Mountain climbers will work up more than just a serious sweat: you'll also target your abs, hip flexors, and shoulders in the process. They not only strengthen your core, they also promote the fat loss necessary to unveil the abs you've been building without aggravating back pain. (Check out these other exercises that you can perform with back pain.)

Jess Sims, personal trainer at The Fhitting Room in New York City, demonstrates six versions of this versatile exercise you can use to get your abs working harder and that heart pumping faster. (To see that six-pack even faster, incorporate these 12 moves into your routine.)

With slow mountain climbers, your core gets challenged under greater time and tension. You rely less on momentum or elastic energy, and as a result, your shoulders and abs will also be feeling the burn. Meanwhile, twisting climbers pick up the pace -- as well as your heart rate -- so you'll get a cardio workout while working your obliques and hip flexors at the same time. And get your shoulders and abs to work overtime with wide-stance mountain climbers, which enhance core stability by opening up your hips.

Speaking of stability, incorporating tools like a Bosu balance trainer or a suspension trainer increase the challenge of a mountain climber. The instability created by these tools will fire up nearly every muscle in your body, but especially the ones in and surrounding your abdominal area.

So add these into your core or total-body workouts and watch your core transform into a pillar of strength. (Kick your abs into overdrive with our Anarchy Abs workout that will get you some serious results.)

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