I would be shocked. Randomised, controlled trials are difficult and expensive.
You need enough subjects.
First problem: how many advanced and elite athletes are there? Not many.
Second problem: how many have coaches who are happy for you to experiment on their charges? Not many.
Third problem: given the small samples, how do you control other factors such as diet and sleeping patterns? With great difficulty.
Fourth problem: funding the dream trial. Most research money is public money, and "give us money to find out how to make healthy adults run slightly faster so we can win an extra medal every 4 years" is a pretty difficult ask next to research into helping sick folk.
There's a reason that a great deal of sports science still relies on research done in the eastern bloc throughout the cold war. Totalitarian societies had the conditions and the motivation to set large, serious experiments up, and they did.
In general though, progress occurs through a cut down version of science. Coaches observe, hypothesise and tinker. Scientists do small studies; the studies compound or refute each other. Over time rough consensus emerges about what works and what doesn't. Things that don't work disappear quickly. Meanwhile, unseen, population effects muddy everybody's waters.
Is it the fully dressed version of science we demand from physics or medicine? It is not. But it's what we can reasonably expect.
> how do we know these types of studies aren't happening right now in other countries that have more lax ethics in science?
The one truly totalitarian society left, AFAIK, is North Korea; they might be doing this.
But pretty much the easiest strategy for a centralised sports system is to just throw bodies at sports until the normal distribution gives you winners. The Chinese are finding that this works well for them.
