A gym is a business whose entire product is people doing physically demanding things with heavy objects, and whose contract with them is designed to make injuries someone else's problem. This article explains what the waiver everyone signs actually does, why it works better than most people assume and worse than gym owners believe, and where it fails entirely. It covers the membership contract and the health club statutes nearly every State has enacted in response to prepaid memberships that outlived the gyms selling them — cancellation rights, cooling-off periods, bonding, and the auto-renewal rules now being enforced aggressively. It covers the duties a facility owes regardless of any waiver: maintaining equipment, supervising where supervision was promised, responding to a cardiac emergency, and providing access. It closes with trainer liability, staff classification, and what to do in the first hour after someone is hurt.