For example, which recommendations should backpackers follow while carrying heavy weights, and should backpack straps be tightened or loosened?
Some things I learnt from books, occasionally an instructor and from others:
- Pack heavy things close to your body. So do not put heavy things in the outside pocket at the back of your main backpack space. There you can pack your lightest items (walking sticks, for example).
- Pack heavy things on the top of your backpack. This is why you often see people carrying a heavy tent or shoes on the top. If you have light sleeping gear, you can put it on the bottom.
- If you have a lot of heavy things, consider putting some on the sides of the backpack (thus still close to your body).
- Pack your backpack so the weight is balanced left and right; otherwise your spine will be forced to turn to compensate.
- Walk slightly bent over (do not exaggerate), keeping the middle point of force over your feet. This makes your walk more stable, and prevents you being pulled backwards.
- Carry the backpack quite high on your back; this makes the force pulling backwards less high if you bend slightly over.
- Consider splitting your load on your front: carry the most heavy things on your back, but if you have another small backpack, put it on your front. This way there is more balance forward and backward, so you do not have to walk bent over, which is better for your spine, and it prevents:
- Do not carry heavy things in your hand (unless you need them for or during the walk almost continuously).
- (Credits for the remark of Weather Vane, see remark below): When carrying a lot of weight, choose a pack with a broad hip belt that will transfer weight directly to your hips, instead of via the spine. The shoulder straps will then carry less weight, and serve mostly to hold the pack close to your back. (My own addition: afaik the weight ratio is about 2/3 to the hips, 1/3 to the shoulder straps).
- I always tighten my backpack straps quite tight. If the load is moving around, you get every step (small) bumps (thus force) on your back; besides it uses energy (even if it slides left/right and doesn't bump). Especially if you go steep (either up up down), put the shoulder straps slightly tighter; the hip straps should always be kept tight.
The tips in the Keijzers' answer are valid. Some additional comments:
Overall the purpose of loading your pack with weight high/close is to reduce the lean you need to compensate for the change in your centre of mass. In the bad old days you could get packs with a frame that you could extend upward past the top of your head to put the weight higher.
While having weight higher helps you walk straighter, it also makes you top heavy. This can be tricky on rough trails, especially steep descents. I saw a young man stumble a bit, and do a 3/4 forward somersault, landing on his back going down rough screen.
Avoid back problems.
Train. Go for walks with your pack but with a light load. Wear the shoes you will wear. Try for trails that resemble your trip. Increase the weight and distance.
Core strength is key to reducing back pain. Part of the problem is that walking uses your glutes and lower back. These muscles get stronger, but your abs remain the same. Net effect is that the back muscles contract and try to arch your back backward. This hurts.
Abs try to balance this, but weak abs can't balance stronger back.
I get this whenever I restart running. First 6 weeks goes well, then I get back aches. My answer has been to do sit ups and planks. Doesn't take a lot. Getting back to doing a few sets of 20 situps, or a few 30 second planks makes the problem go away.