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?
Before After
Stressed Empowered
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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
Other Terminology Slow Twitch Fast Twitch Fast Twitch Fast Twitch
Other Terminology Type Ia Type lla Type lla Type ll(x)
Aerobic Capacity HIGH MED LOW LOW
Myoglobin Content HIGH MED LOW LOW
Color RED PINK WHITE WHITE
Fatigue Resistance HIGH MED LOW LOW
Glycolytic Capacity LOW MED HIGH HIGH
Glycogen Content LOW MED HIGH HIGH
Triglyceride Content HIGH MED LOW LOW
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ATP Is GeneratedThrough 3 Energy Systems

1. ATP-PCr system
2. Glycolytic system
3. 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
Energy Systems Mole of ATP/min Time to Fatigue
Immediate ATP - PCr (ATP phosphocreatine) 4 5 to 10 sec
Short Term Glycolytic (Glycogen-Lactic Acid) 2.5 1 to 2 min
Long Term Oxidative 1 Unlimited time
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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
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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

Variables Tidal Volume (L/min) Breathing Rate (breaths/min)
Rest 10 - 14 10 20
Maximal Exercise 100 180 40 - 60
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Stroke Volume (SV)

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

Rest Exercise (max) Max occurs
80 90 110 200 (Depending on training 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 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
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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.

Age Old Formula New Formula
60 160 166
40 180 180
20 200 194
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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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