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Chapter 8
Responses and Adaptations of
the Cardiorespiratory System
Copyright © 2012 American College of Sports Medicine
Anatomy of the Heart
• Heart
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Pump that circulates blood throughout body
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Four chambers
• Right & left atria: receivers
• Right & left ventricles: pump blood away
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2/3 of mass on left side
–
Weighs 11 oz in men & 9 oz in women (proportional to body
size)
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Anatomy of the Heart (cont’d)
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Anatomy of the Heart (cont’d)
• Cardiac Musculature: Myocardium
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Contracts on its own
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Capable of hypertrophy & adapting to exercise
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Thickness affected by stress; thicker = stronger
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Larger, fewer T tubules compared with skeletal muscle
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Contracts forcefully at lower rate than skeletal muscle
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Cardiocytes: cardiac cells that have the ability to communicate
directly with adjacent cells via intercalated discs
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Intercalated discs enable rapid spread of action potentials
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Major Blood Vessels
• Arteries
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High-pressure vessels that deliver oxygen-rich blood to tissues
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Have walls containing smooth muscle & elastic fibers
• Arterioles
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Smaller arteries that constrict or relax to regulate blood flow
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Branch & form smaller vessels called metarterioles
• Capillaries
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Thin vessels that serve as site for nutrient/oxygen exchange
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2,000 to 3,000 per square mm of tissue
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Major Blood Vessels (cont’d)
• Venules
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Small veins joined to capillaries that drain blood toward heart
• Veins
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Vessels joined to venules that return blood to heart
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Low-pressure structures with extensible walls
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Storage site for blood when circulatory demands are low
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Circulatory System
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Regulation of the Heart
• Intrinsic Regulation of the Heart
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Heart can regulate its own rhythm
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Sinoatrial (SA) node: pacemaker of heart
• Spontaneously generates action potential
• Located in right atrium
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Wave of depolarization spreads across atria
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Atrioventricular (AV) node: delays wave of depolarization
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Bundle of His: arises from AV node & continues depolarization
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Wave spreads through ventricles via bundle branches & Purkinje
fibers
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Conductive System of the Heart
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Regulation of the Heart (cont’d)
• Extrinsic Regulation of the Heart
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Nervous & endocrine systems
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Cardiac center in medulla oblongata controls:
• Heart rate (HR)
• Vessel diameter
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Feedback from sensory motor centers in brain controls:
• HR
• Force of contraction
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Role of autonomic nervous system
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Blood Components
• Plasma
–
55-60% of total blood volume
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Composition
• 90% is water
• 7% is plasma proteins
• 3% is nutrients & waste
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Blood Components (cont’d)
• Formed Elements
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40-45% of total blood volume
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Hematocrit: % of formed elements relative to total blood vol.
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Composition
• 99% red blood cells (RBCs)
• 1% white blood cells (WBCs) & platelets
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RBCs: transport oxygen bound to iron-containing protein
hemoglobin
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Platelets: small molecules required for blood clotting
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WBCs: critical to immune function
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Oxygen-Hemoglobin Dissociation Curve
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Partial Pressure of Oxygen and Carbon
Dioxide
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Blood Components (cont’d)
• Blood Flow
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Body contains about 5 L of blood
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Distribution
• 15-20% to skeletal muscle
• 25% to liver
• 20% to kidneys
• 10% to skin
• 14-15% to brain
• 10-12% to heart & other tissues
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Blood Components (cont’d)
• Blood Flow (cont’d)
–
Blood flow to skeletal muscle increases to >80% of total flow to
meet metabolic demands
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Skeletal muscle contraction pumps venous blood back to heart
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Venous valves prevent backward flow of blood in veins
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Ischemia associated with RT is stimulus for muscle hypertrophy
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Tightly regulated
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Cardiovascular Function
• CV Variables
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Heart rate: frequency of heart beats per min
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Blood pressure: pressure in arteries after left ventricle
contracts
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Systolic blood pressure
• Pressure in left ventricle during systole
• Averages 120 mm Hg
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Diastolic blood pressure
• Peripheral resistance to flow during relaxation (diastole)
• Averages 80 mm Hg
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Cardiovascular Function (cont’d)
• CV Variables (cont’d)
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Stroke volume: blood vol. ejected from left ventricle each beat
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Cardiac output: total volume of blood pumped by heart per min
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Cardiovascular Responses to Exercise
• Heart Rate (HR) Response
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Increases during exercise from resting values to rates >195 bpm
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Upper limits for HR during exercise:
• 220 − person’s age in years = HR max
• Target range is based on % of HR max
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Magnitude of HR increase depends on muscle mass use, exercise
intensity, & degree of continuity of exercise
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HR increases linearly up to maximal
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Cardiovascular Responses to Exercise
(cont’d)
• Stroke Volume (SV) Response
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Increases during exercise from resting values to rates >195 bpm
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Magnitude of SV increase determined by:
• Blood volume returning to heart
• Arterial pressure
• Ventricular contractility
• Distensibility
–
Increases linearly up to about 40-60% of maximal exercise
capacity
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Cardiovascular Responses to Exercise
(cont’d)
• Cardiac Output (Qc)
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Is product of HR & SV
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Increases linearly during aerobic exercise
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May increase to 20-40 L min-1 depending on fitness level
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Increases over course of workout during RT
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Cardiac Output Response to Aerobic
Exercise
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Cardiovascular Responses to Exercise
(cont’d)
• Blood Pressure (BP)
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Increases during exercise
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Increases during RT with increase proportional to effort
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Muscle mass activation plays a role
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BP Response to 3 Sets of Leg Press
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Cardiovascular Responses to Exercise
(cont’d)
• Plasma Volume
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Decreases during exercise
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Decreases up to 20% during endurance exercise
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Reductions can impair endurance performance & VO2max
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Decreased by 7-14% immediately after resistance exercise
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Cardiovascular Responses to Exercise
(cont’d)
• Oxygen Consumption
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Increases proportionally during exercise in relation to:
• Intensity
• Muscle mass activation
• Degree of continuity
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Represented by Fick equation:
• VO2 = Qc × A-VO2 difference
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The A-VO2 Difference
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Relationship Between Exercise Intensity
and Oxygen Consumption
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Chronic Adaptations at Rest and During
Exercise
• Pressure Overload
–
Results from rise in BP & intrathoracic pressure that accompany
exercise
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Can alter several CV variables positively over time
• Volume Overload
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Results from greater venous return & blood flow to heart during
exercise
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Aerobic exercise is superior due to higher level of continuity
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Leads to positive changes in several CV variables
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Increases cardiac chamber size
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Chronic Adaptations at Rest and During
Exercise (cont’d)
• Cardiac Dimensions
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Adaptations governed by Law of Laplace:
• Wall tension is proportional to pressure & size of radius of
curvature
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Greater heart size is characterized by greater left ventricular
cavity & thickening of cardiac walls
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Aerobic training leads to improvements in cardiac function
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RT leads to changes in left-side cardiac muscularity
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RT elicits very small to no changes in left ventricular cavity size
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Chronic Adaptations at Rest and During
Exercise (cont’d)
• Cardiac Output (Qc)
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Qc response to exercise is augmented
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Aerobic training reduces resting HR
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Resting SV may slightly increase or not change during RT
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Resting HR may not change or slightly decrease during RT
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Heart Rate Response During Exercise
Before and After Training
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Chronic Adaptations at Rest and During
Exercise (cont’d)
• VO2max
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Gold standard of aerobic fitness
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Increases during training due to increases in SV, Qc, & small
increase in A-VO2 difference
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Increases 10-30% with aerobic training during first 6 months
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Increases only minimally with anaerobic training
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Comparison of VO2max Data From Different
Male Athletes
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Chronic Adaptations at Rest and During
Exercise (cont’d)
• Blood Pressure
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Decreased systolic & diastolic BP with aerobic training
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Largest reductions seen in hypertensive people
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Not affected or reduced with RT
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Chronic Adaptations at Rest and During
Exercise (cont’d)
• Blood Volume
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Increased with aerobic training, mostly due to increase in plasma
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Plasma volume increases 12-20% within first few weeks of AT
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Endurance athletes have blood volumes about 35% greater than
untrained people
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RT may have limited effect
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Chronic Adaptations at Rest and During
Exercise (cont’d)
• Blood Lipids and Lipoproteins
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Major factors in CV health
–
Include triglycerides, cholesterol, LDL-C, VLDL-C, HDL-C, &
lipoprotein A
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Factors affecting: genetics, diet, stress, smoking, body weight, &
exercise
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Increased HDL-C, decrease in other lipids with AT
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RT has no or very small effects in improving lipid profiles
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Respiratory System
• Overview
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Essential for introducing oxygen into the body & removing CO2
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Respiration includes:
• Breathing
• Inspiration: breathing in
• Expiration: breathing out
• Pulmonary diffusion
• Oxygen transport
• Gas exchange
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The Human Respiratory System
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Respiratory System (cont’d)
• Lung Volumes and Capacities
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Tidal volume: volume of air inspired or expired every breath
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Inspiratory reserve volume: volume of air inspired after
normal tidal volume
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Expiratory reserve volume: volume of air expired after normal
tidal volume
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Residual volume: volume of air left in lungs after maximal
expiration
–
Total lung capacity: volume of air in lungs after maximal
inspiration
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Respiratory System (cont’d)
• Lung Volumes and Capacities (cont’d)
–
Forced vital capacity: maximal volume of air expired after
maximal inspiration
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Inspiratory capacity: maximal volume of air after tidal volume
expiration
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Functional residual capacity: volume of air in lungs after tidal
volume expiration
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Forced expiratory volume: volume of air maximally expired
forcefully in 1 second after maximal inhalation
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Maximum voluntary ventilation: maximum volume of air
breathed rapidly in 1 minute
–
Minute ventilation: volume of air breathed per minute
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Respiratory System (cont’d)
• Control of Breathing
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Involuntary, but can be controlled voluntarily to some extent
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Neural & hormonal factors
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Circulatory (humoral factors)
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Rapid increase in ventilation during exercise, followed by slower
rise as exercise progresses
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Overview of Respiratory Control
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Pulmonary Ventilation During Exercise
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Respiratory System (cont’d)
• Pulmonary Adaptations to Training
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Little change in lung volumes & capacities with AT
• Ventilatory Muscle-Specific Training
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Involves RT during respiration
–
Used to increase respiratory function by improving strength &
endurance of inhalation muscles
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