The body has edges that mark its limits in stretch, strength, endurance, and balance. The flexibility edge can be used to illustrate this. In each posture, at any given time, there is a limit to stretch that I call the final or "maximum edge." This edge has a feeling of intensity, and is right before pain, but it is not pain itself. The edge moves from day to day and from breath to breath. It does not always move forward; sometimes it retreats. Part of learning how to do yoga is learning how to surrender to this edge, so that when it changes you move with the change. It is psychologically easier to move forward than to back off. But it's as important to learn to move back if your edge closes, as it is to learn to move forward slowly as the body opens.

Joel Kramer in 365 Yoga by Julie Rappaport