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Overview andBasics of Exercise
Physiology
Quiona Stephens, PhD,
Department of Military andEmergency Medicine
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Topics to Cover
• Basic Definitions
• Physiologic Responses to Exercise
• Maximal Aerobic Capacity andExercise Testing
• Energy Systems
• Skeletal Muscle Fiber Types• Terms and Concepts Associated
with Exercise
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Pulmonary Ventilation
• Minute ventilation or VE (L/min) = Tidalvolume (L/breathing) X Breathing rate(Breaths/min)
• Measure of volume of air passingthrough pulmonary system:airexpired/minute
Variables Tidal Volume
(L/breathing)
Breathing Rate
(breaths/min)
Rest 10 - 14 10 – 20
MaximalExercise
100 – 180 40 - 60
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Relation BetweenBreathing and Ventilation
20
30
40
50
60
B r e a t h s / M i n u t e
80 100 120 140 160 180
Heart Rate 1.0
1.5
2.0
2.5
3.0
3.5
T i d a l
v o l u m e ( L / B r
e a t h )
10 20 30 40 50 60 70
V O 2 ( m l / k g / m i n )
80 100 120 140 160 180 Heart Rate
0
50
100
150
200
V E ( L / m i n )
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Stroke Volume (SV)
• Amount of blood ejected from heartwith each beat (ml/beat).
Rest Exercise (max) Max occurs
80 – 90 110 – 200
(Depending ontraining status)
40-50% of VO2 max
untrained Up to 60% VO2 max in athletes
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Cardiac Output (CO)
• Amount of blood ejected fromheart each min (L/min).
• Stroke Volume x Heart Rate Fick Equation:
CO = VO2/(a - v O2)
Rest: ~ 5 L/min
Exercise: ~10 to 25 L/min
• Primary Determinant = Heart rate
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Relation Between SV and CO
Cardiac Output = SV x HR Rest: ~ 5.0 L/min Maximal Exercise: up to 30 L/min
60 80 100
120 140 160
S t r o k e V o l u m e ( m l / b e a
t )
50 80
110 140 170 200
H e a r t R a t e ( b p m
)
0 20 40 60 80 100 % of Maximal Oxygen Uptake
05
1015
2025303540
C a r d i a c O
u t p u t ( L / m i n
)
0 20 40 60 80 100
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Maximal Aerobic Power(VO2 max)
• Also known as oxygen consumption, oxygenuptake, and cardiorespiratory fitness.
• Greatest amount of O2 a person can use duringphysical exercise.
• Ability to take in, transport and deliver O2 to
skeletal muscle for use by tissue.
• Expressed as liters (L) /min or ml/kg/min.
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Assessing VO2
• Direct Measure: Rearrange Fick Equation: VO2 =CO X (a - vO2)
• Indirect Measure: gas exchange at mouth: VO2 =VE X (FIO2 - FEO2)
Rest: 0.20 to 0.35 L/min
Maximal Exercise: 2 to 6 L/min
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Importance of VO2 max
• An index of maximal cardiovascular andpulmonary function.
• Single most useful measurement tocharacterize the functional capacity of theoxygen transport system.
• Limiting factor in endurance performance
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Determinants of VO2max
• Muscle Blood Flow
• Capillary Density
• O2 Diffusion
• O2 Extraction
• Hb-O2 Affinity
• Muscle FiberProfiles
• Cardiac Output
• Arterial Pressure
• Hemoglobin
• Ventilation
• O2 Diffusion
• Hb-O2 Affinity
• Alveolar VentilationPerfusion ratio
Peripheral Factors Central Factors
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Factors Affecting VO2max
Intrinsic
• Genetic
• Gender• Body Composition
• Muscle mass
• Age
• Pathologies
Extrinsic
• Activity Levels
• Time of Day• Sleep Deprivation
• Dietary Intake
• Nutritional Status
• Environment
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Common Criteria Used toDocument VO2 max
• Primary Criteria
< 2.1 ml/kg/min increase with 2.5% grade
increase often seen as a plateau in VO2 • Secondary Criteria
Blood lactate ≥ 8 mmol/L
RER ≥ 1.10
in HR to 90% of age predicted
RPE ≥ 17
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Aging, Training, and VO2max
0 10 20 30 40 50 60 70
20
30
40
50
60
70
Age (yr)
V O 2 m a x
( m l / k g / m i n )
Athletes
Moderately Active
Sedentary
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Gender, Age and VO2max
1.5 2.0 2.5 3.0 3.5 4.0
V O 2 m a x
( L / m i n )
10 20 30 40 50 60 Age (Years)
Women Men
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Effect of Bed rest on VO2max
-40 -30 -20 -10
0
0 10 20 30 40 Days of Bedrest
%Decline in VO2max 1.4 - 0.85 X Days; r = - 0.73
Data from VA Convertino MSSE 1997
% D e
c l i n e i n V
O 2 m a x
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VO2max Classificationfor Men (ml/kg/min)
Age (yrs)
20 - 29
30 - 39
40 - 49
50 - 59
60 - 69
Low <25
<23
<20
<18
<16
Fair 25 - 33
23 - 30
20 - 26
18 - 24
16 - 22
Average
34 - 42
31 - 38
27 - 35
25 - 33
23 - 30
Good 43 - 52
39 - 48
36 - 44
34 - 42
31 - 40
High
53+
49+
45+
43+
41+
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VO2max Classification forWomen (ml/kg/min)
Age (yrs) 20 - 29
30 - 39
40 - 49
50 - 59
60 - 69
Low <24
<20
<17
<15
<13
Fair 24 - 30
20 - 27
17 - 23
15 - 20
13 - 17
Average 31 - 37
28 - 33
24 - 30
21 - 27
18 - 23
Good
38 - 48
34 - 44
31 - 41
28 - 37
24 - 34
High
49+
45+
42+
38+
35+
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Respiratory ExchangeRatio/Quotient
• Respiratory Exchange Ratio (RER): ratio of CO2 expired/O2 consumed Measured by gases exchanged at the mouth.
•Respiratory Quotient (RQ): ratio of CO2 produced by cellularmetabolism to O2 used by tissues Measurements are made at cellular level
• Useful indicator of type of substrate (fat vs. carbohydrate)being metabolized: Fat is the first fuel source used during exercise. As RQ/RER
increases towards 1.0 the use of CHO as energy increases.
• RER/RQ typically ranges from .70 to 1.0+
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Estimating MaximalHeart Rate
• OLD FORMULA: 220 – age
• NEW FORMULA: 208 - 0.7 X age New formula may be more accurate for older persons and
is independent of gender and habitual physical activity
• Estimated maximal heart rate may be 5 to 10% (10to 20 bpm) > or < actual value.
Age Old Formula New Formula
60 160 166
40 180 180
20 200 194
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Typical Ways to MeasureVO2max
• Treadmill (walking/running)
• Cycle Ergometry
•
Arm Ergometry• Step Tests
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Maximal Values AchievedDuring Various Exercise Tests
Types of Exercise
Uphill Running Horizontal RunningUpright Cycling
Supine Cycling
Arm CrankingArms and Legs
Step Test
% of VO2max
100%
95 - 98%93 - 96%
82 - 85%
65 - 70%100 - 104%
97%
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Energy Systemsfor Exercise
Energy SystemsMole ofATP/min
Time toFatigue
Immediate: Phosphagen(Phosphocreatine and ATP)
4 5 to 10 sec
Short Term: Glycolytic
(Glycogen-Lactic Acid)2.5 1.0 to 1.6 min
Long Term: Aerobic 1Unlimited
time
A bi A bi
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Anaerobic vs. AerobicEnergy Systems
• Anaerobic ATP-CP : ≤ 10 sec.
Glycolysis: A few minutes
• Aerobic
Krebs cycle Electron Transport Chain
2 minutes +
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Energy Systems
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100%
% C a p
a c i t y o f E n e r g y S y s t e m
10 sec 30 sec 2 min 5+ min
Energy Transfer Systems and Exercise
Aerobic
Energy
System
Anaerobic
Glycolysis
ATP - CP
Exercise Time
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Skeletal Muscle Fiber Types
• Fast-Twitch
Type IIa
Type IId(x)
• Slow-Twitch
Type I
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Skeletal Muscle Fiber Types
• Characterized by differences in morphology,histochemistry, enzyme activity, surfacecharacteristics, and functional capacity.
• Distribution shows adaptive potential in responseto neuronal activity, hormones, training/functionaldemands, and aging.
• Change in a sequential manner from either slow tofast or fast to slow.
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Skeletal Muscle
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Characteristics of HumanMuscle Fiber Types
Other Terminology Slow Twitch Fast Twitch
Type Ia Type lla Type lld(x)
Aerobic Capacity HIGH MED/HIGH MED
Myoglobin Content HIGH MED LOW
Color RED RED PINK/WHITE
Fatigue Resistance HIGH MED/HIGH MED
Glycolytic Capacity LOW MED MED/HIGH
Glycogen Content LOW MED HIGH
Triglyceride Content HIGH MED MED/LOW
Myosin Heavy Chain (MHC) MHCIb MHCIIa MHCIId(x)
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Terms and ConceptsAssociated with Exercise
• Rating of Perceived Exertion
• Training Heart Rate
• Energy Expenditure
• Thresholds and Exercise Domains
• O2
Deficit and Excess Post-ExerciseO2 Consumption
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Rating of PerceivedExertion: RPE/Borg Scale
6 7 8 9 10 11 12 13 14 15 16 17 18
19
Very, very light Very light Fairly light
Somewhat hard
H ard Very hard Ver ver hard
Lactate Threshold
2.0 mM Lactate 2.5 mM Lactate 4 .0 mM Lactate
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Approaches to DeterminingTraining Heart Rate
• 60 to 90% of Maximal HR
Max HR = 180
60% = 108 and 90% = 162• 50 to 85% of Heart Rate Reserve
Max HR = 180 and Resting HR = 70
HRR = 180 - 70 = 110
50% = 70 + 65 = 135; 85% = 94 + 70 = 164
• Plot HR vs. O2 Uptake or Exercise Intensity
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Heart Rate and VO2max
0 20 40 60 80 100 % of VO2max
30 40 50 60 70 80 90
100
% o
f M a x i m a l H e a r
t R a t e
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Energy Expenditure
• MET: Energy cost as a multiple of restingmetabolic rate
1 MET = energy cost at rest ~3.5 ml of O2/kg/min 3 MET = 10.5 ml of O2 /kg/min
6 MET = 21.0 ml of O2 /kg/min
• 1 L/min of O2 is ~ 5 kcal/L
VO2 (L/min) ~ 5 kcal/L = kcal/min
• 1 MET = 0.0175 kcal/kg/min
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Lactate/Lactic Acid
• A product of glycolysis formed from reduction ofpyruvate in recycling of NAD or when insufficientO2 is available for pyruvate to enter the TCA
cycle.
• Extent of lactate formation depends onavailability of both pyruvate and NADH.
• Blood lactate at rest is about 0.8 to 1.5 mM, butduring intense exercise can be in excess of 18
mM.
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Lactate Threshold
• Intensity of exercise at which blood lactateconcentration is 1 mM above baseline.
•Expressed as a function of VO2max, i.e.,65% of VO2max.
• Expressed as a function of velocity orpower output, i.e., 150 W or 7.5 mph.
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Lactate Threshold
1.0 mM above baseline
Bl d L t t
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Blood Lactate as aFunction of Training
B l o o d L a c t a t e
( m M )
Percent of VO2max 25 50 75 100
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Ventilatory Threshold
• Describes the point at which pulmonaryventilation increases disproportionately
with oxygen consumption during gradedexercise.
• At this exercise intensity, pulmonary
ventilation no longer links tightly tooxygen demand at the cellular level.
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Ventilatory Threshold
By V Slope Method
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Ventilatory Threshold
80 100 120 140 160 180 Heart Rate
0
50
100
150
200
V E ( L / m
i n )
By Minute Ventilation Method
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Exercise Intensity Domains
• Moderate Exercise All work rates below LT
• Heavy Exercise: Lower boundary: Work rate at LT
Upper boundary: highest work rate at whichblood lactate can be stabilized (Maximumlactate steady state)
• Severe Exercise: Neither O2 or lactate can be stabilized
O U t k d
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Oxygen Uptake andExercise Domains
2
0 12
Time (minutes)
24
4
2
150
Work Rate (Watts)
I N C R E M E N T A L C O N S T A N T L O A D
Moderate
Heavy
TLac W a
300
V
O 2 ( L / m i n
)
Severe Moderate
Heavy
Severe
0
4
Lactate and E ercise
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Lactate and ExerciseDomains
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Oxygen Deficit and Debt/EPOC
• O2 Deficit = difference between total O2 usedduring exercise and total that would havebeen used if steady state had been achieved
immediately
• Excess Post-Exercise O2 Consumption(EPOC) or O
2debt = increased rate of O
2used
during recovery period. The extra oxygen isused in the processes that restore the body toa resting state and adapt it to the exercise justperformed.
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Oxygen Deficit and Debt
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EPOC or Recovery VO2
Fast component (Alactacid debt??) = whenprior exercise was primarily aerobic; repaid
within 30 to 90 sec; restoration of ATP andCP depleted during exercise.
Slow component (Lactacid debt) = reflects
strenuous exercise; may take up to severalhours to repay; may represent re-conversionof lactate to glycogen.
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Things to remember:
• Know the basic definitions & normal values
• Understand VO2 max
• Recognize differences in terms often usedinterchangeably
• Review energy systems for exercise
• Be familiar w/ terms & concepts associated
w/ exercise