The human energy system is composed of several systems of the body: the respiratory system provides oxygen needed for the burning of the fuel; the cardiovascular system delivers the oxygen and fuel to the muscles; and energy conversion systems in the muscles convert the oxygen and fuel into the muscular activity. There is in addition the digestive system, which of course provides the fuel, but its functioning processes are not dealt with in this chapter.

The respiratory system is an organ system which is used for breathing. This action is achieved by ventilation, which involves two acts: inhalation (inspiration) and exhalation (expiration). The respiratory system consists of the upper and lower airways, the lungs, and the respiratory muscles that mediate the movement of air into and out of the body. The upper airway is formed by the nose, mouth, pharynx and larynx. The lower tract consists of trachea, bronchi and two lungs.

Air moves through the body in the following order:

The major function of the respiratory system is gas exchange. Upon inhalation, air enters the body through the nose and mouth and travels down the trachea, through the bronchial tubes, and finally into the lungs. Once in the lungs, the air is drawn into an enormous number of sacs (alveoli) richly supplied with capillaries. The alveolar walls are extremely thin, and are permeable to gases. The alveoli are lined with pulmonary capillaries, the walls of which are also thin enough to permit gas exchange. All gases diffuse from the alveolar air to the blood in the pulmonary capillaries, as carbon dioxide diffuses in the opposite direction, from capillary blood to alveolar air. At this point, the pulmonary blood is oxygen-rich, and the lungs are holding carbon dioxide. Exhalation follows, thereby ridding the body of the carbon dioxide and completing the cycle of respiration. The respiration is under the control of the respiratory centre in the medulla of the brain and is affected by many factors such as exercise, emotional reactions, pain, elevated temperature, shock, or certain drugs.

There are two ways in which the lungs can respond to the body’s increased demand for oxygen. They can pump faster or they increase the volume of air they pump with each breath. It is more efficient to increase the volume rather than the rate. The average male has a total lung capacity of around 6 litres. If he tried to breathe all the air out, he would still have around 1.2 litres of air left in his lungs, which is his residual volume. The difference between the total capacity and the residual volume is termed vital capacity, which is usually 4-5 litres for men and 3- 4 litres for women. However, elite endurance athletes may have vital capacities of 6 – 7 litres.

 

Fitness can be measured by the volume of oxygen you can consume while exercising at your maximum capacity. VO₂ max is the maximum amount of oxygen in milliliters, one can use in one minute per kilogram of body weight.

Athletic performance is directly related to the amount of oxygen supplied to the muscles. The supply of oxygen is dictated by how often the heart beats, the volume of blood transported by every beat and the amount of oxygen in that blood. It is also dependent on how well the tissue or muscle extracts the oxygen (O₂).

So if we could find the volume of blood pumped in one minute and the difference between the amount of oxygen in arterial and venous blood we would have all the data we need. The stroke volume is usually measured in milliliters per beat. The cardiac output is the product of stroke volume and heart rate and is measured in milliliters per minute. Multiply this by the difference in oxygen concentration and we have the liters of O₂ processed per minute. If we make these measurements when the athlete is working at his or her maximum heart rate, we have VO₂ max.

Those who are fit have higher VO₂ max values and can exercise more intensely than those who are not as well conditioned. Numerous studies show that you can increase your VO₂ max by working out at an intensity that raises your heart rate to between 65 and 85% of its maximum for at least 20 minutes three to five times a week. A mean value of VO₂ max for male athletes is about 3.5 litres/minute and for female athletes it is about 2.7 litres/minute.

To measure VO₂ Max directly an athlete has to be wired to a computer and breathe into an apparatus that analyses exhaled air while he runs on an appropriate ergometer – treadmill or a stationary bicycle. The exercise workloads are selected to gradually progress from moderate to maximal intensity.

We need a big and efficient pump to deliver oxygen-rich blood to the muscles, and we need mitochondria-rich muscles to use the oxygen and support high rates of exercise. Which variable is the limiting factor in VO₂ max, oxygen delivery or oxygen utilization? This is a central question that has created considerable debate among exercise physiologists over the years.

The cardiovascular system includes the heart and system of vessels through which the blood is circulated throughout the whole body. The blood, which is pumped by rhythmic contractions of the heart, carries nutrients, oxygen, and other vital substances throughout the body. The blood is pumped from the heart to the arteries. The main arterial vessel, the aorta, branches into smaller arteries, which in turn branch repeatedly into smaller and smaller vessels and reach all parts of the body. Within the body tissues, the vessels are microscopic capillaries through which gas and nutrient exchange occurs. The blood passes oxygen and nutrients to the cells and picks up waste in the capillaries, then returns to the heart via a system of veins.

HEART
In the human body, the heart is normally situated to the left of the middle of the thorax, underneath the breastbone. The heart is usually felt to be on the left side because the left heart (left ventricle) is stronger, as it pumps the blood to the whole body. The heart is divided into four chambers, two on the right and two on the left side. The upper chambers are called the atria, and the two lower, larger ones are called the ventricles. All chambers of the heart have valves that keep the blood flowing in the right direction. When the right atrium fills, the atrio-ventricular (tricuspid) valve opens, allowing the blood to flow into the right ventricle , then closes to prevent backflow when the ventricle contracts. The mitral (bicuspid) valve does the same function on the left. There is no contact between the right and the left side, which are separated by the septum.

FUNCTION OF THE HEART
The oxygenated blood leaves the lungs and enters the left atrium of the heart through the pulmonary veins, passes through the mitral valve into the left ventricle, from where it is pumped through the aorta around the body, returning to the right atrium of the heart, depleted in oxygen, through the superior and inferior vena cava. From the right atrium the blood passes through the tricuspid valve into the right ventricle, from where it is pumped into the lungs via the pulmonary artery, picking up oxygen and releasing carbon dioxide before returning to its left atrium through the pulmonary veins.

Heart rate is calculated as the number of contractions (heart beats) of the heart in one minute and expressed as "beats per minute" (bpm). Heart rate is widely accepted as a good method for measuring intensity during running, swimming, cycling, and other aerobic activities. Exercise that doesn’t raise your heart rate to a certain level and keep it there for 20 minutes will not contribute significantly to cardiovascular fitness.

Table 2: Age category and heart rate

Exercise is often recommended as a means of improving motor skills, fitness, muscle and bone strength, and joint function. Developing fitness will largely depend on how the components of fitness can be imbedded into a training program.

Physical fitness involves the performance of the cardiorespiratory system - the heart and lungs, and the muscular system of the body. As there are a number of different types of "fitness", it is best to look at fitness by examining the Components of Fitness. From a sporting perspective there are 3 basic components of fitness - endurance, speed and strength, with flexibility at the core of fitness influencing each component.

• Endurance is the ability of the heart and lungs to supply fuel to working areas of the body during sustained physical activity. To improve your cardiorespiratory endurance, it is necessary to perform activities that elevate your heart rate for a sustained length of time.
• Strength is the ability of the muscles to generate force in a short period of time. When you increase your strength, you're often also increasing the size of your muscles, however, athletes should develop their muscular strength and endurance in a manner that will improve performance, and will not simply build larger muscles.
• Strength endurance is a combination of strength and endurance, and is defined as the ability of the muscle to continue to perform generating the same force without fatigue.
• Speed endurance is a combination of speed and is the ability of the muscle to perform at the same speed without fatigue.
• Speed is the ability to perform a movement quickly. Athletes need speed to accelerate, change direction and react quickly to changes in the play.
• Flexibility is the ability to move a joint through its full range of movement without experiencing any pain or discomfort. Increased flexibility will allow the athlete to maximize improvements in endurance, strength and speed.
• Through improving each of the components of fitness, a number of sports specific factors are developed - strength endurance, speed endurance and power.
• Power is a combination of strength and speed.
• Coordination is the ability to move two or more body parts under control, smoothly and efficiently. Coordination tests are not commonly used in a fitness test battery. Coordination is a complex skill that requires good levels of other fitness components such as balance, strength and agility. On a sporting field, someone who appears to be well coordinated may also be displaying good timing.
• Agility relates to the ability to rapidly change the position of the entire body in space with speed and accuracy.
• Body composition is often included as a component of fitness. Body composition refers to the relative amount of muscle, fat, bone, and other vital parts that make up the body.
• Cardiorespiratory endurance involves the ability of the heart and lungs to supply oxygen to the working muscles for an extended period of time. It is also called aerobic endurance or aerobic fitness, which is the ability of the cardiovascular and respiratory systems to adjust to and recover from the effects of vigorous physical activity.

HUMAN ENERGY SYSTEMS

To achieve optimum performance in your workout or sport it is essential that you understand how your body produces the energy that makes you go. When we talk about the body's energy systems we are really talking about the chemical reactions that take place in your body (muscles) involving ATP, or Adenosine Triphosphate. In order for the body to produce energy it must cleave (chemically separate) a phosphate molecule from ATP which causes a release of energy. After the phosphate molecule is cleaved, ATP becomes ADP, or Adenosine Diphosphate, and will need to have another phosphate attached to be able to once again produce energy. The ability of the body to produce energy for activities is, therefore, dependent upon ATP and the replenishing thereof. The human body has three basic energy systems that are responsible for replenishing ATP. Two of these systems are anaerobic, which means without oxygen, and the other is aerobic, which means with oxygen. The ATP-CP system is the first of the anaerobic energy systems. As ATP is used it can quickly be replaced through a chemical reaction with Creatine Phosphate. Figure 1 is the actual chemical reaction where ATP is cleaved to produce energy and is then replenished by a reaction with Creatine Phosphate.

The ATP-CP system is active at the beginning of all forms of activities but is especially important in high intensity exercises. The source of fuel for the ATP-CP system is ATP and CP that is stored in the muscles and since only a small quantity can be stored, this energy source is only effective for activities that last ten seconds or less.

The second anaerobic energy system is called Anaerobic Glycolysis, but is commonly referred to as the lactic acid system because it produces lactic acid as a byproduct. The Anaerobic Glycolysis system is important in moderately high intensity exercises that generally last less than two minutes. Anaerobic Glycolysis works in conjunction with the other two energy systems but can be thought of as picking up where the ATP-PC system leaves off. The source of fuel for Anaerobic Glycolysis is either glucose from the blood or stored glucose and is therefore generally effective for activities lasting two minutes or less.

The third energy system is the Oxidative system, which involves the use of oxygen. This system picks up where the Anaerobic Glycolysis system leaves off and is generally involved after an activity has lasted longer than two minutes. The Oxidative system can use protein, fats, or carbohydrates as the source for energy but carbohydrates are the most efficient source for fuel. The ability of the Oxidative system to be able to use protein, fats, and carbohydrates as fuel is in contrast to the Anaerobic Glycolysis system and the ATP-PC system which can only use Glycogen or stored Creatine Phosphate.

The most important thing to understand about the body's different energy systems is that the intensity of exercise dictates the primary system that is involved. Figure 2 shows the different energy systems and generally when each system is involved based on the intensity of exercise as defined by length of time. It is also important to understand that most activities will involve more than one system but each system has a specific role to fulfill based upon the requirements of the activity.

            Table 3: Energy systems

Energy System	Duration of Activity
ATP-CP	0 seconds – 10 seconds
ATP-CP + Anaerobic Glycolysis	10 – 30 seconds
Anaerobic Glycolysis	30 seconds – 2 minutes
Anaerobic Glycolysis + Oxidative System	2 – 3 minutes
Oxidative system	greater than 3 minutes

Reference:

ability schopnost
accuracy přesnost
adenosine triphosphate, ATP adenosin trifosfát
aerobic aerobní
agility obratnost, hbitost
airways cesty dýchací
alveolar alveolární
alveolus pl. alveoli plicní sklípek
anaerobic anaerobní
aorta aorta
atrium pl. atria srdeční síň
ban  s  zákaz činnosti, startu, v  zakázat, suspendovat, distancovat
    life ban doživotní zákaz startu
banned zakázaný
breathe dýchat
breathing dýchání
bronchus pl. bronchi průduška
byproduct vedlejší produkt
capillary capilára
carbohydrate karbohydrát
carbon dioxid oxid uhličitý
cleave rozštěpit
consumption spotřeba
creatine phosphate, CP kreatin fosfát
deplete (in) zbavit se, být ochuzen (o)
depleted ochuzená
endurance vytrvalost
energy system energetický systém
exercise cvik, cvičení, zátěž
    exercise physiology fyziologie tělesné zátěže
exhalation výdech
exhale vydechnout
expenditure výdej
expiration výdech
expire vydechnout
fat tuk
fitness kondice, zdatnost
    physical fitness tělesná zdatnost
flexibility pružnost, flexibilita
fuel živiny, palivo
gas exchange výměna plynů
glycolysis glykolýza
heart srdce
    heart rate tepová frekvence
    take the pulse, heart rate měřit tepovou frekvenci
imbed začlenit, být součástí
inhalation nádech
inhale nadechnout (se)
inspiration nádech
involve obsahovat, týkat se, vztahovat se k, zapojit
lactic acid laktát
    lactic acid system laktátový systém
larynx hrtan
lid víčko
medulla prodloužená mícha
moderate střední, mírný (zátěž)
motor motorický
    motor skills motorika, motorické dovednosti
nasal cavity nosní dutina
nostrils nosní dírky
oxygen kyslík
    oxygen-rich bohatá na kyslík, okysličená (krev)
oxygenated okysličený
permeable prostupný
pharynx hltan
pot nádobka, kelímek
pulmonary plicní
remainder zbytek
replenish doplnit, znovu naplnit, zásobit
rid of zbavit se
sack plicní sklípek
sample vzorek
    urine sample vzorek moči
    produce the urine sample poskytnout vzorek moči, vymočit se
seal  s  těsný uzávěr, v  těsně uzavřít
septum septum, přepážka
skill dovednost
speed rychlost
strength síla
substance látka
supply (with) zásobit, zásobovat (něčím)
test testovat, otestovat, prověřit
    test positive mít pozitivní dopingový nález
testing officer dopingový komisař
trachea průdušnice
treadmill běhací pás
uptake spotřeba
valve chlopeň
    bicuspid valve dvoucípá chlopeň
    tricuspid valve trojcípá chlopeň
vein žíla
vena cava plicní žíla
ventilation plicní ventilace
ventricle srdeční komora
vessel céva
volume objem
workout tělesná zátěž, zatížení

Content        Chapters: 1 2 3 4 5 6 7        Vocabulary       Listening        References