The russian twist is an excellent exercise for your oblique muscles.
Sit on the ball and walk your feet forward. Keep walking until your head and shoulders rest on the ball. Extend your arms over your chest, set the abdominal muscles with your core parallel to the floor.
Rotate all the way to one side. Ensure that the movement is initiated at the core and not the shoulder. Keep your eyes on your hands, enhancing the total core rotation as you move.
As you reach your end range, change direction and then being moving in the opposite direction.
Once you’re able to complete 20-30 reps easily, hold a medicine ball or dumbbell to obtain greater load.