Carrying your accessories, a drink, or warm clothing when you are out running. The problem was finding a really simple way of carrying things for running (drinks, food, protection, MP3 player, personal effects), with minimum adjustment so that the belongings stay in place in the bag whatever the volume carried (no bouncing around that disturbs the runner), with no straps hanging off the back (might bother the runner and be noisy). The design solution was to use a gusset system, which extends or reduces automatically thanks to the use of elasticised materials around the edges, the elastic band through the bag, and the semi-stiff shell.