specific heart measurement alone.
This same physiological trait has been documented in both elite Thoroughbred and Standardbred racehorses, says Sleeper. That may be due to the similar nature of their sports, she says. “I expect that in any of the sports that require significant cardiac output---for example, polo, racing, endurance or jumping ---the horse with a big heart will probably have an edge, especially at the upper levels. Athleticism comes from a lot of different abilities, though. It is probably less important for a dressage horse to have exceptional cardiac output, although their balance and suppleness must be excellent for them to excel.”
Whether these elite athletes are born with this specific trait or whether training produces it is unclear, says Sleeper. “There are definitely theories that it is genetic, and there is some evidence as well---with lots of popular legends.