(CNN) Since the summer of 2014, Winx has competed in 17 competitive races and won them all, picking up over $9.7 million in prize money.
The five-year-old mare was named Australian horse of the year in 2015/16 -- following in the footsteps of the likes of Black Caviar and Sunline -- and was the world's top-ranked turf horse for 2016.
Hot on the heels of Winx's victory at the Longines Queen Elizabeth Stakes, witnessed by over 25,000 racegoers, equine exercise physiologist Dr. David Evans tells CNN Sport why the horse is so special.
"Winx is the best, of course, and has been acknowledged as the best in terms of almost any point in anatomy and physiology," says Dr. Evans.
"She's obviously got a heart capacity which is far superior. I've studied a lot of good stayers, and they have superior capacity to pump blood and use oxygen in their muscles."
Sired by 2002 Dubai World Cup winner Street Cry, Winx was described as a "supreme athlete" by jockey Hugh Bowman on the back of Saturday's lung-busting win at Royal Randwick.
Winx brought 26,801 racegoers to Randwick, eclipsing the 25,535 who came to see Black Caviar win her 25th, and final, race in 2013.
But heart capacity alone is not enough to propel a racehorse to the upper echelons of the Longines Best Racehorse Rankings.
"Secondly, she will have a larger blood volume," Evans tells CNN Sport.
"Not only has she got a superior heart capacity to pump the blood, she's also got a bigger blood volume relative to body weight.
"Thirdly, she will have efficiency of locomotion; always a very good mover, she's not wasting energy. All the lead stayers will have that attribute."
"Fourthly, temperament," adds Evans. "In these sort of races they have to be able to relax. If a horse can't relax, it's wasting energy.
"Finally, the ability to resist fatigue -- to be able to continue that run and even accelerate at the end. That takes having the right type of muscle fibers, and having those fibers trained so that they resist fatigue."
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"She would have had to be born superior," Evans concludes. "But to be elite, she couldn't just be born that way. The training would have had to be a major contributor to her superiority.
"When you add up all the factors that contribute to superior performance, she will be top or near-top in all of them."