Energy Supply and Fitness



Energy Supply and Fitness



The abilities to perform work, produce change, and maintain life all require energy.




Role in Wellness


Consideration of the physical, intellectual, emotional, social, and spiritual dimensions of health guides our understanding of the value of energy supply and fitness. To achieve optimal physical health and fitness, dietary intake and regular physical activity are essential. Exercise affects all muscles; even the muscles of our gastrointestinal tract function better when we regularly exercise. To strengthen our intellectual health dimension, the old saying “A sound body makes for a sound mind” still holds true.


imagehttp://evolve.elsevier.com/Grodner/foundations/ imageNutrition Concepts Online


By being physically fit, we may be able to devote our full intellectual capacity to our work. The emotional health dimension may be supported by fitness because for some people, depression seems to lift if they regularly engage in sustained aerobic activities. Even if we are not depressed, our general state of mind improves with daily physical exercise. Group sports provide an excellent opportunity for social activity while pursuing healthful goals that enhance social health. A sense of belonging and sharing occurs whether the group is a formal organization, such as a running club, or consists of friends who bike together. Respecting and caring for our bodies by engaging in regular physical activity reflects the understanding of the unique nature of the human body, which reflects spiritual health (see the Personal Perspectives box, Detecting a Deficiency).



imagePersonal Perspectives


Detecting a Deficiency


George Sheehan, MD, was as comfortable writing articles as medical editor for Runner’s World magazine as he was practicing medicine. His running habit began at age 45, “a decisive age, an age for change.” He was responsible for inspiring many to find the athlete within themselves to achieve their own personal best. His message was that physical excellence leads to achievements in other arenas of life. Here is an excerpt from his book Personal Best.


Are you feeling run-down, sluggish, low in energy? Is simply getting to school or work becoming too much for you? Are you exhausted by three o’clock in the afternoon? Do you feel depressed? Have you lost your initiative?


If you answer yes, you may be suffering from a lifestyle disease that, surveys tell us, affects about one-half of all Americans. It is called exercise deficiency, it is undoubtedly a leading cause of ill health, and no household is exempt.


Exercise deficiency—the sweat deficit-—is a self-inflicted disease. It is an old and familiar story: Our greatest tendency is to cheat on ourselves. We think we can enjoy the fullness of life without paying for it. But that is not the way the world works—or the human machine, either: Nothing is free.


Full-blown exercise deficiency states are evident to the most inexperienced observer—sufferers are manifestly out of shape. These extreme cases usually fatigue easily and early and spend most of the day in physical and mental torpor. They are much too tired when they get home at night to even consider taking any physical exercise. For them, repose is the natural state, and any activity is an effort.


Many people with exercise deficiency are unaware that they have it. They expect no more from their bodies than they are getting. They believe their lack of energy and enthusiasm goes with age. They think they are normal. The reality: They are average, because it’s average to slow down, average to become less productive, average to have less energy—and since that’s exactly what happens to most of us, we confuse the two. But average is not normal. Normal is the best you can be.


The notion that loss of physical vigor is inevitable usually comes in the mid-thirties. At the FBI Academy, where recruits are placed in a fitness program to get them back in condition, one aspirant complained to the director, “I’m 35; I’m too old for this stuff.”


But we are never too old to be fit, and never too young to start preserving fitness. We need to be physically fit whether we are 20 or 35 or even 70. Being unfit at any age is settling for less than your best and is a classic example of the sort of thinking that is behind the widespread incidence of exercise deficiency.


Fortunately, the movement toward fitness is equally widespread. Half the people in this country now realize the need for physical exercise. They know there is no need to lose the gleam in their eye, the bloom in their cheek, the lift in their walk, and the life in their day.


And all it takes is sweat.


From Sheehan G: Personal best: The foremost philosopher of fitness shares techniques and tactics for success and self-liberation, Emmaus, Pa, 1989, Rodale Press.


Physical activity has always been recognized as a component of health. Within the past decade this importance has increased because an inverse relationship between level of fitness and risk of development of chronic degenerative disorders is becoming better understood. This means that the less physical activity a person experiences, the greater the risk of developing disorders such as diabetes, coronary artery disease (CAD), cancer, and hypertension. This chapter addresses the health benefits of exercise as complementing optimum nutrition to decrease risk factors and as improving quality of life. In the nursing profession, we may also work with athletes of all ages who will benefit from our knowledge of their physical requirements. Consequently, this chapter discusses specific nutrient issues that affect the athlete, defined as “a person who is trained or skilled in exercises, sports, or games requiring physical strength, agility, or stamina.”1 Finally, as nurses we have a responsibility to maintain our own fitness levels as role models for our clients and for our own benefits to function comfortably in our sometimes physically demanding profession.



Energy


The abilities to perform work, produce change, and maintain life all require energy. Energy exists in many forms, such as mechanical, chemical, heat, electrical, light, and nuclear energies. The laws of thermodynamics tell us that each type of energy can be converted from one form to another. As our bodies function, chemical energy from food is converted to mechanical energy and heat.


The ultimate source of energy is the sun. Sunlight is used by plants to produce chemical energy in the form of carbohydrates, proteins, or fats. These foods possess stored energy. People are not capable of doing this. We must convert the chemical energy from the foods we eat into forms usable by the human body.


The energy released from food is measured in kcal (thousands of calories), or Calories. Technically, a calorie is the amount of heat necessary to raise the temperature of a gram of water by 1° C (0.8° F). As first noted in Chapter 1, to ensure accuracy, the term kilocalories is used throughout this text, abbreviated as kcal.


Two methods are used to determine the energy a food contains. One is through the use of a bomb calorimeter (Figure 9-1). This instrument is designed to burn a food while measuring the amount of heat or energy released. This provides an estimate of the energy available to humans. Because the bomb calorimeter method is more efficient than the human body, the kcal value assigned to a food item is adjusted to reflect the limitations of the human system. Amounts listed in food tables reflect this adjustment.


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FIG 9-1 Cross section of a bomb calorimeter. To determine energy, a dried portion of food is burned inside a chamber charged with oxygen that is surrounded by water. As the food is burned, it gives off heat. This raises the temperature of the water surrounding the chamber. The increase in water temperature indicates the number of kcal contained in the food. One kcal equals the amount of heat needed to raise the temperature of 1 kilogram of water by 1° C (0.8° F).

The other method of assessing food energy is proximate composition, which determines the grams of carbohydrates, proteins, and fats of a food item. The grams are then multiplied by the energy value of each (carbohydrates 4 kcal/g; proteins 4 kcal/g; fats 9 kcal/g). The sum of these calculations equals the total energy content of a specific food.



Energy Pathways


The processes of digestion, absorption, and metabolism for each of the three energy-supplying nutrients—carbohydrates, fats, and proteins—have been presented in previous chapters. (Alcohol also provides energy but is not considered a nutrient category.) Carbohydrate digests to glucose, triglycerides (fats) to fatty acids and glycerol, and protein to amino acids. Here we continue to follow their journey as they are used for energy in individual cells.


The nutrients release energy when they are catabolized (broken down), forming carbon dioxide and water. The released energy becomes caught within adenosine triphosphate (ATP), the fuel for all energy-requiring processes in the body (Figure 9-2).


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FIG 9-2 Summary of key steps in the metabolism of glucose, fatty acids, glycerol, and amino acids. ADP, Adenosine diphosphate; ATP, adenosine triphosphate; TCA, tricarboxylic acid cycle. (From Thibodeau GA, Patton KT: Anatomy and physiology, ed 4, St Louis, 1999, Mosby.)


Carbohydrate as a Source of Energy


Glucose releases energy and is converted to carbon dioxide and water through three processes: glycolysis, tricarboxylic acid (TCA) cycle, and oxidative phosphorylation. These complicated processes are reviewed in general here; the intricate details are beyond the scope of this text.


Through glycolysis, which results in the conversion of glucose to carbon compounds, a glucose molecule produces pyruvic acid and ATP. Part of this process depends on niacin and other B-complex vitamins. Oxygen is not needed for glycolysis to occur because it is an anaerobic pathway. The anaerobic pathway provides energy for sprint or speed-type exercise such as soccer, basketball, and football. We also depend on this energy source to run for the train, chase after toddlers, or bound across the room to answer the phone. This type of exertion is limited because oxygen is not available quickly enough to continue its support. Instead, the incomplete use of glucose causes the pyruvic acid to be converted to lactic acid. As lactic acid builds up, the muscles become sore and stiff. Consequently, the exertion ceases because of pain. Within a few minutes, enough oxygen is available to break down the lactic aid, relieving the physical discomfort. The effect is called oxygen debt.


Anaerobic glycolysis takes place in the cell cytoplasm, but oxygen-dependent aerobic glycolysis (the aerobic pathway) occurs in the mitochondria of the cell. In the mitochondria, pyruvic acid (made without oxygen) reacts with coenzyme A (CoA) creating acetyl CoA. The energy process continues as acetyl CoA reaches the TCA cycle. The reactions that are part of that cycle lead to the formation of additional ATP and carbon dioxide. The aerobic pathway is the primary energy source for exercise that is low enough in intensity to be carried on for at least 5 minutes or longer. This includes endurance-type exercise (e.g., swimming, bicycling, running), as well as walking and most of our daily activities.


The last process of glucose conversion to energy is oxidative phosphorylation. A number of actions lead to the release of hydrogens in the forms of water and additional energy that is captured in ATP. The term oxidative reflects the combination of hydrogen with oxygen to form water; phosphorylation is the creation of the phosphate bond to form ATP.




Protein as a Source of Energy


Amino acids are first catabolized through deamination, as described in Chapter 6. Whereas the liver and kidneys process the nitrogen-containing amino acid groups, the other amino acid components enter the energy metabolism pathway, with each component entering at a different location. Some of the amino acid components are converted to pyruvic acid; others become intermediaries of the TCA cycle or part of the acetyl groups. If sufficient energy is available, amino acids are used for protein synthesis rather than for energy.


It is important to note that just as all three nutrients (carbohydrate, protein, and fat) can be used for energy when consumed in excess, they can also be stored as fat in the body. Likewise, when too little energy is consumed, these processes reverse. Energy that is consumed is used immediately, regardless of its source. The first stored energy used is glycogen, followed by the energy reserve of body fat in adipose cells. Glucose must be available to the brain. Only a small portion of triglycerides (glycerol) can yield glucose, and continuous use of this source results in a buildup of ketones and the potential imbalance of the body pH (see Chapter 6). The body prefers to spare protein for its more important function: building and repairing cells and tissues.



Anaerobic and Aerobic Pathways


How do anaerobic and aerobic energy pathways work together to supply energy? For the first minute or two of exertion, oxygen has not arrived at the muscles, and therefore energy must come from anaerobic sources. After several minutes the aerobic pathway takes over. However, as the exertion or exercise continues, there is a constant interchange or use of energy sources.


The energy source that muscles use during exercise depends on the intensity and length of exercise, the person’s fitness level, and the foods eaten. Short-term, high-intensity activities such as sprinting rely mostly on the anaerobic pathway for energy, and only carbohydrates (primarily from muscle glycogen) can be used. On the other hand, exercise of low to moderate intensity is supported primarily by the aerobic system, and both carbohydrate and fats are used. Fats are an important energy source during exercise because, unlike carbohydrates, fatty acids are abundant in the body and their use spares muscle glycogen.


The length of activity also determines what type of fuel the muscles will use during exercise. As the duration of exercise increases, glycogen stores become depleted and fat becomes the primary source of energy (Figure 9-3). A sedentary person breaks down glycogen faster and as a result accumulates more lactic acid in the tissues. The lactic acid causes muscle fatigue. A physically fit person has a higher aerobic capacity (the ability of the heart to supply oxygen) so that oxygen is available sooner and in greater quantity; this allows use of the aerobic pathway of energy, avoiding lactic acid buildup. This also means that more fat than glycogen can be used for fuel.


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FIG 9-3 Relative use made of energy sources in the body as exercise continues. (From Guthrie HA, Picciano MF: Human nutrition, New York, 1995, McGraw-Hill, with permission from Helen A. Guthrie.)

If we eat a diet high in carbohydrates, more glycogen can be stored as energy. The amount of carbohydrate stored in the body depends on how much carbohydrate we consume and our level of fitness. Endurance training increases the capacity of the muscles to store glycogen, but there is still a limit to the total amount of energy that can be stored. The more glycogen that we store, the more energy we have available for all kinds of activities, not just for marathons.



Energy Balance


To maintain a healthy weight, our energy intake should equal energy expended. Because of our sedentary lifestyles, some of us may need less energy than standard energy requirement charts recommend. In contrast, the serious competitive athlete’s energy intake must support a training and competition schedule that allows the athlete to achieve his or her personal best.


Individuals who are acutely ill and hospitalized or adapting to chronic disorders may require energy intake levels specifically calculated to meet their changing physiologic needs. Consultation with a registered dietitian may be warranted for patients, their family members, and other caregivers. Misconceptions about energy needs can be eliminated by nutrition counseling regardless of the nature of the health disorder.



Estimating Daily Energy Needs


The recommended energy allowances published by the National Research Council appear in Table 9-1. These energy values are based on individuals with a light to moderate activity level. The average daily energy intake for the referenced 19- to 24-year-old man is 2900 kcal, or 40 kcal/kg. It is 2200 kcal or 38 kcal/kg for the same age-referenced woman. If a person is more active or of a larger or smaller body size, further adjustments must be made. Most important, these levels are simply guidelines; the only accurate recommendation for individuals is one that supports healthy weight levels.



Many different formulas have been developed to estimate energy expenditure, some of which are complicated. An easy way to determine kcal need is to multiply weight by one of the numbers in Table 9-2. For example, a 77-kg (170-pound) man who participates in moderate exercise needs about 3060 kcal a day. Remember that these numbers represent averages. Some people need fewer kcal; others need more.




Components of Total Energy Expenditure


Our daily energy requirement depends on many variables, including basal metabolism, physical activity, and the thermic effect of food. Basal metabolism represents the amount of energy required to maintain life-sustaining activities (e.g., breathing, circulation, heartbeat, secretion of hormones) for a specific period. Basal metabolic rate (BMR) is the rate at which the body spends energy to keep all these life-sustaining processes going. BMR is measured in the morning on awakening, before any physical activity, and again at 12 to 18 hours after the last meal. Two methods are used. One consists of human subjects being placed in a chamber; the body heat given off changes the temperature of the chamber, reflecting the energy used by their bodies for the most basic functions. The second method, indirect calorimetry, uses a calorimeter. The calorimeter measures the respiratory quotient or exchanges of gases as a person breathes into the mouthpiece of the machine. This determines the amount of oxygen used and carbon dioxide (CO2) expired.


imageSeveral factors affect BMR, including age, body size, sex, body temperature, fasting/starvation, stress, menstruation, and thyroid function. BMR varies with the amount of lean tissue in the body; higher levels of lean body mass increase BMR. For example, men have higher BMRs than women because of larger body size and more lean body tissue. The BMR of adults slowly lowers after age 35 because of decreases in lean body tissue associated with aging. As a physically fit person ages, the BMR may not slow down as much as that of a person who is physically unfit. The process of sustaining fitness maintains the muscle mass of lean body tissue and slows the loss caused by aging. It is never too late to develop fitness; with the approval of a primary health care provider, exercise is appropriate at any age.


BMR also depends on thyroid function. The thyroid hormone thyroxine is a key BMR regulator; the more thyroxine produced in the body, the higher the BMR. Of course, production of too much thyroxine is not desirable either.


Many scientists, however, prefer to use a more practical measurement called resting energy expenditure (REE). REE is the energy a person expends in a normal life situation while at rest, and it includes some energy the body uses following meals and exercise. It accounts for approximately 60% to 75% of our total energy needs, similar percentages to those of BMR (Figure 9-4).


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FIG 9-4 Breakdown of human energy expenditure. (From Rolin Graphics.)


Physical Activity


The second largest component of energy expenditure after REE (or BMR) is physical activity. Physical activity is any body movement produced by skeletal muscles that results in energy expenditure. It demands about 20% to 30% of our total energy needs. Of all the components, it varies the most among people. The amount of energy we expend depends on the intensity and duration of the activity. Walking requires more energy than sitting, and walking for 60 minutes uses more energy than walking for 15 minutes. Thus even a moderate activity can become one of high energy if it is carried on for a long time.


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Physical fitness consists of flexibility, muscular strength and endurance, and cardiovascular endurance. (Photos.com.)

Body size affects energy expenditure more than any other single factor. A heavier person uses more energy to perform a given task than does a lighter person. Table 9-3 shows the number of kcal burned per hour for two individuals, one weighing 205 pounds and the other 125 pounds, as they engage in various activities.


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Feb 9, 2017 | Posted by in NURSING | Comments Off on Energy Supply and Fitness

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