How Strength Training Improves Bone Density
By: SPARTA
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June 5, 2008 | Filed Under (Exercise Science, Strength Training) |
Ken (a very spry 70 year old) asked me, “How does strength training increase bone density?”
Well, the basic mechanism is very simple: Think of your skeleton as the framework of the body, the base upon which the body is built. Load up that framework with weight, and the body, being that dynamic organism it is, makes the framework stronger. Certainly an explanation you’ve heard before from your doctor, your trainer, or your media talking head of choice.
Here’s the implied but rarely mentioned “twist” that makes this all possible: Your bones are alive.
Not in a Night of the Living Dead creepy sort of way, but alive just like the rest of your body’s cells are (save hair and some skin cells). Bone isn’t some inorganic matter like the 2 X 4s in your bed frame or the piping under your kitchen sink. It’s a dynamic, ever-changing organ, constantly building and breaking itself down.
Cells called osteoblasts and osteoclasts work 24-7 at reshaping and remodeling your bone structure (even after you reach full adulthood). Load a bone with a heavy weight, and osteoblasts lay down new bone tissue to reinforce the points of stress, much like a young beach-going lad would add more sand and water to reinforce a wall of his sand castle. Repetitively load a bone in the same way, and you make that bone stronger by stimulating osteoblast activity, over and over again. Over time, these osteoblasts lay down so much new bone tissue that they trap themselves in it, becoming osteocytes (which always remind me of this). Not to worry for our osteocytes, however; they continue to chug away and do their job of reinforcing bone in a less…mobile…fashion.
Osteoclasts have a less celebrated but equally important role: They break down bone tissue by acidifying the bone matrix, releasing its constituent minerals into the bloodstream. Now, why would a fine, upstanding cell like an osteoclast want to do something like break down bone tissue? Well, low levels of calcium ions (one of the main minerals in bone) would be one reason. Calcium ions feature heavily in intracellular function, from DNA transcription, neurotransmitter release, and (most importantly for our discussion) muscular contraction. If you don’t have enough calcium available, the body simply draws from its calcium stores, and the largest calcium stores in the body? You guessed it: Bone.
(Aside: Why are osteoclasts always depicted in mechanism diagrams as goofy-looking Metroids?)
Without going into the ridiculously complex and numerous mechanisms for osteoporosis, let’s just say for brevity’s sake that you want to stimulate osteoblast activity, not osteoclast activity. And strength training just happens to be a fantastic tool for doing just that.
And now, you know why.

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