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Turning on the television, I inhale deeply as the Olympic marathoners stride across cities to compete for their shot at a medal. As an exercise physiologist, I find all athletes particularly amazing. These men and women devote themselves to their training, pushing for just one more mile with each run. That extra mile provides a sense of accomplishment, but it also strengthens bones with every step taken.

Bone is not a solid block of calcium: It’s a three-dimensional spider-web-like lattice filled with bone cells and fluid containing calcium, phosphate and other nutrients needed by bones. High-impact activities like running compress bone, moving fluid throughout the lattice and increasing the flow of calcium into the cells in the bone. Certain cells in the bone called osteoblasts use the calcium to form new bone material. More calcium entering the osteoblasts means more bone is formed, and the bone becomes denser and harder to break.

A recent study found that not only did running make bones denser, but bone density increased with the distance ran. Researchers in exercise and sport physiology went to the Rock ‘n’ Roll Madrid Marathon and Half Marathon and measured the bone stiffness—which represents a bone’s mineral composition and density—of the marathoners, half marathoners and 10K runners participating in the race. The researchers found that all the runners had stiffer bones than individuals who were sedentary. What was interesting though was that the farther the participants ran, the denser their bones. Longer-distance runners who regularly ran 28 to 33 miles per week had stiffer bones than shorter-distance runners who ran 17 to 24 miles per week. The study also showed that both the male and female runners had greater bone density, suggesting that running is a universal builder of bones.

Increasing and maintaining bone density is important as we age because our risk for osteoporosis—a condition when bones become weaker—increases. On your next run, go that extra mile. Your bones will thank you.

Jessica C. Taylor, PhD, is an assistant professor of physiology in the College of Osteopathic Medicine at William Carey University in Hattiesburg, Miss.