It's amazing what you can do if you straighten your back leg. In any pose. Various warriors, pyramid, side angle–anything where you've got a leg striding behind you.

I went to a random yoga class at a strange gym not too long ago, and the teacher kept talking about pressing the thigh back. I think this might be an Anusara thing. When you press your thigh back, mysteriously there is room to scoop your tailbone, giving you more stability through the lower back. This seems counterintuitive to me. I would think that if you pressed your thigh backward in a lunging pose, it would in fact compress your back. But not so. In fact, it gives you a lot of space to bring your pelvis underneath you, creating more stability.

So: You're in warrior 1. Your back leg is straight, your back thigh is pressing vigorously, your tailbone is tucked, your lower back is stable, and now it's all of a sudden much easier to backbend from the mid-to-upper back. Holy crap, you think, as your eyes graze the ceiling.

So, a couple of days after I received this gem at the random gym yoga class, Jen started talking about valves. A student was having trouble with crescent lunge. She couldn't open her chest the way she wanted. Jen had her do the pose in the center of the room, and pointed out that the student's back leg was soft. The knee was bent. Jen said that the knee was like a valve: energy and strength were leaking from it. The student straightened her leg strongly, tucked her tailbone, and her chest and shoulders flew open.

I'm sure there is some lovely metaphorical point I could make here about groundedness and flight. But I'm not interested in metaphor right now. I'm interested in this plain, real challenge of straightening my back leg. Tightening the valve.