Keep the Body Moving –Part I: It’s All About the Energy



Keep the Body Moving –Part I:  It’s All About the Energy



Over 2,000 years ago Hippocrates (460 B.C. – 370 B.C.), the father of modern medicine, understood the importance of exercise when he said, “Eating alone will not keep a man well; he must also take exercise” (Hippocrates, 400 B.C./1953). Plato (427 B.C. – 347 B.C.) also recognized the importance of physical activity and exercise when he commented, “Lack of activity destroys the good condition of every human being, while movement and methodical physical exercise save it and preserve it” (Plato).

Without the benefit of modern science and double-blind, placebo, controlled studies, Hippocrates and Plato suggested over 2,000 years ago that keeping our bodies moving with regular physical activity and exercise are fundamental to overall good health and physical fitness, while a sedentary lifestyle is the harbinger of ill health and a poor physical condition.

There are some grim statistics showing the dominance of a sedentary lifestyle over a physically active lifestyle. For example, more than 60% of American adults are not regularly active, with 25% of the adult population being totally sedentary during their leisure time. Only approximately 15% ofU.S.adults are involved regularly (i.e., three times a week for at least 20 minutes) in vigorous physical activity during leisure time. About 22% of adults engage regularly (i.e., five times a week for at least 30 minutes) in sustained physical activity of any intensity during their leisure time (U.S. Department of Health & Human Services, 1996). The statistics for children and adolescents are not any better. Nearly 50% of American youths 12-21 years of age do not engage in regular, vigorous activity, with physical activity declining dramatically during adolescence. Twenty-five percent of young people report that they are not involved in any vigorous physical activity during their leisure time (see U.S. Department of Health & Human Services, 1996).

The March, 2012, issue of Health and Wellness Monthly is a reissue of Part I of a three part series on why and how people need to engage in regular physical activity or otherwise keep their bodies moving. It addresses the (1) proven health benefits of regular physical activity, (2) barriers to regular physical activity, (3) relationship among energy, food and physical activity (4) characteristics of energy and what it is, (5) types of energy and (6) forms in which energy is stored in the body. It also addresses some conceptual confusion surrounding the use of the terms “physical activity,” “exercise” and “physical fitness.”

Concepts & Terminology

There are three terms used in the literature and this newsletter which merit special attention because they often create conceptual confusion for health consumers due to their prolific use by professionals and lay people. They are physical activity, exercise and physical fitness.

Physical Activity

Generally speaking, “physical activity is defined as bodily movement that is produced by the contraction of skeletal muscle and that substantially increases energy expenditure” above the basal metabolic rate (U.S. Department of Health & Human Services, 1996, p. 21). [1] According to this definition, there is a broad range of bodily movements which would qualify as physical activity such as walking three miles, doing sets of push-ups, pull-ups and sit-ups, lifting and carrying boxes, running in a 5k race, holding a plank position for several minutes and doing household chores such as mowing the lawn, vacuuming, etc., assuming these activities would result in a substantial expenditure of calories/energy above the basal metabolic rate.

Physical activity can be categorized in a variety of ways, including type, intensity and purpose (U.S. Department of Health & Human Services, 1996). One common approach is to talk about physical activity in terms of muscle contraction using either a mechanical classification or metabolic classification. A mechanical classification of physical activity includes static movement where there is no movement of limbs (i.e., isometric – the muscle retains essentially the same length) or dynamic movement where there is movement of limbs (i.e., isotonic – the length of the muscle shortens and there is the same tension on the muscle through the movement). An example of static movement would be holding several boxes with the arms in a fixed position. An example of a dynamic movement would be walking, perhaps while carrying the boxes, which would be a combining of static and dynamic movement.

The metabolic classification involves the availability of oxygen for muscle contraction and includes aerobic (available oxygen) and anaerobic (unavailable oxygen) metabolic processes. Hence, physical activity can be categorized as either static-dynamic or aerobic-anaerobic.

Another way of classifying physical activity is to identify the context in which it takes place. Frequent categories used are household, occupational and leisure time. Leisure time is often subdivided further into the categories of competitive sports, recreational activities (e.g., hiking & cycling) and exercise-training/working out. Of course, professional athletes participating in competitive sports typically consider exercise-training or working-out to be part of their job and not a leisure time activity (see U.S. Department of Health & Human Services, 1996).


Exercise is a subcategory of physical activity.[2]  It is a particular type of “physical activity that is planned, structured, repetitive and purposive in the sense that improvement or maintenance of one or more components of physical fitness is the objective” (Caspersen et al., 1985, p. 126). The terms “exercise,” “exercise-training,” and “working-out” are often used interchangeably.

Physical Fitness

Physical fitness refers to a set of attributes people inherently possess or achieve, giving them the ability to perform physical activity with varying degrees of duration and intensity. Physical fitness is important both to athletes and non-athletes. One common approach geared more toward the non-athlete is to define “physical fitness as the ability to carry out daily tasks with vigor and alertness, without undue fatigue, and with ample energy to enjoy leisure-time pursuits and to meet unforeseen emergencies” (U.S. Department of Health & Human Services, 1996, p. 20).

Another approach is to define physical fitness using more precise, performance-related criteria including cardiorespiratory fitness, skeletal muscular strength, skeletal muscular power, speed, flexibility, agility, balance, reaction time, and body composition. Athletes and lay people can both strive to achieve physical fitness with these criteria in mind. However, “because these attributes differ in their importance to athletic performance versus health, a distinction has been made between performance-related fitness and health-related fitness” (U.S. Department of Health & Human Services, 1996, p. 20). Health-related fitness includes cardiorespiratory fitness, muscular strength and endurance, body composition and flexibility, a less stringent set of criteria but nonetheless useful and worthy of achievement for the non-athlete.

Proven Health Benefits of Regular Physical Activity

It is established firmly in the scientific literature that chronic disease and premature death are inevitable consequences of a sedentary lifestyle. In contrast, regular physical activity improves health in ways that can modulate and even eliminate the development of chronic diseases and conditions and extend life (see U.S. Department of Health & Human Services, 1996; U.S. Department of Health & Human Services, 2002). In a report on Physical Activity and Health, the Surgeon General of the United States, relying on hundreds of studies, stated that “the body responds to physical activity in ways that have important positive effects on musculoskeletal, cardiovascular, respiratory, and endocrine systems” (U.S. Department of Health & Human Services, 1996, p.5).

Established health benefits associated with regular physical activity include the following:

  • Reduces the risk of either becoming sick or dying prematurely from CVDs and conditions and other leading chronic conditions and diseases (e.g., cancer & diabetes)
  • Reduces the risk of developing Type II/non-insulin dependent diabetes mellitus
  • Reduces the risk of developing colon cancer (Findings are either too inconsistent or insufficient to draw firm conclusions regarding a relationship between physical inactivity and the development of endometrial, ovarian, testicular, prostate or breast cancer)
  • Helps to lose weight and sustain a healthy weight, thereby, preventing overweight and obesity, risk factors for CVDs
  • Helps build and maintain healthy bones, muscles and joints, thereby, resulting in managing osteoarthritis better, reducing the risk of developing osteoporosis and becoming stronger so as to walk and move about without falling
  • Psychologically speaking, helps to lessen depression and anxiety, improve mood/state of mind and increase ability to accomplish daily tasks throughout the life span
  • Improves quality of life for individuals suffering from poor health by enhancing physiological and psychological well-being (see U.S. Department of Health and Human Services, 1996; U.S. Department of Health & Human Services, 2002)

Furthermore, on average, people who are physically active tend to outlive those individuals whose day-to-day existence is sedentary.[3]  Even a moderate amount (i.e., 30 minutes a day) of moderately intense physical activity on a regular basis helps prevent disease and promote physiological and psychological health for young people and adults, while lowering morbidity and mortality rates for both older and younger adults. There is “an emerging consensus among epidemiologists, experts in exercise science, and health professionals that physical activity need not be of vigorous intensity for it to improve health” (U.S. Department of Health & Human Services, 1996, p.3).

On the flipside of the health coin, epidemiologic studies, cohort studies, case-control studies, cross-sectional studies and clinical trials have established that physical inactivity is a major risk factor for a variety of diseases and conditions, including the following:

  • All-cause mortality
  • Musculoskeletal problems (e.g., sarcopenia/loss of muscle mass, strength & function)
  • Osteoporosis and bone fractures, osteoarthritis, low back/lumbar pain
  • Metabolic conditions (e.g., overweight & obesity, Type 2 diabetes mellitus, hypertension/high blood pressure & metabolic syndrome)
  • Cancer
  • Neurological conditions (e.g., cognitive impairment & dementia)
  • Cardiovascular disease (e.g., coronary heart disease & stroke) (see U.S. Department of Health & Human Services, 2002; U.S. Department of Health & Human Services, 2000; U.S. Department of Health & Human Services, 1996; Vuori, 2004).

Barriers to Regular Physical Activity

Given all the research and reasons to motivate people to engage in regular physical activity, too many people succumb to a sedentary lifestyle. It is too easy to conclude that people fail in their effort to stay physically active because they lack the will power or are just lazy. In my view, it is far more complicated in that remaining physically active, especially sustaining an exercise regimen, is not just a matter of will power or motivation. Engaging in regular physical activity includes behavioral, psychological, sociological and nutritional factors. It is reported that 50% of people who start an exercise-training program quit within six months. They quit for a variety of reasons such as the following:

  • ·        Not knowledgeable enough about what to do or how to do it
  • ·        Suffer from medical problems/health issues
  • ·        Not enough time because of busy career schedule
  • ·        Not enjoyable or just not plain fun
  • ·        Not convenient or compatible with lifestyle
  • ·        Not fast enough results because of unrealistic expectations
  • ·        Too difficult to do
  • ·        Too boring because of having to do the same thing over and over again
  • ·        Too uncomfortable or painful because of joint and muscle pain

Many of these same reasons why people quit an exercise-training program can be applied to folks failing in their effort to be more physically active in their day-to-day lives.

Poor Nutritional Status

In addition to the above mentioned factors, it is my view that too many people are erratic with or unable to sustain their exercise-training program or engage in regular physical activity because they suffer from a poor nutritional status and, thus, lack the optimal energy levels to meet the physiological energy demands of being physically active on a regular basis. Unfortunately, well-intentioned and highly motivated people are too frequently unaware they are suffering from suboptimum energy levels due to a poor nutritional status and do not understand fully the connection among energy, food and physical activity.

Energy, Food and Physical Activity

There is a dynamic interaction involving energy, food and physical activity. Nutrition (i.e., the supplying, ingesting, digesting, absorbing and assimilating of nutrients containing and enhancing energy) is a necessary condition for regular physical activity. Without the energy derived from food, engaging in regular physical activity is impaired.

In a real sense, when it comes to physical activity (no matter its form, intensity or duration) it is all about energy.  The human body is a virtual energy machine. Above all of the other functions it must perform, the first priority of the human body is to satisfy its need for energy. Every cell of every type of tissue, organ and system of the body requires an ongoing supply of energy to function, especially when the body is engaged in physical activity. Hence, without a sufficient amount of energy the processes implicated in physical activity such as metabolism regulation, muscle contraction and the building and repairing of tissues become impaired.



Technically, energy is the capacity to do work. Work is achieved when there is a release of energy resulting in movement and change (e.g., a change in the amount and type of energy). In physiological terms, work can include anything involved in or implicated with the movement of molecules to muscles. Consequently, humans evolved with a number of physiological processes to carry out different types of work including (1) initiating various chemical reactions resulting in increases and decreases in energy (i.e., metabolic processes), (2) growing and reproducing through the acquisition and processing of nutrients (i.e., generative processes), (3) responding to internal and external changes (i.e., responsive processes) and (4) coordinating/sequencing and regulating of all metabolic functions/chemical reactions through specific pathways by the use of enzymes (i.e., control processes) (see Enger, et al., 2005). All of these and other specific related types of work occurring within the human body require the intake, transformation and expenditure of energy.

Transformation of energy. It is important to understand that energy is not created. The law of conservation of energy, also known as the first law of thermodynamics, states that energy cannot be created or destroyed but can only be transformed or converted from one form to another. For example, in order to engage in any sort of physical activity of any kind, whether running a marathon, walking down the street, mowing the lawn or weight-training at the gym, there is a conversion of potential chemical energy stored in the body into mechanical energy resulting in movement of the body through the contraction of muscles.

Potential & kinetic energy. Generally speaking, there are two major types of energy, potential energy and kinetic energy. Potential energy is stored energy. Kinetic energy is potential energy which has been released, thereby, causing things to be put into motion. In short, when potential energy is released it is transformed into kinetic energy. A sprinter ready to run a 100 yard dash possesses the potential energy required to complete the run. The conversion of the sprinter’s potential energy into kinetic energy occurs during the actual running of the 100 yards.

Six types of energy. There are six specific forms of energy all of which can be in either a potential or kinetic state and all of which are interchangeable with one another according to the laws of thermodynamics: 1. chemical, 2. mechanical, 3. heat, 4. electrical, 5. light, and 6. nuclear. Humans are in one way or another implicated with all of these forms of energy. However, the chemical, mechanical, heat and electrical forms of energy are of special importance in physical activity. For example, during physical activity chemical energy is converted into mechanical, electrical and heat energy to allow for muscle contraction and movement of the body, electrical nerve impulses to stimulate muscle contraction and warming of muscles for ease of movement, respectively.  

Food = Calories = Energy

The energy humans require to engage in physical activity is derived from three major types of foods called macronutrients. They are carbohydrates, fats and proteins. Chemical energy is contained within the chemical bonds of these macronutrients. The amount of chemical energy contained in carbohydrates, fat and protein is measured in terms of calories. A calorie is a unit of heat reflecting the energy value of food. More precisely, a calorie (more accurately a kilocalorie or kcal) is the amount of heat required to increase the temperature of one kg of water by one degree Celsius. Generally speaking, one gram of carbohydrate and one gram of protein each are equal to four calories each, while one gram of gram of fat equals nine calories. The calories contained in these macronutrients serve as potential energy for the body to engage in physiological work of one sort or another.

Through the process of digestion, carbohydrates, fats and proteins are broken down into molecules the body can use and store as energy. Carbohydrates are broken down and stored as serum glucose, liver glycogen and muscle glycogen. Fat is broken down and stored as serum-free fatty acids, serum triglycerides, muscle triglycerides and adipose tissue triglycerides. Protein is broken down and stored as muscle protein. (see Williams, 2005).

Energy Currency of the Body = Adenosine Triphosphate

An important principle of energy is that cells neither acquire nor are able to use the energy directly from food for their continuous, immediate and long-term energy needs. Instead, the chemical energy in food needs to be transformed into a form the body can use for its immediate purposes. Through a complex series of chemical reactions (a topic too broad to consider here) the energy-containing chemical bonds found in carbohydrates, protein and fat are broken and energy is released, converted, transported to and stored in the cells of the body.

All the different forms of energy extracted from carbohydrates, protein and fat and then stored in the body serve to replenish adenosine triphosphate (ATP). ATP is a complex, energy-rich molecule. It is the primary energy currency used to satisfy the body’s continuous and immediate need for energy to carry-out all of its physiological functions. Only a relatively small amount of ATP is stored in the tissues of the body. At any one time, the amount of available or stored ATP in the body is approximately 85 grams or three ounces. This amount of ATP would be only enough energy to fuel running full-out for a few seconds (Katch & McArdle, 1993). Therefore, ATP must be continuously synthesized to allow the body to function physiologically. When carbohydrates, fat and protein are consumed, all the potential energy contained within these macronutrients is utilized for the purpose of re-synthesizing ATP.


Given that macronutrients contain energy and all of the body’s physiological functions require energy, it is useful to think of energy in the form of calories as being a common denominator in the relationship between food and physical activity (see Katch & McArdle, 1993). 



Regular physical activity is fundamental to good health. While I consider nutrition to be the first principle of health, it must be accompanied by regular physical activity in order to achieve and maintain optimal health over the lifespan.

Since the time of Hippocrates and Plato and throughout the history of Western civilization, numerous health benefits derived from regular physical activity and exercise have been identified and scientific evidence supporting these benefits has steadily accumulated (see U.S. Department of Health & Human Services, 1996). Thus, people have good reasons to keep their bodies moving. For example, regular physical activity, whether in the form of a structured exercise program or just part of daily living routines, will help to keep the body energized, healthy and less vulnerable to disease as the aging process proceeds through the lifecycle. Yet, despite the accumulated knowledge about the health benefits of physical activity, a sedentary lifestyle is one of the distinguishing features of modern life in theUnited States.


Many people are well-intentioned and really want to live a physically active lifestyle. Typically, they do not have too much difficulty getting started but find it far more difficult to sustain a regimen of regular physical activity. There are a variety of reasons as to why such a large segment of the population fail at being physically active on a day-to-day basis and give way to a sedentary lifestyle, even though they know that regular physical activity will improve the quality of their lives and health. Notwithstanding all of the behavioral, psychological, sociological and physiological variables that bear upon whether or not people will engage in regular physical activity, nutritional factors cannot be underestimated.

Specifically, too many people have difficulty in being physically active because they are neither nutritionally informed nor nutritionally prepared enough to meet the energy demands associated with living a lifestyle characterized by regular physical activity. Stated another way, many people who are well-intentioned about keeping their bodies moving suffer from an overall poor nutritional status and, thus, are unable to meet the physiological energy demands of being physically active on a habitual basis.

Therefore, if it is all about the energy, then the first step in being energy-ready to live a physically active lifestyle is to become informed about basic concepts and principles of energy from a nutritional perspective. The second step is to energize the body with proper nutrition. The primary goal of Healthful Hints for February, 2008, was to help readers accomplish the first step by discussing the characteristics of energy, sources of energy, different types of energy and the way in which energy is stored in the body, along with outlining proven health benefits of regular physical activity, barriers to regular physical activity and the relationship among energy, food and physical activity. The March issue will present specific dietary and nutritional strategies to energize and maximize physical activity. Until then, make a commitment to keep your body moving.





Caspersen, C.J., Powell, K.E. & Christensen, G.M. (1985). Physical activity, exercise, and physical fitness: definitions and distinctions for health-related research. Public Health Reports 100, 126-131.

Enger, E.D., Ross, F.C. & Bailey, D.B. (2005). Concepts in biology (11th ed.).Boston: McGraw Hill.

Hippocrates (1953).  Regimen I (W.H.S. Jones, Trans.),Cambridge, Mass: Harvard University Press (Original work published, 400 B.C.).

Katch, F.I. & McArdle, W.D. (1993). Introduction to Nutrition, exercise, and health. (4th ed.).Philadelphia: Lea & Febiger.

U.S.Department of Health and Human Services (2002). Physical activity fundamental to preventing disease.U.S. Department of Health and Human Services, Office of the Assistant Secretary for Planning and Evaluation.

U.S.Department of Health and Human Services (2000). Healthy people 2010: Understanding and improving health and objectives for improving health ( 2nd ed.). (Vol. 2, pp. 22/1 – 22/39). Washington,DC:U.S. Government Printing Office.

U.S.Department of Health and Human Services (1996). Physical activity and health: A report of the surgeon general.U.S. Department of Health and Human Services, Centers for Disease Control and Prevention,NationalCenter for Chronic Disease Prevention and Health Promotion.Atlanta,GA.

Vuori, I.(2004). Physical inactivity as a disease risk and health benefits of increased physical activity. Perspectives, 6, 1-72.

Suggested Citation: Garko, M.G. (2012, March). Keep the body moving – Part I: It’s all about the energy. Health and Wellness Monthly. Retrieved (insert month, day, year), from