As you move and breathe and feel within, you will find that tension-free requires some muscles to relax (and sometimes some muscles need to be activated so that others may relax). You will find that sometimes an arm needs to be repositioned, a stance needs to be altered, a jaw needs to be reminded to let go. Sometimes abandoning the pose or the challenge entirely is the only sane response to the quest for less stress.
More often, you'll discover that the mind is the source of unnecessary tension in your life. Perhaps you need to relinquish your quest for the perfect, or even the good. Maybe it's time to let go of the thought that life needs to be earned through hard work, and that therefore if your work is not difficult it's not deserving. Maybe it's time to flip-flop your goals, to abandon the effort to sculpt everyone and everything into your ideal of what should be, and instead to consider what you have as perfect as it already is.
Maybe you need to remember how very, very small you (and your tensions) are. Maybe you need to be reminded how very, very gigantic you (and your life) are. Maybe you need to hand your life over to something greater than your small self.
Or, maybe you simply need to be reminded to lighten up, to let go, to play. And sometimes that's as simple as whispering, "tension free, tension free, tension free."