Based on some of the other comments on this string, I wanted to clarify and expand on what I had written previously.

Modern methods (e.g., better training routines, nutrition and drugs) enable a horse (even a slow one) to get the maximum effort possible out of its natural physique (whatever that might be). This type of effort will stress the horse much more than the less-than-maximal effort that was typically acheived under "old-fashioned," "hard-boot" training methods.

An analogy might help make this clearer. I could decide to take up power lifter using "old-fashioned methods" and I would get stronger but not nearly as strong as I would if I used modern methods (e.g., modern training routines and equipment, nutrition and drugs).

Using the old methods, let's assume that I might be able to eventually peak out at a bench press of 250 lbs, which would be stressful but probably would not be pushing the limits of what my joints and ligaments, etc. could handle. I could probably repeat my peak "max lift" several times a week without much recovery time required between efforts.

Using the new methods, I might be able to eventually peak out at 350 lbs, maybe more, which would be much closer to stress levels that are likely to damage joints, ligaments, etc. I might need weeks, months, or years between peak efforts at such a high level or I may not ever be able to repeat the peak performance due to some sort of major injury. In general, the recovery period is likely to be much longer between peak efforts using modern methods than it would be using the traditional methods.

Now take a good look at thoroughbred's legs and make the analogy-replacing running at max speed with power lifting.

Then maybe it starts to make a little more sense...

Chris