In a recent lesson, my teacher and I focused on coiling the body before issuing a strike. We were using the context of a single change, kobu-ing in and drawing the arms across one another before stepping out and striking towards the center of the circle (pretty routine stuff).

My question is, should the muscles be tightly drawn while "coiling" up? If so, should the coiling be confined to the abdominal region? I ask because it seems detrimental to have the chest muscles tightly drawn, as it restricts bloodflow (and presumably chi-flow) and possibly reduces the power of the strike.

Hopefully I'm wording this in a way that'll make sense. I'm having difficulty understanding how to properly coil my body in an art that stresses softness and relaxed muscles. Any input is appreciated.