I DEAPERSONALTRAI NER A P R I L 2 0 0 3By Carole A. Conn, PhD, RD, and Len Kravitz, PhDIts sources, uses and ultimateeffect on weight gain and loss.theFIGURE 1:Pick up any packaged food, and you will see thenumber of calories listed on the label. Of course,nonpackaged foods, such as fresh produce, havecalories, too; they just dont carry labels telling youhow many. Most people know that the body uses thecalories contained in foods for energy and that, ifthey consume more calories than they expend, theywill gain weight. (They also know that, if they do theopposite, they will lose weight.) Nonetheless, whatexactly is a calorie, why do foods have calories andhow does the body use them? This article answersthese and other questions.What Is a Calorie?In the United States, calorie is the most commonterm used to express energy expenditure. A calorie isdefined either as the heat energy required to raise thetemperature of 1 gram of water by 1 degree Celsiusor as 4.184 joules, 1 joule being the heat energygiven off when 1 ampere of electrical current flowsthrough a resistance of 1 ohm for 1 second (Dirckx2001).In scientific writing, the energy expended duringphysical activity and stored in foods is actually mea-sured in kilocalories (kcal), the heat energyrequired to raise the temperature of 1 kilogram ofwater by 1 degree Celsius. However, because acalorie is such a small unit of energy, the word calo-ries is generally used to mean kilocalories outsidethe realm of scientific literature. We follow this cus-tom in this article.Why Do Foods Have Calories?All foods come either from plants or from animalsthat have eaten plants. Plants create the primaryfood molecules that contain the energy quantified ascalories (Taiz & Zeiger 1998). Green plants createthese molecules from carbon dioxide and waterthrough the process of photosynthesis. In photosyn-thesis, the chlorophyll in these plants absorbs radi-ant energy from the sun. This energy is then con-verted into chemical energy contained in the bondsthat link the carbon from carbon dioxide (CO2) towater (H2O) to create carbohydrates (CH2O); theloose oxygen (O2) is freed into the atmosphere.From carbohydrates, plants can create othermolecules (including fats and proteins) that also con-tain captured energy. Figure 1 shows the Calvincycle and shikimic acid pathway, two important pro-cesses that enable plants to synthesize carbohy-drates and the essential amino acids that becomeparts of plant proteins.Like plants, humans can use carbohydrates tosynthesize most fatty acids, fats, nonessential aminoacids and proteins. However, the primary source ofall calories remains carbohydrates themselves,which only plants create.remarkablecal orieI DEAPERSONALTRAI NER A P R I L 2 0 0 3Why Do Di fferent Foods Have Different Calorie Levels?Foods contain six classes of nutrients:carbohydrates, fats, proteins, vitamins, minerals andwater. Only carbohydrates, fats and proteins providethe substrate that the body needs to break down forenergy. Because these three classes of nutrientsare consumed in large quantities (50 to 500 gramsper day), they are called macronutrients. In con-trast, the micronutrient classes of vitamins andminerals need to be consumed in only very smallquantities (1 to 100 milligrams per day). Althoughvitamins, minerals and water provide no calories,they are essential to the bodys ability to break downmacronutrients to release their stored energy for bodily functions.Most foods are mixtures of some or all of the sixclasses of nutrients, and different foods contain dif-ferent amounts of each class. For example, buttercontains a lot of fat; some protein, vitamins, mineralsand water; and very little carbohydrate. Meat con-tains a lot of protein and water; some fat, vitaminsand minerals; and very little carbohydrate. Whole-wheat bread contains a lot of carbohydrate, vitaminsand minerals; some protein and fat; and very littlewater. Different foods have different calorie levelsbecause their regular servings contain differentamounts of carbohydrates, proteins and fats andthese energy-providing nutrients supply differentamounts of energy per gram. Fats supply the mostenergy at 9 calories per gram. Carbohydrates pro-vide 4 calories per gram, as do proteins (Merrill &Watt 1973).How Do Calories BecomeAvailable to the Body?The energy stored in the chemical bonds ofmacronutrients is transformed into high-energy phos-phate bonds usable in the myriad metabolicprocesses of the body (Groff & Gropper 2000). Themain molecule containing these phosphate bonds isadenosine triphosphate (ATP). The transformation offood into ATP involves not only digestion but alsoabsorption and metabolic catabolism (the chemi-cal breakdown of large molecules into smaller ones).During digestion, carbohydrates are broken downinto the simple sugars glucose (primarily), fructoseand galactose. Proteins are broken down first intoamino acids and dietary fats and then into free fattyL E A R N I N GOB J E C T I V E SAfter reading this article, readersshould be able to:Explain the different definitions of a calorie.Discuss why different foods havedifferent caloric values.Explain how the bodys energysystems work and identify the bestways to use exercise to optimizecalorie expenditure.Describe the mechanisms ofcalorie-burning supplements andthe potential risks associated with using them.T OTA L C E C S1 contact hour from ACECredits from ACE may be appliedtoward the ACSM continuingeducation process. They are alsoaccepted by W.I.T.S. and NFPT.I DEAPERSONALTRAI NER A P R I L 2 0 0 3acids and glycerol. These small molecules areabsorbed by the cells lining the intestines andpassed into the bloodstream, where they circulateuntil they enter the cells in the rest of the body. Thesubsequent creation of ATP from the metaboliccatabolism of glucose, free fatty acids and aminoacids occurs within each cell.The Role of ATPWhen split with the help of enzymes, the high-energy bonds in ATP release that energy for use bythe muscles, liver and brain and all of the bodysmetabolic systems. Essentially, the energyharnessed from the breakdown of food is directlyused not to exercise but to produce ATP, which thebodys tissues store in very small amounts. Phos-phocreatine (PC, also known as creatinephosphate), another high-energy compound, is alsostored in tissues in limited amounts. The breakdownof PC is also used not to produce energy directly butto regenerate ATP quickly during high-intensity exer-cise.Can DietarySupplementsEnhanceCalorieBurning?Many dietary supplements promise toenhance calorie burning and cause weightloss without requiring changes in diet andactivity level. The major constituent in thesesupplements is either ephedra (also known as Ma Huang) or ephedrine, its syntheticequivalent.E P H E D R AEphedra is the alkaloid found in the extractof the plant Ephedra sinica and several otherEphedra species (Betz et al. 1997; Foster &Tyler 1999; Jellin et al. 2000). (Alkaloids aremolecules that are made by plants, contain ni-trogen and have significant action in the body.)In folk medicine, ephedra has been used as ashort-term remedy for nose colds andasthma. In the early 1900s, Americanphysicians prescribed it as a central nervoussystem stimulant (Foster & Tyler 1999). Theidea of using ephedra several times per dayfor several weeks to foster weight loss hasbeen traced back to 1972, when a Danishgeneral practitioner noticed unintentionalweight loss in his asthma patients who tookephedrine as part of their medication(Greenway 2001).The ephedra in dietary supplements thatclaim to increase energy and foster weightloss stimulates the sympathetic nervoussystem. Despite ephedras popularity, theInternational Olympic Committee (IOC),National Football League (NFL) and NationalCollegiate Athletic Association (NCAA) havebanned its use by their athletes. In addition,the U.S. Department of Health and HumanServices has recently called for an evaluationof ephedra-containing products and, becausethese products can be purchased easily,recommended that the strongest possiblewarning label be placed on them to protectthe public.Health Canada has asked for a halt on thesale of dietary supplements containing morethan 8 milligrams of ephedra per dose(Palevitz 2002). Unfortunately, label claimshave been found to differ substantially fromsupplement contents, so it is not easy toknow exactly how much active ephedra ispresent in a supplement. In one study of 20supplements, the actual ephedra content ofhalf of the supplements measured varied bymore than 20 percent from what their labelsclaimed. In one of the supplements, noephedra alkaloids were present; amongothers, variation among lots of the sameproduct was as much as 1,000 percent(Gurley, Gardner & Hubbard 2000).When checking supplement labels forephedra content, also look for Sida cordifolia,another herb containing ephedra alkaloids.E P H E D R A - C A F F E I N EIn combination with caffeine, anothersympathetic nervous system stimulant,ephedra has been shown to increase oxygenconsumption and, therefore, calorie burningin humans (Greenway, Raum & DeLanyF I GU R E 2 :How the Ephedra-Caffeine-Aspirin Stack Enhances Calorie BurningIn response to both ephedra and caffeine, the sympathetic nerve endings releasenorepinephrine (NE). NE acts on the beta-adrenergic receptors to incite the production ofintracellular cyclic AMP (cAMP), which increases calorie burning in the muscle cell.As indicated by the plus (+) symbols, both ephedra and caffeine can act directly on themuscles beta-receptors to activate calorie burning. They can also act indirectly by enhancingthe action of NE. As indicated by the negative (-) symbols, three molecules limit the ability ofNE to foster calorieburning: adenosine,phosphodiesterase andprostaglandin. Caffeineinhibits the effects of both adenosine andphosphodiesterase;aspirin inhibits thesynthesis ofprostaglandin.theremarkablecalorieI DEAPERSONALTRAI NER A P R I L 2 0 0 3How Do the Energy Systems of the Body Burn Calories?Every movement that a person makes in his dailylife requires the breakdown of ATP. Therefore, tosustain life, ATP is consistently used and regener-ated. However, the body stores such a limited sup-ply of ATP and PC, which lasts only as long asabout 30 seconds. Consequently, it depends onstored carbohydrates and fats and sometimes on proteins as backup to regenerate ATP. Thebodys ability to store these macronutrients forenergy production makes possible the successfulcompletion of various physical activities (Wilmore &Costill 1999).The high-energy, rapid-delivery ATP-PC system(also known as the phosphagen system) providesa very short supply of energy for use in physical2000). Several studies have shown that thecombination of ephedra and caffeine iseffective in enhancing weight loss (Boozer etal. 2002; Greenway 2001). Consequently,either synthetic caffeine or several differentherbs containing caffeine are included invarious weight loss supplements.Whether the ephedra-caffeine combination in a supplement consists of ephedrine andsynthetic caffeine or natural substancesfound in herbal extracts, its safety has beenquestioned. Several clinical trials regardingits effect on weight loss have reported fewadverse effects (Greenway 2001).Nonetheless, enough instances of severecardiovascular and nervous system problems(such as agitation, dizziness, insomnia,headache, weakness, sweating, heartpalpitations and tremors) and deaths havebeen attributed to the consumption ofephedra to warrant concern (Palevitz 2002;Haller & Benowitz 2000). On the other hand,some contend that the risks of being obeseoutweigh the risks of taking these stimulantsshown to promote weight loss (Greenway2001). These two arguments make the use ofdietary supplements containing ephedra andcaffeine very controversial.These are some of the ingredient names thatindicate the presence of caffeine in ephedra-containing supplements:guarana (also known as Paullinia cupana,Brazilian cocoa or Zoom)kola nut (also known as Cola acuminata, Colanitida, bissey nut or cola seed but not to beconfused with gotu cola, which does not con-tain caffeine)green tea (also known as Camellia sinensis)yerba mat (also known as Ilex paraguarien-sis, mat, Paraguay tea or St. Bartholomewstea)E P H E D R A - C A F F E I N E -A S P I R I NAspirin is also often added to supplementssold to promote weight loss. Bodybuildershave used the ephedra-caffeine-aspirin stackwith synthetic compounds to reduce theirweight for competition. (See Figure 2.)The calorie-burning effects of ephedra andcaffeine last longer when aspirin is added(Dulloo 1993). Unfortunately, aspirin maymake the undesirable side effects of thesenervous system stimulants last longer aswell. Considering that either aspirin or anherb containing natural aspirin-likemolecules can exacerbate the effects ofephedra and caffeine (or caffeine-containingherbs, such as guarana, cola and tea), youshould look on the labels of dietarysupplements for these aspirin-like herbs:willow (also known as white willow)aspen barkblack cohoshpoplarsweet birchwintergreenS Y N E P H R I N EProbably because of the adverse publicitysurrounding ephedra, some newer weightloss or calorie-burning supplements containsynephrine instead and claim to benonstimulating to the nervous system.Derived from Citrus aurantium (also known asthe Seville, or bitter, orange), synephrine issimilar to ephedrine, but little regarding itseffects in humans has been published.According to a recent study, it appears tohave minimal effects in healthy adults(Penzak et al. 2001). However, individualswith hypertension or rapid heartbeat andthose taking decongestant-containing coldtablets are warned to avoid bitter orange.C ON J U GAT E DL I N OL E I C A C I DConjugated linoleic acid is anothersupplement sold to promote weight loss. Thisunsaturated fatty acid occurs naturally in beefand beef fat, which many Americans eat lessthese days. Fortunately, it has several differentforms, and substantial evidence shows thatcertain forms can decrease body fat in animalssignificantly (Evans, Brown & McIntosh 2002).However, its mechanism of action in animalshas not yet been identified, and the datareflecting its effect in humans are conflicting.Therefore, at this point, its unknown whetheror not conjugated linoleic acid enhancescalorie burning.C U R R E N T S TAT U SOF T H E R E S E A R C HCurrently, no dietary supplement sold to pro-mote calorie burning can be recommended for maintaining a healthy body weight, eitherbecause none of them has proven effectivein humans or because the risks of heart ornervous system problems that they carry mayoutweigh their benefits.activities such as a sprint or a single set of a resis-tance exercise. Continued muscular exercise relieson the glycolytic and aerobic energy systems.The glycolytic system provides energy throughthe partial breakdown of glucose (found in the blood)and glycogen (glucose molecules stored in the liverand muscles). Through the process of glycolysis,glucose used by active muscles is incompletely bro-ken down into pyruvate in intracellular fluid (cyto-plasm). At every step of glycolysis, specializedenzymes are employed to speed up the chemicalreactions to provide energy for activities lasting 30seconds to 3 minutes, such as a 400-to-800-meterrun.Whereas glycolysis is sometimes called anaero-bic glycolysis because it does not require oxygen,aerobic metabolism, the bodys third and longest-I DEAPERSONALTRAI NER A P R I L 2 0 0 3lasting energy system, is driven by oxygen. Aerobicmetabolism is also called mitochondrial respirationbecause it occurs in the mitochondria, specializedorganelles within cells and dispersed richly amongmuscle cells to supply ATP to active muscles. Allphysical activities lasting 3 minutes or longer dependprimarily on mitochondrial respiration. During thisprocess, the products of carbohydrate breakdownare broken down further into carbon dioxide andwater, releasing energy used to regenerate ATP.ATP Production From Fat and ProteinWhereas carbohydrates can be broken down with orwithout oxygen, fats, which also help produce ATP,are metabolized only in the presence of oxygen.Free fatty acids, derived from triglycerides in dietaryfat, can be broken down into two-carbon compoundsfor use in mitochondrial respiration.At rest, proteins play a very minor role in ATP pro-duction. However, during prolonged endurance exer-cise, they may supply as much as 10 percent of theenergy needed.What Regulates ATP ProductionDuring Calorie Burning?Although the bodys three energy systems interactwith each other simultaneously to produce ATP, therelative extent of their roles depends on (1) exerciseduration and intensity, (2) fitness level and bodycomposition and (3) diet. How do cells control andregulate which macronutrients supply the caloricneeds of exercise? What tells cells to use more ofthe phosphagen system or transition into mitochon-drial respiration by predominantly using fats andcarbohydrates?Two methods of metabolic control are at work dur-ing exercise. One operates inside cells; the otheroperates outside cells. Specific regulatory hormoneseither activate or inhibit both of these control sys-tems.Intracellular regulation depends on key enzymesthatdepending on the levels of ATP, adenosinediphosphate (ADP) and other molecules present (orabsent) in cellsinhibit or activate ATP productionto meet the bodys energy needs. Because intracel-lular regulation is quick, it is closely linked to thephosphagen and glycolytic systems.In extracellular regulation, the second majorregulatory system, if the bodys glycogen level islow, the hormone glucagon stimulates gluconeogen-esis (glucose production from noncarbohydratesources) and releases glucose into the blood for useInterval TrainingDesignInterval training, which combines segments of high-intensity workand segments of moderate-to-light-intensity work, has been anintegral part of exercise programs for many years. Recently, ithas been more recognized as an essential component of programsdesigned specifically to improve cardiovascular function and bodycomposition. The specific design of an interval training programdepends on the energy systems for which training adaptationsare desired. Although a certain combination of training variablesmay stress a particular energy system, all three energy systemsare likely to experience training adaptations to some extent.Here is a sample interval training program designed to enhancethe bodys calorie-burning capacity. For this program, choose anendurance activity that your clients enjoy (such as walking, jogging,cycling, rowing, stair climbing or elliptical cross-training).S A MP L E I N T E RVA L P R OGR A MAlways begin gradually with a 3-to-5-minute warm-up of light-intensity cardiovascular activity to prepare the heart, lungsand musculoskeletal system for the workout to follow.After the warm-up, train for 4 minutes at a high intensity fol-lowed by 4 minutes at a moderate to light intensity.Alternate these 4-minute intervals for the entire workout toenhance the calorie-burning cellular systems. During the high-intensity interval, clients should feel comfortably challenged(hard on the Borg scale). During the moderate-intensityinterval, they should feel somewhat challenged (somewhathard on the Borg scale).Start with a 20-minute workout duration and progress up to 60minutes over several weeks, according to each clients fitnesslevel.For variety, regularly alternate the interval program with acontinuous cardiovascular exercise program.theremarkablecalorieI DEAPERSONALTRAI NER A P R I L 2 0 0 3by the muscles. During prolonged exercise,epinephrine and other hormones may activate hor-mone-sensitive lipase to begin breaking down storedtriglycerides for metabolism through mitochondrialrespiration.How Does Endurance TrainingEnhance Calorie Burning?Endurance (cardiovascular) training contributes to anumber of metabolic adaptations that enhance calo-rie burning.Increase in the Size of Slow-Twitch Muscle Fibers.Cardiovascular exercise relies primarily on slow-twitch muscles, and research has demonstrated thatthese muscle fibers become 7 to 22 percent largerthan corresponding fast-twitch fibers in response tocardiovascular training (Wilmore & Costill 1999).This increase in the size of a muscle increases itsmetabolic demands, improving calorie burning.Increase in the Number of CapillariesSurrounding Muscle Fibers. Capillaries are theblood vessels that form within muscle tissue the com-plex networks necessary for the exchange of oxygen,carbon dioxide, water and other cellular products.Cardiovascular exercise has been shown toincrease the number of capillaries surrounding mus-cle fibers by 5 to 15 percent for greater exchange ofgases, water and nutrients between the blood andthe working muscles to enhance calorie burning(Wilmore & Costill 1999).Increase in Myoglobin Content. Oxygen enteringthe muscle is bound to myoglobin, which storesoxygen and transports it to the mitochondria formitochondrial respiration when needed. Regularendurance training has been shown to increasemyoglobin content by 75 to 80 percent to increasethe trained muscles local storage capacity for oxy-gen (Wilmore & Costill 1999).Increase in the Size, Number and Efficiency ofMitochondria/Improved Efficiency of MitochondrialOxidative Enzymes. Research has demonstrated thatendurance training contributes to an increase in thesize (35%), number (15%) and efficiency ofmitochondria. In addition, cardiovascular exerciseenhances the efficiency of the mitochondrial oxida-tive enzymes that facilitate the breakdown reactionsof nutrients and subsequent production of ATP. Inone study, the oxidation of free fatty acids in cycle-trained males was 30 percent higher than that of thesame men in their pretraining status (Wilmore &Costill 1999).These metabolic changes improve submaximalendurance and maximal aerobic capacity to help thebody burn calories more efficiently during cardiovas-cular exercise (Wilmore & Costill 1999).How Does Resistance Training Enhance Calorie Burning?The largest component of the bodys total calorieexpenditure is the energy needed to maintain itsresting metabolic rate (RMR). RMR represents thecalories needed at rest to maintain all of the bodysvital processes and systems. Therefore, increasingRMR helps enhance calorie burning.Various factors influence RMR, but the bodysamount of muscle tissue, one of the most metaboli-cally active kinds of tissue, is particularly important.Therefore, the more muscle one has, the higherones RMR, and, as you know, resistance trainingbuilds muscle.One well-designed and meaningful studyshowed a 7 percent increase in RMR in men andwomen ages 56 to 80 after 12 weeks of resistancetraining. The exact reasons for the increase in theirRMR are complex but may include an increase inthe turnover of proteins, an increase in the activity ofvarious enzymatic reactions, an increase in the con-centration of metabolic hormones, the replenishmentof glycogen stores and the repair of muscle tissue(Campbell et al. 1994).Which Exercises Are Best for Burning Calories?Both endurance and resistance training programsare needed to optimize calorie expenditure.Endurance exercise should use the large muscles ofthe body in a continuous, rhythmic fashion; be rela-tively easy to maintain at various workout intensities;and, to encourage adherence, satisfy the exerciserspersonal interests. To avoid overuse injury, vary themode of endurance training regularly.A major way to optimize energy expenditure inendurance exercise is to vary the intensity with vari-ous interval training schemes. Using exercise modesthat can be easily adjusted or graded to overloadthe cardiorespiratory system is quite helpful. Forinstance, increasing the grade of a treadmill canmake walking on it more challenging, and stationarycycling becomes more demanding when the pedalingresistance is increased.Although the type of resistance training programbest for optimal calorie expenditure is unknown,recent research on periodized programs has shownfavorable results (Marx et al. 2001). See Circuit vs.Periodized Resistance Training for Women (IDEAPersonal Trainer, November-December 2002, pp.28-33) for an extensive review of a contemporaryperiodized training program.I DEAPERSONALTRAI NER A P R I L 2 0 0 3How Does ThisInformation HelpClients?Understanding the origins of calo-ries, the processes by which calo-ries are turned into energy and theenhanced calorie-burning effectsof regular exercise should enableyou to help your clients controltheir weight not by taking poten-tially risky supplements but byeating a sensible diet and partici-pating in properly designed car-diovascular and resistance train-ing.Carole A. Conn, PhD, RD,teaches nutrition science at theUniversity of New Mexico,Albuquerque (UNMA); is a fellowof the American College of SportsMedicine (ACSM); and lecturesinternationally on nutrition, exer-cise and health. Her researchfocuses on the effects of nutritionand exercise on immune functionand cardiovascular health.Len Kravitz, PhD, is aresearcher and the coordinator ofexercise science at UNMA. He isalso the author of four books, theproducer of six exercise videos,an international lecturer on healthand fitness and a contributing edi-tor of IDEA Personal Trainer andIDEA Health & Fitness Source. 2003by IDEA Health & Fitness Inc. All rightsreserved. Reproduction without permission isstrictly prohibited.REFERENCESBetz, J.M., et al. 1997. Chiral gas chromato-graphic determination of ephedrine-typealkaloids in dietary supplements containingMa Huang. Journal of the Association ofAnalytical Communities International, 80 (2),303-15.Boozer, C.N., et al. 2002. Herbal ephedra/caf-feine for weight loss: A 6-month randomizedsafety and efficacy trial. International Journalof Obesity and Related Metabolic Disorders,26 (5), 593-604.Campbell, W.W., et al. 1994. Increased energyrequirements and changes in body compositionwith resistance training in older adults.American Journal of Clinical Nutrition, 60 (2),167-75.Dirckx, J.H. (Ed.). 2001. Stedmans ConciseMedical Dictionary for the Health Professions(4th ed.). Philadelphia: Lippincott, Williams &Wilkins.Dulloo, A.G. 1993. Ephedrine, xanthines andprostaglandin-inhibitors: Actions and interac-tions in the stimulation of thermogenesis.International Journal of Obesity and RelatedMetabolic Disorders,17 (Supplement 1), S35-40.Evans, M., Brown, J., & McIntosh, M. 2002.Isomer-specific effects of conjugated linoleicacid (CLA) on adiposity and lipid metabolism.Journal of Nutritional Biochemisty, 13 (9), 508-16.Foster, S., & Tyler, V.E. 1999. Tylers HonestHerbal (4th ed.). New York: Haworth HerbalPress.Greenway, F.L. 2001. The safety and efficacy ofpharmaceutical and herbal caffeine andephedrine use as a weight loss agent. ObesityReviews, 2 (3), 199-211.Greenway, F.L., Raum, W.J., & DeLany, J.P.2000. 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Energy Value ofFoods...basis and derivation. Washington,DC: U.S. Government Printing Office.Palevitz, B.A. 2002. Harmless energizers ordangerous drugs? The Scientist, 16 (24), 18-20.Penzak, S.R., et al. 2001. Seville (sour) orangejuice: Synephrine content and cardiovasculareffects in normotensive adults. Journal ofClinical Pharmacology, 41 (10), 1059-63.Taiz, L., & Zeiger, E. 1998. Plant Physiology(2nd ed.). Sunderland, MA: SinauerAssociates.Wilmore, J.H., & Costill, D.L. 1999. Physiologyof Sport and Exercise (2nd ed.). Champaign,IL: Human Kinetics.theremarkablecalorie