I make two 320 mile return journeys to Cornwall twice a month. My legs, knees and lower back crease me unless I stop and stretch....a right pain I know 'cos it adds time to the journey, and probably not that easy in an aircraft. (Was once directed to
Charnock Richards by 121.7 but that's another story
)
A short swim prior to traveling also seems to help. Mechanical back pain is a pain, no real magic answer other than avoidance, movement etc