Backpacks have been used for many years to carry a given load of contents on the back of a user. Modern backpack designs configured to carry moderate to large loads (in terms of weight and/or bulk) usually fall into one of two categories: external frame backpacks and internal frame backpacks. Both internal and external frame backpacks have a waist or hip belt and a yoke. The hip belt is designed to transfer a substantial amount of the weight of the backpack and contents from rigid or semi-rigid supports of the backpack to the hips of the backpack user. The yoke is primarily designed to stabilize the backpack load and more properly position portions of the backpack relative to the user's torso and shoulders. However, the yoke may also transfer a small amount of the weight of the backpack and contents to the user's shoulders, and in certain situations, may alternatively be called on to support the full weight of the backpack and contents without the use of the hip belt.
External frame backpacks typically include rigid, tubular frames (e.g., formed of aluminum or other metals or rigid materials) for supporting the weight of a pack bag. Such external frame backpacks can be particularly useful in securely holding bulky or heavy contents. The frame members of these frames are usually rigidly interconnected by a welded or pinned connection. A load is typically carried inside the pack bag or can be connected directly to the external frame. Pack bags and the like may be connected with the frame by, for instance, stitching a sleeve, loop or pocket formed on the pack bag over the frame members.
One drawback of the rigid frame design is that forces generated by an impact incident on the attached pack bag or the frame itself create stresses that tend to remain concentrated at either (1) the region of impact, (2) in the pack bag itself, or (3) at the associated connection points of the pack bag with the frame. For example, because of the rigid nature and lack of give of the typical external frame under force loading, loads on the pack bag must often generate a high level of tension on the pack bag material before appreciable transferring of the loads to the frame occurs. When an impact is severe, the locations of stress concentration tend to tear or fracture, and because pack bag material is not as strong as the rigid frame material, the bag may rip open and scatter the contents that were held therein.
Some external frame backpacks allow users to attach extra pack bags to the frame as needed. However, these extra bags are often connected via pins or strapping wrapped around the tubular frame members. Such connections are prone to fractures and tearing when the frame is under stress. Another disadvantage of external frame backpacks is the tendency for such packs to be unstable relative to internal frame packs because the load is usually placed laterally farther away from the user's center of gravity, a situation which is exacerbated by the rigidness of the external frame.
Internal frame backpacks generally allow a carried load to better conform to the profile of a user's back so that stresses on the user's body are reduced as compared to load carrying with an external frame backpack. However, the frame components of typical internal frame packs tend to become distorted from their original shape under the weight and shape of the backpack's load. Another disadvantage of internal frame backpacks is that the shape of the pack bag is dictated largely by the shape of the frame. Accordingly, the load side of the backpack often tends to mirror the wearer's back shape which may not be optimum for organizing a load thereon. As a result, internal frame backpacks do not effectively store contents that could otherwise be retained in the backpack. The relationship between the bag and the support members also prevents internal pack bags from being removable and modular. As such, the user is unable to swap a larger pack bag for a pack smaller bag without changing backpacks entirely.
Therefore, current external and internal frame designs lack the ability to form a backpack with modular pack bags or load carriers while also providing a frame structure that conforms well to a user's body profile, efficiently transfers loads to the user's body frame, and is resistant to impact loads incident either directly on the frame or indirectly through components attached to the frame.