Medicine Ball Russian Twist

The medicine ball russian twist trains rotation, which is the movement most abdominal work leaves out entirely. Sitting in a V position with the feet off the floor and the torso leaning back, you rotate the ball from side to side, and the obliques have to produce that rotation while the whole midsection holds the V against gravity. Adding a medicine ball increases the leverage the obliques work against and lets the exercise progress beyond bodyweight, which a plain twist cannot. The position is what makes it hard: lifting the feet removes the support that would otherwise let the hip flexors take over. Speed is the enemy here. Swinging the ball fast lets momentum carry it across and the obliques stop working, so move deliberately and keep the chest lifted rather than collapsing over the ball.