Overview and Basics of Exercise Physiology

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Overview and Basics of Exercise Physiology

• Dianna Purvis MS, ACSM Department of Military
  and Emergency Medicine
• CHAMP

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Topics to Cover

• Background
• Skeletal Muscle Fiber Types
• Energy Systems
• Physiological Responses to Exercise
• Maximal Aerobic Capacity and Exercise Testing
• Terms and Concepts Associated with Exercise

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As a NationWe Are Getting Fatter, More Unfit,
and at a Younger Age!
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Physical Activity Plays a Key Role Disease
Prevention
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The Dose-Response Relationship for Exercise
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Why Is This Important?

• The importance of cardiorespiratory fitness (VO2
  max) cannot be overemphasized
• ? cardiorespiratory fitness ? morbidity
  mortality all causes
• NHANES survey 2001/2002
• that 11-30 of adults surveyed had VO2 max values
  in ACSMs poor category33.6 adoloscents!
• Despite importance of high aerobic fitness,
  public health surveys show a high level of poor
  aerobic fitness in the US population

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How do YOU want YOUR Patients to look and feel?
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How Much Exercise?

• Daily Aerobic Activity
• 10,000 steps per day
• 150 300 min/week (CDC)
• ACSM guidelines
• Strength exercises 2-3 times per week
• Body weight
• Resistance
• Stretch daily
• Consider yoga for flexibility and stress
  management

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CDC/ACSM

• http//www.cdc.gov/physicalactivity/everyone/guide
  lines/adults.html (CDC)
• http//www.acsm.org (ACSM)
• http//www.aafp.org/online/en/home/clinical/public
  health/aim/foryouroffice.html (AIM Exercise
  Prescription Tools for Clinicians)

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The Exercise and Physical Activity Pyramid
Adapted with permission of the Metropolitan Life
Insurance Company.
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Skeletal Muscle
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Skeletal Muscle Fiber Types

• Slow-Twitch
• Type I
• Fast-Twitch
• Type IIa
• Type IIx

• Characterized by differences in morphology,
  histochemistry, enzyme activity, surface
  characteristics, and functional capacity
• Distribution shows adaptive potential in response
  to neuronal activity, hormones,
  training/functional demands, and aging

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Characteristics of Human Muscle Fiber Types
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ATP Is GeneratedThrough 3 Energy Systems

• ATP-PCr system
• Glycolytic system
• Oxidative system

The process that facilitates muscular contraction
is entirely dependent on bodys ability to
provide rapidly replenish ATP
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Energy Systems for Exercise
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1. The ATPPCr System
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ATP-PCr Stores Deplete Rapidly
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2. The Glycolytic System

• Requires 10-12 enzymatic reactions to break down
  glycogen to pyruvate or lactic acid, producing
  ATP
• Occurs in the cytoplasm
• Glycolysis does not require oxygen (anaerobic)
• Without oxygen present, pyruvic acid produced by
  glycolysis becomes lactic acid
• ATP-PCr and glycolysis provide the energy for 2
  min of all-out activity

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Conversion of Pyruvic Acid to Lactic Acid
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Energy Sources for the Early Minutes of Intense
Exercise
The combined actions of the ATP-PCr and
glycolytic systems allow muscles to generate
force in the absence of oxygen thus these two
energy systems are the major energy contributors
during the early minutes of high-intensity
exercise
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3. The Oxidative System

• The oxidative system uses oxygen to generate
  energy from metabolic fuels (aerobic)
• Oxidative production of ATP occurs in the
  mitochondria
• Can yield much more energy (ATP) than anaerobic
  systems
• The oxidative system is slow to turn on
• Primary method of energy production during
  endurance events

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Common Pathways for the Metabolism of Fat,
Carbohydrate, and Protein
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Anaerobic vs. Aerobic Energy Systems

• Anaerobic
• ATP-PCr 10 30 sec
• Glycolysis lt 2 3 min
• Aerobic
• Krebs cycle
• Electron Transport Chain

2 minutes
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INTERACTION OF ENERGY SYSTEMS
Immediate
Short-term
Long-term
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Energy Transfer Systems and Exercise
100
Capacity of Energy System
Anaerobic Glycolysis
Aerobic Energy System
ATP - CP
10 sec
30 sec
2 min
5 min
Exercise Time
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Aerobic and Anaerobic ATP Production
Pyruvate
Limited O2
Lactate
Acetyl-CoA
ATP
Krebs Cycle
FADH2 NADHH
H2O

ATP
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Pulmonary Ventilation

• Minute ventilation or VE (L/min) Tidal volume
  (L/breathing) X Breathing rate (Breaths/min)
• Measure of volume of air passing through
  pulmonary systemair expired/minute

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Stroke Volume (SV)

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

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Cardiac Output (CO)

• Amount of blood ejected from heart each min
  (L/min)
• CO SV X HR
• Rest 5 L/min
• Exercise 10 to 25 L/min
• Stroke Volume x Heart Rate
• Fick Equation VO2 CO X (a - v O2)
• Primary Determinant Heart rate

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Heart Rate and VO2max
100
90
80
70
of Maximal Heart Rate
60
50
40
30
0
20
40
60
80
100
of VO2max
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Maximal Oxygen Consumption (Aerobic Power or VO2
max)

• Greatest amount of O2 a person can use during
  maximal physical 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
• Single most useful measurement to characterize
  the functional capacity of the oxygen transport
  system
• Provides a quantitative measure of capacity for
  aerobic ATP resynthesis

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Factors Affecting VO2max

• Intrinsic
• Genetic
• Gender
• Body Composition
• Muscle mass
• Age
• Pathologies

• Extrinsic
• Training Status
• Time of Day
• Sleep Deprivation
• Dietary Intake
• Nutritional Status
• Environment

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Determinants of VO2max
Peripheral Factors
Central Factors

• Muscle Blood Flow
• Capillary Density
• O2 Diffusion
• O2 Extraction
• Hb-O2 Affinity
• Muscle Fiber Profiles

• Cardiac Output
• Arterial Pressure
• Hemoglobin
• Ventilation
• O2 Diffusion
• Hb-O2 Affinity

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Requirements for VO2max Testing

• Minimal Requirements
• Work must involve large muscle groups
• Rate of work must be measurable and reproducible
• Test conditions should be standardized
• Test should be tolerated by most people
• Desirable Requirements
• Motivation not a factor
• Skill not required

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Common Criteria Used to Document VO2 max

• Primary Criteria
• lt 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 max /- 10 bpm
• RPE 17

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Aging, Training, and VO2max
70
Athletes
Moderately Active
60
Sedentary
50
40
VO2max (ml/kg/min)
30
20
10
0
20
30
40
50
60
70
Age (yr)
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Effect of Bed rest on VO2max
0
Decline in VO2max
1.4 - 0.85 X Days r - 0.73
-10
Decline in VO2max
-20
-30
-40
0
10
20
30
40
Days of Bedrest
Data from VA Convertino MSSE 1997
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VO2max Classification for Men (ml/kg/min)
Age (yrs) 20 - 29 30 - 39 40 - 49 50 - 59 60 - 69
Low lt25 lt23 lt20 lt18 lt16
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 for Women (ml/kg/min)
Age (yrs) 20 - 29 30 - 39 40 - 49 50 - 59 60 - 69
Low lt24 lt20 lt17 lt15 lt13
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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Typical Ways to Measure VO2max

• Treadmill (walking/running)
• Cycle Ergometry
• Arm Ergometry
• Step Tests

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Terms and Concepts Associated with Exercise

• Rating of Perceived Exertion
• Training Heart Rate
• Energy Expenditure
• Thresholds and Exercise Domains
• O2 Deficit and Excess Post-Exercise O2 Consumption

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Approaches to Determining Training Heart Rate

• Rating of Perceived Exertion
• 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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Rating of Perceived Exertion RPE/Borg Scale
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Estimating Maximal Heart 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 (10
  to 20 bpm) gt or lt actual value.

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Energy Expenditure

• MET Energy cost as a multiple of resting
  metabolic 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 of
  pyruvate in recycling of NAD or when insufficient
  O2 is available for pyruvate to enter the Krebs
  Cycle
• Extent of lactate formation depends on
  availability of both pyruvate and NAD
• Blood lactate at rest is about 0.8 to 1.5 mM, but
  during intense exercise can be in excess of 18 mM

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Lactate Threshold

• Intensity of exercise at which blood lactate
  concentration is 1 mM above baseline
• Production exceeds clearance
• Expressed as a function of VO2max, i.e., 65 of
  VO2max
• Can indicate potential for endurance exercise
• Lactate formation contributes to fatigue
• Impairs oxidative enzymes

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Lactate Threshold
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PyruvateLactate
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Blood Lactate as a Function of Training
Blood Lactate (mM)
25
50
75
100
Percent of VO2max
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Ventilatory Threshold

• Point at which pulmonary ventilation increases
  disproportionately with oxygen consumption during
  an increase in workload
• At this exercise intensity, pulmonary ventilation
  no longer links tightly to oxygen demand at the
  cellular level

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Ventilatory Threshold

• During incremental exercise
• Increased acidosis (H concentration)
• Buffered by bicarbonate (HCO3-)

H HCO3- ? H2CO3 ? H2O CO2

• Marked by increased ventilation

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Ventilatory Threshold

• Methods used in research
• Minute ventilation vs VO2, Work or HR
• V-slope (VO2 VCO2)
• Ventilatory equivalents (VE/VO2 VE/VCO2)
• Relation of VT LT
• highly related (r .93)
• 30 second difference between thresholds

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Ventilatory Threshold
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Ventilatory Threshold
By V Slope Method
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Respiratory Exchange Ratio

• Respiratory exchange ratio (RER or R)
• R for fat (palmitic acid)
• R for carbohydrate (glucose)

Indicates type of substrate being metabolized .7
FAT to 1.0 CHO
C16H32O2 23 O2 ? 16 CO2 16 H2O
C6H12O6 6 O2 ? 6 CO2 6 H2O
R can be gt 1 during heavy, non-steady state
exercise due to ? metabolic respiratory CO2
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Adaptations to Aerobic Training

• ? Oxidative enzymes
• ? Size and number of mitochondria
• ? SV and a VO2 SV ? VO2 max
• ? RHR HR _at_ submax exercise
• ? Capillary density
• ? Blood volume, cardiac output, and O2 diffusion

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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 which blood
  lactate can be stabilized (Maximum lactate steady
  state)
• Severe Exercise
• Neither O2 or lactate can be stabilized

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Lactate and Exercise Domains
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Rest-to-Exercise Transitions

• Oxygen uptake increases rapidly
• Reaches steady state within 1-4 minutes
• Oxygen deficit
• Lag in oxygen uptake at the beginning of exercise
• Suggests anaerobic pathways contribute to total
  ATP production
• After steady state is reached, ATP requirement is
  met through aerobic ATP production

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Oxygen Deficit and Debt
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Recovery From Exercise Metabolic Responses

• Oxygen debt
• VO2 elevated above rest following exercise to
  repay debt
• Excess post-exercise oxygen consumption (EPOC)
• Rapid portion of O2 debt
• Resynthesis of stored ATP PCr
• Replenishing muscle and blood O2 stores
• Slow portion of O2 debt
• Elevated heart rate and breathing ? energy need
• Elevated body temperature ? metabolic rate
• Elevated epinephrine norepinephrine ?
  metabolic rate
• Accumulated lactate clearance

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EPOC Following Exercise
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Determinants of Endurance Performance
Endurance
Other
Maximal SS
O2 Delivery
Lactate Threshold
VO2max
Economy
Performance measure
Performance measure
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