Question for personal Trainers or marathon Runners!

miffkins

I am doing some research on the cardiovascular system with regards to an extreme activity such as marathon running. If you could answer these as best as you can to your own knowledge and not from the internet that would be great.
Thanks for taking you time to answer these questions.
Sorry if the questions are confusingly written haha

How does the cardiovascular system differ of someone who is of average fitness level than of someone who is a fully trained and consistent marathon runner?

also How does there Lung capacity differ from each others?

Under these extreme conditions (marathon running) how does the heart and lungs work and advance? what happens to blood flow?

miffkins

Bump
Would be great help thanks!