I agree that keeping fit (torso wall) lowers the stress on the back and thus reduces the risk.
... actually most back problems come from a combination of a twisted spine and low left arm (due to poor collective position and often a poor cyclic) interacting with vibration (usually low level and minimised by design for the pilot's seat, but usually present during some of the flight regime). Trying to keep your feet near the pedals doesn't help either. Perhaps of Chief Designers spent a little more time on the ergonomics before fixing the flight control geometry ... and perhaps if there was up-to-date anthropometric data ....
IHMO, having evaluated seats for several projects and with many Test Pilots, comfort and crashworthiness are
completely independent. Indeed the original Simula seat in WS-70 Blackhawk was rated by many as the most comfortable on-site (hats off nick
). The fully armoured, crashworthy design for the A129 LAH project (shows my age) outscored it though, even with the side panels fitted.
A comfortable design
is one of the first aims of a crashworthy seat. The better shape your back is in at intial impact, particularly disk spacing, the better able it is to absorb the shock load. Nick's right, there are loads of 'retired' pilots whose careers should have been much longer. We've many here doing desk jobs ...
I'm surprised that there isn't a better retrofit market for seat installations, given the awful standard of most seats and the fact that pilots (or ex-pilots in management) do tend to a say in buying aircraft and selecting mods.
Nimby