Ah yes, Im not sure whether it is possible for me to give an explanation which makes any kind of sense, but I'd like to give it a go. Bear with me...
My backache had a lot to do with my posture. Lots of tests and things with doctors to rule out any medical problem. I tended to, and still do, if i dont think about it, hollow out my back, in a duck like posture. Lots of people tried to help me to relax it but i misunderstood, so that i was trying to change by doing the opposite of what i thought i was trying to do.
A teacher once, when standing in fromt of me, pressed a finger very gently on my breatbone and said 'soften' here. At the time, i didnt know what to do, as it felt as if my whole body was quite rigid and nothing could soften.
Since then , through much physical therapy, massage, exercise etc of lots of different kinds, i discovered that i could think of my pelvis as a bowl. It is possible for that bowl to be held as if dangled from my spine, so that it is level. When i stand in the duck posture, it is as if the bowl is tipping forward, its front edge down so that its contents spilling out of my front. Its back ledge is therefore higher than it should be.
Starting in an exagerated duck posture, i have an exaggerated s shape in my spine. For convenience, i do this sitting down, the principles are the same for standing but im much more likely to fall over. As i do it slowly to explain. someone standing in front of me, pressing their finger to my breastbone, if the rest of me is flexible and i allow it, that finger pressing can encourage my spine to straighten so that as the breastbone goes back the part attached to the pelvis moves forward and the pelvis becomes more level so that if it was filled with liquid, the liquid would no lonegrr tip out the front.
The spine still has a gentle bend or s shape but it is much less exaggerated, the spine is much closer to being straight.
If you continued applying the finger to the breastbome, the spine would hunch in a c shape, shoulders forward, the stomach and abs would become all squashed and the pelvis might eventually allow liquid the tip out the back.
I find moving through that range of postures is very relaxing, its probably best described as a cat stretch ( but cat is typically on all fours, which means that the finger works less well) and the liquid filled pelvis picture is a non starter. Another way is to talk about pointing the point whereva tail would attach, down towards the ground.
Thats what does it for me, sorry if it makes no sense. Im sure others could explain it much better. Not having that chronic, low level discomfort which became pain any time i did any kind of exercise was nit easy. Being rid of it, with a few simple stretches, is bliss. I would love to help someone else in the same way. HTH, xx