Overview and Basics of Exercise Physiology Quiona Stephens, PhD, Department of Military and Emergency Medicine.

Overview and Overview and Basics of Exercise Basics of Exercise

PhysiologyPhysiology

Quiona Stephens, PhD, Quiona Stephens, PhD, Department of Military and Department of Military and

Emergency MedicineEmergency Medicine

Topics to CoverTopics to Cover

• Basic DefinitionsBasic Definitions

• Physiologic Responses to ExercisePhysiologic Responses to Exercise

• Maximal Aerobic Capacity and Maximal Aerobic Capacity and Exercise TestingExercise Testing

• Energy SystemsEnergy Systems

• Skeletal Muscle Fiber TypesSkeletal Muscle Fiber Types

• Terms and Concepts Associated Terms and Concepts Associated with Exercisewith Exercise

Pulmonary VentilationPulmonary Ventilation

• Minute ventilation or VE (L/min) = Tidal Minute ventilation or VE (L/min) = Tidal volume (L/breathing) X Breathing rate volume (L/breathing) X Breathing rate (Breaths/min)(Breaths/min)

• Measure of volume of air passing through Measure of volume of air passing through pulmonary system:air expired/minutepulmonary system:air expired/minute

VariablesVariables Tidal VolumeTidal Volume

(L/breathing)(L/breathing)

Breathing RateBreathing Rate

(breaths/min)(breaths/min)

RestRest 10 - 1410 - 14 10 – 2010 – 20

Maximal Maximal ExerciseExercise

100 – 180100 – 180 40 - 60 40 - 60

Relation Between Relation Between Breathing and VentilationBreathing and Ventilation

20

30

40

50

60

Bre

ath

s/M

inu

te

80 100 120 140 160 180Heart Rate

1.0

1.5

2.0

2.5

3.0

3.5

Tid

al v

olu

me

(L

/Bre

ath

)

10

20

30

40

50

60

70

VO

2 (

ml/k

g/m

in)

80 100 120 140 160 180

Heart Rate

0

50

100

150

200

VE

(L

/min

)

Stroke Volume (SV)Stroke Volume (SV)

• Amount of blood ejected from heart Amount of blood ejected from heart with each beat (ml/beat). with each beat (ml/beat).

RestRest Exercise (max)Exercise (max) Max occursMax occurs

80 – 9080 – 90 110 – 200110 – 200(Depending on (Depending on training status)training status)

40-50% of VO40-50% of VO22 max max

untraineduntrained

Up to 60% VOUp to 60% VO22 maxmax

in athletesin athletes

Cardiac Output (CO)Cardiac Output (CO)

• Amount of blood ejected from Amount of blood ejected from heart each min (L/min). heart each min (L/min).

• Stroke Volume x Heart RateStroke Volume x Heart Rate Fick Equation: Fick Equation:

CO = VOCO = VO22/(a - v O/(a - v O22)) Rest: ~ 5 L/minRest: ~ 5 L/min Exercise: ~10 to 25 L/minExercise: ~10 to 25 L/min

• Primary Determinant = Heart ratePrimary Determinant = Heart rate

Relation Between SV and CORelation Between SV and CO

Cardiac Output = SV x HRRest: ~ 5.0 L/minMaximal Exercise: up to 30 L/min

60

80

100

120

140

160

Str

oke

Vo

lum

e (m

l/bea

t)

50

80

110

140

170

200

Hea

rt R

ate

(bp

m)

0 20 40 60 80 100

% of Maximal Oxygen Uptake

05

10152025303540

Car

dia

c O

utp

ut

(L/m

in)

0 20 40 60 80 100

Maximal Aerobic PowerMaximal Aerobic Power (VO (VO2 max2 max))

• Also known as oxygen consumption, oxygen Also known as oxygen consumption, oxygen uptake, and cardiorespiratory fitness.uptake, and cardiorespiratory fitness.

• Greatest amount of OGreatest amount of O22 a person can use during a person can use during physical exercise.physical exercise.

• Ability to take in, transport and deliver OAbility to take in, transport and deliver O22 to to skeletal muscle for use by tissue.skeletal muscle for use by tissue.

• Expressed as liters (L) /min or ml/kg/min.Expressed as liters (L) /min or ml/kg/min.

Assessing VOAssessing VO22

• Direct Measure: Rearrange Fick Equation: VODirect Measure: Rearrange Fick Equation: VO22 = =

CO X (a - vCO X (a - vO2O2))

• Indirect Measure: gas exchange at mouth: VOIndirect Measure: gas exchange at mouth: VO22 = =

VVEE X (F X (FIO2IO2 - F - FEO2EO2))

Rest: 0.20 to 0.35 L/minRest: 0.20 to 0.35 L/min Maximal Exercise: 2 to 6 L/minMaximal Exercise: 2 to 6 L/min

Importance of Importance of VOVO2 max2 max

• An index of maximal cardiovascular and An index of maximal cardiovascular and pulmonary function. pulmonary function.

• Single most useful measurement to Single most useful measurement to characterize the functional capacity of the characterize the functional capacity of the oxygen transport system.oxygen transport system.

• Limiting factor in endurance performanceLimiting factor in endurance performance

Determinants of VODeterminants of VO2max2max

• Muscle Blood FlowMuscle Blood Flow

• Capillary DensityCapillary Density

• OO22 Diffusion Diffusion

• OO22 Extraction Extraction

• Hb-OHb-O22 Affinity Affinity

• Muscle Fiber Muscle Fiber ProfilesProfiles

• Cardiac OutputCardiac Output

• Arterial PressureArterial Pressure

• HemoglobinHemoglobin

• VentilationVentilation

• OO22 Diffusion Diffusion

• Hb-OHb-O22 Affinity Affinity

• Alveolar Ventilation Alveolar Ventilation Perfusion ratioPerfusion ratio

Peripheral Factors Central Factors

Factors Affecting VOFactors Affecting VO2max2max

IntrinsicIntrinsic

• GeneticGenetic

• GenderGender

• Body CompositionBody Composition

• Muscle massMuscle mass

• AgeAge

• PathologiesPathologies

ExtrinsicExtrinsic

• Activity LevelsActivity Levels

• Time of DayTime of Day

• Sleep DeprivationSleep Deprivation

• Dietary IntakeDietary Intake

• Nutritional StatusNutritional Status

• EnvironmentEnvironment

Common Criteria Used to Common Criteria Used to Document VODocument VO2 max2 max

• Primary CriteriaPrimary Criteria < 2.1 ml/kg/min increase with 2.5% grade < 2.1 ml/kg/min increase with 2.5% grade

increase often seen as a increase often seen as a plateauplateau in VO in VO22

• Secondary CriteriaSecondary Criteria Blood lactate ≥ 8 mmol/LBlood lactate ≥ 8 mmol/L RER ≥ 1.10RER ≥ 1.10 in HR to 90% of age predictedin HR to 90% of age predicted RPE ≥ 17RPE ≥ 17

Aging, Training, and VOAging, Training, and VO2max2max

0

10

20

30

40

50

60

70

20 30 40 50 60 70Age (yr)

VO

2m

ax (

ml/

kg/m

in)

AthletesModerately ActiveSedentary

Gender, Age and VOGender, Age and VO2max2max

1.5

2.0

2.5

3.0

3.5

4.0V

O2

ma

x

(L/m

in)

10 20 30 40 50 60Age (Years)

Women

Men

Effect of Bed rest on VOEffect of Bed rest on VO2max2max

-40

-30

-20

-10

0

0 10 20 30 40Days of Bedrest

%Decline in VO2max

1.4 - 0.85 X Days; r = - 0.73

Data from VA Convertino MSSE 1997Data from VA Convertino MSSE 1997

% D

eclin

e in

VO

2max

VOVO2max2max Classification Classification for Men for Men (ml/kg/min)(ml/kg/min)

Age Age (yrs)(yrs)

20 - 29

30 - 39

40 - 49

50 - 59

60 - 69

LowLow

<25

<23

<20

<18

<16

FairFair

25 - 33

23 - 30

20 - 26

18 - 24

16 - 22

AverageAverage

34 - 42

31 - 38

27 - 35

25 - 33

23 - 30

GoodGood

43 - 52

39 - 48

36 - 44

34 - 42

31 - 40

HighHigh

53+

49+

45+

43+

41+

VOVO2max2max Classification for Classification for Women Women (ml/kg/min)(ml/kg/min)

Age Age (yrs)(yrs)

20 - 29

30 - 39

40 - 49

50 - 59

60 - 69

LowLow

<24

<20

<17

<15

<13

FairFair

24 - 30

20 - 27

17 - 23

15 - 20

13 - 17

AverageAverage

31 - 37

28 - 33

24 - 30

21 - 27

18 - 23

GoodGood

38 - 48

34 - 44

31 - 41

28 - 37

24 - 34

HighHigh

49+

45+

42+

38+

35+

Respiratory Exchange Respiratory Exchange Ratio/QuotientRatio/Quotient

• Respiratory Exchange Ratio (RER): ratio of CORespiratory Exchange Ratio (RER): ratio of CO22 expired/O expired/O22 consumed consumed Measured by gases exchanged at the mouth.Measured by gases exchanged at the mouth.

• Respiratory Quotient (RQ): ratio of CORespiratory Quotient (RQ): ratio of CO22 produced by cellular produced by cellular metabolism to Ometabolism to O22 used by tissues used by tissues Measurements are made at cellular levelMeasurements are made at cellular level

• Useful indicator of type of substrate (fat vs. carbohydrate) Useful indicator of type of substrate (fat vs. carbohydrate) being metabolized: being metabolized: Fat is the first fuel source used during exercise. As RQ/RER Fat is the first fuel source used during exercise. As RQ/RER

increases towards 1.0 the use of CHO as energy increases.increases towards 1.0 the use of CHO as energy increases.

• RER/RQ typically ranges from .70 to 1.0RER/RQ typically ranges from .70 to 1.0++

Estimating Maximal Estimating Maximal Heart RateHeart Rate

• OLD FORMULA: 220 – ageOLD FORMULA: 220 – age

• NEW FORMULA: 208 - 0.7 X ageNEW FORMULA: 208 - 0.7 X age New formula may be more accurate for older persons and is New formula may be more accurate for older persons and is

independent of gender and habitual physical activity independent of gender and habitual physical activity

• Estimated maximal heart rate may be 5 to 10% (10 to 20 Estimated maximal heart rate may be 5 to 10% (10 to 20 bpm) > or < actual value. bpm) > or < actual value.

AgeAge Old FormulaOld Formula New FormulaNew Formula

6060 160160 166166

4040 180180 180180

2020 200200 194194

Typical Ways to Measure Typical Ways to Measure VOVO2max2max

• Treadmill (walking/running)Treadmill (walking/running)

• Cycle ErgometryCycle Ergometry

• Arm ErgometryArm Ergometry

• Step TestsStep Tests

Maximal Values Achieved Maximal Values Achieved During Various Exercise TestsDuring Various Exercise Tests

Types of ExerciseTypes of Exercise

Uphill RunningUphill RunningHorizontal RunningHorizontal RunningUpright CyclingUpright CyclingSupine CyclingSupine CyclingArm CrankingArm CrankingArms and LegsArms and LegsStep TestStep Test

% of% of VOVO2max2max

100%100%95 - 98%95 - 98%93 - 96%93 - 96%82 - 85%82 - 85%65 - 70%65 - 70%

100 - 104%100 - 104%97% 97%

Energy Systems Energy Systems for Exercisefor Exercise

Energy SystemsMole of

ATP/minTime to Fatigue

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

Anaerobic vs. Aerobic Anaerobic vs. Aerobic Energy SystemsEnergy Systems

• AnaerobicAnaerobic ATP-CP : ≤ 10 sec.ATP-CP : ≤ 10 sec. Glycolysis: A few minutesGlycolysis: A few minutes

• AerobicAerobic Krebs cycleKrebs cycle Electron Transport ChainElectron Transport Chain

2 minutes +

Energy Systems

100%%

Cap

acit

y o

f E

ner

gy

Sys

tem

10 sec 30 sec 2 min 5+ min

Energy Transfer Systems and Exercise

Aerobic Energy System

Anaerobic Glycolysis

ATP - CP

Exercise Time

Skeletal Muscle Fiber TypesSkeletal Muscle Fiber Types

• Fast-TwitchFast-Twitch

Type IIaType IIa

Type IId(x)Type IId(x)

• Slow-TwitchSlow-Twitch

Type IType I

Skeletal Muscle Fiber TypesSkeletal Muscle Fiber Types

• Characterized by differences in morphology, Characterized by differences in morphology, histochemistry, enzyme activity, surface histochemistry, enzyme activity, surface characteristics, and functional capacity.characteristics, and functional capacity.

• Distribution shows adaptive potential in response Distribution shows adaptive potential in response to neuronal activity, hormones, training/functional to neuronal activity, hormones, training/functional demands, and aging. demands, and aging.

• Change in a sequential manner from either slow to Change in a sequential manner from either slow to fast or fast to slow.fast or fast to slow.

Skeletal Muscle

Characteristics of Human Characteristics of Human Muscle Fiber TypesMuscle 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)

Terms and Concepts Terms and Concepts Associated with ExerciseAssociated with Exercise

• Rating of Perceived ExertionRating of Perceived Exertion

• Training Heart RateTraining Heart Rate

• Energy ExpenditureEnergy Expenditure

• Thresholds and Exercise DomainsThresholds and Exercise Domains

• OO22 Deficit and Excess Post-Exercise Deficit and Excess Post-Exercise

OO22 Consumption Consumption

Rating of Perceived Rating of Perceived Exertion: RPE/Borg ScaleExertion: RPE/Borg Scale

678910111213141516171819

Very, very light

Very light

Fairly light

Somewhat hard

Hard

Very hard

Very, very hard

Lactate Threshold

2.0 mM Lactate

2.5 mM Lactate

4.0 mM Lactate

Approaches to Determining Approaches to Determining Training Heart RateTraining Heart Rate

• 60 to 90% of Maximal HR60 to 90% of Maximal HR Max HR = 180Max HR = 180 60% = 108 and 90% = 16260% = 108 and 90% = 162

• 50 to 85% of Heart Rate Reserve50 to 85% of Heart Rate Reserve Max HR = 180 and Resting HR = 70Max HR = 180 and Resting HR = 70 HRR = 180 - 70 = 110HRR = 180 - 70 = 110 50% = 70 + 65 = 135; 85% = 94 + 70 = 164 50% = 70 + 65 = 135; 85% = 94 + 70 = 164

• Plot HR vs. OPlot HR vs. O22 Uptake or Exercise Intensity Uptake or Exercise Intensity

Heart Rate and VOHeart Rate and VO2max2max

0 20 40 60 80 100

% of VO2max

30

40

50

60

70

80

90

100%

of

Ma

xim

al H

ea

rt R

ate

Energy ExpenditureEnergy Expenditure

• MET: Energy cost as a multiple of resting MET: Energy cost as a multiple of resting metabolic ratemetabolic rate 1 MET = energy cost at rest ~3.5 ml of O1 MET = energy cost at rest ~3.5 ml of O22/kg/min/kg/min

3 MET = 10.5 ml of O3 MET = 10.5 ml of O22 /kg/min /kg/min

6 MET = 21.0 ml of O6 MET = 21.0 ml of O22 /kg/min /kg/min

• 1 L/min of O1 L/min of O2 2 isis ~ 5 kcal/L ~ 5 kcal/L

VOVO2 2 (L/min) ~ 5 kcal/L = kcal/min(L/min) ~ 5 kcal/L = kcal/min

• 1 MET = 0.0175 kcal/kg/min1 MET = 0.0175 kcal/kg/min

Lactate/Lactic AcidLactate/Lactic Acid

• A product of glycolysis formed from reduction of A product of glycolysis formed from reduction of pyruvate in recycling of NAD or when insufficient pyruvate in recycling of NAD or when insufficient OO22 is available for pyruvate to enter the TCA is available for pyruvate to enter the TCA cycle. cycle.

• Extent of lactate formation depends on Extent of lactate formation depends on availability of both pyruvate and NADH.availability of both pyruvate and NADH.

• Blood lactate at rest is about 0.8 to 1.5 mM, but Blood lactate at rest is about 0.8 to 1.5 mM, but during intense exercise can be in excess of 18 during intense exercise can be in excess of 18

mM.mM.

Lactate ThresholdLactate Threshold

• Intensity of exercise at which blood lactate Intensity of exercise at which blood lactate concentration is 1 mM above baseline.concentration is 1 mM above baseline.

• Expressed as a function of VOExpressed as a function of VO2max, 2max, i.e., 65% i.e., 65%

of VOof VO2max2max..

• Expressed as a function of velocity or Expressed as a function of velocity or power output, i.e., 150 W or 7.5 mph.power output, i.e., 150 W or 7.5 mph.

0

4

8

12

16

0 1000 2000 3000 4000 5000

Oxygen Uptake (ml/min)

Lactate ThresholdLactate Threshold

1.0 mM above baseline1.0 mM above baseline

Blood Lactate as a Blood Lactate as a Function of TrainingFunction of Training

Blo

od

La

cta

te (

mM

)

Percent of VO2max

25 50 75 100

Ventilatory ThresholdVentilatory Threshold

• Describes the point at which pulmonary Describes the point at which pulmonary ventilation increases disproportionately ventilation increases disproportionately with oxygen consumption during graded with oxygen consumption during graded exercise.exercise.

• At this exercise intensity, pulmonary At this exercise intensity, pulmonary ventilation no longer links tightly to ventilation no longer links tightly to oxygen demand at the cellular level.oxygen demand at the cellular level.

Ventilatory ThresholdVentilatory Threshold

1000

2000

3000

4000

5000

6000

2000 2500 3000 3500 4000 4500

VO 2 (ml/min)

AT

By V Slope Method

Ventilatory ThresholdVentilatory Threshold

80 100 120 140 160 180

Heart Rate

0

50

100

150

200

VE

(L

/min

)

By Minute Ventilation Method

Exercise Intensity DomainsExercise Intensity Domains

• Moderate ExerciseModerate Exercise All work rates below LTAll work rates below LT

• Heavy Exercise: Heavy Exercise: Lower boundary: Work rate at LT Lower boundary: Work rate at LT Upper boundary: highest work rate at which Upper boundary: highest work rate at which

blood lactate can be stabilized (Maximum blood lactate can be stabilized (Maximum lactate steady state)lactate steady state)

• Severe Exercise: Severe Exercise: Neither ONeither O22 or lactate can be stabilized or lactate can be stabilized

Oxygen Uptake and Oxygen Uptake and Exercise DomainsExercise Domains

2

00 1212

Time (minutes) 24

4

2

150 Work Rate (Watts)Work Rate (Watts)

INCREMENTAL CONSTANT LOAD

ModerateModerate

HeavyHeavy

TLac Wa

300

VO

2 (L

/min

)

SevereSevereModerateModerate

HeavyHeavy

SevereSevere

00

4

Lactate and Exercise Lactate and Exercise Domains Domains

0

6

12

0 12 24

Time (minutes)

Heavy

Moderate

Severe

Oxygen Deficit and Debt/EPOCOxygen Deficit and Debt/EPOC

• OO22 Deficit Deficit = difference between total O = difference between total O22 used used during exercise and total that would have during exercise and total that would have been used if steady state had been achieved been used if steady state had been achieved immediatelyimmediately

• Excess Post-Exercise OExcess Post-Exercise O22 Consumption Consumption (EPOC) or O(EPOC) or O22 debt debt = increased rate of O = increased rate of O22 used used during recovery period. during recovery period. The extra oxygen is The extra oxygen is used in the processes that restore the body to used in the processes that restore the body to a resting state and adapt it to the exercise just a resting state and adapt it to the exercise just performed. performed.

Oxygen Deficit and DebtOxygen Deficit and Debt

EPOC or Recovery VOEPOC or Recovery VO22

Fast componentFast component (Alactacid debt??) = when (Alactacid debt??) = when prior exercise was primarily aerobic; repaid prior exercise was primarily aerobic; repaid within 30 to 90 sec; restoration of ATP and within 30 to 90 sec; restoration of ATP and CP depleted during exercise.CP depleted during exercise.

Slow componentSlow component (Lactacid debt) = reflects (Lactacid debt) = reflects strenuous exercise; may take up to several strenuous exercise; may take up to several hours to repay; may represent re-conversion hours to repay; may represent re-conversion of lactate to glycogen.of lactate to glycogen.

Things to remember:Things to remember:

• Know the basic definitions & normal valuesKnow the basic definitions & normal values

• Understand VOUnderstand VO2 max2 max

• Recognize differences in terms often used Recognize differences in terms often used interchangeablyinterchangeably

• Review energy systems for exercise Review energy systems for exercise

• Be familiar w/ terms & concepts associated Be familiar w/ terms & concepts associated w/ exercise w/ exercise

Questions???Questions???