1. Toned Bodies
They already have seen what their history with you has done for their bodies. They've seen the results and just want to keep those results. Giving them constant reminders that simply by walking in the doors again and again, they immerse themselves in the idea of keeping their bodies as pure and strong as possible. They are likely already addicted to the endorphins, so it won't take much to please them so long as you keep giving them a reliable place to exercise.