It has everything to do with fit. It is usually the case that if someone has a problem with their pack, the backpack they bought is too big. They think that because it is bigger they can pack more into it and buy more souvenirs. That will just create a higher chance that you will have back problems during your journey that can even become permanent.
To make sure you get the right pack, have the guy at the sporting goods store measure you and tell you the right sized packs for you. Try to put some weight into the bag before trying it on. Some places have 25 lb. sandbags to put in. If they don’t try putting in some heavy rope. The hip belt should rest just above the hip bone. The shoulder straps should be wide enough so that it evenly distributes weight on your chest. They shouldn’t be too wide or they will pinch in the arms or chest. They shouldn’t be too narrow or they will just cut into where they are resting on your chest. You should feel the weight pulling you back and not down. All the weight should be sitting right at your hip. If it’s not then something is wrong. Either you didn’t tighten the straps correctly or the bag is wrong for you. Make sure your hips feel comfortable and that it is easy to move. Fine tune the shoulder straps, load straps at the top of the shoulders, sternum straps across your chest
Checklist before you purchase:
- Shoulder straps aren’t too narrow or wide
- Shoulder straps pulls back with weight
- Inner frame feels solid
- Hip belt sits right at the top of your hips