Use PEDs or born again with different genetic setup.
I have never met a pro who exercise/practice "3-4 hours a day, 5 days a week". But on the other hand, I met a lot of people who say publicly that they practice with such a volume. Why? Nobody will sponsor a pro athlete who train hard 3 times per week and all the other time is "easy/recovery work" and rest. There is huge bias between reality and presentation of the professional athletes.
Of course there are exceptions - I would guess that most of them are freaks or PED users. Even though they cannot admit it. It just does not seems right to say: "I won the gold medal because of lucky genetic and shitload of drugs". The important message is - the huge volume of training is not for everyone - especially if you do not want to sacrifice health or other live aspects.
This is how may really look a training of a professional MMA fighter:
This is how train pro soldiers in reality:
According to the links above: if you cut the marketing bullshits, it seems that professionals does not do the crazy volume that much.
Disclaimer: I met only few professionals in sport or other demanding fields. My answer is based mainly on the stuff they (or their trainers, supervisors) told me personally. So it still can be biased someway.