Back pain from backpacking can start from certain issues. Some veteran backpackers note that one problem is that the upper body tilts back instead of being aligned with the mid-hip and shoulder; the hips also tilt forward in the process. Such overarching induces lower back pain.
The weight of the backpack also has its own way of disrupting your posture. Depending on how much you’ve loaded it, your upper body might lean forward. Klagge said you can counter this by simply carrying only the essential materials in the backpack; tighten the straps to bring the bag closer to your body and ease the strain.