To strengthen the muscles of the lumbar spine the gluteals (buttocks) and hamstrings muscles. Also helps to strengthen your abdominal oblique muscles and improve core strength.
Lie on your back on an exercise mat. Place your lower legs on top of a well-pumped Swiss ball. Open your arms out by your sides to ensure that the upper back remains fixed on the floor.
Fully inhale then contract the muscles of your abdomen, low back and buttocks and slowly raise your pelvis a few inches off the floor. Hold this position for 5-10 seconds, fully exhale and contract the above muscles further then relax. Repeat this for the prescribed number of times.
You can increase the level of difficulty by raising your pelvis higher and then rotate the ball slightly to the left and right. This is more of a strengthening exercise.
Consult your osteopath for more advice.