Exercise Physiology

J.M. Cairo, Ph.D.

LSU Health Sciences Center

New Orleans, Louisiana

jcairo@lsuhsc.edu

Bioenergetics Storage Fuels Fuel Intake

Oxygen Uptake Cardiac Output

• Heart Rate• Stroke Volume

(A-V)O2 Difference• Pulmonary Ventilation

Nature of WorkIntensityDurationRhythm

TechniquePosition

Somatic FactorsSex and Age

Body DimensionHealth

Psychic FactorsAttitude

Motivation

Training Adaptation

EnvironmentTemperature

AltitudeInhaled Gases

Energy Yielding Processes

Physical Performance CapacityFrom Astrand and Rodahl,

Textbook of Work Physiology, New York

McGraw-Hill, 1972

From Richardson, DR, Randall, DC, Speck, DF: Cardiopulmonary System. Madison, CT, Fence Creek, 1998

From Wasserman, K., Hansen, J.E., Sue, D.Y., Casaburi, R, and Whipp, B.J.: Principles of Exercise Testing and Interpretation, 3rd Edition. Philadelphia, Lippincott Williams and Wilkins, 1999.

The Fick Principle

VO2 = Q x (CaO2 - CvO2)

Oxygen Consumption versus Workload

0

500

1000

1500

2000

2500

3000

10 20 30 40 50 60 70 80 90 100

Percent of Maximum Workload

Oxy

gen

Com

sum

ptio

n (m

L/m

in)

VO2 = 250 ml/minQ = 5 L/minCaO2 = 200 ml/L of whole bloodCvO2 = 150 ml/L of whole bloodCaO2-CvO2 = 50 ml/L of whole blood

RESTING CONDITIONS FOR A TYPICAL HEALTHY ADULT

VO2 = 5000 ml/minQ = 25 L/minCaO2 = 200 ml/L of whole bloodCvO2 = 20 ml/L of whole bloodCaO2-CvO2 = 180 ml/L of whole blood

MAXIMUM EXERCISE RESPONSE FOR A

WORLD CLASS ATHLETE

Cardiac Output

Heart Rate Stroke Volume

Preload

Afterload

Contractility-

++

+ +

Heart Rate Response to Increasing Work

0

20

40

60

80

100

120

140

160

180

200

10 20 30 40 50 60 70 80 90 100

Percent of Maximium Oxygen Consumption

Hea

rt R

ate

Maximum Heart Rate and Age

100

120

140

160

180

200

220

20 30 40 50 60 70

Age (years)

Ma

xim

um

Hea

rt R

ate

HRMAX = 220 - age (yrs)

Stroke Volume vs Workload

0

20

40

60

80

100

120

140

160

10 20 30 40 50 60 70 80 90 100

Percent Maximum Oxygen Consumption

Str

oke

Vol

ume

(mL

/bea

t)

PRELOAD

Volume of blood in the ventricle at the end of diastoleLVEDV

Venous Return

StrokeVolume

LVEDV

Frank-Starling Mechanism

PRELOAD

Volume of blood in the ventricle at the end of diastoleLVEDV

Venous ToneSkeletal Muscle

PumpThoraco-abdominal

Pump

Venous Return

StrokeVolume

LVEDV

Contractility

Factors influencing the Pulmonary Response to Exercise

• Ventilation

• Diffusion of Oxygen and Carbon Dioxide Across the Alveolar-Capillary Membrane

• Perfusion

• Ventilation/Perfusion

• O2 and CO2 Transport

• O2 uptake by the tissues

Control of Breathing During Exercise

• Immediate Response– Neural Component

• Central Command– Learned Response

– Direct Connection from Motor Cortex

– Coordination in Hypothalamus

• Proprioceptors or Mechanoreceptors

From Levitzky, MG: Pulmonary Physiology, 5th Edition. New York, McGraw-Hill, 1999

Control of Breathing During Exercise

• Response to Moderate Exercise– Arterial

Chemoreceptors– Metaboreceptors– Nociceptors– Cardiac Receptors– Venous

Chemoreceptors– Temperature

Receptors

• Response to Severe Exercise

– Arterial Chemoreceptors

– Central Chemoreceptors

Factors Influencing the Maintenance of the Arterial Oxygen Content (CaO2)

• Increase in Alveolar Ventilation– Decrease in VD/VT

• Increased Perfusion of the Lungs– Decrease in Pulmonary Vascular Resistance

– Recruitment and Distension of Pulmonary Capillaries

• Improvement in VA/QC

• Increased Diffusion of O2 and CO2 across the Alveolar-Capillary Membrane

Effective Ventilation – VD/VT

VD/VT

Rest Max

0.40

0.25

Factors Influencing Unloading/Uptake of Oxygen at the Tissues (CvO2)

• Shifting of the Oxyhemoglobin Dissociation Curve to the Right– Increase in Core Temperature

– Increase in CO2 Production

– Increase in H+

Bioenergetics Storage Fuels Fuel Intake

Oxygen Uptake Cardiac Output

• Heart Rate• Stroke Volume

(A-V)O2 Difference• Pulmonary Ventilation

Nature of WorkIntensityDurationRhythm

TechniquePosition

Somatic FactorsSex and Age

Body DimensionHealth

Psychic FactorsAttitude

Motivation

Training Adaptation

EnvironmentTemperature

AltitudeInhaled Gases

Energy Yielding Processes

Physical Performance Capacity

VO2 = 5000 ml/minQ = 25 L/minCaO2 = 200 ml/L of whole bloodCvO2 = 20 ml/L of whole bloodCaO2-CvO2 = 180 ml/L of whole blood

MAXIMUM EXERCISE RESPONSE FOR A

WORLD CLASS ATHLETE

VO2 = 2500 ml/minQ = 15 L/minCaO2 = 200 ml/L of whole bloodCvO2 = 33 ml/L of whole bloodCaO2-CvO2 = 167 ml/L whole blood

MAXIMUM EXERCISE RESULTS FOR A TYPICAL

HEALTHY ADULT

Principles of Physical Training

• Overload

• Specificity

• Reversibility

Training for Improved Aerobic Endurance

• Type of Exercise

• Intensity

• Duration

• Frequency

Anaerobic Threshold

• The anaerobic threshold is defined as the level of exercise VO2 above which aerobic energy is supplemented by anaerobic mechanisms and is reflected by an increase in lactate and lactate/pyruvate ratio in skeletal muscle and arterial blood.– See Wasserman, K., Hansen, J.E., Sue, D.Y., Casaburi, R, and Whipp,

B.J.: Principles of ExerciseTesting and Interpretation, 3rd Edition. Philadelphia, Lippincott Williams and Wilkins, 1999.

Karvonen Formula for Prescribing Exercise Heart Rate

HREx = HRRest + 0.60 (HRMax – HRRest)

Detraining and VO2 MAX

• Decreased maximum attainable cardiac output and arteriovenous O2 difference– Initial (12-14 days)

• Decrease due to decreased stroke volume• Decreased plasma volume

– Prolonged (3 weeks – 12 weeks)• Attenuation of arteriovenous O2 difference

changes• Decreased muscle mitochondrial density

Effects of Endurance Training on Skeletal Muscle Morphology

• Capillary Density

• Myoglobin

• Mitochondria

Effects of Endurance Training on Skeletal Muscle Metabolism

• Mobilization of FFA

• Transport of FFA from Cytoplasm to the Mitochondria

• Mitochondrial Oxidation of FFA– Beta-oxidation

• Lactate Removal

Effect of Conditioning on Heart Rate Response

Effects of Chronic Physical Activity on Aerobic Function

Resting Values Effect

Oxygen Consumption Unchanged

Heart Rate Decreased

Systolic Blood Pressure Unchanged-Decreased

Diastolic Blood Pressure Unchanged-Decreased

Rate-Pressure Product Decreased

Effects of Chronic Physical Activity on Aerobic Function

Submaximal Values Effect

Oxygen Consumption Unchanged-Decreased

Cardiac Output Unchanged

Heart Rate Decreased

Stroke Volume Increased

Systolic Blood Pressure Decreased

Rate-Pressure Product Decreased

Minute Ventilation Decreased

Effects of Chronic Physical Activity on Aerobic Function

Maximal Values Effect

Oxygen Consumption Increased

Cardiac Output Increased

Heart Rate Unchanged-Decreased

Stroke Volume Increased

Arteriovenous O2 Difference Increased

Systolic Blood Pressure Unchanged

Rate-Pressure Product Unchanged

Ejection Fraction Increased

Exercise Testing Strategies

• Incremental versus steady state tests

• Modes of exercise– Treadmills

• Bruce versus Balke Protocol

– Cycles• Ramp Protocol

Noninvasive Measurements

• Respiratory– Vt

– Fb

– VE

– FIO2

– FEO2

– FECO2

– Pulse oximetry

– PtcO2, PtcCO2

Noninvasive Measurements

• Cardiovascular– Heart rate– Arterial blood pressure– Electrocardiogram

• Modified chest leads

• 12 lead ECG

Normal ECG Changes During Exercise

• P wave increases in height

• R wave decreases in height

• J point becomes depressed

• ST segment becomes sharply up sloping

• QT interval shortens

• T wave decreases in height

Reasons for Stopping a Test

• ECG criteria– Severe ST segment depression (>3 mm)

– ST segment elevation (>1 mm in non-Q wave lead)

– Frequent ventricular extrasystole

– Onset of ventricular tachycardia

– New atrial fibrillation or supraventricular tachycardia

– Development of new bundle branch block (if the test is primarily to detect underlying coronary disease)

– New second or third degree heart block

Invasive Measurements

• Arterial blood gases– pHa, PaCO2, PaO2

• Blood lactate levels

• Pulmonary artery catheterization– Pulmonary vascular pressures (PA, PAWP)

– Mixed venous blood gases (pHv, PvCO2, PvO2)

Derived Variables• Peak VO2 versus VO2Max

• Respiratory– VD/VT

• VD/VT = PaCO2- PECO2/PaCO2

– P(A-a)O2

– P(a-et)CO2

– Breathing reserve• Breathing reserve = MVV – VE max

Derived Variables• Cardiovascular

– Heart rate reserve• HR reserve = HRmax (predicted) – HRmax (achieved)

– O2 pulse• O2 pulse = VO2/HR = SV X (CaO2-CvO2)

Reasons for Stopping a Test

• Symptoms and signs– Patient requests stopping because of severe

fatigue– Severe chest pain, dyspnea, or dizziness– Fall in systolic blood pressure (>20 mmHg)– Rise in blood pressure (>300 mmHg, diastolic

> 130 mmHg)– Ataxia

Case #20020240

Resting Data

– Age 75 yrs

– Sex Male

– VC 3.5L (100%)

– IC 2.3L (102%)

– TLC 6.0L (110%)

– FEV1 3.90L (95%)

– FEV1/VC 80%

– MVV 100L

– Hct 44%

Exercise Data

– VO2 (Peak) 1.75L (100%)*

– HRMAX 140 bpm

– SBP 155/84 180/75

– VEMAX 70L/min

– VD/VT 0.35 0.25

– P(A-a)O2 20 torr

– θAT 1.4L

*Patient stopped exercise due to dyspnea

Case #20000512

Resting Data– Age 48 yrs– Sex Male– VC 4.75L (93%)– IC 3.94L (95%)– TLC 5.90L (98%)– FEV1 3.90L (93%)– FEV1/VC 80%

– MVV 90L

Exercise Data

– VO2 (Peak) 1.55L(58%)*– HRMAX 168 bpm– SBP 150/92

205/120 – VEMAX 48L– VD/VT 0.40 0.30– P(A-a)O2 20 torr– θAT 1.30L

* Patient stopped exercise due to angina and presence of multiple PVBs

Findings Suggesting High Probability of Coronary Artery Disease

• ST segment depression ≤ 2 mm

• Downsloping ST segment depression

• Early positive response within 6 minutes

• Persistence of ST depression for more than 6 minutes into recovery

• ST segment depression in 5 or more leads

• Exertional hypotension

Case #20011120

Resting Data

– Age 60 yrs

– Sex Male

– VC 3.75L (80%)

– IC 2.75L (70%)

– TLC 6.53L (130%)

– FEV1 2.80L (65%)

– FEV1/VC 60%

– MVV 65L

Exercise Data

– VO2 (Peak) 1.75L (68%)*

– HRMAX 128 bpm

– SBP 135/88 200/110

– VEMAX 60L/min

– VD/VT 0.40 0.38

– P(A-a)O2 45 torr

– θAT 1.10L

* Patient stopped exercise due to extreme dyspnea

Case #20011452

Resting Data

– Age 70 yrs

– Sex Male

– VC 3.65L (78%)

– IC 2.28L (72%)

– TLC 6.03L (81%)

– FEV1 2.20L (6%)

– FEV1/VC 60%

– MVV 95L– DLCO 10.8 (35%)

Exercise Data

– VO2 (Peak) 1.32L (65%)*

– HRMAX 152 bpm

– SBP 175/86 227/90

– VEMAX 90L/min

– VD/VT 0.45 0.48

– P(A-a)O2 45/68 torr

– PaO2 64/52 torr

– θAT 0.95L

* Patient stopped exercise due to extreme dyspnea

Case #2001367

Resting Data

– Age 60 yrs

– Sex Male

– VC 1.75L (40%)

– IC 1.55L (42%)

– TLC 8.03L (120%)

– FEV1 0.54L (15%)

– FEV1/VC 30%

– MVV 35L

– DLCO 19 (59%)

Exercise Data

– VO2 (Peak) 1.75L (68%)*

– HRMAX 128 bpm

– SBP 135/88 200/110

– VEMAX 60L/min

– VD/VT 0.40 0.38

– P(A-a)O2 45 torr

– θAT 1.10L

* Patient stopped exercise due to extreme dyspnea

Temperature Regulation

Definitions• Core Temperature

– Measured as oral, aural, or rectal temperature– Temperature of deep tissues of the body– Remains relatively constant (1ºF or 0.6ºC) unless a

person develops a febrile condition– Nude person can maintain core temperature even

when exposed to temperatures as low as 55ºF or as high as 130ºF in dry air

• Skin Temperature– Rises and falls with the temperature of the

surroundings

Basal Metabolic Rate

Metabolism Associated with Muscular Activity

Hormonal Effects on Metabolism

Insulation

Blood Flow

Radiation Conduction Evaporation

Heat Production Heat Loss

REGULATION OF BODY TEMPERATURE

Heat Production

• Laws of Thermodynamics– Heat is a by-product of metabolism

• Basal metabolic rate of all cells of the body

• Effect of muscular activity on metabolic rate

• Effect of endocrinology on metabolic rate (i.e., thyroxin, growth hormone, testosterone)

• Effect of autonomic nervous system on metabolic rate

Heat Loss

• How fast is heat transferred from deep tissues to the skin

• How rapidly is heat transferred from the skin to the surrounding environment

How Fast Is Heat Transferred From Deep Tissues to Skin

• Insulation Systems– Skin and subcutaneous tissue (i.e., fat)

• Blood Flow– Cutaneous circulation

How Fast Is Heat Loss From the Skin to the Surrounding

Environment

• Radiation

• Conduction

• Evaporation

Definitions• Radiation

– Loss of heat by infrared heat rays (5-20m or 10-20X wavelength of visible light)

• Conduction– Loss of heat from the body to a solid object

• Evaporation– Loss of heat from the body through water vapor to

the surrounding atmosphere

• Convection– Effects of changes in the external environment (e.g.,

wind and water)

“Wind Chill Factor”

• Effect of wind on skin temperature – temperature of calm air that would produce equivalent cooling of exposed skin

• Cooling effect of air convection equals the square root of the wind velocity– For example, air temperature feels twice as

cold at a wind velocity of 4 mph than if the wind velocity is 1 mph

ºF = 35.74 + 0.6215T - 35.75V(100.16) + 0.4275V(100.16)

http://www.nws.noaa.gov/om/windchill/wind_chill_compare.pdf

Regulation of Body Temperature Role of the Hypothalamus

• Anterior Hypothalamus – Preoptic Area– Heat-sensitive neurons

• Demonstrate a 10-fold increase in firing rate when there is a 10°C increase in body temperature resulting in profuse sweating and cutaneous vasodilation

– Cold-sensitive neurons• Increase in firing rate to a decrease in body

temperature resulting in cutaneous vasoconstriction and inhibition of sweat production

Temperature RegulationSkin and Deep Tissue Receptors

• Although the skin contains both cold and warmth sensory receptors, there are far more cold receptors than warmth receptors (10 times more cold than warmth)– Stimulation of these cold receptors will

result in shivering, inhibition of sweating, and promotion of cutaneous vasoconstriction

Temperature RegulationSkin and Deep Tissue Receptors

• Deep tissue receptors are found in spinal cord, in the abdominal viscera, and in the great veins in the upper abdomen and thorax– Although these receptors are exposed to core

body temperature rather than skin temperature, they function like the skin receptors in that they are concerned with preventing hypothermia

Hormonal Control of Temperature

• Chemical Thermogenesis– Ability of norepinephrine and epinephrine to

uncouple oxidative phosphorylation• “Brown fat”

• Thyrotropin-releasing hormone Thyroid-stimulating hormone Thyroxine– Stimulated by cooling of the anterior hypothalamic-

preoptic area– Requires several weeks of exposure to cold to cause

hypertrophy of the thyroid gland

Abnormalities of Body Temperature Regulation

• Fever– Effect of pyrogens– Brain lesions

• Heatstroke

• Frostbite

• Malignant Hyperthermia