It was a crazy day at work, you’re meeting up with your friends later, and now you have less than half an hour to squeeze in some exercise. At that point, you're wondering: Will a workout that short be just a waste of time?

Not by a long shot.

In fact, a single 20-minute session of exercise can stimulate your immune system and strengthen the anti-inflammatory defenses your cells use to fight off conditions like arthritis, fibromyalgia, and obesity—in other words, it can keep you stronger, thinner, and all-around healthier.

That’s the deal from a new study by researchers at the U.C. San Diego School of Medicine, who put 47 healthy volunteers on treadmills and found that just 20 minutes of running at a moderate pace raised the level of proteins that boost the immune system by 5%.

“Our study shows a workout session doesn’t actually have to be intense to have anti-inflammatory effects. Twenty minutes to half an hour of moderate exercise—including fast walking—appears to be sufficient,” said senior author Suzi Hong, Ph.D., in a press release. The fact that a workout doesn’t have to be superlong—or kill you, effort-wise—to benefit your body can make exercising more often a less-bitter pill to swallow, especially if you’re just starting out or in less-than-great shape.

“Feeling like a workout needs to be at peak-exertion level for a long duration” can seem intimidating, says Hong, when the truth is “each time we exercise, we’re truly doing something good for our body.”

So the next time you spy a free 20-or-so-minute window in your day, supercharge your immune system with one of these totally un-boring aerobic workouts.

Not bad for something you can do in less time than it takes to watch the new cat fails compilation your mom just tweeted.