You've heard that high intensity interval training (HIIT)—periods of hard effort followed by rest—is effective and efficient for burning calories and torching fat. But have you ever wondered just how long you need to rest? (A minute? Until you catch your breath?) Wonder no more: Research published in the latest issue of the Journal of Strength and Conditioning had found that 2:1 is the optimal work-to-rest ratio. That means, if your intervals of effort are 1 minute long, you should recover for 30 seconds before picking up the pace again.
For the study, researchers asked 16 people to run as hard as they could for six, 4-minute treadmill intervals. The subjects were given either a 1, 2, or 4-minute recovery. Two minutes—or a 2:1 work-to-rest ratio—was the sweet spot, the researchers found. Intensity suffered after only 1 minute of recovery. But resting for 4 minutes didn't improve speed any more than resting 2 minutes.
The 2:1 ratio is enough time to allow for proper recovery, so you can work hard during the next interval—but it's still short enough to keep your heart rate up for the whole workout, explains lead study author Matt Laurent, PhD, an assistant professor of exercise science in the School of Human Movement, Sport, and Leisure Studies at Bowling Green State University. If you’re used to taking longer breaks between intervals, reducing your recovery time will mean you’re on and off of the treadmill quicker, while maximizing the effort of your workout.
The study also found while women didn’t self-select the highest running speeds, they worked their heart and lungs harder. Ultimately you should listen to your body and pay attention to how you feel, explains Laurent. If it feels tough but sustainable, you’re probably at the right intensity for your body.
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Bari Lieberman is the former Senior Associate Fitness Editor for Prevention and Prevention.com. She's a certified personal trainer and Spinning instructor, and University of Miami graduate. She owns more sneakers than stilettos and tries to wear spandex as often as possible. Follow her on Twitter at @barilieberman.
