> actual athletes

Probably need to define. Are we talking about professional athletes or just people who have a lot of training experience?

Exercising hard for a person who has never trained is very different than someone with years under their belt training. An untrained person can't even tap into what hard means compared to a trained person.

I'm also confused about the focus on endurance. Yes, all people need some cardio, but everyone would do better with additional strength. The stronger someone is going into their 50s, they better they will end up in the 60s and 70s.