Shanna Duvall is loading 45-pound plates onto a barbell for a set of squats. After that, she’ll move to pull ups, then back to squats. It’s a typical scene in any CrossFit studio, where athletes combine Olympic style weightlifting, gymnastics, and functional movements in what has become the biggest fitness trend in the last decade. The only difference is that Duvall is a runner, using CrossFit to accomplish her goal of running a sub-five-minute mile.

Conventional wisdom dictates that if you want to be a better runner, you have to run more. It’s a simple training philosophy that most athletes follow with varying degrees of success, but a growing number of runners like Duvall are turning to CrossFit Endurance (which combines CrossFit with some running) to get faster and run farther while avoiding injuries associated with over-training.

“I spent more time on the elliptical than on the track in college,” says Duvall, who ran the 10K and 5K at Kent State University, but was plagued by constant injuries. “I had imbalances that my coaches never addressed. There was no strength training. We never stepped back to look at the big picture.”

According to Duvall, CrossFit addresses the big picture by building total body strength, something that most runners tend to ignore for fear that the extra bulk associated with strength training will result in slower finish times.

Adam Eidson is an ultrarunner who owns RARE CrossFit in Fredericksburg, Va. He sees skeptical runners on a daily basis. “Runners don’t want to be big like body builders, but we need power. CrossFit can get you the strength and power without the bulk.”

It’s a tough sell. Type CrossFit into YouTube and you’ll find vids of really big dudes doing power squats, but Eidson says CrossFit is completely scalable to an athlete’s specific goals, especially for runners looking to get fast.

“Eighty percent of new athletes come in here and automatically ask, ‘Where’s the cardio?’” Eidson says. “I tell them not to worry: I’ll get their heart rate up.”

Here’s why CrossFit works for runners: exercise sessions are timed. You may be doing sets of squats and pull-ups, but you’re doing them for speed, which creates intensity. CrossFit workouts also tend to combine exercises that work different muscle systems. The combination of full body movements and power lifting set to a clock creates an intensity that you simply don’t find in other workout programs, making CrossFit an ideal cross training program for runners who crave cardio, but need strength training whether they realize it or not.