Augustus
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It was later on (though that's wider spread than we pretend, with tons of chemical enhancers not even banned) but he still had extremely large, record breaking lung capacity, hyper efficient heart and low resting pulse, and other innate advantages. As do all the 'dominating' record holders.
He actually had no natural physiological advantages over other professional cyclists.
Dominating record holders tend not to have any physiological metric that separates them from their elite peers.
Such things help you to become an elite athlete, but they don't predict which elite athletes will win.
It's like being 7ft tall makes it more likely you will play in the NBA, but once you compare NBA players height doesn't dictate which one will be best.