Is there an ideal time to keep your heart rate up during interval training to get the most benefit? It turns out the answer is yes, and the amount of time is less than you might think.

Sports scientists with McMaster University in Canada found that just 20 seconds of high-intensity exercise is enough to maximize the benefits of cardiovascular activity, The New York Times reports.

But there is a catch: Even short periods of all-out exercise can be grueling.

For the study, lead researcher Martin Gibala, a professor of kinesiology at McMaster, asked volunteers to engage in all-out 30-second intervals performed at 100 percent of the men’s aerobic capacity. The volunteers became much more fit after a few minutes a week of such strenuous training, but they hated the workouts, Gibala said.

As a result, he developed a less taxing 60-second interval program that requires the hard exercise be performed at only about 90 percent of a volunteer’s maximum aerobic capacity. The drawback was that the men had to do more of these intervals to gain the same fitness benefits as from the 30-second variety.

So Gibala and other researchers experimented with intervals as short as 20 seconds performed all-out, followed by a recovery period of two minutes between each interval.

Gibala said these 20-second intervals are more tolerable than 30 seconds of the same exercise and more potent than gentler 60-second intervals. The results indicate the volunteers boosted their fitness and health after only a few of the 20-second intervals per week.