Backpacks are, simply put, a cloth or leather sack carried on the back and carried with one or two straps that go over the shoulders. Backpacks are usually preferred to other bags for heavier loads for longer time periods since the shoulders can carry the weight better. Large backpacks, those designed to carry over 25 pounds, offload the weight onto padded hip belts, which permits the shoulder straps to stabilize the weight. This permits greater weight loads since the hips are stronger than the shoulders and the weight is closer to the person’s center of gravity. Backpacks, as a word, originated in the United States in the early 20th century and despite other permutations of the word continues to be the most popular term for this type of bag, although backpacks are referred to as packs, particular hiking backpacks.