All through the ACE personal trainer course, my instructor constantly emphasized maintaining as much of a neutral spine as possible. He also spent a great deal of time on explaining to us what a “delicate yet flexible” system the spine is. From what I know about the spine, like everyone has answered, it has the potential to be affected by pretty much any part of the body. Everything is interconnected, and when you compensate in one area too often, it leads to muscular imbalances and structural deviations in the body. Gymnasts come to mind. Gymnasts have to sort of “side step” along the balance beam quite often. Usually with one foot turned sideways and the other flat behind that foot. If that gymnast favors turning one foot sideways and does nothing to sort of “balance it all out” through training, then it leads to some problems down the road with knee pain and a messed up kinetic chain of mobility.
The spine is just like that. Tight muscles or structural deviations in the body can definitely affect the spine. I think everyone here has great answers that are backed up with experience and facts. So to answer the question, I was taught to encourage neutral spine, and I recognize the importance of neutral spine, so that’s what I encourage with clients.