jeffrey brown went to the american ballet theater recently to stay in step with twyla tharp. it's part of our ongoing arts and culture coverage, canvas. >> sternum up,reathe deep, shoulders back, and now we stride. tharp in allowing our bodies to take up space, even as we grow older. what she refers to as amplitude. >> amplitude: moving out,ng constantly feehat you can move out. r as age becomlity, i think we start to retreat, we retract, we become protective, we become secluded, and we begin to ossify and decline and degenerate, as >> brown: but the body becoming smaller, in a way it is becoming smaller. >> well, that's its problem. let's just get on with i shall we? >> brown: tharp is one of the great choreographers of our age, and at 78 she's got a new dance. we met at a rehearsal at the american ballet theater, and a new book: "keep it moving: lessons for the rest of your life." >> i wrote this to help others believe that constantly you can be evolving. that you do not stop learning. that you don't acceprumor that as the body ages it becomes less. it becomes different. hop