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 O
2
– PC breakdown and glycolysis
• Aerobic pathways 有氧代謝
– Require O
2
– 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 +

FADH
2

Production of Lactic Acid (lactate)
• Normally, O
2 is available in the mitochondria to accept H + (and electrons) from NADH produced in glycolysis
– In anaerobic pathways, O
2 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
– O
2 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 O
2 water to form

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
2 NADH
ATP from
Oxidative
ATP Subtotal
Phosphorylation
—
6
2 (if anaerobic)
6
8 (if aerobic)
14 Pyruvic acid to acetyl-CoA
Krebs cycle
Grand Total
2 GTP
6 NADH
2 FADH
—
18
4
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+P i
– High levels of ATP inhibit ATP production
– Low levels of ATP and high levels of ADP+P i stimulate ATP production
• Calcium may stimulate aerobic ATP production

Action of Rate-Limiting Enzymes

Control of Metabolic Pathways
Pathway Rate-Limiting
Enzyme
Stimulators
ATP-PC system
Creatine kinase ADP
Glycolysis
Krebs cycle
Phosphofructokin ase
Isocitrate dehydrogenase
AMP, ADP, P
 pH i
,
ADP, Ca
++
,
NAD
Electron transport chain
Cytochrome
Oxidase
ADP, P i
Inhibitors
ATP
ATP, CP, citrate,
 pH
ATP, NADH
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
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 + O
2

ATP + Heat
Cell work
Heat
• Indirect calorimetry
– Measurement of oxygen consumption as an estimate of resting metabolic rate
Foodstuff + O
2

Heat + CO
2
+ H
2
O

Direct calorimetry chamber
Ex Nutr c4-energy 30

Indirect calorimetry
Closed circuit method
Ex Nutr c4-energy 31

Indirect calorimetry
Open-Circuit Spirometry

Douglas bags for gas analysis
Ex Nutr c4-energy 33

Breath-by-breath gas analyzer
Ex Nutr c4-energy 34

Ex Nutr c4-energy 35

Estimation of Energy Expenditure
• Energy cost of horizontal treadmill walking or running
– O
2 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 VO
2
Walking or Running Speed and

Calculation of Exercise Efficiency
• Net efficiency
Work output
% net efficiency =
Energy expended above rest
• Net efficiency of cycle ergometry
– 15-27% x 100

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)
Ex Nutr c4-energy 39

Ex Nutr c4-energy 40

Ex Nutr c4-energy 41

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 VO
2 economy
(ml•kg -1 •min -1 ) indicates better running
• 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