text: why does my pulse accelerates when i run ? i want to know why if a person runs very fast his pulse will be faster than the one that walks.i need a quotation. when you are running your muscles are working harder than they usually do.  when your muscles are working harder than they usually do they require more oxygen, which is their fuel.  oxygen is supplied to the muscles via your blood stream, which is sent through your body by your heart.  the heart is beating faster to get the oxygen rich blood to your muscles as fast as possible.