JUST after 2 p.m. on a September Saturday, the heavy drinking began at Alyson Luck’s bachelorette party.

“I’m already in pain,” said Ms. Luck, 29, wearing a veil and a white sash that read “Sexy Little Bride.”

This was no bacchanalian bender. The bride-to-be and eight friends were partying at Flywheel Sports studio in the Flatiron district, downing half-liter bottles of water as they bellied up to the barre for an hourlong workout that mixed Pilates, dance and weights. After a final stretch, to the sounds of “Chapel of Love,” the crew refueled with sips of Champagne (Moët) and bite-size cupcakes. Then they headed out for manicures, pedicures and sushi.

Dancing on tables used to be the only activity remotely resembling exercise at a bachelorette party. Not now. The pre-wedding rite has taken to the gym — and the stationary bike, the yoga studio, even the 10K road race. During prime wedding season, April to October, Exhale Spa’s Midtown branch alone hosts an average of four bachelorette parties a month (cost: $675 to $1,200) for its signature Core Fusion workout, a barre-based blend of weights, interval training and stretching.