The other day in the locker room at the Exhale Spa on Central Park South in New York, I noticed that I was not the only one furtively sipping a bottle of forest green liquid while hurrying to change for my 6:15pm Core Fusion exercise class. It seems many women have already signed up for the joint program, launched recently, between Exhale and Blueprint Cleanse. (It's a three-day cleanse, three exercise classes at Exhale, and one spa treatment for $295.)

I was skeptical of how useful such a package would be, considering that three hardcore Exhale exercise classes in three days is more than I can bear even on my normal diet. (You aren't obligated to take the three classes during the cleanse period, though that's sort of the idea.) I was certain I'd pass out halfway through the first plank series.

Turns out, the best exercise to do while on a cleanse--or undergoing some other bodily experiment that carries the risk of lower energy levels--is one that brings out the competitive spirit. On my own, on the treadmill, I would have been sunk, but surrounded by 20 lithe bodies determined to show each other up (many of whom were operating only on juice themselves) and a stern instructor, I managed to have three good workouts on three consecutive days (plus a fourth this morning at my gym before breaking the cleanse) despite a lack of solid food.

[Read another W staffer's account of her Blueprint experience HERE

But just because I didn't get carted away in an ambulance doesn't mean there weren't side effects. Mine came in the form of ersatz celebrity sightings. I could have sworn the tall, high-energy woman with the million-dollar smile I commiserated about green juice with one evening in the Exhale locker room was Hilary Swank. But would Swank really admit to perfect stranger that she was hoping to shed a couple of last-minute pounds before a trip to Miami
next week? Was the lack of chewing affecting my brain? And another morning, I was certain the hunk who entered my gym in big black sunglasses and hopped on an elliptical trainer was Jon Bon Jovi. But does JBJ actually work out with the masses at New York Sports Club? A WWD colleague I ran into at the gym cased the scene after I left and sent me an email moments later, saying: "It looked a lot like him, but surely this gym is too populist for a big star. Then again, he is from Jersey."