“Tough times don’t last, tough people do!... Pain is temporary,” reads a t-shirt prominently displayed on the Tough Mudder website. Vomit or no vomit, the experience will be unpleasant, but you will be better for it. This is the promise of extreme exercise.

But to determine why people are attracted to exercise programs where vomiting or being shocked by a live wire seem to be at least somewhat more likely than in day-to-day life, we must first ask: Why exercise at all?

The reasons people exercise can’t be boiled down to dichotomies: Either they like working out or they don’t, they’re motivated or they’re not. The truth is that motivation is complex, and some reasons for working out are healthier than others.

Philip Wilson, an associate professor in the department of kinesiology at Brock University in Canada, has been studying exercise motivation for the past 10 years. He says that while intrinsic motivation—exercising because you think it’s fun, and you actively want to do it—is the ideal for creating a long-term habit, ultimately exercise can’t make you love it if you don’t.

In the absence of a genuine love for running on the elliptical, exercising because you know it’s good for you, or because you want to be the type of person who exercises, are better motivations (in terms of feeling good and sticking with it) than exercising because you’d feel bad about yourself if you didn’t, or because you think someone else wants you to.

Wilson says it could be that people who are attracted to intense exercise programs are intrinsically or autonomously motivated, that they are looking to prove themselves at a new challenge, and they enjoy the hard work these programs involve. (They may also like exercise itself less than “having exercised”—one 2007 study found that participants felt tense and distressed during their workout, but felt better once it was over.)

“These CrossFit programs do not draw couch potatoes,” Wilson says.

That certainly seems to be the case for Darsh.

“[CrossFit] was a way to throw myself into yet another sport that demanded a lot of me, [where] I really had to bear down and go to a different place in order to get where I wanted to go,” she says. “I’d found that in cycling and in triathlons, and then moved on to CrossFit.”

But Wilson says it’s also possible that some of the more troubling motivations are behind the trend—that people are seeking a reward (such as losing weight), “or they have a very fragile sense of self-worth.” Unhealthy motives are more likely, according to Wilson, when people take extreme exercise to, well, its extreme—pushing through intense pain, or continuing to work out through nausea.

Nausea is a warning sign, says Anthony Wall, director of professional education at the American Council on Exercise. There are a few things that can cause nausea during a workout. One is a full stomach, which isn’t much of a cause for worry. (Just maybe next time, do your daily P90X video before entering a hot dog eating contest, not after.) Another is dehydration, when an imbalance of the body’s electrolytes can cause vomiting.