Difficulty Level: Intermediate
Muscle Groups Worked: Abdominals, Back
Equipment: Bodyweight Only
Movement: Secure your feet either by placing them under something that won’t move or by having a partner hold them. Start in the position shown above, leaning slightly back and clasping your hands in front of you. Moving only at the trunk, rotate to one side. At the end of your range of motion, quickly reverse the movement and rotate to the opposite side. Repeat in a rapid fashion for the full number of reps. You can also hold a weight or medicine ball to increase the difficulty.