Pressure

Two year olds so good they leave the field come along once in a while. The
Doctor Ak-Sar-Ben in mid '80s got his own cap, and Arazi at right came along shortly, and now Overdose. If you've yet to watch the YouTube videos of Overdose, do.
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I was also interested in the Overdose videos because they show more clearly than most the pressure undergone by the front lead leg as the horse motors down the track. Overdose is a bounder, elevates the lead unusually high, and with his speed and effort causes (from the videos) more than normal concussion.

If you have any interest, as you watch the above video focus your attention exclusively on the front lead leg. Initially your reaction will be "so what". Keep an eye directly on the lead as the race progresses. Your reaction will change.

What you see over time in the video is the front lead beating against the track over and over. One or two strides make little impression, but, as you see the multiple beatings on the thin legs, my reaction was to begin to worry. If you look closely you can see with each stride the moment of max concussion. The talented animal both runs fast an is pretty hard on himself, which is even more clear in some of the other YouTube videos.

In this respect I want to imagine a singe bone cell in the cannon of Overdose and imagine what's happening with that bone cell during the race.

The particular bone cell will come from the mature calcified matrix from the mid-interior portion. We'll presume (to the extent we can identify a single cell in this area), that the cell is part of the calcified lattice, i.e. mature, finished calcium crystals surrounding living collagen that is in itself in a particular state of calcifying.

Of particular importance here is the concept of "density" and whether there is any spacing between the crystals and collagen, or whether the material is tightly packed together. We'll assume, in our appropriately trained bone, that the material is dense, tightly packed and without spacing.

The question then becomes what happens to this cell when Overdose repeatedly hits it against the track surface.

Training:
Sun. 8/10: Art does his first post injury exercise. Both horses were trotted riderless with some gallop 6 or 7 minutes. Rod then walked-trotted a mile under tack walking for the second time on the pasture track.
Mon: 8/11 Both horses riderless--mostly play gallop for 10 min with plenty of stops. We're watching the tendon. Both trotted a mile under tack with stops, and Rod did his first trotting in the pasture. Race prep is around the corner. Tendon appears fine.