By the second day of silence at last week's five-day meditation retreat, the mental static of everyday thoughts had mostly passed. During the 9am-11am session we switched techniques from focusing on breathing to scanning the body for sensations and letting them pass. After one or two scans I found I could hardly sense anything subtler than, say, my shirt on my arm. Frustrating. Another scan brought me back to my last retreat, a twelve-day in 2007. I realized then I was holding tension in my chest muscles and how, until released, that tension blocked my ability to sense subtle sensations near that muscle. This time my chest muscles weren't tense; my back muscles were. Later I realized how tense my whole back, shoulders, and neck…