The "natural abilities" you describe are real and, to a great extent,
measurable. For example, one mode we use with TBs is Rate of Acquisition.
Works like this: two horses get the same series of workouts, one of them
benefits greatly, the other benefits a little. Probably has to do with
hormones, or with muscle fiber type ratios, or a dozen other factors. Anyway,
with a heartrate monitor under controlled circumstances, you can measure how
many feet the horse travels per heartbeat at a given submaximal (sub
anaerobic, actually) rate today--say both horses begin at 5.5 feet per
heartbeat. In three weeks of good conditioning, one may have moved to 7.5
FT/BT, the other to 6.2 FT/BT. This Efficiency Score (my invention, but
recently cited in the German AESM proceedings) moves along at a measureable
rate--the Rate of Acquisition--superior athletes (untrained) move along at a
faster rate than lesser animals.
ti