A rucksack’s capacity should be matched by its harness so when it is full it is still comfortable to carry. A bigger pack will have a more structured harness, allowing weight to be channelled to the hips for more comfortable carrying, while smaller packs can have simpler harnesses to reduce weight, complexity and cost.
The human body’s preferred load-carrying point is the hips/pelvis. It is also the most comfortable place to carry loads – anatomically, carrying weight here reduces skeletal stress. This is where a rucksack’s frame comes in: its purpose is to transfer most of the weight to the hipbelt, from where it is distributed to the small of the back and the hips for comfortable carrying. The balance between freedom of movement and pack stability should be able to be adjusted easily.
The primary purpose of the shoulder straps is to stabilise and balance the upper pack. However, in order to maintain the rucksack’s stability some load must be carried on the shoulders. The amount of weight carried on the shoulders should be comfortable, and able to be easily adjusted by the wearer. (This is a personal preference – there isn’t a right or wrong amount, rather whatever is comfortable for the individual.)
A pack’s frame length needs to match a person’s back length so the shoulder straps and hipbelt can be correctly positioned for comfortable carrying. Many rucksacks come in a few different frame lengths for this reason. Fully adjustable shoulder straps will also help to ensure that the shoulder straps and hipbelt are the correct distance apart.
How harness straps contour to an individual’s body also affects the comfort of a pack. To this end, harnesses are often available in different sizes to fit a variety of body shapes. This includes women’s harnesses, with specially moulded shoulder straps and hipbelts to better match the female form.
Some rucksacks can be adjusted while they are being worn. This is useful for tweaking the pack’s fit while on the move without having to stop and take the pack off.