The Heart and Cardiovascular System
5.2. Heart and Cardiovascular System
The cardiovascular system provides the body with a continuous source of oxygen and nutrients while removing metabolic by-products. Blood is transported from the heart to the rest of the body through a complex network of arteries, arterioles and capillaries, and it is returned to the heart through venules and veins. The heart is a muscle that consists of four chambers, and is located in the chest cavity (medially between the lungs in the space known as the mediastinum) and provides the impulse for blood flow. The myocardium (heart muscle) is a striated involuntary muscle whose rate and strength of contraction is modulated by the autonomic nervous system.
A typical heart is approximately the size of a fist around 12 cm in length, 8 cm wide, and 6 cm in thickness and the weight is between 250 g (females) and 350 g (men). The heart of a well-trained athlete, especially one specializing in aerobic sports, can be considerably larger than this.
A typical heart is approximately the size of a fist around 12 cm in length, 8 cm wide, and 6 cm in thickness and the weight is between 250 g (females) and 350 g (men). The heart of a well-trained athlete, especially one specializing in aerobic sports, can be considerably larger than this.
Physiologically and anatomically, the heart consists of two left chambers (left atrium and left ventricle; also called the »left heart«) and two right chambers (right atrium and right ventricle, also called the »right heart«). The heart pumps blood into two vascular systems (circulations): the left heart is responsible for pumping the blood throughout the body (systemic circulation), and the right heart into the lungs (pulmonary circulation). The two circulations are interconnected sequentially. The unidirectional flow through the heart is ensured by four valves that prevent blood from flowing back.
The cardiac cycle involves consecutive stages in which the atria, filled with blood received from the pulmonary and systemic circulations, transfer their content to the ventricles (diastolic phase). Then the ventricular chambers contract and blood is propelled to the systemic and pulmonary circulations (systolic phase).
Heart rate (HR) refers to the frequency of the cardiac cycle (beats per minute), while the amount of blood ejected by a single ventricular contraction is called the stroke volume. Cardiac output expresses the total volume of blood pumped by the ventricle per minute (cardiac output = stroke volume X HR).
5.2.1. Blood Pressure and the Effects of Exercise
Blood pressure is the pulsatile pressure applied by the circulating blood on the walls of blood vessels. At rest, a young, healthy subject generally shows a maximal (systolic pressure) of 120 mm Hg. During the relaxation phase of the cardiac cycle, arterial pressure decreases to 60 to 80 mm Hg (diastolic pressure)in the aorta and large arteries. Pressure and blood flow velocity in the vascular system tend to progressively decline in proportion to the resistance encountered and the increase of the total cross-sectional area of the vascular bed. Arterial blood pressure reflects the product of cardiac output and total peripheral resistance (the resistance encountered by blood flow, mainly at the arteriolar level).
The blood pressure response to exercise differs depending on the exercise modality. During aerobic exercise, the increase in systolic blood pressure is directly proportional to the exercise intensity and can reach over 200 mm Hg. In contrast, diastolic pressure does not change significantly. It may even decrease at submaximal intensities and can slightly increase at the highest exercise intensities.
Resistance exercise, particularly during the concentric and static phases, induces a clear-cut increase of both systolic and diastolic pressure, mainly due to the mechanical compression of peripheral arterial vessels supplying active muscles. In general, upper-body exercise induces a greater arterial pressure response compared with lower-body exercise performed at the same relative intensity.
At the end of exercise, independent of its modality, blood pressure tends progressively to decrease, normally reaching pre-exercise levels within a few minutes and then falling below those values. This post-exercise hypotension can last up to 22 hours. Performing regular exercise (both aerobic and resistance) can induce a sustained reduction of blood pressure, particularly in hypertensive subjects.
5.2.2. Maximal Heart Rate
The maximal amount of work an individual can perform is affected not only by the individual’s physical fitness and health but also by the amount of blood that can circulate in one minute. This is called cardiac output, which means the amount of blood pumped by the heart in one minute, providing blood flow to the brain and other vital organs (King et al., 2022).
The maximal cardiac output is determined by the individual’s maximal stroke volume and heart rate. The maximum heart rate (HRmax) is determined by genetics and by age.
The gold standard for measuring your maximum heart rate is to do a graded maximum exercise test in a laboratory setting. Such tests should only be performed by qualified exercise physiologists under the supervision of a physician.
Since physiologists have determined that there is a relationship between maximal heart rate and age, we can easily calculate an estimate of an individual’s maximal heart rate.
The age-predicted HRmax equation (220 – age) is commonly used as a basis for prescribing exercise programs, as a criterion for achieving maximal exertion and as a clinical guide during diagnostic exercise testing.This formula is based on research which found that the average maximal heart rate of healthy adults decreases with age. However, it is important to note that this formula is based on averages, and does not take into account individual variations. As such, it should not be used to determine an individual’s maximal heart rate with 100% accuracy.
The majority of any population, approximately 67%, will have a maximal heart rate of 220 minus their age plus or minus 10 beats per minute. This is why this equation is also used:
HRmax = 220 – age (+/- 10) beats per minute
According to more recent research, it has been acknowledged that another equation is more valid for use in the healthy young college-aged population regardless of sex or training status (Roy 2015):
HRmax = 208 – (0.7 x age)
The maximal cardiac output is determined by the individual’s maximal stroke volume and heart rate. The maximum heart rate (HRmax) is determined by genetics and by age.
The gold standard for measuring your maximum heart rate is to do a graded maximum exercise test in a laboratory setting. Such tests should only be performed by qualified exercise physiologists under the supervision of a physician.
Since physiologists have determined that there is a relationship between maximal heart rate and age, we can easily calculate an estimate of an individual’s maximal heart rate.
The age-predicted HRmax equation (220 – age) is commonly used as a basis for prescribing exercise programs, as a criterion for achieving maximal exertion and as a clinical guide during diagnostic exercise testing.This formula is based on research which found that the average maximal heart rate of healthy adults decreases with age. However, it is important to note that this formula is based on averages, and does not take into account individual variations. As such, it should not be used to determine an individual’s maximal heart rate with 100% accuracy.
The majority of any population, approximately 67%, will have a maximal heart rate of 220 minus their age plus or minus 10 beats per minute. This is why this equation is also used:
HRmax = 220 – age (+/- 10) beats per minute
According to more recent research, it has been acknowledged that another equation is more valid for use in the healthy young college-aged population regardless of sex or training status (Roy 2015):
HRmax = 208 – (0.7 x age)