I keep coming back to an article, What science Can Teach Us About Flexibility by Fernando Pagés Ruiz, appearing in the Yoga Journal March/April 2000 issue. It’s a long read, but it goes into the details of what happens to your muscles, and, more importantly, tendons, ligaments, and muscle fascia when you’re stretching.
This reference comes to mind because I went to my Friday evening yoga class and discovered that there was a substitute instructor. She led us in a few sun salutations and then spent the rest of the class doing some Pilates exercises. I don’t know whether it was the newness of the exercises, the emphasis on forward bends (pressure on my lumbar area), the different approach of Pilates or the lack of careful planning for the combination of positions. I ended up not feeling the normal release I get after a class. This morning, I woke up and my lower back had stiffened up.