There are lots of websites which suggest a wide range of exercise and stretching for treating lower back pain. Heck, this is one of them. But do you ever wonder what evidence supports these exercises? I've decided to start reading the primary academic literature on back pain treatment, and summarizing the approaches which have more than anecdotal support.
One of the old standards of lower back pain treatment is the back extension exercise. The idea is to increase the strength of the muscles that allow you to bend backwards when you are lying on your stomach. At the same time, this helps with mobility, and supposedly can help improve blood flow to the disks and reduce pain by recalibrating the pain-sensitive sensory neurons in your back. Because this exercise has been around for a while, there's lot of documented evidence that it can help chronic lower back pain. For more info, see this review article "Evidence-informed management of chronic low back pain with lumbar extensor strengthening exercises" published in 2008 in The Spine Journal (Note that a journal subscription is required, so you'll need to go to your local university library to read this, unless the following PDF link still works :-). This posting is largely based on the info in that artcle, so if you want more detail, be sure to check it out.
The back extension exercise can be done with a yoga ball (aka balance ball), as shown in the picture. Face toward the floor, and place your hips on the ball. Trap your feet against a wall. Place your hands on your hips (or behind your head for more resistance), and bend backwards to the pain-free limit of your range. Be sure to take it slow and smooth, with about 2 seconds to bend backward, and 4 to return to the starting position.
How often and with what intensity should you perform this exercise? Evidence suggests that doing a little is better than nothing, so you may see benefit with as little as 1 session a week, 3 sets of 6 reps, for a period of 12 weeks. If you want to work harder, build up slowly to 3 sessions a week, with 3 sets of 25 reps, but keep in mind you are much more at risk of injury, and like most back exercises doing a little is much better than doing a lot and then injuring yourself. Interestingly, there is little published evidence that doing the more intense workout leads to a significantly better outcome; I would guess that's because people tend to over-do it.
Once caveat that the 2008 journal article mentions is that there isn't conclusive evidence that the balance ball version of this exercise leads to a measurable strength gain that can help lower back pain. They recommend using gym equipment to ensure effectiveness, but I suspect here that doing the balance ball exercises religiously over 2 months will give more benefit than going to the gym 3 times and then losing motivation. In any case, here are some external links for more info - the first is a video instruction on how to do the exercise on a balance ball, and the second shows how to do the supposedly more effective version of the exercise on more specialized gym equipment.
figure - exercise on a specialized equipment you might find in a gym. You could duplicate this at home if you lay over the edge of a bench or bed, and have somebody to hold/sit on your legs.