As Orb charged to the wire at Churchill Downs last weekend, he established his clear superiority to the other 18 thoroughbreds on horse racing's biggest stage, the Kentucky Derby.

But compared to Derby champions of the past, Orb's time is less impressive — his 2:02.89 run doesn't rank among the top 10 in the race's history. It is slower than the times of many winners from the 1950s and 1960s, and well behind Secretariat's 1973 record. Blame the muddy track? Fair enough, but none of the past decade's Derby winners recorded a top 10 time either.

This is hardly a Kentucky phenomenon. Among recent Preakness winners, only Curlin in 2007 recorded a time that ranks among the 10 fastest in that race. Recent winning times in the Belmont Stakes were even slower compared to historical standards

Triple Crown thoroughbreds are not running as fast as they used to. And those in the racing industry cite any number of reasons, including lax training schedules, new track surfaces and breeding that stresses short-distance speed.

"In general, American horses have not been as good as in the past, and they have not been as good at the classic distances," said longtime racing writer Andrew Beyer, whose analysis of running times is used throughout the industry. "I haven't seen horses in the last 20 years that deserve to be mentioned in the same breath as Seattle Slew or Secretariat or Affirmed."

The discussions about speed come as Orb — and Baltimore — prepare for the 138th running of the Preakness at Pimlico Race Course next Saturday. The race, annually the largest sporting event in Maryland, drew a record crowd of 121,309 last year, and organizers said ticket sales were up nearly 10 percent with the race a week away.

In the early 1970s, Beyer devised "speed figures" for each race, accounting not only for raw times but for track conditions. Even by those figures, which make it easier to compare races across decades, recent winners of the Derby, Preakness and Belmont have run at speeds below historical norms.

Forty years after he won the Triple Crown, Secretariat still holds the record in each race.

This stands in stark contrast to human performance, where time records fall every few years in running and swimming.

Consider Mark Spitz, who was the Secretariat of swimming, winning seven gold medals at the 1972 Olympics. His records range from 5 to 10 seconds slower than those of Michael Phelps, meaning that by the stopwatch, Spitz wouldn't have even belonged in the pool at the 2012 Olympics.

In running, Jim Hines set a 100-meter world record at the 1968 Olympics. Now Hines' time is no longer among the 300 fastest in history, and the 10 fastest sprints have all been run since 2007.

The question then: Why has U.S. thoroughbred performance in the biggest races stalled?

The explanations are varied and often conflicting. Some analysts say American breeding has focused too much on producing precociously fast 2-year-olds rather than durable racehorses built for the duress of the Triple Crown. In a related issue, some say the genetic pool has become too narrow, with too much emphasis on a few prominent sires.

Others blame modern training, saying the best horses are underworked and too many mediocre horses are pointed toward the Kentucky Derby.

And then there are those who say the whole issue is overblown. These defenders of the modern horse say thoroughbreds are trained to win races, not set time records. Besides, they add, the tracks themselves are kept slower these days because safety, not raw speed, is the chief concern.

"There's an internal debate in the sport about this very topic," said NBC horse racing anlyst Randy Moss. "If you look at most tracks and most stakes times, the fastest times are relatively recent. But if you look at it through the prism of the Derby, the Preakness and the Belmont, it's a different story. And that's partly because of Secretariat, the greatest racehorse of the last 50 years."

On one side of that debate are analysts such as Beyer, who have crunched the numbers and found recent Triple Crown horses wanting.

But Jerry Brown, a statistically minded New York handicapper who founded the service Thoro-Graph, looks at the same numbers and comes to a different conclusion. Brown's studies have found that track surfaces are significantly different than they were in the 1970s, with as much as an inch more cushioning and more sand as opposed to hardened clay.

"It's like they're running in a sandbox," he said of contemporary racehorses.

Accounting for this difference, Brown concludes that many of the most impressive runs in Triple Crown and other races have come in recent years. In fact, a 3-year-old filly named Dreaming of Julia recently delivered the best performance Brown has measured in his 31 years of analyzing races. Orb's Derby run was among the three best Brown has measured in that race.