Aim: To investigate how exercise affects heart rate.
             Introduction: The heart is rate is how many times the heartbeats in a certain period, normally a minute; this gives the unit bpm (beats per minute). During rest, the heart beats about 70 times a minute in the adult male, while pumping about 5 litres of blood. The heart rate is affected by many things these included;
             Heat Rate The body senses the need for an increased pulse rate through two main mechanisms. The first is a series of baroreceptors (these are specialized cells that can sense the pressure of the blood). These cells are in the carotid sinus. The carotid arteries are the major blood vessels that feed your brain; there is one artery on each side of your head. The baroreceptors in the carotid sinus can tell when the blood pressure is low (thus, not enough blood is making it to the brain). They then send signals over nerves to the heart, telling it to speed up and contract more forcefully. This raises blood pressure. Since the brain is the most important organ, it makes sense that these baroreceptors are in the blood vessels feeding the brain.
             The second major way is by our brains sensing danger or excitement and telling the heart to speed up. This is called the fight or flight response. If we see some danger (like a saber-toothed tiger) approaching us, our brains get excited and tell the heart to speed up so we will have enough blood flow to allow us to run away.
             In addition to the nerves that transmit signals from the brain to the heart, some nerves go to the adrenal glands and tell them to secrete adrenaline, a hormone that makes the heart go faster. This way, if there is a problem with the nerves from the brain to the heart, the message to the heart can still get there by way of the adrenal glands (which are located right next to your kidneys). The adrenal glands stimulate the heart by making adrenaline.
             I predict the harder the subject exercises, th...