That's a good question. A study I did around 1995 showed three groups of about equal size, of people who joined an employee fitness center: people lacking exercise for a long time, moderate exercisers, and people who exercise almost every day (including bodybuilders, marathoners, etc.). The results showed that the middle group made the most progress in their exercise programs and seemed to enjoy exercising more than the other two groups enjoyed it.
My thoughts continue to be that the least physically fit group was struggling with acute pain, soreness, and feeling winded; while the most fit were not seeing many results and feeling discouraged, because they were at a plateau. I wonder today if our moderate exercisers in America have a more positive attitude toward fitness than does anyone else?