A backpack also called bookbag, kitbag, knapsack, rucksack, pack, or sackpack or backsack is, in its simplest form, a cloth bag carried on one's back and secured with two straps that go over the shoulders, but there may be variations to this basic design. Lightweight types of backpacks are on occasion worn on only one shoulder strap.
Backpacks are usually used by hikers and students, and are frequently favored to handbags for carrying heavy loads or carrying any sort of equipment, due to restricted capacity to carry heavy weights for long periods of time in the hands.
Big backpacks, used to carry loads over ten kilograms, also as smaller sports backpacks. Running, cycling, hiking and hydration, typically offload the biggest part up to about 90 of their weight onto padded hip belts, leaving the shoulder straps primarily for stabilizing the load. This improves the possible to carry heavy loads, as the hips are stronger than the shoulders, and also increases agility and balance, since the load rides nearer the wearer's own center of mass.
In ancient times, the backpack has been used as a means to carry the hunter's bigger game and other types of prey and as a way of easier transport for other materials. They were also easy to carry and made of cloths. In the cases of bigger hunts, the hunters could dismember their prey and distribute the pieces of the animal around, every one packing the meat into many wrappings, then into bags which they placed on to their backs. The bag itself could be made up of animal hide and skin and sewn together by animal intestines, which could be woven together tightly to make a tough thread like material.
Backpacks overall fall into one of four categories: frameless, external frame, interior frame, and bodypack. A pack frame, when present, serves to support the pack and distribute the weight of its contents across the body more properly, by transferring most of the weight to the hips and legs. Most of the weight is so taken off the shoulders, decreasing the chance of injury from shoulder strap pressure. Many backpacks equipped exclusively with shoulder straps can influence the posture of a person carrying more than 14 kg, also as being less restrictive of the upper body range of motion. Most backpacks are able of being closed with either a buckle system, a zipper, or a dry bag type closure although some models use a drawstring fitted with a cord lock for the major compartment.
A bodypack is a backpack fitted with one or more pockets that are suspended on the wearer's chest and loaded in such a way that the load in the front and the load in the back are close to equal. The most of the load in a bodypack is carried by the hips. The ideal load carrying system shouldn't disturb the wearer's natural posture, balance and maneuverability. The load must be dispersed onto the skeletal structure in a manner, and shouldn't produce unbalanced forces on the body.