This post will be longish seeing as there is nothing difficult in it, pretty much a refresher for most.
Circulatory System
The circulatory system is essentially like the filtering system of a swimming pool. The pool is like the tissues of the body, principally the muscles. The heart is the pump. The arteries and veins are the pipes going to and from the pool. The blood is like the water that is pushed out to the pool after being cleaned and then pulled back from the pool for subsequent cleaning. The left side of the heart pumps blood out to the muscles and other tissues of the body through the arteries and arterioles which are like branching sets of pipes that become smaller in diameter until they reach their destinations in the tissues. Arterioles end in capillaries which are the smallest vessel units and surround individual muscle fibres.
The blood delivers oxygen, glucose, and other substances to the capillaries. At that point, blood is at its greatest proximity to muscles, and some of these substances diffuse out of the capillaries and into the muscle fibres they surround. At the same time the carbon dioxide, lactate, and hydrogen ions produced in the muscles during exercise diffuse and are transported out of them into the capillaries. Blood then leaves the tissues through the same capillaries and travel through another set of progressively larger tubes, the venules and veins, back to the right side of the heart. The heart pumps the blood out to the lungs through pulmonary arteries and arterioles, ending in pulmonary capillaries that surround small sacs in the lungs called alveoli. Here, carbon dioxide diffuses out of the blood and into the alveoli when it reaches the lungs, where it is exhaled. At the same time, oxygen inhaled into the lungs diffuses into the capillaries, and blood transports it back to the left side of the heart through venules and veins. Once it reaches the heart, the process begins again.
The lactic acid picked up from the muscles will be dropped off at several locations as the blood makes its way back to the heart. Some of it will be dropped off at other muscle fibres and the liver, where it will be converted back to glycogen for use later as a source of energy. Some of the remaining amount will be picked up by the heart muscles and used as fuel or converted to glycogen and stored for later use.
Heart Rate
The number of times your heart contracts during each minute is your heart rate (right and left sides contracting simultaneously counting as one beat). Resting heart rates are in the neighbourhood of 60 to 80 beats per minute (bpm) for most untrained persons and 30 to 50 bpm for trained athletes. Cardiac muscles of the heart become larger and stronger from training, and they can push more blood out with each beat so the heart requires fewer beats to supply the usual quantity of blood the athlete needs at rest.
Stroke Volume
The amount of blood pushed out of the ventricles of the heart with each beat is termed stroke volume. A normal range of values at rest is between 60 and 130ml per beat. These amounts can increase to between 150 and 180 ml per beat during exercise. These values refer only to blood pumped out of the left ventricle. Stroke volume increases with endurance training. Many factors contribute to the increase, including increased strength of the cardiac muscle fibres, an increase in ventricle size, and a decrease in the thickness of the blood. The stroke volumes of athletes are usually greater after training than before, which explains why they have a lower resting heart rate.
Cardiac Output
The amount of blood ejected from the heart during each minute is referred to as cardiac output. Again, we consider only the amount ejected from the left ventricle when citing values for the cardiac output (right ventricle will eject an equal amount).
Cardiac output is calculated by multiplying the heart rate by the stroke volume. Normal cardiac output for a person at rest is between 5 and 6 L per minute (L/min). The bodies of females and males contain between 4 and 6 L of blood; therefore, each red blood cell usually makes one round-trip from the lungs to the muscles and back again in approximately 1 min when athlete’s bodies are resting. Resting cardiac output does not increase with training, but the heart becomes more efficient in the way it supplies the blood. Stroke volume increases and heart rate decreases. So when a person is resting the heart does not have to work as hard to push the same 5 L of blood out to the body each minute. Training does not increase an athlete’s cardiac output during similar submaximal efforts because there is no need for it.
Athletes can increase their maximum cardiac output by training. Maximum cardiac output values of 30 and 35 L/min are not unusual for trained endurance athletes.
Blood Pressure
Blood flowing through vessels exerts pressure on the walls of those vessels. This pressure is measured by the number of millimeters that the blood causes a column of mercury (Hg) to rise. Two measurements of pressure are needed to identify the force of blood flow: (1) the pressure when the heart beats, known as systolic pressure, and (2) the pressure when it is resting between beats, diastolic pressure. Typical resting systolic and diastolic blood pressures are 120 and 80 mm Hg, respectively.
Systolic blood pressure increases in proportion to the intensity of work because a larger amount of blood is present in the vessels at any one time.
Endurance training reduces both systolic and diastolic blood pressure by 6 to 10 mm Hg at rest and by an equal amount during submaximal exercise. This reduction in pressure probably occurs because the elasticity of blood vessels increases through constant expansion and constriction that occurs in training.
Ok, so nothing hard there. We’re up to the respiratory system. I’m going to leave that to another post because this goes a bit into what we do with the oxygen we take in and measuring VO2max, oxygen debt and some other stuff so is probably worthy of its own post. Then we get into energy metabolism (that we use up our creatine phosphate in the first few seconds of exercise is a bit of a downer isn’t it but hey, we’ve got glycogen so why did we even get given CP in the first place I don’t know – actually, because it can be utilized really really quickly), how we produce and clear lactate. Then there is a section on metabolic training. Finally we get to the info on the energy zones – EN1, EN2, EN3, SP1, SP2, SP3.