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Donkey kickbacks

A killer move that will torch calories as it works your core. 

Kneel on all fours, toes tucked under, keeping your back neutral. Draw your belly in toward your spine as you contract your abs and lift both knees about 2 inches off the ground.

Keeping abs engaged, bring right knee to nose (shown). Then kick right leg straight out behind you, squeezing your butt (shown); keep lower abs contracted and hips facing the ground to protect your back.

Repeat 8 times; switch legs and repeat.

Next: Advanced leg crunches