Images: Beautiful horses get spruced up, ready for Kentucky Derby

There is no doubt about the preferred running style of American Pharoah, the probable Kentucky Derby favorite. He is a speed horse who has passed only one rival in his career. He led all the way to score three straight victories, then won the Arkansas Derby after sitting second behind a front-runner and shooting past him in midrace.

Will this style help him or hinder him on Saturday?

In the 140-year history of the Derby according to Churchill Downs' statistics, horses have led from start to finish 22 times. Like many Derby statistics, these numbers may be deceptive, because long-ago races are much different from those the modern day. In contrast to the era of, say, Citation, who beat five rivals in 1948, owners and trainers are now so obsessed by the Derby that the race almost always draws the maximum number of entrants. In every year since 2005, 20 horses have been entered and at least 19 have run. These bulky fields affect the dynamics of the race.

With 20 in the starting gate, it is almost certain that a few of the entrants will be speedsters. Their jockeys have to hustle early to secure a good position by the time they reach the first turn. So the early pace of the Derby is usually fast, putting pressure on the leaders. Sometimes, it is so extraordinarily fast that every horse near the lead falters. In the fast-paced 19-horse Derby of 2013, won by Orb, the horses running 1-2-3-4 after a half mile finished 12-14-19-18.

In the postwar period, there have been 21 Derbies with a field of 19 or more starters, and no horse has led all the way in any of them.

No front-runner has won the Derby since War Emblem beat an 18-horse field largely devoid of speed in 2002.

This is not to suggest that fast horses are unable to win modern-day Derbies. Unless a superfast pace creates a made-to-order scenario for them, come-from-behind runners have problems of their own, for they can be impeded by the heavy traffic in a big field. The Derby is often won by a horse quick enough to secure a position stalking the leaders. Big Brown was a fast front-runner when circumstances demanded, but in the 2008 Derby he sat in sixth place, about three lengths behind the pacesetters, until he moved to victory. Barbaro, another very fast colt, won with a similar trip in 2006.

Based on ample historical evidence, the lesson for front-runners like American Pharoah is this: They can win the Kentucky Derby, but only if they are able to conserve some of their natural speed.

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