This is an installment of Good Fit, a column about exercise. At Form Fitness, in Brooklyn, you’ll find an assortment of squat racks, dumbbells, and pull-up bars—which is to say, it’s a typical gym.

After spending "literally 30,000 hours of [her] life" in front of a mirror, celeb trainer Ashley Borden said enough is enough. The newest addition to the Revenge Body all-star trainer lineup took all ...