The forum pointed toward a few directions. Collagen supplements came up repeatedly.
I tried two different ones over the following months. I felt no meaningful difference. I later read something that explained why:
Oral collagen supplements are broken down by digestion into basic amino acids before they reach your tendons.
The amino acids enter the general circulation. The body uses them wherever it decides they are most needed.
Almost none of it reaches the lumbar tendons, and even if it did, the cellular machinery that would use it to rebuild has been shut down since estrogen dropped.