I designed this posture to let the stress of the day go, and I refer to it often. My grandfather was the first to introduce me to this posture. His doctor recommended it to ease his back pain. I found it many books promising pain relief since then. The idea is to release the tension in your lower back.
Find a chair, bed, foot stool, anything that is about the height of your knees and wide enough for your legs to lie on. In this example, I use a chair.
Lie on your back, with your arms extended at your sides, and put your feet onto the chair. Slide your bottom next to the chair so that you form two 90-degree angles: one from your knees to your thighs, and the second from your thighs to your hips and back.
When you assume this posture, there may be a large arch in your lower back. The psoas major muscle could form this by contracting to manage some disfunction in your posture. Ideally, you would remain on the floor until your back flattens, but this is a relaxing posture, and it is not doing anything to strengthen your shoulders, hips, legs, or lower back. Try not to stay in the Bear for more than 15 minutes at a time. Trust me.