SACH-SAWCH

Concentric Isometric Eccentric In walking, only the Iliopsoas is concentric , meaning that it shortens when active. Nearly all the power of walking is from this one concentric muscle which is not actually in the leg but in the body. Having huge multi-segment vascularity, it contributes to body heat. Nothing wasted. Only the briefest beginning of swing phase is “concentric”. Nearly all of the energy of efficient walking that comes from the iliopsoas is from a very brief oomph. /\__________________ Think of a mother pushing her child in a swing seat. It goes away and returns as a pendulum. Her next push is minimal needing only what air resistance and swivel drag took away, not much. Mother pushes swing concentrically. The Iliopsoas pulls it concentrically. Same deal.

The stance leg behaves like a Joe Palooka punching object (Joe stand on the floor, bottom weighted, and rights itself after being punched). That down to up return must time itself to the opposite side swinging double pendulum (which not chaotic as it is bounded by damping and energy transfer mechanisms).