Lie on your back in the supine position with your legs bent and your feet flat on the floor.
Extend your arms at a 45 degree angle to your trunk with your palms facing downwards.
Raise your head just off the floor and keep your chin tucked in.
Maintain contact between your knees and feet, and tighten your abdominal muscles for the duration of the exercise.
Now rotate your legs to the left to the limit of your ability, make sure the opposite shoulder remains in contact with the floor throughout the movement.
Move back to the neutral position and repeat, alternating sides for the desired number of repetitions. Do not rotate the legs to a point beyond which the arms and shoulders can no longer maintain contact with the floor.
Perform this exercise in a slow controlled, manner within the range of your mobility.