Fitter in 12 Minutes a Week?

Norwegian study finds three 4-minute high-intensity workouts a week can boost fitness

It’s an increasingly common question in our time-strapped, under-exercised culture: what’s the shortest workout you can do to stay fit?

A few weeks ago, a “scientific 7-minute workout” published by the American College of Sports Medicine’s fitness journal went viral with a little help (and branding) by the New York Times. So there’s been a surge of interest in high-intensity interval training, or HIIT, and its ability to get you fit with minimal time invested.

So far, the standard by which short HIIT workouts have been judged is the Tabata method, developed for a landmark 1996 study by Izumi Tabata and his colleagues at Japan’s National Institute of Fitness and Sports. The method compresses an entire aerobic workout into four minutes, to be done four or five times a week. It requires alternating 20-second bursts of very high-intensity exercise with 10-second rest-periods for eight cycles.

In the years since that study, more research has expanded on the benefits of HIIT and more methods have been devised to bring these micro-workouts to the masses. But the question remains: how low can you go?

If you’re looking for shortcuts to better athletic performance, you’re barking up the wrong tree: HIIT is only a complement to your normal endurance training and strength-building exercises.

But if your goal is to see fitness gains after some time away from the gym, a new study suggests that as little as 12 minutes of high-intensity exercise a week may do the trick.

Researchers at the Norwegian University of Science and Technology decided to conduct a 26-person “proof-of-principle” study of healthy, but inactive, middle-aged men to see if three 4-minute sessions of high-intensity exercise a week would improve a marker of overall fitness called VO2max. (VO2max measures your body’s maximum ability to burn oxygen during exercise.)

The researchers had previously developed a successful method, their “4x4 protocol,” which alternates four minutes of running on an inclined treadmill at nearly peak heart rate with 3-minute “breaks” of slower jogging for four rounds—a total of 25 minutes, plus a 10-minute warm-up.

When, in the new study, they compared the 4x4 protocol with a single 4-minute burst, thrice weekly over ten weeks, they found similar increases in VO2max, with an average 10-percent boost for the 12-minute-a-week group.

“Our data suggest that a single bout of [high-intensity training] performed three times per week may be a time-efficient strategy to improve VO2max,” said lead author Arnt Erik Tjønna.

But he cautions that the study was small and the results don’t necessarily apply to everyone.

“It has to be noted that the subjects were previously inactive, and the same effect on physical fitness cannot be expected in active individuals,” said Tjønna. “Nevertheless, since we know that more and more people are inactive and overweight, the kind of improvement in physical fitness that we saw in this study may provide a real boost for inactive people who are struggling to find the motivation to exercise.”

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