There’s an absolutely fascinating episode of the Planet Money podcast up on NPR now (or subscribe via iTunes) about the tactics that low-cost gyms use in order to make a fortune on low $10 a month membership fees. I’m particularly fascinated by it because I’m the exact kind of gym member that a place like Planet Fitness craves. I’ve been a member for five or six years, and I’ll go five times a week for three or four months and then get sidetracked by work or kids or other commitments and not attend the gym again for three or four more months.

I’m the ideal gym member.

Why? Because places like Planet Fitness are not actually designed to accommodate the number of people who enroll as members. For instance, the gym used as an example in this episode of Planet Money had about 6,000 members, and yet the facility itself could only accommodate about 300 people at a time. If all the members who signed up actually went, franchises like that Planet Fitness would have to charge far more than $10 a month.

In fact, of the members who get gym memberships, about HALF never actually visit the gym once.

So, how does a place like Planet Fitness attract a clientele that’s earnest enough to sign up for the gym but not dedicated enough to actually go?

Part of it has to do with design: They create gyms that are meant to look like bars. They are designed to make out-of-shape people feel comfortable being there, because the gyms know out-of-shape people are not likely to attend frequently once they sign up. They do that with mirrors and disco music and even massage chairs. Meanwhile, the actual gym part of the gym — the free weights and weight machines — are typically hidden away from the main part of the gym, back in a more intimidating space that those comfortable in the bar-like atmosphere would be less likely to visit. Low-cost gyms don’t actually want the body-builder types — they’d actually go to the gym more frequently — they want those who climb on the treadmill every once in a while. (I can confirm this: In the five or six years I’ve been attending my gym, I’ve visited the weight room twice, and both times, felt like an alien outsider).

Psychologically, when it comes to gym memberships, contrary to what you might think, we also LIKE the idea of long-term contracts, because it locks us into a commitment of going to the gym that we will feel compelled to follow through on. The thinking is, “Well, I’m paying $10 a month, so I HAVE to go,” except when it comes right down to it, the thinking is more like, “Well, it’s only $10. I’m not losing that much. I think I’ll have a pizza and watch The Blacklist tonight, instead.”

Speaking of pizza, I always found it strange that the gym I attend has pizza night and bagel breakfast once a month. That seems kind of self-defeating for a gym, but again, that’s part of the design. The average low-cost gym loses about half of its members each year, so in order to entice people who don’t go to the gym to sign up for another year, these gyms offer free food so at least members get something out of their membership. Many, in fact, will attend only on those days with free food — it doesn’t make them any more healthy but hey! For $10 a month, you get two slices of pizza.