It does offer a good alternative in the off season or in bad weather. We get old because we're inactive. We don't become inactive because we become old. Muscles atrophy by lack of use. Aerobic exercise does not build muscle tissue.
Resistance training does.
Another myth in the industry is that a half hour walk will help you loose fat. Fat is not metabolized in the first 30 minutes of exercise. Extend the workout to at least an hour if you want to burn fat. To exercise the lower back, use back extension exercise.