Bones, when stressed, create more bone. Bone cells called osteoblasts create new bone tissue, while cells called osteoclasts destroy it. The hollow interior of the bone expands in specific patterns in proportion to the solid exterior, preventing bones from being overly solid and heavy. Just as muscles respond to a weight training program by creating more muscle mass, bones, too, will create more mass to accommodate the stress. Bone is living tissue, and needs balanced activity to maintain health.
Bone tissue is permeated with blood vessels, lymph channels and nerve branches.
It is surrounded by a thin layer of connective tissue called periosteum that is rich in both blood and nerve supply, and interfaces with ligaments and tendons. Thus, bone is neither solid nor insensitive.