because your body needs more oxygen
Because the person is tired and it worked its heart so that when the humans heart is beating faster it gets harder to breath.
When exercising, most of the muscles in our body speed up their metabolism. As they run out of energy, the body needs to produce more energy. More oxygen is required to produce the energy needed to...
Your body requires more oxygen for cellular respiration so that you can keep exercising.
your heart beats faster in order to pump oxygenated bloodcells to all of your organs.