We spend so much time working our legs with squats and running, our arms with strength training, and abs with crunches, so we can't forget about our backs. Strengthening this part of the body is excellent for posture; it keeps the spine healthy and prevents injuries due to imbalances in muscles. Prone Leg Raises [1] are an awesome exercise, but this one will work your upper back and truly challenge your core.

If you want to know how to do this move .

• Lay your belly on a ball. Stabilize yourself by placing your hands underneath your shoulders, and your feet hip distance apart.
• Simultaneously lift your right arm and your left leg straight out. Hold for two seconds and then release back to the ground. Now lift your left arm and your right leg. Hold for two seconds and slowly release. Try to move slowly and with control. Try to keep the ball as steady as possible. Use your deep abs [2] to help stabilize.
• Repeat this move for a total of 15 to 20 reps on each side.

Do you work your core? You should do moves like this at least two times a week. Add this one to your strength-training routine and your back will love you for it.