It has been 41 years since Secretariat dominated the competition to win Kentucky Derby on the way to winning the Triple Crown.
Since then, no horse has run faster at Churchill Downs and only a couple of horses have even come close to Secretariat’s average speed of 37.7 mph at the Derby. Meanwhile, humans keep getting faster.
If we compare the winning speeds of the Kentucky Derby and the men’s 100 meters at the Summer Olympics, horses and humans showed a similar rate of improvement over the first seven decades of the 20th century. After a brief regressing in the 1970s by humans, speeds have once again been increasing at a steady rate over the last 30 years while horse speeds have remained relatively unchanged since the 1960s.
If the fastest humans can continue to show a rate of improvement similar to the last 30 years (unlikely), they will be as fast as the fastest horses in abut 300 years.
There are several reasons why horses have stopped improving and humans have not.
Usain Bolt is 6-foot-5, muscular, and would dwarf sprinters from the past. Meanwhile, thoroughbred horses today are no bigger than horses 50 years ago.
In addition to shoes, which have become lighter while also improving the traction between the foot and the track, humans have gone from running on gravel tracks to the hi-tech vulcanized rubber track used at the 2012 Olympics designed specifically to “maximum energy return for the athlete” and make runners faster.
While maintaining horse tracks has improved, horses are still running on dirt or grass.
With the specialised breeding of race horses, most thoroughbreds today are being produced from the same gene pool. Without introducing new genes into the lineages, most horses now are going to have similar physical traits and abilities to generations before.
If the average horse is not changing it limits how far the extreme cases can deviate from that group in terms of speed.
In the end, the combination of factors has allowed humans to keep getting faster while horse speeds have stopped improving.
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