When I'm at the health club working out, I often see people hanging straight out over the edge of a table for as long as they can. What does this exercise do?

What you may be seeing is a test that has turned into an exercise. The Sorensen Test (ST) is a reliable way to measure muscular endurance of the lumbar spine in healthy people.

As you described it, the goal is to support the hips and lower body on a table. From there the person holds him or herself in a horizontal position without supporting the chest or upper body. The idea is to stay in this position for as long as possible. After a short rest period (two minutes), the exercise can be repeated.

Studies show that when it comes to preventing low back pain, muscle endurance is more important than muscle strength. The ST is an easy tool to build that endurance.

If you find you can't do this test starting from the horizontal position, it can be modified. A special piece of equipment called the Roman chair (or a similar piece of equipment) is needed. This chair allows you to start in a more upright position. You can gradually lower yourself closer to the horizontal position as you build up your endurance in the more upright positions.

If you've never done this exercise before, ask the physical fitness coordinator or trainer on staff to help you. It's best to start doing this exercise with guidance and supervision from someone who has been trained in using this equipment for this purpose.