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Running improperly provides a painful lesson in the biology of bones

No one seeing the ring of fat decorating my middle would take me for a runner. Only in my memory do I get up with the robins, lace on my running shoes, bounce out the front door, and run the streets of University City for an hour before going to work. Now my 5 K runs are twenty-year-old memories. Any mention I make of my running in a race only evokes screams of laughter from my daughters, and an arch look from my wife. Memory is cruelest when it is accurate.

I remember clearly the day I stopped running. It was a cool fall morning in 1978 and I was part of a mob running a 5 K (that’s five kilometers for the uninitiated) race winding around the hills of Clayton. I started to get flashed of pain in my legs below the knees -- like shin splints, but much worse. Imagine fire poured on your bones. Did I stop running? No. Like a bone head I kept going, “working through the pain,” and finished the race. I have never run a race since.

I had pulled a muscle in my thigh, which caused part of the pain. But that wasn’t all. The pain in my lower legs wasn’t a shin splint, and didn’t go away. A trip to the doctor revealed compound stress fractures in both legs. The X-rays of my legs looked like tiny threads had been wrapped around the shaft of each bone, like the red stripe on a barber’s pole. It was summer before I could walk without pain.

What went wrong? Isn’t running supposed to be GOOD for you? Not if you run improperly. In my enthusiasm to be healthy I ignored some simple biology, and paid the price. The biology lesson I ignored had to do with how bones grow. The long bones of your legs are not made of stone, solid and permanent. They are dynamic structures, constantly being reformed and strengthened in response to the stresses to which you subject them.

To understand how bone grows, we first need to know a bit about what bone is like. Bone is made of fibers of a flexible protein called collagen stuck together to form cartilage. While an embryo, all your bones are made of cartilage. As your adult body develops, the collagen fibers become impregnated with tiny needle-shaped crystals of calcium phosphate, turning the cartilage into bone. The crystals are brittle but rigid, giving bone great strength. Collagen is flexible but weak, but like the epoxy of fiberglass, it acts to spread any stress over many crystals, making bone resistant to fracture. As a result, bone is both strong and flexible.

When you subject a bone in your body to stress -- say, by running -- the bone grows to withstand the greater workload. How does the bone know just where to add more material? When stress deforms the collagen fibers of a leg bone, the interior of the collagen fibers becomes exposed, like opening your jacket and exposing your shirt.

The fiber interior has a minute electrical charge. Cells called fibroblasts are attracted to the electricity like bugs to night lights, and secrete more collagen there. As a result, new collagen fibers are laid down on a bone along the lines of stress. Slowly, over months, calcium phosphate crystals convert the new collagen to new bone. In your legs, the new bone forms along the long stress lines that curve down along the shank of the bone.

Now go back twenty two years, and visualize me pounding happily down the concrete pavement each morning. I had only recently begun to run on the sidewalk, and for an hour or more at a stretch. Every stride I took those mornings was a blow to my shin bones, a stress to which my bones no doubt began to respond by forming collagen along the spiral lines of stress. Had I run on a softer surface, the daily stress would have been far less severe. Had I gradually increased my running, new bone would have had time to form properly in response to the added stress. I gave my leg bones a lot of stress, and no time to respond to it. I pushed them too hard, too fast, and they gave way.

Nor was my improper running limited to over-stressed leg bones. Remember that pulled thigh muscle? In my excessive enthusiasm I never warmed up before I ran. I was having too much fun to worry about such details. Wiser now, I am sure the pulled thigh muscle was a direct result of failing to properly stretch before running.

I was reminded of that pulled muscle last weekend, listening a good friend of my wife’s describe how she sets out early each morning for a long run without stretching or warming up. I can see her in my mind’s eye, bundled up warmly on the cooler mornings, an enthusiastic gazelle pounding down the pavement in search of health. Unless she uses more sense than I did, she may fail to find it.

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