Think of high-intensity interval training (HIIT) like baking: You need a precise amount of time in the oven as well as a cooling-off period. In workout terms, that means balancing intervals of work with rest.
"The primary goal of a HIIT workout is to perform at maximal effort with a specific exercise, followed by a predetermined rest break," says Grayson Wickham, DPT, CSCS, personal trainer and founder of Movement Vault.
But if your work intervals are too long, you're not recovered enough for the next interval. And too much rest means you lose momentum and the after-burn benefits. Here's how to find the sweet spot in the work-to-rest ratio that works for your fitness level and goals.
Find the Ideal Work-to-Rest Ratio
The benefits of HIIT have been well studied and include improved endurance, heart health and decreased body fat percentage, according to an October 2016 review in the British Journal of Sports Medicine.
What hasn't been studied as thoroughly, however, is the ideal interval time. A 2019 study from the The Physiological Society compared results from two groups: those who did 60 seconds of exercise with a 60-second rest (60/60) and those who did 30 seconds of exercise and 120 seconds of rest (30/120). Participants performed HIIT workouts three times a week for six weeks.
Researchers found that the 60/60 group increased their aerobic capacity, while the 30/120 group showed no improvement. The 120 seconds of rest was too long to be effective as their heart rates didn't stay up.
Don't rewrite all your HIIT workouts to the 60/60 format just yet, though. The study only compared two interval times, and there are other timing strategies that are also effective. But it does bring up an important point: Don't let your rest periods get too long.
Consider Your Fitness Level and Workout Time
When determining the ideal interval time, you should look at several factors. "A big factor in the rest-to-work ratio is how long your total workout will be," Wickham says. A 30-minute workout would be great with the 60/60 ratio, however shorter workouts could have shorter rest breaks and longer periods of work, he says.
You should also consider your current fitness level and the type of workout you're doing, says Mike Donavanik, CSCS, founder of Sweat Factor.
"If you're new to exercise, you'll typically need longer rest intervals as you're trying to gauge your body and understand how hard you can push it," he says. "As you start to get the hang of your body and what it can accomplish, you can start to push it harder during the 'work intervals' and/or you can start lowering the amount of time during your 'rest intervals.'"
For beginners, he says to start with a 1:2 work/rest ratio. "Meaning you go hard for 20-seconds, then take a 40-second rest."
As you progress, go for a 1:1 work/rest ratio. For example, 20 seconds of exercise and a 20-second rest — or the 60/60 ratio mentioned above. "Then once you're getting the hang of things, you go for a 2:1 work/ rest ratio. So you go hard for 20-seconds, then only take 10-seconds of rest."
The National Academy of Sports Medicine (NASM) also recommends these interval times, including the 20 seconds of work with a 10-second rest (which is a Tabata-style workout) and 1:1 ratio (30 seconds of work with 30 seconds of rest).
Don’t do HIIT every day, as your body needs time to rest and recover between sessions, according to the American Council on Exercise (ACE). Plan on doing HIIT workouts on non-consecutive days no more than two to three times a week.
Structure HIIT Intervals to Your Fitness Goals
HIIT workouts are most suited to losing weight or improving endurance and overall conditioning but not recommended if you're trying to gain muscle mass or improve explosive power, according to Donavanik. If that's the case, you're better off sticking to a weightlifting routine or sport-specific with longer rest intervals.
"Strength-based work will need longer rest periods — especially if strength increases are the goal," says Michael Julom, ACE-certified personal trainer and founder of ThisIsWhyImFit.com. "Sixty seconds often isn't enough time to adequately rest from explosive or strength-based exercise. You wouldn't be able to perform well on a 100-meter sprint with only 60 seconds of rest between rounds."
But for both weight loss and improving endurance or conditioning, Donavanik says the 1:1 ratio is ideal, and you can progress to the 2:1 ratio. For example, start with 30 seconds of work with a 30-second rest, then increase to 40 seconds of work with a 20-second rest.
"[This ratio] is going to be the most efficient in regards to spiking your heart rate, keeping it spiked and creating an oxygen deficit during exercise," he says. "That essentially means that your body needs more oxygen after your workout than it did before — meaning you'll be burning more calories after your workout (at rest) than you were prior to your workout."
During the “max effort” intervals, you should be working out hard enough and long enough that you're breathless and unable to talk, according to the NASM.
And the rest periods need to be long enough that your breathing is back under control before you jump back into the work interval. You can't rest too long, however, as you need your heart rate to stay up.
Your Guide to HIIT Interval Times
While there's no one "ideal interval time" that works for everyone and every workout, the guide below based on the input of our experts will provide some work-to-rest ratios that can help when planning your workouts:
- Beginner interval: 1:2 ratio (ex: 20 seconds of work and 40 seconds of rest)
- Intermediate interval or longer workout (30 minutes or more): 1:1 ratio (ex: 30 seconds of work and 30 seconds rest or 60 seconds work with 60 seconds of rest)
- Advanced interval or shorter workout (less than 30 minutes): 2:1 ratio (ex: 40 seconds of work and 20 seconds of rest)
And remember to keep your rest periods on the shorter side. Donavanik says 30 to 60 seconds of rest is ideal for weight loss or general conditioning, but he doesn't recommend going above 90 seconds. Also, take into account the type of activity you are doing.
"It really depends on what you're asking your body to do and how hard you're pushing your body during a given activity or workout," he says. For example, jumping lunges or high knees will require longer rest times than squats or crunches. "Typically, the harder or more demanding the activity, the more rest is needed."
In general, though, listen to your body and adjust your intervals accordingly. Once you hit your sweet spot, you'll feel it. You'll be working hard with just enough recovery to tackle the next interval.
- National Academy of Sports Medicine: "HIIT Workouts: Programming, Exercises, and Benefits"
- American Council on Exercise: "The Perfect HIIT Workout for 2020"
- The Physiological Society: "Longer Home-Based HIIT Intervals Elicit a Greater Improvement in Aerobic Capacity – a 6-Week Intervention Study"
- British Journal of Sports Medicine: "Effects of High-Intensity Interval Training on Cardiometabolic Health: A Systematic Review and Meta-Analysis of Intervention Studies"