Bone strength. Conceptual computer artwork of skeletons lifting weights. This can represent bone strength. Bones are rigid structures built mainly from calcium minerals. They provide structure for the human body, but a dietary intake of minerals is needed to rebuild them. A mineral deficiency, or a bone disorder, can cause degeneration of the bones, as can a lack of load-bearing activities. If the bones are not put under regular strain, the body may start to reabsorb them. Skeletal muscle (not seen) is used to move the bones.