Responses and Adaptations to Aerobic Endurance Training

intensity, duration, and frequency

The effects of aerobic exercise are regulated by the , , of the activity.

the heart and the vasculature

The cardiovascular system consists of two components, , (i.e., blood and blood vessels).

stimulation or excitation

During aerobic exercise, an increased , , of the heart occurs in order to supply blood to the exercising skeletal muscle.

reduction

Although not the only reason for an increase in blood flow, a simple explanation is an increase in stimulation of the heart by the sympathetic nervous system and, at the same time, a , , in parasympathetic nervous system stimulation.

stroke volume (SV)

amount of blood ejected per beat from the left ventricle

cardiac output (Q)

The increase in HR and SV ultimately increases the = HR x SV

40% to 60%

Stroke volume has been shown to increase to maximal levels at , , of maximal oxygen consumption (VO2 max) and plateau long before exhaustion. This finding is not conclusive; other studies indicate that SV continues to rise more linearly until exhaustion.

venous filling

During exercise, an increase in , , of the heart contributes to an increased pressure and stretching of the walls of the heart, resulting in an increase in elastic contractile force that is independent of neural and humoral factors.

Frank-Starling mechanism

The result from the increase of venous filling is one explanation for why more blood is ejected from the left ventricle (increasing SV), and it is known as the , , ; that is, the stroke volume of the heart increases proportionally to the volume of blood filling the heart.

total peripheral resistance (TPR)

resistance to blood flow in the systemic vascular system.

50% to 60%

As aerobic exercise intensity increases from a resting state to maximal exercise, there is a , , reduction in total peripheral resistance

vasodilation

TPR reduction resulting from exercise intensity increasing from a resting state to maximal exercise is due to , , that occurs in an effort to supply the working skeletal muscle with blood

shunted

During exercise, a greater proportion of blood is , , to the exercising skeletal musculature where it is needed. At the same time, blood flow to other areas of the body, such as the splanchnic region, is decreased.

Blood pressure (BP, mmHg)

is the force exerted by the blood on the vessels to drive blood through the circulatory system.

ventricular systole (contraction) and diastole (relaxation)

Measurements of systolic blood pressure (SBP) and diastolic blood pressure (DBP) represent the pressure exerted on the vessels during , , respectively.

negligible

During aerobic endurance exercise involving large muscle groups, such as walking, jogging, cycling, and swimming, there is a linear increase in SBP in direct proportion to the exercise intensity and cardiac output and a , , change in DBP.

Q increases

During aerobic endurance exercise involving large muscle groups, total peripheral resistance also decreases (but , , to a greater extent) as the exercise intensity increases and has a major effect on blood pressure.

mean arterial pressure (MAP)

As a result, , increases during exercise and can be expressed quantitatively by the following formula: 1/3 × SBP + 2/3 × DBP Q x TPR

intercellular space

During exercise, the increase in BP helps facilitate the increase in blood flow through the vasculature and also the amount of plasma forced from the blood into the , , (becoming part of the interstitial fluid).

hematocrit

proportion of blood that consists of red blood cells

plasma volume

Thus, during exercise, a decrease in , , and an increase in hematocrit (proportion of blood that consists of red blood cells) occur, even though the total number of red blood cells does not change.

Coronary vasculature

composed of the right and left coronary arteries, dilates (vasodilation) during exercise as a result of the increased oxygen demand placed on the heart muscle.

rate–pressure product (RPP)

indicates how much oxygen the heart needs. It is a fairly easy measurement to take and provides a good noninvasive index of how hard the heart is working: HR x SBP

Pulmonary minute ventilation (Ve)

is the product of breathing rate (BR) and tidal volume (TV) and represents the amount of air moved into or out of the lungs in 1 minute.

Ve

During exercise, , increases because of the body’s increased oxygen requirement and consumption.

respiratory quotient (RQ)

is the ratio of the volume of carbon dioxide production (CO2) to oxygen consumption (Vo2) at the cellular level. RQ = VCO₂ / VO

respiratory exchange ratio (RER)

RQ cannot feasibly be measured at the level of the cell, but the CO2 and O2 ratio is commonly assessed via expired gases from the mouth, termed the , , : RER = VCO₂ / VO₂

fat, carbohydrate, and protein

Essentially, the RER and RQ estimate the proportion of , , during rest and exercise.

anerobic processes

However, since the ratio involves the measurement of O2 use, the contribution of , , (i.e., phosphocreatine and glycolysis) is not included.

0.7 and 1.0

If measured at the cellular level, the RQ scale ranges between

metabolism

Because many factors can alter the exchange of oxygen and carbon dioxide in the lungs, the RQ does not fully explain all the contributing factors in the calculation of

dieting, fed or fasted.

Among the other factors that affect resting RER are

0.82

The average RER in a fed, nonketogenic individual is

60%

in a fed, nonketogenic state approximately , , of energy derived from fat and 40% derived from carbohydrate.

1.0

As exercise intensity increases, both RQ and RER approach , , and the proportion of energy derived from carbohydrate increases

cellular level

Because the RQ is measured at the , , it cannot exceed 1.0;

greater than

however, since RER is assessed via expired gases from the mouth, it can increase to levels , , 1.0.

buffering of hydrogen ions

increasea to levels greater than 1.0 typically occur during high-intensity exercise from the rapid breathing rate (i.e., hyperventilation) and the increased

acidity that is neutralized

The increase in hydrogen ions is accompanied by an associated increase in , , by buffers, such as bicarbonate, which are eventually removed as CO2 during respiration.

buffers

Thus, a greater presence of , , increases the amount of CO2 expired in comparison with the amount of O2 consumed, driving the RER value above 1.0.

carbohydrate metabolism

at RER value above 1.0, the RER no longer reflects

exercise intensity and fatigue

Alternatively, RER values that exceed 1.0 are often seen as an indicator of , , as well as a criterion measure for attaining Vo2max during a progressive exercise test

inefficient

Aerobic exercise in an untrained person beginning an exercise program is

aerobic exercise

Limitations in the cardiovascular and respiratory systems impose a limit on the metabolic processes that take place in order to allow , , to occur. Poor performance for a short time is the ultimate result.

adenosine triphosphate (ATP)

During exercise, the demand for , , is higher, causing the body to consume more oxygen.

arteriovenous oxygen difference (a–Vo2 difference)

The difference between the amount of oxygen in the arterial and mixed venous blood is the , , representing the extent to which oxygen is removed from the blood as it passes through the body.

20 and 14 ml

Normal values for resting arterial and venous oxygen per 100 ml of blood are , , respectively

6 ml of oxygen

the normal resting a–Vo2 difference is approximately , , per 100 ml of blood.

18 ml of oxygen

a–Vo2 difference value increases almost linearly with exercise intensity and can reach approximately , , per 100 ml of blood at O2max

Fick equation

The volume of oxygen consumed (O2) is determined as the product of and the a–O2 difference, which is known as the , , : Q x a–Vo2 difference

CO2 and lactate

During aerobic exercise the body’s metabolism is increased, producing more , , (which results in higher concentrations of H+ ions) than at rest.

anaerobic pathways

At high exercise intensities, there is an increased reliance on the , , for energy production.

blood acidity (a decrease in pH)

As with the RER when it exceeds 1.0, hydrogen ions accumulate in the active muscles, causing a marked increase in

bicarbonate ions (HCO3−)

response to the increase in blood acidity, , are released, resulting in greater CO2 expiration.

energy demands

In response to a bout of aerobic exercise, a major purpose of the endocrine system is to facilitate metabolism by maintaining the availability of carbohydrates (glucose) and fats (free fatty acids) that are needed to meet increased

Catecholamines

also facilitate cardiovascular responses to enhance the delivery of oxygen and nutrients and the removal of waste products.

pancreas, adrenal cortex, and adrenal medulla

Glands of major concern with regard to aerobic exercise include the

pancreas

is an endocrine gland that plays a major role in acute exercise metabolism because of the production and release of glucagon and insulin.

glucagon and insulin

These hormones release or uptake glucose from the tissues, which is vital to the survival of the body.

plasma glucose concentration

Plasma glucagon stimulates an increase in

insulin

facilitates glucose transport into the cells of the body.

glucagon secretion

Because of the increased metabolic demands of acute exercise, , is increased whereas insulin secretion is decreased.

conversion of glycogen

An increase in plasma glucagon stimulates the , , to glucose, thus increasing the plasma glucose concentration so that more glucose is available to be transported into cells.

insulin sensitivity

During exercise, insulin plasma concentration decreases, , is improved, and non–insulin-mediated glucose transport into cells is increased

fat breakdown in tissue (lipolysis)

The increased glucagon release (and reduced insulin release) during acute exercise enhances , , and triggers an increase in plasma fatty acids, making more fat available as a fuel for exercise.

Cortisol

is the only substance released from the adrenal cortex that plays a direct role in metabolism.

Proteins

Cortisol is responsible for stimulating the conversion of , , is responsible for stimulating the conversion of

normal blood sugar levels

cortisol plays a role in the maintenance of , , it also promotes the use of fats.

plasma levels

Exercise intensity affects the level of cortisol secretion; , , of cortisol have been shown to decrease with low-intensity exercise and increase with moderate- to high-intensity exercise

anterior pituitary

During exercise, growth hormone is secreted from the , , which assists cortisol and glucagon in making more fat and carbohydrate available in the plasma for the increased metabolism of exercise

catecholamines

(epinephrine and norepinephrine) are the “flight-or-fight hormones” released from the adrenal medulla when it is acted upon by the sympathetic nervous system during stressful situations.

stressor

The adrenal medulla perceives exercise as a , , and releases additional catecholamines during exercise.

Catecholamine plasma concentration

increases during exercise because these hormones help the body deliver blood and oxygen to the working muscles (e.g., by increasing heart rate and blood pressure)

glucagon, cortisol, growth hormone, epinephrine, and norepinephrine

In general, during exercise of increasing intensity, progressive elevations in plasma hormone concentrations of , , occur

progressive

These changes are accompanied by a , , decrease in insulin.

moderate intensity

Similar progressive changes in these hormones (glucagon, cortisol, growth hormone, epinephrine, and norepinephrine) also occur as exercise of , , continues for a long duration

Vo2max, maximal oxygen uptake, maximal oxygen consumption, and aerobic capacity

Several terms are used to refer to maximal aerobic power, a key component for improving aerobic exercise performance:

the effective function and integration

Increasing maximal aerobic power relies greatly on , , of the cardiovascular and respiratory systems.

increase in stroke volume

One of the hallmark adaptations to chronic aerobic training is an increase in maximal cardiac output, resulting primarily from an

Aerobic endurance

training does not affect maximal heart rate or decreases it slightly

aerobic power

Maximal cardiac output correlates closely with maximal aerobic power; the higher the cardiac output, the higher the

submaximal exercise intensity

In response to aerobic endurance training, cardiac output remains essentially unchanged at rest and is either unchanged or slightly decreased at any fixed

decrease in heart rate and an increase in stroke volume

At rest and at any fixed submaximal exercise intensity, adaptations include a

10 weeks

A training-induced reduction in heart rate has been shown to occur in two weeks, but depending on the intensity, duration, and frequency of training, may take up to

lower intrinsic heart rate

This response (training-induced reduction in heart rate) is believed to come from an increased parasympathetic influence, decreased sympathetic influence, and

left ventricular cavity enlargement and increased myocardial wall thickness

Long-term aerobic exercise training leads to moderate cardiac hypertrophy characterized by

bradycardia (slower heart rate), and improved cardiac contractile

The increased left ventricular volume, along with increased ventricular filling time resulting from training-induced , , function are major factors accounting for chronic stroke volume increases

blood volume

An increase in , , occurs very quickly as an adaptation to aerobic endurance training and contributes to ventricular cavity enlargement and improvements in Vo2max.

plasma volume and red blood cell volume.

Blood volume can be broken down into the two components of

red blood cell volume

Aerobic exercise training induces a very rapid increase in plasma volume (a measurable change occurs within 24 hours), but the increase in , , takes a few weeks

3/2 mmHg

effects of chronic aerobic endurance training on resting blood pressure. For individuals with normal BP, SBP/DBP values average only , , lower

7/6 mmHg

effects of chronic aerobic endurance training on resting blood pressure. in people with hypertension (SBP >140 or DBP >90 mmHg), greater reductions are noted, with an average of

normotensive and hypertensive

Immediate reductions in resting blood pressure occur after a bout of aerobic exercise in both , , individuals, which may persist for up to 22 hours

postexercise hypotension

is used to describe these changes in immediate reductions in resting blood pressure after a bout of aerobic exercise

SBP

At the same submaximal exercise work rate, chronic aerobic training also results in a decrease in

myocardial oxygen consumption and reduced workload

Since both SBP and HR are reduced at a given level of submaximal exercise with aerobic endurance training, it should be obvious that the RPP is also decreased, indicating a reduction in , , on the heart

density of capillaries

In trained peripheral skeletal muscle, prolonged aerobic training leads to an increase in the , , per unit of muscle

diffusion distance

increase in the density of capillaries per unit of muscle allows for improved oxygen and substrate delivery and a decrease in , , between blood and exercising muscle.

cardiovascular system and skeletal muscle

chronic aerobic training produces considerably less adaptation than occurs in the

no changes at rest

Adaptations in pulmonary minute ventilation (Ve) in response to chronic aerobic training occur during submaximal and maximal exercise, with