system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If not steroids/PEDs, how do we continually set world records in running, swimming, etc.?

I understand the basic idea that we can run faster today in the 100M or swim faster than 100 years ago or 50 years ago because of improved techniques, nutrition, better training and sports science, etc. But at a certain point and time, it would seem that we have hit the fastest time possible, unless a super human specimen is born tomorrow that trumps everything.

So barring the ubermensch, how can we break some records from the very recent past by a few SECONDS? Are we really still improving sprinting and swimming technique and training methods that much? If not, how is it that the gifted athletes of today are just better than previous gifted athletes? Or is the answer, just the obvious steroids/PEDs are better and more potent now than even 5-10 years ago?
gpt
* Better health and nutrition worldwide means that a greater fraction of the population is able to live up to their genetic potential.  100 years ago, Michael Phelps might have gotten polio or barely survived a famine.  

* A more developed, mechanized world means a greater fraction of the population is wealthy enough to spend the time become an Olympic athlete.  100 years ago, Michael Phelps might have been working 18-hour-days as a farm hand.  

* A larger world population gives us more chances to roll the genetic dice and get lucky.

* And finally, even if nothing had changed, sports involve a lot of random chance.  Every time we hold a new Olympics, there's a new chance for someone to get even luckier than before.