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Abs and back: Crab crunch

Sit with legs in front of you, knees bent, and feet hip-width apart on the floor. Place hands shoulder-width apart on floor behind you, with thumbs forward and fingertips at a slight diagonal. Lift butt and extend right leg just barely off floor; bring left hand behind head.

Crunch forward, bringing right knee toward chest and rotating left elbow in to meet it; for more challenge, simultaneously bend right elbow to dip toward floor.

Return to previous position. Do 12–15 reps, then switch sides and repeat.

Next: Legs and butt: Leap frog