Why is it dangerous to just 'stop' exercising to take your heart rate?

Answer 1

I wouldn't say it is "Dangerous", just not a good idea. The idea of aerobic exercising is to keep your heart rate at a constant pace for 20 to 30 minutes. When you stop to take your heart rate, your heart rate goes down(contributing to not getting an accurate reading of your heart rate.) Also, after you have finished exercising, you should cool down, because changing your heart rate drastically can be bad for you, because it suddenly changes the amount of oxygen you need, or something like that. Marge answered it better. Read the other question in this section titled "Why would your legs shake badly after exercise?" I thought her answer was good.

While exercising, for example jogging, the muscles of the leg help blood return to the heart and lungs (venous return) as they contract around the veins, aiding by squeezing the blood through. While exercising the body requires a certain amount of oxygen delivered to the body at a specific rate for that exercise. If you suddenly stop exercising, venous return is slower as the muscles are no longer helping with the 'squeeze'. Now the heart and lungs can not provide the blood and therefore oxygen to the expectant muscles and head at the required rate. The DANGER is that the jogger may become dizzy, black out, fall over and hit their head etc.

In addition to the previous response, blood tends to pool around your extremities when the heart slows down too quickly. This may also lead to lightheadedness, similar to what you feel if you stand abruptly after a long period of sitting.