Rubber and Lysol meet me at the door. Bright fluorescent lights illuminate the rows of steel machines and neatly stacked weights. Windows to the street line one wall, mirrors on the other—a place to watch and be watched. In this quiet morning hour there’s no one else here. On the other side, where we train for martial arts, stretches a large open space. Heavy bags hang along the back wall, and the rubber mats lie waiting. Soon we’ll step onto those mats to learn a new technique. Health and...