Rucksacks are load carriers, so must be selected based on the weight and volume of said load. Lightweight loads can be accommodated in a simple frameless rucksack – perhaps with a stiffened backpad and simple hipbelt – but once weight reaches about 10kg some kind of frame will be appreciated. This frame should transfer the weight of the load from the weak muscles in the shoulders to the waist to take advantage of those large leg muscles which are also closer to an adult’s centre of gravity. External frames have been largely superseded by internal frames, usually of flat aluminium bar but occasionally a…