Good question. TGJB had some comments on this a while back. Modern training methods, nutrition and drugs (some legal and some not so legal) have tranformed today's equine athlete into a running machine that can routinely operate at peak levels that were seldom seen in the past. Very similar to the top track and field athletes of today as compared to their predecessors.

The problem with the equine athlete is that all of that power rests on 4 spindly legs that were probably not designed for such repeated high levels of stress.

I guess the bottom-line is that yesterday's horse simply did not run fast enough to bounce. At least not very often. Today's horse can get cranked up to run incredibly fast races even at 2. Races fast enough to overstress the physique and cause a reaction.

At least, this is the theory...

Chris