he1Aviator: I concur with rockpecker, I too suffer the occasional back problem - or rather used to. I seem to have less trouble now on average however, protracted flight in turbulent conditions does seem to aggravate any weakness. I paid an awful lot of money some years ago, to get a consultant to give me a once over though I considered being ripped off at the time, I now begin to think I was not.
1. Remove yer wallet to the breast pocket. The bulk on the upper buttock acts as a lever and assists bad posture. [really!]
2. How you plant yer arse in the seat has a direct bearing. Make sure the buttocks are fully in the right angle of the seat with the upper body canted forwards before placing the upper body upright.
3. Ensure flight suit is not too tight around the bum. Sacrifice looking cool for a more roomy fit to ensure adequate blood flow.
4. Quit smoking, smoking has the effect of drying out the liquids around the spine [dunno the technical term] the effect can be seen on MRI scans compared between smokers and non-smokers.
5. When fastening harness and if the harness mounting is lower than the nape of the neck, tighten before engaging inertia reel lock. There is a tendency for people to 'pull' themselves down into the seat otherwise, thus promoting bad posture.
6. Do lower abdomen strengthening exercises.
7. Do not accept aircraft that have a high level of vibration. Not easy I know but the body has a way of responding to every movement imperceptibly and without conscious effort. This tires muscles and leaves you weaker when trying to cope with something more arduous.
Very often it is the physical activity we engage in outside of but related to the cockpit that causes lower back stress. Even if un noticeable, the weakness can be made worse by all of the above to a point where it becomes a problem.
Best Wishes