Transcript Chapter 6

Chapter 3, 6
Bioenergetics
Measurement of Work, Power,
and Energy Expenditure
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
PC + ADP
Creatine kinase
ATP + C
– 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
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)
NAD + 2H+  NADH + H+
• Flavin adenine dinucleotide (FAD)
FAD + 2H+  FADH2
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
Aerobic ATP Tally
Metabolic Process
High-Energy
Products
Glycolysis
2 ATP
2 NADH
Pyruvic acid to
acetyl-CoA
Krebs cycle
2 NADH
ATP Subtotal
ATP from
Oxidative
Phosphorylation
2 (if
—
anaerobic)
6
8 (if aerobic)
14
6
2 GTP
6 NADH
2 FADH
—
18
4
Grand Total
16
34
38
38
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
Phosphofructokin AMP, ADP, Pi,
ase
pH
Isocitrate
ADP, Ca++,
dehydrogenase NAD
ATP, CP, citrate,
pH
ATP, NADH
Cytochrome
Oxidase
ATP
Krebs cycle
Electron
transport
chain
ADP, Pi
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:
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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
Work = force x distance
• Lifting a 5 kg weight up
a distance of 2 m
Work = force x distance
Work = 5 kg x 2 m
Work = 10 kgm
1 kgm = 9.8 joule
1 joule = 0.24 calorie 卡
(不是 Kcal 大卡, 千卡)
Power 功率
Power = work  time
• Performing 2,000 kgm of
work in 60 seconds
Power = work  time
Power = 2,000 kgm  60 s
Power = 33.3 kgm•s-1
1 kgm/s = 9.8 watt
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
Foodstuff + O2  ATP + Heat
Cell work
Heat
• Indirect calorimetry
– Measurement of oxygen consumption as an
estimate of resting metabolic rate
Foodstuff + O2  Heat + CO2 + H2O
Direct calorimetry chamber
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Indirect calorimetry
Closed circuit method
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Indirect calorimetry
Open-Circuit Spirometry
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
Work output
% net efficiency = Energy expended x 100
above rest
• Net efficiency of cycle ergometry
– 15-27%
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 longdistance 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 relationship
power 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
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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