Which is why when I went hiking, I attached a couple of home-made carriers to the front straps of my rucksack. One to carry a water bottle, and the other to carry a camera. Having some of the weight on the front (rather than all of it on the back) helps. There's (quite old now) research that shows that people in Africa who carry immense loads on their heads actually have a more efficient walking gait than people who carry loads on their backs.
