The Effect of Exercise on Heart Rate

Introduction

The heart is the organ that works as a pump to circulate the blood around the body. It is a four-chambered double pump that is the centre of the circulatory system. It is located between the two lungs and slightly to the left of centre. The heart consists of several layers of a tough muscular wall, known as the myocardium. A thin layer of tissue, called the pericardium, covers the outside, and another layer, the endocardium, lines the inside. There are two chambers in the heart. The upper chamber is called an atrium or auricle, and the lower chamber is called a ventricle. The two atria act as receiving chambers for blood entering the heart. The more muscular ventricles pump the blood out of the heart. Blood is a fluid substance that circulates in the arteries and veins of the body. Blood is bright red when it has been oxygenated in the lungs and flows into the arteries. It becomes a bluish red when it has given up its oxygen to take part in respiration. In the lungs, the blood gives up the carbon dioxide wastes it has taken from the tissues, receives a new supply of oxygen, and begins a new cycle. This movement of blood is produced by the synchronized activity of the heart, lungs, and blood vessels. It delivers glucose and oxygen to the muscle cells allowing respiration to take place.

The heart, although it is a single organ, it can be considered as two pumps that circulate blood through two different circuits. The right atrium receives venous blood from the head, chest, and arms through the large vein called the superior vena cava and receives blood from the abdomen, pelvic region, and legs through the inferior vena cava. Blood then passes through the tricuspid valve to the right ventricle, which pumps it through the pulmonary artery to the lungs. In the lungs venous blood comes in contact with oxygen from inhaled air and loses carbon dioxide. Oxygenated blood is returned to the left atrium through the pulmonary veins. Valves in the heart allow blood to flow in one direction only and help maintain the pressure required to pump the blood. The pumping of the heart, also known as the heartbeat, is caused by constant contractions and relaxations of the myocardium. These contractions are stimulated by electrical impulses from a natural pacemaker, the sinoatrial, which can be found in the muscle of the right atrium. An impulse from this causes the two atria to contract, forcing blood into the ventricles. Contraction of the ventricles is controlled by impulses from the atrioventricular located at the link of the two atria.

After a contraction, the ventricles relax, and the pressure in them falls. Blood flows into the atria again, and an impulse from the sinoatrial restarts the cycle. This process is called the cardiac cycle.

In humans the heart rate depends on many things. At birth your heart rate is no more than 130 beats per minute (BPM), and as you develop into a teenager the rate decreases and then increases in older age. The average adult heart rate is 70 BPM at rest. The rate increases temporarily during exercise, emotional excitement, and fever and decreases during sleep and rest. To ...

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For example, if a fifteen year old were to use this equation, he would subtract 15 from 220 to get 205, giving him his peak heart rate. This method only gives you a rough calculation, not an exact amount.

Aim

The aim of this investigation is to examine the effect of exercise on heart rate.

Prediction

The amount of exercise a person does will affect the pulse rate. For example, more exercise means more movement so more energy will be needed. In order to get more energy, respiration needs to take place at a faster rate.

I predict that the heart rate will increase as a result of exercise. I think that there will be a fairly quick increase, then a slow increase. Then on the next exercise level the same will happen.

I have made these predictions because I believe that the supply of oxygen to the muscles will decrease which will make the heart work harder. Also a lot of energy will be used up as the exercise takes place, thus resulting in a further increase. If the body is unable to continue aerobic respiration anaerobic respiration will take place. This results in lactic acid being formed. Finally, the carbon dioxide levels would also rise which would also contribute to the heart rate rising.

Apparatus

PowerJog® CardioSport – Treadmill

Stopwatch

Pulsar Monitor

Three Human Subjects

Method Evaluation

In this investigation there are many possibilities in the way that it can be constructed. The subjects could have done one of many types of exercise and the subject’s heart rate or pulse could have been measured in a number of ways.

To measure the heart rate with a stethoscope would be unwise due to the movement while the subject exercises. Using your fingers to measure the pulse in the subject’s neck or wrist would cause the same problems and would also be irritating for the subject.

Running around a track has been ruled out because someone would have to run around with the subject, taking the heart rate. It is easier if the subject is running in one spot, like on a treadmill.

With this information I have come to the decision that I am going to use a treadmill and pulsar monitor. The pulsar monitor measures the electric signals given off by the heart, thus enabling us to record the heart rate every thirty seconds. The cardiometer could also be used, as it is a heart rate averaging device. I prefer the pulsar monitor.

Method

To find out what strength of exercise was easy, moderate and hard, the subject ran on the treadmill and was asked what he thought was easy, moderate and hard. Once this information was taken the investigation took place.

The pulsar monitor was fitted onto the subject to monitor his heart rate. The subject lay down to rest for ten minutes, not moving, talking or doing anything that would excite him. After the ten minutes the subject’s pulse was taken. This is the resting heart rate. Once the heart rate had been taken, the subject got onto the treadmill and walked at his chosen easy pace. This was 5km/h. This exercise was continued for three minutes and the heart rate was recorded every thirty seconds. After the three minutes, the speed was taken up to the subject’s moderate choice. This was 10km/h. The exercise at this pace was carried out for another three minutes and the heart rate was again recorded every thirty seconds. Again after the three minutes the speed was taken up to the subject’s hard choice, which was 15km/h. This was done for three minutes with recordings every thirty seconds.

The pulsar monitor had to be kept behind the subject because the treadmill was giving off electric waves, interrupting the results that were being obtained. The exercise part of the investigation for this subject has now been completed. After this his heart rate was taken every thirty seconds as he stood resting.

The investigation was repeated on two other subjects after they had all decided on appropriate levels of exercise.

Results

The graphs show that once exercise had started, the subject’s heart rate ascended very quickly. When the subject had got used to the level of exercise a plateau forms in the graph. Once the next level of exercise had been introduced, the heart rate shot up again and then levelled off. When exercise had finished the heart rate remained high for quite a long period of time. It gradually fell to the resting heart rate.

Conclusion

From this investigation I have learnt that the heart rate goes up when exercise takes place. From the results you can see that there is a very quick increase in heart rate once the exercise had started. This means that as the cells needed to respire a lot more as soon as exercise had begun.

The heart rate after the exercise fell gradually because during the exercise the subjects had built up an oxygen debt. This is where the subject could no longer continue with aerobic respiration because the work was too hard. His body then used anaerobic respiration, which gives a huge amount of energy but lasts for only a short time. More oxygen is used so more carbon dioxide is produced. Carbon dioxide is a waste product and it must be removed, as it is a toxin. Because of the extra carbon dioxide being produced, blood is pumped around the body faster in order to transport it. This process will give you a faster pulse rate. You will also get cramp if lactic acid is produced due to not enough oxygen being taken in. The oxygen debt had to be paid back, so while in rest the heart rate remained high repaying cells with a sufficient amount of oxygen.

Evaluation

This investigation could have been better and could have received more reliable results if the weight and height of the subjects were similar. Also if there was a big difference in height, weight and age then I could have obtained varying results. If I were to redo this experiment, I would use a group of people with the same height, age and weight and a group with varying ages, weights and heights. With this investigation I only had the people in my class to experiment with. Therefore I could not choose a certain group of people. They were all different sizes, shapes and had different levels of fitness. If I had longer, I would repeat the experiment to make sure that the results are reliable.

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