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Defining and Measuring Energy

Defining and Measuring Energy. Chapter 2 Nutrition for Sport and Exercise Dunford & Doyle. Learning Objectives.

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Defining and Measuring Energy

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  1. Defining and Measuring Energy Chapter 2 Nutrition for Sport and Exercise Dunford & Doyle

  2. Learning Objectives • Define and explain bioenergetics (using in your definition ATP, calorie, kilocalorie, and other energy-related terms), explain the concepts of energy transfer and utilization in the body, and identify the primary source of energy in the body and how it is used by skeletal muscle during exercise

  3. Learning Objectives • Explain how the energy content of food and energy expenditure are measured directly and indirectly and how the most accurate estimates can be made • List and explain the components of the energy balance equation, the factors that influence metabolic rate, how metabolic rate is measured or predicted, and the impact of physical activity on energy expenditure

  4. Sport and exercise require the use of energy p37

  5. Key Words • Bioenergetics • Potential vs. kinetic energy • Adenosine Triphosphate (ATP) & Adenosine Diphosphate (ADP) • Calorie = kilocalorie, and one kilocalorie = 4.2 kilojoules, expressions of thermal energy (heat) • Direct and indirect calorimetry • Basal and Resting Metabolic Rate • Total Energy Expenditure

  6. Bioenergetics • Definition of Bioenergetics: The process of converting food stuffs into a biologically useful form of energy • Energy In = Energy Out • “Energy In” is food intake • “Energy Out” includes resting metabolism, and physical activity, exercise and sport • Definition of Energy: The ability to do work • Types of Energy – atomic, chemical, electrical, mechanical, radiant, and thermal

  7. Energy Concepts • First Law of Thermodynamics: “Conservation of Energy” • Energy is neither created nor destroyed • Energy can be transformed from one type to another

  8. Energy Concepts • In the human body, energy is consumed in the form of food • Humans do not create energy or lose energy, rather they have a variety of processes that are used to transfer energy from one form to another for use by the body • Not all energy is used for force production – large amount of energy transferred to heat

  9. Energy Concepts • Humans are relatively inefficient in energy conversion • Ex/ ~25% of the energy used by humans when bicycling is converted to useful work, while a steam engine converts ~85% of electrical or thermal energy used to mechanical work

  10. Energy Concepts • Types of Energy (See Figure 2.3) • Potential energy—stored energy for future use • Ex/ stored water in reservoir behind dam • Kinetic energy—potential energy as its released to perform work • Ex/ stored water converted to mechanical energy

  11. Potential and Kinetic Energy – Figure 2.3

  12. Energy Concepts • Types of Chemical Reactions (See Figure 2.5) • Endergonic reactions—store energy • Ex/ Setting a mousetrap requires input of energy – this energy is then stored • Exergonic reactions—release energy • Ex/ When mousetrap is triggered, the stored energy is released

  13. Endergonic and Exergonic Reactions – Figure 2.5 Figure 2-5 p41

  14. ATP • ATP = Adenosine Triphosphate • High-energy phosphate compound • Stores energy in its phosphate bonds • Adenosine formed by: • Protein molecule (adenine) • Sugar molecule (ribose) • Energy is released from ATP very rapidly in a one-step chemical reaction when a phosphate group is removed • ATPase (enzyme) breaks down ATP into ADP and inorganic phosphate (Pi)

  15. ATP

  16. ATP and Release of Energy

  17. ATP and Release of Energy • ATP is energy source available to all cells in body • Exercise or sports activities may require a large total amount of energy (marathon running) or may require a high rate of energy expenditure (sprinting) • In skeletal muscle, globular heads of a thick protein called myosin must form crossbridges with a thin contractile protein called actin to produce force • Myosin heads swivel in a power stroke causing actin strands to be pulled so they slide over myosin filaments • “The Sliding Filament Theory” of muscle contraction

  18. ATP and Release of Energy • ATP molecules are stored on the myosin head at the site where energy is needed for production • When ATP is hydrolyzed (split), the energy released from the phosphate bonds puts the myosin heads in an energized state allowing them to form crossbridge with actin • ATP must be reloaded onto myosin head, which allows a brief period of relaxation and prevents muscle strain

  19. Model of Muscle Contraction

  20. ATP in Muscle During Exercise • Research shows that ATP concentrations in exercising muscle rarely drop more than 20-30%, even during highest exercise intensity (Hirvonen, 1987) • Fatigue occurs once ATP concentration is reduced to approximately 70% • Response of ATP concentration in muscle to exercise reveals: • A relatively large proportion of ATP stored in muscle is not able to be used for force production, even during high intensity exercise • ATP used to provide energy for muscle force is replaced very rapidly

  21. ATP in Muscle During Exercise ATP does not drop more than 20-30% Muscle fatigues and protects against ATP depletion

  22. Resynthesis of ATP • ATP must be resynthesized to be used in the future – this is called rephosphorylation • Rephosphorylation is an endergonic reaction requiring input of energy • Inorganic phosphate (Pi) is chemically joined to ADP to produce ATP • The body uses 3 major energy systems during exercise to rephosphorylate ADP into ATP: • Creatine phosphate • Anaerobic glycolysis • Oxidative phosphorylation

  23. Rephosphorylation of ADP to ATP

  24. Resynthesis of ATP— The Three Energy Systems

  25. Measuring Energy – Definitions

  26. Measuring Energy

  27. Measurement of Energy in Food or “Energy In” • Bomb calorimeter • Device used to determine energy by amount of heat produced • Method of direct calorimetry analysis of food • The “bomb” is a metal container in which the food sample is burned in a pressurized, pure oxygen atmosphere • Bomb is surrounded by water bath that is insulated from outside temperature changes • Temperature of surrounding water bath is recorded to determine thermal energy of food

  28. Measurement of Energy in Food

  29. Measurement of Energy in Food or “Energy In”

  30. Measurement of Energy in Food or “Energy In” • Fat = 14g x 9 kcals/g = 126 kcals • CHO = 26g x 4 kcals/g = 104 kcals • Pro = 4g x 4 kcals/g = 16 kcals • TOTAL = 246 kcals/serving

  31. Measurement of Energy Expenditure or “Energy Out” • Direct calorimetry • Measures changes in thermal or heat energy • Heat emitted from human subject is recorded as a temperature change in an insulated water layer around a room-like calorimeter • Used only for research purposes • Not portable • Very expensive

  32. Measurement of Energy Expenditure or “Energy Out” • Indirect calorimetry • Measures changes in oxygen consumption (VO2) and carbon dioxide (VCO2) production • Air is circulated through chamber of calorimeter, and the difference in the oxygen and CO2 in air entering and leaving is calculated • 1 L of oxygen consumed is ~5 kcals energy expended • Can be room-sized or open-circuit mobile system (metabolic cart)

  33. Whole-room Calorimeter

  34. Metabolic Cart • Measures Resting Metabolic Rate (RMR) • Subject rests in supine position while connected to the metabolic cart through a breathing tube with a mouthpiece, face mask, or ventilated hood • High degree of accuracy • More accurate than prediction equations! • Equipment is expensive • Requires trained personnel to operate • Requires time for setup, cleanup, maintenance

  35. Metabolic Measurement System

  36. Measuring Resting Metabolic Rate

  37. Simplified Portable RMR Measurement System

  38. Portable Metabolic Measurement System

  39. Portable fitness devices can measure RMR Figure 2-20 p51

  40. Measuring Energy • Doubly Labeled Water (DLW) • Involves ingestion of a quantity of water labeled with a known concentration of naturally occurring, stable isotopes of hydrogen and oxygen  • Amount of radioactivity being eliminated as water is measured in urine samples at specific time intervals • Differences in rates of excretion of oxygen and hydrogen used to calculate total energy expenditure  • Measured over longer time period, usually 1-3 weeks, which helps to capture habitual energy expenditure patterns • High validity and reliability • High cost of materials • Expert required to analyze

  41. Concepts of Energy Balance

  42. Estimating Energy Intake • Self-report food intake using food diary • Software programs compute energy and nutrient intake • Foods and beverages must be recorded accurately • 1/3 of adults underreport food intake • Issues – snacks, fluids, portion size, memory, tedious

  43. Total Energy Expenditure (TEE) or “Energy Out” • TEE = Total Energy Expenditure • Definition: The total amount of energy required by the body over the course of a day • 3 components of TEE: • Resting metabolism – makes up ~70% of TEE • Thermic effect of food – about 10% of TEE • Physical activity – about ~ 20% of TEE

  44. Components of Total Energy Expenditure (TEE)

  45. Basal and Resting Metabolism • Basal Metabolic Rate (BMR) • Energy necessary to keep body alive a complete rest (circulate blood, breathe, digest food, maintain body temperature, etc.) • Minimal energy expenditure compatible with life • Also referred to as BEE • Measured under defined laboratory conditions • Used for research

  46. Basal and Resting Metabolism • Resting Metabolic Rate (RMR) • The amount of energy needed by the body to maintain a nonactive, but alert state • Also referred to as REE • Estimate of BMR • Measured under less strict conditions • RMR is typically 10% greater than BMR • Used for practical purposes • ~ 70% of TEE is attributed to RMR

  47. RMR • 2 factors that decrease RMR in a healthy individual: • Age • 1-2% decline per decade • Starvation • Famine, dieting, severe self-restriction • Can reduce RMR by 20% or more • The reduction in RMR may actually impede weight loss

  48. RMR • Individuals with more fat-free mass have higher RMR than those with less fat-free mass (Leonard et al, 2004) • Adipose (fat) tissue has low metabolic activity • Fat-free tissues are more metabolically active, even at rest • Larger body size (taller, broader) associated with higher RMR • Metabolic rate of females tends to be ~100 kcals/day less than of males

  49. RMR • Hormones can affect RMR • Thyroid hormones influence metabolism • When thyroid hormones are elevated, RMR is high • When thyroid hormones are low, RMR is low • Increase in estrogen and progesterone can increase RMR • Menstruation, pregnancy • Decrease in estrogen can decrease RMR • Menopause • Exercise increases some hormones (epinephrine, norepinephrine), which increases RMR

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