I don't have the facts and figures but I do recall reading [ a good while ago too ] about Japanese research following yearlings [ weanlings? can't recall which, now ] that were allowed controlled treadmill exercise, as against control groups that had only paddock exercise. The data wrt overall soundness and longevity of careers as against their more sedentary peers was irrefutable.
The value of exercise loading to maintain skeletal integrity is now widely accepted, even to the point of encouraging elderly folk to exercise, rather than sit around with a rug over their knees.
I was sent for a bone density scan a while ago, my usual doc had retired and his replacement thought it was advisable. Off I went and came back to hear the result...which was 100%.
That's amazing, he said, given your age [ !! ] he said. I told him his predecessor had said to me, just keep doing what you are doing, that's the best protection you'll get.
Given the above posts, and the knowledge inherent in them, I'm very surprised that some of the data wasn't produced at that symposium in Holland [ ? ] where there was a real push to have not just two year old racing, but even training, outlawed. Driven by sporthorse folk I believe.
There were several very good trainers who attended, I think Gosden may have been one, and possibly Dermot Weld. But it surprised me that some of this data wasn't produced to support the facts that overall, measured stress is beneficial, not detrimental to a horse's soundness.