I discovered recently, that once you start suggesting that stretching your back  isn’t a good idea (at all)  the yoga  and pilates lobby comes out. So you engage with them. You point them to research, they  come back with belief, you point out that stretching  the back only deadens the nerve endings, you supply references, they supply none.
Eventually, though, even they get a bit  worried by their lack of causality  and science.  What does stretching do, they ask themselves. They come back with, what  I call, “the old faithful Argument”
The Old faithful argument runs like this. You need to move your back, and stretch it,  to pump the blood in an out.
To begin to understand “bad backs” we need to understand the vascular and neuro anatomy of the spine. I am no expert on this, but here is my 1st attempt at some cut and pasting to inform my future thinking

This following link goes into worrying detail about the blood supply of the spine.  My take home message , I think , is this. The spine is amazingly well supplied with blood. Things may go wrong,  but in  most cases, if you need to move the spine to pump blood in and out,  you have very , very severe problems.Nothing to do with normal back pain.
The veins in the back are quiet amazing too
“In 2011, researchers from the Department of Neurological Surgery at Ohio State Medical Center summarized the significance and current understanding of several aspects of the CSVS in their review article: “Today, the vertebral venous plexus is considered part of the cerebrospinal venous system, which is regarded as a unique, large-capacitance, valveless plexiform venous network in which flow is bidirectional that plays an important role in the regulation of intracranial pressure with changes in posture and in venous outflow from the brain, whereas in disease states, it provides a potential route for the spread of tumor, infection, or emboli.”
Maybe we need to pump the spinal lymphatic system?
“the lymphatic system does not extend into the brain or spinal cord, despite the high metabolic activity of neural tissue and its high sensitivity to changes in the extracellular environment, including the build-up of metabolic waste products. Such an absence of lymphatic vessels has led scientists to believe that an alternative process exists, which takes the place of this critical lymphatic function” ( well according to Wikipedia)
In the same review, it suggests this
“In 2012, it was shown that AQP4 is essential for paravascular CSF–ISF exchange. Analysis of genetically modified mice that lacked the AQP4 gene revealed that the bulk flow-dependent clearance of interstitial solutes decreases by 70% in the absence of AQP4. Based upon this role of AQP4-dependent glial water transport in the process of paravascular interstitial solute clearance, Iliff and Nedergaard termed this brain-wide glio-vascular pathway the ‘glymphatic system’.”
Sooo, we need to get a handle on what the hell the “glymphatic system” is! maybe this helps. As the PR says, “It’s as if Dr. Nedergaard and her colleagues have uncovered a network of hidden caves and these exciting results highlight the potential importance of the network in normal brain function,” said Roderick Corriveau, Ph.D., a program director at NINDS.
Take home message: get more sleep. Stretching a bit to pump blood in and out of your spine is probably incorrect