Reformer Pilates, once a niche practice on specialized machines, has become one of New York's dominant fitness trends. Boutique studios built around the spring-loaded apparatus are opening at a pace that rivals coffee shops, often clustering blocks apart.

The fictional chain Coil in the West Village runs classes nearly around the clock and still turns away walk-ins. Its instructors credit the low-impact intensity, which appeals to a broad age range wary of pounding joints.

The boom has driven up prices and spawned membership tiers, waitlists, and a secondary market for coveted class times. For its devotees, though, the reformer has become non-negotiable — the workout they'll rearrange their week around.