Large backpacks, used to carry loads over 10 kg (22 lbs), and smaller sports backpacks, usually offload the biggest part of their weight onto padded hip belts. This leaves the shoulder straps mainly for keeping the load in place. This makes it easier to carry heavy loads, because the hips are stronger than the shoulders. It also improves agility and balance, because the load lies closer to the center of mass of the person wearing it.