT?
HIIT is like medicine: The right dose works wonders; too much can have ill effects. If you’re not racing or doing big events on the weekends, you can do up to three HIIT workouts a week to stay fit, so long as you allow ample recovery, ideally a day or two of easier activity between sessions to allow your body to bounce back.
Once you’re out there putting in longer runs and/or pushing it hard on the weekends, you can dial back your HIIT workouts to just once or twice a week to stay sharp between events.
Cindy is a freelance health and fitness writer, author, and podcaster who’s contributed regularly to Runner’s World since 2013. She’s the coauthor of both Breakthrough Women’s Running: Dream Big and Train Smart and Rebound: Train Your Mind to Bounce Back Stronger from Sports Injuries, a book about the psychology of sports injury from Bloomsbury Sport. Cindy specializes in covering injury prevention and recovery, everyday athletes accomplishing extraordinary things, and the active community in her beloved Chicago, where winter forges deep bonds between those brave enough to train through it.
