Bioenergetics Measurement of Work, Power, and Energy Expenditure Chapter 3, 6
BioenergeticsMeasurement of Work, Power,
and Energy Expenditure
Chapter 3, 6
Bioenergetics• Muscle only has limited stores of ATP• Formation of ATP
– Phosphocreatine (PC) 磷酸肌酸 breakdown– Degradation of glucose and glycogen (glycolysis)– Oxidative formation of ATP
• Anaerobic pathways 無氧代謝– Do not involve O2
– PC breakdown and glycolysis• Aerobic pathways 有氧代謝
– Require O2
– Oxidative phosphorylation
Anaerobic ATP Production
• ATP-PC system– Immediate source of ATP
– Onset of exercise, short-term high-intensity (<5 s)• Glycolysis 醣解作用
– Energy investment phase• Requires 2 ATP
– Energy generation phase• Produces ATP, NADH (carrier molecule), and pyruvate 丙酮酸
or lactate 乳酸
PC + ADP ATP + CCreatine kinase
The Two Phases of Glycolysis
Glycolysis: Energy Investment Phase
Glycolysis: Energy Generation Phase
Oxidation-Reduction Reactions• Oxidation
– Molecule accepts electrons (along with H+)
• Reduction– Molecule donates electrons
• Nicotinomide adenine dinucleotide (NAD)
• Flavin adenine dinucleotide (FAD)
FAD + 2H+ FADH2
NAD + 2H+ NADH + H+
Production of Lactic Acid (lactate)
• Normally, O2 is available in the mitochondria to accept H+ (and electrons) from NADH produced in glycolysis– In anaerobic pathways, O2 is not available
• H+ and electrons from NADH are accepted by pyruvic acid (pyruvate) to form lactic acid
Conversion of Pyruvic Acid to Lactic Acid
• Recycling of NAD (NADH NAD)• So that glycolysis can continue• LDH: lactate dehydrogenase 乳酸去氫脢
Aerobic ATP Production• Krebs cycle 克氏循環 (citric acid cycle, TCA
cycle, tricarboxylic acid cycle)– Completes the oxidation of substrates and
produces NADH and FADH to enter the electron transport chain
– O2 not involved• Electron transport chain
– Oxidative phosphorylation– Electrons removed from NADH/FADH are passed
along a series of carriers to produce ATP– H+ from NADH/FADH: accepted by O2 to form
water
The Three Stages of Oxidative Phosphorylation
The Krebs Cycle
Relationship Between the Metabolism of Proteins, Fats, and Carbohydrates
Bioenergetics of fats
• Triglycerides 三酸甘油酯– Glycerol + 3 fatty acids– Fatty acids converted to acetyl-CoA ( 乙輔酶 A)
through beta-oxidation– Glycerol can be converted to glycolysis
intermediates (phosphoglyceraldehyde) in liver, but only limited in muscle
– Glycerol is NOT an important direct muscle energy source during exercise
Formation of ATP in the Electron Transport Chain
The Chemiosmotic Hypothesis of ATP Formation
• Electron transport chain results in pumping of H+ ions across inner mitochondrial membrane– Results in H+ gradient across membrane
• Energy released to form ATP as H+ diffuse back across the membrane
• O2 accept H+ to form water• O2 is essential in this process
The Chemiosmotic Hypothesis of ATP Formation
Metabolic Process High-Energy Products
ATP from Oxidative Phosphorylation
ATP Subtotal
Glycolysis 2 ATP 2 NADH
— 6
2 (if anaerobic) 8 (if aerobic)
Pyruvic acid to acetyl-CoA
2 NADH 6 14
Krebs cycle 2 GTP 6 NADH 2 FADH
— 18 4
16 34 38
Grand Total
38
Aerobic ATP Tally
Efficiency of Oxidative Phosphorylation
• Aerobic metabolism of one molecule of glucose– Yields 38 ATP
• Aerobic metabolism of one molecule of glycogen– Yields 39 ATP
• Overall efficiency of aerobic respiration is 40%– 60% of energy released as heat
Control of Bioenergetics• Rate-limiting enzymes
– An enzyme that regulates the rate of a metabolic pathway
• Levels of ATP and ADP+Pi
– High levels of ATP inhibit ATP production– Low levels of ATP and high levels of ADP+Pi
stimulate ATP production
• Calcium may stimulate aerobic ATP production
Action of Rate-Limiting Enzymes
Control of Metabolic Pathways
Pathway Rate-Limiting Enzyme
Stimulators Inhibitors
ATP-PC system
Creatine kinase ADP ATP
Glycolysis Phosphofructokinase
AMP, ADP, Pi, pH
ATP, CP, citrate, pH
Krebs cycle Isocitrate dehydrogenase
ADP, Ca++, NAD
ATP, NADH
Electron transport chain
Cytochrome Oxidase
ADP, Pi ATP
Interaction Between Aerobic and Anaerobic ATP Production
• Energy to perform exercise comes from an interaction between aerobic and anaerobic pathways– 水龍頭 不是電燈開關
• Effect of duration and intensity– Short-term, high-intensity activities
• Greater contribution of anaerobic energy systems
– Long-term, low to moderate-intensity exercise• Majority of ATP produced from aerobic sources
Units of Measure 單位
• Metric system– Used to express mass, length, and volume– Mass: gram (g)– Length: meter (m)– Volume: liter (L)
• System International (SI) units– Standardized terms for measurement of:
• Energy: joule (J) 能量 : 焦耳• Force: Newton (N) 力 : 牛頓• Work: joule (J) 做功 : 焦耳• Power: watt (W) 功率 : 瓦特
Work and Power Defined
Work 功 作功
• Lifting a 5 kg weight up a distance of 2 mWork = force x distanceWork = 5 kg x 2 mWork = 10 kgm1 kgm = 9.8 joule1 joule = 0.24 calorie 卡
( 不是 Kcal 大卡 , 千卡 )
Power 功率
• Performing 2,000 kgm of work in 60 secondsPower = work timePower = 2,000 kgm 60 s Power = 33.3 kgm•s-1
1 kgm/s = 9.8 watt
Work = force x distance Power = work time
Measurement of Work and Power• Ergometry: measurement of work output• Ergometer 測功儀 : apparatus or device used
to measure a specific type of work
Measurement of Work and Power
• Bench step– Work = body weight (kg) x distance•step-1 x steps•min-1 x
minutes– Power = work minutes
• Cycle ergometer– Work = resistance (kg) x rev•min-1 x flywheel diameter (m)
x minutes– Power = work minutes
• Treadmill– Work = body weight (kg) x speed (m•min-1) x grade x
minutes– Power = work minutes
Determination of Percent Grade on a Treadmill
Measurement of Energy Expenditure
• Direct calorimetry– Measurement of heat production as an indication
of metabolic rate
• Indirect calorimetry– Measurement of oxygen consumption as an
estimate of resting metabolic rate
Foodstuff + O2 ATP + Heat Cell work Heat
Foodstuff + O2 Heat + CO2 + H2O
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Direct calorimetry chamber
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Indirect calorimetryClosed circuit method
Indirect calorimetryOpen-Circuit Spirometry
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Douglas bags for gas analysis
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Breath-by-breath gas analyzer
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Estimation of Energy Expenditure• Energy cost of horizontal treadmill walking or
running– O2 requirement increases as a linear function of
speed
• Expression of energy cost in METs– 1 MET = energy cost at rest, metabolic equivalent– 1 MET = 3.5 ml•kg-1•min-1
Linear Relationship Between VO2 and Walking or Running Speed
Calculation of Exercise Efficiency• Net efficiency
• Net efficiency of cycle ergometry– 15-27%
% net efficiency = x 100Energy expended above rest
Work output
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Upper limits of energy expenditure
• Well-trained athletes can expend ~1000 kcal/h for prolonged periods of time
• Up to 9000 kcal/d in Tour de France• More than 10,000 kcal/d in extreme long-
distance running• Energy requirements can be met by most
athletes, if well-planned (e.g. 20% CHO solution during exercise)
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Factors That Influence Exercise Efficiency
• Exercise work rate– Efficiency decreases as work rate increases– Energy expenditure increase out of proportion to the
work rate• Speed of movement
– There is an optimum speed of movement and any deviation reduces efficiency
– Optimum speed at power output– Low speed: inertia, repeated stop and start– High speed: friction
• Fiber composition of muscles– Higher efficiency in muscles with greater percentage of
slow fibers
Net Efficiency During Arm Crank Ergometery
Relationship Between Energy Expenditure and Work Rate
Force-velocity relationshippower output-velocity relationship
Effect of Speed of Movement of Net Efficiency
Running Economy
• Not possible to calculate net efficiency of horizontal running
• Running Economy– Oxygen cost of running at given speed– Lower VO2 (ml•kg-1•min-1) indicates better running
economy
• Gender difference in running economy– No difference at slow speeds– At “race pace” speeds, males may be more economical
that females
Comparison of Running Economy Between Males and Females
Estimate O2 requirement of treadmill running
• Horizontal:• VO2 (ml/kg/min) = 0.2 ml/kg/min/m/min x
speed (m/min)• Vertical:• VO2 (ml/kg/min) = 0.9 ml/kg/m/min x
vertical velocity (m/min)• = 0.9 ml/kg/m/min x speed (m/min) x grade
(%)• Total VO2 (ml/kg/min) = horizontal +
vertical + rest (3.5 ml/kg/min)
Estimate energy consumption according to O2 requirement
• ml/kg/min x kg x min• 1 L O2 consumed = 5 kcal
Example
• 50 kg, 30 min• Speed: 12 km/hr, grade 1%• Speed: 200 m/min• H: 0.2 x 200 = 40• V: 0.9 x 200 x 0.01 = 1.8• Total: 40 + 1.8 + 3.5 = 45.3 ml/kg/min• Total O2: 45.3 x 50 x 30/1000 = ? L O2• Total energy: ? X 5 = Kcal