Dave demonstrates a back bend that has some advantages over (for example) the Cobra pose from Yoga.
On advantage is that, if you follow the instructions, you can into the start position without your back muscles tightening up. In beginning students especially, the lower back muscles tighten up in back bends because these muscles are working in the *contracted end* of their range of movement—and like when you point your foot strongly, these muscles can go into spasm. Unlike like a foot, though, a spasm in your back muscles will normally be experienced as something quite serious.
If you have had back problems in past, this tightening can feel like the old problem returning.
A second advantage is that because the elbows are used for support, little effort is required, and you can stay in the position for a while and explore the sensations. If you let your body really relax, the final extension can be quite strong, but because all the muscles around the spine are relaxed, there will be little, or no, discomfort.
Follow the directions, and see if this feels good for you. And have a look at his end position: there is quite a strong extension in the lumbar spine, yet he is completely relaxed.
Dave is lying face down in preparation for the most gentle of the backward bends and one that avoids the most common problem with this exercise, and that is the tightening of the lower back muscles. Now look how he gets into the position. He gently rolls over onto one side like this, not using the back muscles at all. And then he brings the other arm into position roughly underneath the shoulder, like this, and then uses the outstretched arm as the means of lifting himself up onto that second elbow like so. Thus he's got into position without having to tighten the lower back muscles at all. In fact, he's only used his arm muscles to get into that position.
Now you can make this pose a little bit stronger by doing the following. First, let the tummy rest on the floor completely. Now see how that increases the backward bend. Then you can think about pulling the shoulders back gently as well. That increases it considerably. And then ,last of all, let the tummy relax on the floor once more. Last of all, then think about pulling the elbows gently back towards the hips. Not so much that you actually move them, just enough to activate the lats. And as you can see, his spine is very strongly bent now in that position and all of this achieved without using the back muscles at all.
Now when you stayed in this position for long enough, you then let yourself come out and immediately curl up into some sort of position that stretches the lower back muscles, because what we found is that even if you're very careful and do it like this, those lower back muscles tend to tighten up a little bit anyway. And curling up and bending the spine forward will just make everything feel that much more comfortable. So our recommendation is to treat the forward and backward bending components of this exercise as one complete exercise. Beautiful. By rounding the back like this, you can pull out any of that tension that might've been generated. The back muscles tend to tighten because they're trying to help you get into a better back bend. The only disadvantage is that they're liable to cramp a little bit, and this is the cure for that.