Question

John Likes hiking he observes that whenever he hikes up a hill he breathe heavier than when he is on flat ground which two statements explain why this happened

Answer 1

because when he hikes up a hill he does much more effort than when he walks in flat ground, also the heart beats faster in order to send blood to all his organism

Answer 2

Sensors in the brain detect a lack of oxygen.

The muscles in his body need more energy and therefore more oxygen