Exercise can effect the cardiovascular system in both long-term and short-term ways. The short-term effects are:
- Heart rate increases
- Stroke volume increases
- Cardiac output increases
- Blood pressure increases
- Blood redistributed
The heart rate increases depending on the intensity of exercise you are carrying out. This is because the heart also prepares itself before exercise. Just before exercise is carried out, the heart rate will rise. This is known as the anticipatory rise. This is caused by a release of hormones such as adrenaline, which then causes the SA node to increase the heart rate. After exercise, the heart rate takes a while to return to its resting level; this is the body’s recovery period. During this phase, the heart rate must remain slightly elevated to eliminate the body’s waste products such as lactic acid. The stroke volume is the volume of blood pumped out of the heart with each contraction. The same as the heart rate, the stroke volume also increases depending on the intensity of the exercise. Stroke volume can increase for two reasons:
- Increased venous return – this is the volume of blood that returns from the body to the right side of the heart.
- The frank starling mechanism
Cardiac output is the volume of blood pumped out of the heart per minute and produces stroke volume and heart rate. Therefore when the heart rate and stroke volume increase results in the cardiac output increases. The cardiac output will continue to increase until the maximum level of exercise is being carried out. Blood pressure increases depending on the intensity of exercise being carried out. During steady aerobic exercise involving large muscle groups, the systolic pressure increases, while diastolic pressure remains constant or in well-trained athletes, it may drop. Systolic pressure increases when a greater intensity is carried out, so the right amount of blood is delivered to the working muscles quickly. During high-intensity exercise, both systolic and diastolic pressure rise due to increased resistance of blood vessels. This is caused by muscles squeezing veins.
Blood flow changes once the exercise is taking place. During exercise, the blood flow is changed from directed at the liver and kidneys to the most needed areas. The working muscles need more oxygen, so more blood is needed to meet this demand. So this demand can be met, and the muscles and keep working efficiently at a high impact. The blood is redirected from the liver, kidneys, and digestive system to the muscles that demand oxygen. The long-term effects are:
- Decrease in blood pressure
- Hypertrophy of the heart
- Increase in thickness of the myocardium
- Increase in stroke volume at rest
- Increase in cardiac output
- Decrease in resting heart rate
Cardiac hypertrophy is the enlargement of the heart. Hypertrophy of the heart muscle occurs due to increased stress on the heart. The extra work of pumping blood against the increased pressure causes the ventricle to thicken over time. The same way a body muscle increases, such as an athlete continuously working his legs, his leg muscles will become bigger. The myocardium increases in thickness due to hypertrophy. This is because the heart is being forced to work harder and more regularly. As it grows stronger, it can meet the required demands with ease and at a quicker pace.
Stroke volume at rest decreases if regular exercise takes place. This is because the heart becomes bigger, meaning it can hold a larger volume of blood. Because the heart can hold a larger amount of blood, it can also pump out a larger volume in a single circuit, decreasing the stroke volume. Bradycardia is defined in adults as a pulse rate below 40 beats per minute. If this occurs, the patient is usually put on medication to help solve this problem. This often occurs in elite athletes due to hypertrophy of the heart and the increase in stroke volume; their hearts are so efficient they do not need to beat any faster as their bodies are efficient enough to deal with only 40bpm. Cardiac output is increased due to a larger volume of blood; therefore, the heart doesn’t have to work as hard as before, and the cardiac output is then decreased.
Resting heart rate is effected by exercise because the muscles in the body demand more oxygen. This means the heart needs to work harder to ensure enough oxygen is delivered to the blood to carry oxygen to the working muscles, and the carbon dioxide and lactic acid are removed. Therefore the more you exercise, the stronger the heart will become and won’t have to work as hard when it is at rest, lowering the resting heart rate. Therefore the resting heart rate is decreased, and the heart doesn’t need to beat as quickly as it did; now the heart is larger, it can beat slower but still achieve pumping the same amount of blood.