There are 206 bones in your body, from the large, thick femur that spans the length of your thigh to the tiny, thin stapes, a stirrup-shaped bone that transmits sound inside your ear. Your skull alone has 22 bones (my mother always told me I have a hard head!).
Bones serve a number of important roles. They provide shape to our bodies, cause movement as muscles pull on them, support and protect internal organs, store minerals, and produce and store red and white blood cells in the marrow that fills bones’ many cavities. And, like muscles, bones get stronger when you give them stress.
BONE ARCHITECTURE
Although we think of bones as hard, solid structures, it depends on what part of them you’re talking about. There are three different kinds of bone tissue: hard compact tissue, which comprises the exterior of bones, spongy cancellous tissue, which comprises the interior of bones, and smooth subchondral tissue, which lies at the ends of bones and is covered with cartilage. These tissues comprise four different kinds of bones: long bones, such as the humerus (funny bone) in your upper arm, short bones, such as the cuboid and navicular in your foot, flat bones, such as the occipital bone in your skull, and irregular bones, such as the vertebrae in your spine.
BONE GROWTH
Like a fickle home owner who can’t decide if the kitchen should be remodeled in Asian fusion or art deco, bones are constantly remodeling themselves. Bone cells called osteoclasts remove small areas of old bone (called resorption) and other cells called osteoblasts synthesize new bone in its place (called formation). This cyclic process of bone resorption and formation occurs throughout your life, with formation exceeding resorption until about age 30, when your bone mass peaks. During your 30s, resorption begins to exceed formation, with bone mineral density (BMD) decreasing by about one percent per year.
BONE HEALTH
As a runner, you’re already doing great things for your bones. Research has shown that people who participate in sports involving running and jumping—soccer, running, basketball, and volleyball—have greater BMD compared to non-active people and even compared to people in non-impact sports, such as swimming, cycling, cross-country skiing, and rowing. Research has also shown that tennis players have greater BMD in their playing arm compared to their non-playing arm, suggesting that the effect of forceful muscle contractions alone is enough to increase BMD. While athletes have greater BMD, it’s hard to say that exercise is its cause since research has shown that BMD increases by only 1 to 2 percent in response to a training program. It’s possible that people with genetically denser bones are more likely to participate and succeed in sports that are stressful on the skeleton.
