Ruth, one of my favorite Tuesday-morning regulars at the Y, cornered me by the stretching mats last week. She is seventy-one, sharp as a tack, and she wanted to know why three different people had told her to buy a “shaking platform” for her bones this month alone. I laughed, and then I started counting. Between my clients, my inbox, and the longevity clinic that just opened two streets from my gym, I had fielded the same question eleven times in September. Vibration plates — those humming platforms that quietly faded from gym floors a decade ago — are having…