The floor
You must be able to walk 8km comfortably, jog 400m if required, and stand for four hours without stopping. That is the operational baseline.
The programme to reach it
Two 30-minute walks daily, three bodyweight strength sessions per week, one mobility session. Six weeks to visible improvement.
Joint and back protection
Proper boots, deliberate posture on static shifts, hip-mobility work, avoidance of prolonged one-position standing. Small daily habits, big career-length payoffs.