Sit faceup on a mat holding a challenging-weight dumbbell in both hands, elbows at sides, knees bent about 90 degrees. Lift feet off floor a few inches.
Straighten legs and arms and lean torso back until shoulders touch floor and dumbbell is overhead, legs straight out. Curl back to starting position, bringing weight in front of chest and knees in.
Perform a Russian twist to the left and right with the dumbbell. Return to center.