Assessment descriptor: Comprehensive and detailed analysis of collected data, thorough and insightful understanding of the mechanisms responsible for acute

UNIT 3 – OUTCOME 2THE MECHANISMS RESPONSIBLE FOR

THE ACUTE RESPONSES TO EXERCISE IN THE CARDIOVASCULAR, RESPIRATORY

AND MUSCULAR SYSTEMS

Assessment descriptor: Comprehensive and detailed analysis of collected data, thorough and

insightful understanding of the mechanisms responsible for acute effects of the cardiovascular,

respiratory and muscular systems of the body.

What makes up the CV system

Cardiovascular system

Heart Blood vessels Blood

List all the physiological

variables that could change in the CV

with exercise!


The CV system regulates the delivery of 02 and fuel to the body cells.

As we begin exercising the CV system assists us to meet the additional demands that the exercise is placing on the body.

They assist to deliver more 02 to the working muscles.

They also assist to remove more CO2 and other waste products


HR

SV

Q

BP

AV02 diff

Blood flow

HEART RATE

Heart rate (HR)

HR is the simplest measure to gauge how hard the CV system is working – it measures the hearts function.

Measured in beats per minute - bpm There is a direct link between HR and exercise

intensity. HR can be affected by variables such as fatigue,

hydration, ambient temp, illness, and altitude. Resting HR ranges from 60 to 82bpm! However,

endurance athletes have HR’s recorded as low as 28bpm.

Lance Armstrong’s resting HR is 32-34 with a MaxHR of 201!!!! WOW!!!

Heart Rate Just before beginning exercise you often get

an increase in HR – this is as a result as anticipating the exercise.

This occurs because of a release of hormones such as epinephrine (adrenaline).

HR will increase linearly with exercise intensity, so as exercise intensity gets harder heart rate will increase.

This continues until a person reaches their max HR (MaxHR) and then it will plateau (even if exercise intensity continues to increase)

We use this MaxHR to set athlete’s training zones.

HR vs intensity

Max heart rate

The general rule for working out a person’s max HR is MaxHR = 220 - age

For example a 20 year old will have a MaxHR of 220-20 = 200bpm

This is only an estimate and is based on MaxHR slowly declining with age.

HR will vary for each individual

Mechanisms controlling HR

HR is controlled by the parasympathetic and sympathetic nervous system as well as the endocrine system.

HR control via the parasympathetic NS

We have no conscious control over the parasympathetic nervous system

This system originates in the brain stem and extends to the heart via the vagus nerve

At rest it the parasympathetic NS is dominant – when HR is less than 100bpm

HR control via the sympathetic NS

Is the opposite side of the autonomic sympathetic nervous system

It has the opposite effect of the parasympathetic NS

It stimulates the heart causing an increase in HR and an increase in the force of contractions

It is dominant when HR is over 100bpm

Conditions SV(mL/beat)

HR(beats/min)

Cardiac Output(L/min)

Untrained Rest 75 82 6.2

Untrained Max exercise

112 200 22.4

Trained Rest 105 58 6.1

Trained Max exercise

126 192 24.2

STROKE VOLUME

Stroke volume

Stroke volume is the amount of blood ejected from the left ventricle of the heart per beat

Stroke volume will increase with exercise to assist meet the increased energy demands

Stroke volume is controlled during exercise by: Volume of venous blood return Capacity of the ventricle to expand

(distensibility) Capacity of the ventricle to contract

(contractility) The pressure the ventricles have to contract

against

Stroke Volume

Untrained athlete SV at rest 60-75ml/beat SV during max exercise – 80-115ml/beat

Trained athlete SV at rest 80-110ml/beat SV during max exercise – 160-200ml/beat

Stroke volume will reach its maximum value between 40-60% of a person’s VO2 max.


HR(beats/min)




112 200 22.4



126 192 24.2

Question

Why do you think a trained athlete has a larger SV then an untrained athlete

Why do you think the trained athlete has a lower resting HR?

Why do you think the trained athlete has a lower HR whilst exercising?

Mechanisms responsible for increases in SV

There are 3 main factors that account for the increase in SV during exercise How much the ventricle fills and

stretches during diastole (relaxation period)

Increase in neural stimulation Decrease in peripheral resistance as a

result of vasodilation of the vessels supplying blood to the exercising muscles. This decrease means it is easier for the heart to empty blood from the ventricle and increases SV.

Frank-Starling mechanism

During exercise venous blood flow increases

This causes the ventricle to stretch more as it fills more fully with blood

This results in a more forceful contraction as a result of the greater elastic recall

An increased amount of blood in the ventricle results in a stronger contraction of the ventricle, thereby increasing the amount of blood ejected (increased SV)

Has the greatest effect at lower intensities

SV

At rest, the left ventricle only ejects 40-50% of blood in it.

During exercise, the left ventricle ejects more then that

CARDIAC OUTPUT

Cardiac Output (Q)

Cardiac output = the total volume of blood ejected from the heart per minute

Measured in litres per min L/min Q = SV x HR Q(L/min) = SV(mL/beat) x HR (bpm) Cardiac output = stroke volume x heart rate

Changes in HR and SV lead to changes in Q. When exercising, both the SV and HR will increase, therefore Q increases

Cardiac Output (Q)

At the beginning of exercise and up until approx 60% VO2 max the increase in Q comes from the increase in HR and SV.

However, after approx 60% VO2max what causes the increase in Q?

SV increases to its max when you are working submaximal (upto 60%), so when you increase intensity, the body compensates by increasing HR, that allows Q to continue to rise

Cardiac Output (Q)


HR(beats/min)




112 200 22.4



126 192 24.2

Cardiac Output

Subject SV HR Q

REST

Untrained male 70 x 72 = 5.0Untrained female 60 x 75 = 4.5Trained male 100 x 50 = 5.0Trained female 80 x 55 = 4.4MAX EXERCISE

Untrained male 110 x 200 = 22.0Untrained female 90 x 200 = 18.0Trained male 180 x 190 = 34.2Trained female 125 x 190 = 23.8

BLOOD PRESSURE

Blood pressure

Systolic = the contraction or pumping phase of the heart

Diastolic = the relaxation or filling phase of the heart

Systolic BP = the pressure in the arteries following contraction of ventricles as blood is pumped out of the heart

Diastolic BP = pressure in the arteries when the heart relaxes and the ventricles fill with blood

Blood pressure

BP increases with exercise During exercise when we are using large

muscles groups such as running, swimming and cycling affects the systolic BP more than the diastolic BP

During max exercise systolic BP can increase from 120mmHg to 200mmHg

Upper body exercises often see a greater increases in BP than lower body exercises

Doing resistance activities can cause even greater increases to systolic BP

Blood pressure

Blood pressure

During exercise, arterioles vasodilate (increase in diameter), which means more blood drains from the arterioles into the muscles capillaries.

It also means the blood needs to be ejected out of the heart better to cater for this, therefore increase in blood pressure

VENOUS RETURN

Venous Return

The blood returning to the heart When exercising, Q increases, which

means more blood is taken away from the heart, therefore more blood needs to be returned to the heart

This occurs in three ways: The muscle pump – muscles constantly contracting

squashed veins together, which makes blood travel back to the heart in the ‘smaller’ vein at a more forceful pace

The respiratory pump – (similar as above) Breathe in increase abdominal pressure, which pushes blood in veins in thorax and abdomen towards the heart. Breathing out allows pressure to drop and veins to refill. When RR increase due to exercise, this pump increases

Vasoconstriction – forces the veins to constrict, which forces blood to be pushed back to heart quicker

BLOOD VOLUME

Blood Volume

Blood volume decreases during exercise, especially in the first 5minutes (it then stabilises)

The amount of decrease in blood volume is dependant on the intensity of the exercise, environmental factors such as temperature and level of hydration

REDISTRIBUTED BLOOD FLOW

Blood flow

During exercise blood flow redistributes – know as redistributed blood flow

A person of average fitness, during max exertion has blood flow greater than water from a kitchen tap!

As soon as exercise begins blood flow is redistributed – WHY?

To increase the blood flow to the working muscles and a reduction the blood flow to organs

This occurs to meet the bodies needs for increased O2 and nutrients and removal of CO2

Redistributed blood flow

Redistributed blood flow occurs as a result of vasoconstriction and vasodilation

Vasodilation = widening of the blood vessels causing an increase in blood flow

Vasoconstriction = narrowing of the blood vessels causing a decrease in blood flow

The blood vessels in regions requiring increases in 02 and nutrient delivery vasodilate

The blood vessels in regions requiring decreases in 02 and nutrient delivery vasoconstrict

These adjustments occur according to intensity


Vasodilation occurs with blood vessels near the: Working muscles

Vasoconstriction occurs with blood vessels near the: Spleen Kidney Gastrointestinal tract Inactive muscles


Blood directed at the brain doesn’t decrease by as much

Heart gets greater supply of blood during exercise, not just more pumped there but the heart muscle itself gets more blood because of vasodilation of the coronary arteries


This also allows for increases in the surface area of capillaries

This increases the area over which gaseous exchange occurs

This occurs because we need to increase blood supply up to 20 times greater than rest and this can not be achieved by Q alone


Blood flow to the skin increase as it needs to assist in the regulations of body temperature through heat exchange with the environment

As exercise intensity increases, blood flow to the skin also increases

A-V02 DIFFERENCE

Arteriovenous oxygen difference

VO2 is the volume of O2 that can be taken up and used by the body

As intensity increases, so does O2 consumption (we know this occurs because ventilation and cardiac output increase.

A-VO2 difference also increase


A-VO2 diff is the measure of the difference in the concentration of O2 in the arterial blood and the concentration of oxygen in the venous blood

Measured in millilitres per 100millilitres of blood

At rest our a-VO2 diff is approx 5mL per 100mL – arteries contain approx 20mL/100mL and the veins carry approx 15mL/100mL


About 25% of 02 is extracted from the arterial blood by the working muscles at rest. The other 75% goes back to the heart in venous blood

During exercise that increases to approx 75% of available 02 is extracted – up to 15-18mL/100mL


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Assessment descriptor: Comprehensive and detailed analysis of collected data, thorough and insightful understanding of the mechanisms responsible for acute