Reclining seat has higher ultimate G tolerance for the pilot if he is just looking forward, but that typically results in the pilot sustaining higher Gs while trying to turn his head. This commonly blows out a cervical disc or in severe cases can either fracture vertebrae or cause a weird spine dislocation waaay up in the neck. Not good.
F-15 pilots typically see lower or mid back injuries because unlike the F-16 pilots who simply turn their heads when under Gs, the F-15 pilot leans forward a bit, twists at the waist, and then braces a shoulder against the seatback and leans against the side of the canopy. That puts the strain on the lower and middle back. Neck strains are still common in the F-15 but the permanent damage is in the lower back vs. the neck.
I think I probably blew out my L5-S1 disc pulling as low as 6 to 6.5 Gs. I was strong enough to move around quite a bit at up to 6 Gs so I didn't unload as much as I should have before moving/twisting around in the cockpit. At the time of the injury I was also pulling up to 8.5 Gs while looking forward and up to 7 or 7.5 while already twisted around looking backwards, so I don't really know exactly when it happened. I just noticed symptoms when I moved from one base to another since loading/unloading my stuff probably aggravated it, and then it just gradually got worse over the next 7 years flying high performance fighters and trainers. I've had one surgery and have been told by 3 surgeons and a pain management specialist that it will never get better and will always hurt and restrict my lifestyle. Further surgery has 1/3 chance of making it better, 1/3 chance it won't change anything, and 1/3 chance it could make it worse or cripple me completely.
