Question

What happens to the rate of breathing during vigorous exercise and why?

Answer 1

breathing rate becomes faster as for respiration oxygen is needed and during exercise the amount of oxygen in our body becomes less so breathing rate becomes faster so as to fulfil the requirements of oxygen in our body.

Answer 2

during vigorous exercise or any physical work, our body need more and more energy to do that work. for this more and more food need to be utilised by our cells of body to release energy and for this break down of food to release energy(respiration) more oxygen is needed, because respiration in our body can take place only in presence of oxygen. so to get oxygen, we breathe more and more.
so during vigorous exercise, our breathing rate increases.