Lie supine on the floor with knees and hips bent at 90 degrees. Squeeze a stability ball firmly between your hands and knees, pressing your lower back into the floor.

1. Inhale and brace your core to keep your lower back flat against the floor.
2. Simultaneously extend your right arm overhead and straighten your left leg toward the floor.
3. Maintain pressure on the ball with your left hand and right knee.
4. Pause briefly at the point of greatest extension without arching your back.
5. Return the arm and leg to the starting position while exhaling.
6. Repeat the movement with the left arm and right leg.
7. Continue alternating sides for the prescribed reps.