Finding the sweet-spot ratio of activity to rest might not be as tricky as you think.

By Rebecca Norris
December 19, 2019
Shutterstock/Rido

There's nothing like the rush you get from powering through a round of high-intensity interval training (HIIT). The workout technique—which involves alternating between intense bursts of activity and fixed periods of rest (or, sometimes, less intense movement)—has skyrocketed in popularity, with study after study demonstrating its benefits for everything from heart health to metabolism.

But few studies have explored just how long those bursts of rest and activity should be. HIIT intervals can last anywhere from six seconds to four minutes, and the rest periods between each interval can vary just as much. Confused? A new study may shed some light. (Related: Do the Risks of HIIT Outweigh the Benefits?)

For the study, researchers from Liverpool John Moores University in the UK recruited 26 sedentary men and women to perform bodyweight HIIT workouts three times a week for six weeks. To determine the optimal timing of intervals and breaks in HIIT, researchers broke participants up into two groups that each performed a separate workout routine:

  • 60HIIT: 6 to 10 rounds of 60-second intervals with 60 seconds of rest in between
  • 30HIIT: 4 to 8 rounds of 30-second intervals with 120 seconds of rest in between

During the six-week study period, researchers tracked participants' progress and adherence to their training regimen via heart rate monitors that fed data through a mobile app. They also measured participants' aerobic capacity (aka their ability to use oxygen to fuel bursts of exercise), body composition (meaning the body's muscle-to-fat ratio), and arterial stiffness (a measure that can help to identify conditions like high blood pressure and is often improved by consistent, cardio-based exercise) before and after the study.

After six weeks, the researchers said they found that 60HIIT appears to be a more effective HIIT method than 30HIIT, particularly in terms of improving aerobic capacity. The study's results showed that participants' aerobic capacity increased significantly after six weeks of 60HIIT, while the 30HIIT method wasn't found to be associated with any meaningful changes in the researchers' parameters.

In fact, the study's findings suggested that 30HIIT may not be intense enough. "We found that 30-second intervals with 120 seconds of rest meant that participants' heart rates didn't stay up," Hannah Church, a researcher involved in the study, noted in a press release. "120 seconds is just too long to be resting for!" (Related: Are Shorter HIIT Workouts More Effective Than Longer HIIT Workouts?)

Of course, it's worth pointing out that this study was small, relatively short, and only assessed bodyweight HIIT workouts as opposed to those involving free weights or machines. Still, Nick Poulin, certified trainer and CEO/founder of Poulin Health & Wellness in New York City, argues that the findings are on-point. He says that, in his experience, he's found that 60 seconds of intense training followed by 60 seconds of rest tends to be a consistently effective ratio for his clientele. "I've seen this firsthand with many ages and fitness levels based on heart-rate tracking," he explains. BTW, if you can't measure your heart rate during a HIIT workout, an easy alternative is to pay attention to your breathing, Shannon Fable, director of exercise programming at Anytime Fitness, previously told us. If you're hitting the right intensity during the bursts of activity, you'll likely be so out of breath that you won't be able to talk, and you'll probably feel like you need that period of rest once it comes, she explained. (Here's why hard exercise is actually more fun, according to science.)

However, Poulin also notes that it's important to always check with your doc before performing these types of fast-paced workouts, regardless of the exact method you choose. "I recommend when doing HIIT to leave your ego at the door, focus on the form rather than weight (or speed), and to know your max heart rate and overall threshold," he adds. "Remember, everyone has a different body and genetic aptitude. Find what works for you and be consistent."

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