Your Tough, Growing Bones

Did you know that your leg bones could hold a force of one ton without snapping or bending? (Don't try this at home!) Your bones are tough and strong. Bones have to hold you up while you run, jump, skip. Bones are almost as tough as cast iron, but a lot lighter, of course! That's why it's been so tough to design artificial replacements for bones.

Bones contain collagen, a tough protein fiber. Collagen comes from Greek words meaning, "glue forming." Mineral salts are on the collagen making it very strong. Calcium and phosphorus are packed tightly. Seventy percent of an adult's bone is made of minerals. The remaining percentage is made of organic matter. Babies' bones have reversed proportions.

Your bones are hard and firm, so they don't stretch or bend. So how do bones grow? Your skull grows slowly. Long bones grow more rapidly. The bones of your arms and legs grow faster than the bones of your trunk.