Oblique crunch v. 2

Lie on your back with your knees bent and feet flat on the ground. Place your hands behind your head or cross them over your chest. Engage your abs and lift your shoulder blades off the ground, rotating your torso to one side. Pause for a moment, then lower your shoulder blades back down to the starting position. Repeat on the other side. Continue alternating sides for the desired number of repetitions.