Exercise is one of the primary interventions used with people with chronic, mechanical low back pain. It is unknown, however, which exercise is best for which person, which exercises a person will adhere to and for how long, and the effect of adhering to a specific type of exercise on how the person functions, particularly in the long run. The purpose of this study is to examine if the short- and long-term effects are different between 1) commonly prescribed strength and flexibility exercises for the trunk and limbs, and 2) individualized practice in daily functional activities that are difficult or painful to perform. Adherence to the different interventions, the relationship between adherence and outcomes,as well as the effect of a booster intervention also will be examined.