(Sylvie is at the gym in her building for a trial session with a trainer named Fielding (Rip).) He started me on the treadmill and worked his way around the room, explaining the purpose of each exercise and the form to maintain for optimal benefit. I found the gray metal architecture of the exercise stations reassuringly solid. Footrests were right where I needed, hand grips where I instinctively reached to brace myself. He instructed me which muscles to focus on, but the machines isolated the correct ones, keeping me on the physical straight and narrow. I could have done without the mirrors lining the walls. I knew they were there so that clients could see if they were doing their exercises correctly, but I couldn’t help feeling they were sitting in judgment. Though Rip kept the weights light and the repetitions few, I worried that if I failed to control the weight on the resistance machines, I would be snapped forward, back, up, or down. “This may sound irrational, but are these machines safe?” “We haven’t crushed any noses or launched anyone butt-first so far. Your muscles will take care of you.” “These? I’ve got less muscle than a lox.”…