Why is it so hard for a horse to win the triple crown?

Question

Why is it tough for a horse to run three ~1 mile races within 5 weeks to win the triple crown (Kentucky Derby, Preakness, Belmont)?

Perhaps I don't understand horse physiology verse human physiology but why is this the case? Humans can run many miles per day while training and/or can run a 1-2 mile race once or twice a week (well, my friends did in HS for track and field).

EDIT: Here's an article that shows the owner complaining the field was stacked with fresh horses against his "tired" horse but again, for a horse to run three 1 mile races in 5 weeks, fatigue shouldn't be an issue unless I'm totally off regarding horse vs. human physiology.

http://www.usatoday.com/story/sports/horseracing/2014/06/08/california-chrome-belmont-stakes-triple-crown-steve-coburn-angy/10196373/

Answer 1

The 3 races in 6 weeks isn't the issue. While some horses will race only in one race - particularly the Derby - most of them are racing all three unless they get hurt.

Instead, there are several contributing factors making it harder to win the triple crown.

• The three races are of different lengths, meaning different horses will run them differently. The Belmont is 1.5 miles, while the Kentucky Derby is about 1.25 miles, and the Preakness is in between (1 3/16ths mile). That seems like a small difference, but it does matter - and human racers definitely see differences between a 50 meter dash and a 100 meter dash, at least, if not quite that small of differences.

• Even if the races were identical, each race has a different number of horses, horses start out at a different spot in each race, and weather conditions may vary how a horse performs at each race.

• Finally, you have the problem of repeatedly winning a race. Unless a horse is far superior to all of the other horses out there, it's very hard to win 3 consecutive races, beating the same field (roughly) three times. It's the same reason why golfers rarely win the single-year grand slam - you have to be perfect four times, and it's very hard to do that. Even a horse who (by himself) had a 75% chance to win each race, which is far more than nearly any horse is considered to have in any given year, that's 3/4*3/4*3/4 or 27/64ths to win all three - under 50%.