Wednesday, February 17, 2010

Updating the mechanostat theory

Zydrunas Savickas is the athlete pictured above.  You can see a bruise on his left forearm.  Perhaps a hematomma from a microfracture.  I couldn't find a good image of Zydrunas Savickas in stationary mode to compare his bone length in performing the farmers walk versus stationary.  If the loads that a multi-time strongman champion are not enough to provide a measurable increase in bone length then that does not bode well for the rest of us.

Strongman is the sport with the greatest potential to cause microfractures.  Exercises like the shield carry, farmer's walk, and the refrigerator carry are high impact, high load exercises that have the potential to cause cortical bone microfractures.

The extremely large muscles of most strongmen competitors makes it hard tell exactly how their bones have adapted to the stress placed upon them.  That's exactly the problem with the mechanostat theory at present.

The microstrain graph is vague.  Bone Density can increase in the following ways: size, BMC, and porosity.  Bone Mineral Content can be induced by chemical means so it's logical to assume that it's threshold to induce that method of adaptation is lower.  Periosteal width is not directly inhibited such as how growth in the long bones are inhibited so at some amount of chemical and mechanical theory periosteal growth is induced.

Trabecular microfractures occur before cortical microfractures.  The definition of the fracture point by a mechanostat model is when maximum deformation is exceeded.  Cortical microfractures should occur before then as when you're breaking a pencil when you bend their is a microscopic denaturing(change in the pencils shape) before the pencil finally snaps.  So here's what needs to be added to the mechanostat model:

At 1500 microstrain is probably where Bone Mineral Content begins to increase as that is the easiest form of bone adaptation.

Other points needed on the graph:

X1: Point where Trabecular microfractures begin to occur
X2: Point where periosteal width increases(although the periosteum is not likely to increase in width as a result of the pulling apart of bones it is possibly that the periosteum will increase in width as a result of impact which does temporarily change the length of the bone)
X3: Point where Cortical Microfractures occur

What good is knowing the bone modeling range if we don't receive data on when a specific form of bone modeling(cortical microfracture healing) to increase height occurs?

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