When it comes to training your abdominal muscles, it's good to introduce new moves into your routine so you continue to "surprise" your muscles. Otherwise there's a tendency for them to go on autopilot and you won't get the maximum benefit of your efforts.
Sit upright on a flat, padded surface or mat with a small inflatable ball or firm pillow behind your waist. Place your feet hip-width apart with your knees bent and feet flat on the floor. To begin, place your left hand behind your head and your right hand behind your right thigh. On an exhalation, push your lower back against the ball and raise your right leg. Pause with your shin parallel to the ceiling.
