It really is easier than you expect. Some of the more common ones allow players to take their body beyond their natural limits.
Fernandinho being the prime example. The amount of games he played and the amount of ground he covered in 2017-2019 as a 33/34 year old, was unimaginable. It's also the very reason why he's declined so rapidly after that. His body completely deteriorated from the overuse.
I know Dani Alves was another player that was highly rumored to be on PEDs