DENVER -- How would you like to combine cardio and strength training all in one?

Kettlebell training is the new fat-burning method many people are turning to. It's even in this month's Tennis magazine as a tool that can help your game.

Rocky Balboa used kettlebell training and now many others are using the bells too as the fitness trend hits gyms across the country. Workouts with the kettlebells combine strength and cardio.

"I really break out in a sweat and it's really hard for me to sweat," said Dolores Huntoon, who uses the kettlebells.

"The folks in eastern Europe use it as counter balance at a marketplace. People found out you can use these moving around for a workout," said personal trainer Michael Huntoon.

The kettlebells are basically a cast iron ball with a handle, with the weights ranging from 9 to 70 pounds. Experts say it's functional strength training at its best.

"With weights being on the outside of the handle, it just as realistic as a child pulling you or dog pulling you or throwing your bag over the shoulder. The weight is going to sling," said personal trainer Brittany Baudoin.

Experts said just 15 minutes of kettlebell training can burn as many calories, if not more, than 30 minutes of walking on a treadmill.

"You get your heart rate up at a very quick pace," said Michael Huntoon.

"It trains the brain to train the muscle. It's more of a conscious effort to work out," said Dolores Huntoon.

Greenwood Athletic Club is one of many gyms around the Denver metro area offering kettle training classes.

To learn more about the kettlebell workout, click here for information about Greenwood Athletic Club.