We all have friends who, despite hectic schedules, never miss a day at the gym. Who can’t stop talking about the next 10K. Who can’t stop smiling after yoga class. Sure, they’re a little, well, obsessive about working out. But we envy them! The good news is we all have the potential to become fitness-obsessed, says Tom Holland, a Connecticut-based celebrity fitness trainer, exercise physiologist, and expert in sports psychology. Here are 20 proven ways to make exercise a habit.