The best fitness tool to strip fat and strengthen your total body probably isn't already in your gym -- but it is underneath your beach towel. "Forget the dumbbells and sling some sand," says Josh Henkin, C.S.C.S., inventor of the Ultimate Sandbag Training System (ultimatesandbagtraining.com). Well, Henkin would say that, given that he's created an entire business around sandbag training.

But then we tried out his innovative sandbags ourselves -- and we were amazed. "Even with what I would consider a light load, the sandbag created an incredible challenge that was unlike conventional weight training," says Men's Health fitness director Adam Campbell, author of The Men’s Health Big Book of Exercises. "It also caused a level of deep muscle soreness that I hadn't felt in a very long time."

Henkin says that Campbell's experience is typical. The reason: “As you lift a sandbag, its shape shifts, forcing more muscles to work together to maintain balance,” explains Henkin. So unlike free weights or machines, the ever-changing sandbag doesn’t let you settle into a lifting groove. That means every rep is unique and challenging.

Take the side lunge and snatch, for instance. Don’t be thrown by the name: the snatch simply describes a movement in which you explosively lift an object -- such as dumbbells, a barbell, or a sandbag -- above your head. When done with dumbbells, the side lunge and snatch requires you to move from side-to-side, which strengthens your body in an all-new direction. It also trains your glutes -- your body’s largest but often-neglected muscle group -- and requires a coordinated effort from your core, upper body, and legs to lift the weight from the floor to above your head.

Great total-body exercise, right? The sandbag makes it even better. With its awkward shape, the sandbag requires you to use more energy to lunge with it than the dumbbells did. That means you're instantly burning more calories with the same move.

Then, when you go to snatch the bag, your balance is challenged like never before. (Watch the video below to see the exercise.) That's because the bag's weight distribution shifts as it soars above your head. This requires your body’s stabilizing system to kick into action, which improves your coordination, chisels your core, and strengthens your joints.

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And yes, it makes you really sore, too, since it works your muscles in ways that other equipment can't. Try this just once, and you'll never look at the sand the same way again. (You'll find that simply doing the side lunge by itself can be a highly effective movement.)

"I think sandbags are the best kept secret in fitness," says Campbell. "They've changed the way I train my body forever." Want to experience a cutting-edge sandbag workout for yourself -- on the actual sand? Then check out the Men's Health and Women's Health Beach Boot Camp this summer. We'll not only introduce you to sandbags, but 11 more of the hottest trends in fitness -- all packed into an awesome 90-minute beach workout.

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