What are you paying for at the gym? The machines, free weights, televisions, and shower, of course. But you're also investing in motivation. If you're like me, you suspect you can guilt yourself into frequenting the gym by paying a monthly fee that goes to waste if you never stop by. But if you're like me, you also know that this tactic doesn't always work, and you occasionally find yourself hitting the couch significantly more than the bench press machine for weeks at a time.

Is there a solution? Maybe...

A couple of Harvard graduates are working to improve the commitment device by giving it a twist: they have launched a plan in which customers get a free gym membership if they agree to work out at least four times a week and pay a $25 penalty each week that they fail to follow the schedule. This would impose an immediate cost on slacking.

No gym will accept this plan, because gyms make most of their money off two sorts of people: 1) Slackers who pay for a service they don't use or 2) Super-users who pay for not only the monthly fee but also the add-ons, like trainers and classes and whey smoothies.

But here's an idea. Why not offer New Years customers two membership options. "You can join Atlantic Gym for our regular fee of $40 a month," you say, "or, if you want an extra incentive, you can join for $20 a month and pay a $15 penalty for each week you don't show up." In other words, the gym asks you to put a price on your eagerness to not be lazy in the future.

Which option would you choose? Which option do you think would make the gym more money?

I don't know! But read more at Eduardo Porter's blog.

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