That is called aerobic exercise.
Your pulse rate increases when you exercise because your heart is pumping faster. Your heart is trying to provide your tissue with more oxygen as your muscles will require more oxygen when you're being active.
As you exercise, the muscles need more oxygen to work. The heart beats faster to get the oxygenated blood from the lungs to the muscles. The harder you exercise, the more oxygen the muscles need, the faster the heart beats.
It increases because your body needs blood and oxygen pumping around your body more. This is because the muscles in your body have been used more and therefore needs more oxygen
Aerobic exercise
As we exercise, we use our muscles. Our muscles need oxygen to function. Therefore, the more we exercise, or the harder we exercise, the more oxygen we need. In order for our muscles to get that extra oxygen, we need to breathe more. The oxygen then enters our blood and our hearts beat stronger and faster in order for the oxygen to reach the muscles as quickly as possible, thus why our blood pressure increases.
Exercise increases the heart rate, because the blood has to supply additional oxygen to the muscles.
The reason my heart beat changed is because when you exert your muscles they need extra oxygen so your heart beat increases to pump the requires oxygen amount to the muscles. So by running up and down stairs (or running on the spot as I have no stairs) you require more oxygen for your muscles. When you stop working your muscles they don't need the extra oxygen so your heart stops pumping the blood so fast around the body which then slows down your pulse to what it was to start with.
because you need more oxygen to be delivered to the muscle and more waste to the lungs. when you are exercising your muscles need oxygen so the blood stars pumping faster to get the oxygen to the muscles.
when you exercise, the heart rate increases, (as does your breathing pace), so that more oxygen can be carried in the blood to your muscles. The more intense the exercise, the more your muscles have to work, so more oxygen is required and your heart rate will increase. The quicker you heart rate returns to normal, the better your fitness.
because most of the muscles needs oxygen and glucose
Every time you exercise you use up more oxygen which is carried around your body in your blood. Your heart rate goes up meaning your heart is pumping faster to get more blood and oxygen around your body.
The more you exercise - the more oxygen your body's muscles need. In order for your heart to supply more oxygen - it must beat faster.