Partial sit ups are recommended for people with back pain. The same muscle groups are worked out without putting stress on the lower back. You will start just like a regular sit up with your back on the floor, both feet on the floor, and your knees bent. Raise your head, neck, and shoulders off of the floor and hold that position for 5 seconds. This exercise will strengthen your core and is simple to do. Repeat as many times as you can, with a goal of increasing your reps each day.