Strengthen Muscles to Prevent Back Pain
There are a number of things you can do to prevent lower back pain; losing excess weight and improving joint flexibility in the upper legs and hips are good starts. Another solid strategy is to strengthen the muscles in the lower back.
Your gym's back extension machine works theses muscles directly. To get the best results from your time on this machine, be sure that you are using the muscles in your lower back -- and not your legs -- when pushing backward. It's also important to use slow, controlled motion both when pushing back and when returning to your starting seated position.