Large bulky ropes, or battle ropes, have become the fitness world’s go-to tool for people searching for a fun workout. Battle ropes have been long-used for training in sports like football. However, experts say they have gone mainstream.

Dragging, slamming and whipping these ropes is “like running with the upper body,” according to spokesperson on the American Council on Exercise Jonathan Ross. He explained that the ropes work different muscles and train the muscles in different ways.

Ross, author of Abs Revealed, said that the ropes are great for engaging the muscles as well as the mind with “the grace of a wave,” as reported by Reuters. He added that the ropes are responsible for showing a person how he or she moves. He said that one “sees the physical manifestation of body movement” while watching the ropes.

Coordination and posture are two large elements of the workout, according to Ross. They also help users burn serious calories and require shoulder stability and strength. Additionally, a study in the Journal of Strength and Conditioning Research published in April 2015 revealed that 10 minutes of rope training greatly increased heart rates and raised cardio respiratory fitness.

The ropes are becoming so popular that fitness centers, such as the national chain Crunch, are building group fitness classes around battle ropes. The senior vice president of programming at Crunch said that the ropes are great for the core and upper body toning. They also work the glutes, back and abs simultaneously while burning “a lot of calories.”

The classes consist of a warm-up followed by competitions. The participants compete to see who can keep the rope movement rolling the longest.

Ross said that the longer the rope, the more challenging it is to keep the rope going since a person has to “generate more force.” “You want to see that move travel all the way down to that anchor point.”