Most people with pain, especially back pain, are afraid to move. Early on, especially before their doctor gives them permission to get going, that may make sense. But if they don't get past the fear, they become weak, their muscles tighten up, and they lose endurance. They complain of pain getting worse as the day goes on, and difficulty doing things they used to be able to do. So active exercise - weight training, aerobics, stretching, etc., can make a big difference.
Exercise certainly increases strength and endurance to do active things.
On their own, people often do too much or too little, exercising one group of muscles, but forgetting other important parts. Motivation is tough, especially early on when everything seems to ache and hurt. Many patients often need coaching from an exercise physiologist or physical therapist to help them get started with an exercise program. There are smart ways to do things, and dumb ways. There are things you love to do, things you need to do, and things you really can give up.