Two Harvard students use behavioral economics to reinvent the gym membership. Gym-Pact offers what Zhang calls motivational fees — customers agree to pay more if they miss their scheduled workouts, literally buying into a financial penalty if they don’t stick to their fitness plans. The concept arose from Zhang’s behavioral economics class at Harvard, where professor Sendhil Mullainathan taught that people are more motivated by immediate consequences than by future possibilities. “If you have a toothache, you go to the dentist. If there’s a cavity, you know it needs to get filled in, but if it doesn’t hurt right now, you may not bother,’’ Mullainathan said. “In traditional gym memberships, not going is not very costly. In this one, you actually might feel the pain of not going immediately.’’

Zhang and Oberhofer translated that principle to workout motivation. If missing a workout cost people money, they’d be more motivated to stick with it, they thought.

Details on two pilots with Bally Total Fitness and Planet Fitness in Boston are in the . Hat tip: Derek Reed