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!
Cardiovascular system 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
Cardiovascular systemHR
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 6.2Untrained Max
exercise112 200 22.4
Trained Rest 105 58 6.1Trained Max
exercise126 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.
Conditions SV(mL/beat)
HR(beats/min)
Cardiac Output(L/min)
Untrained Rest 75 82 6.2Untrained Max
exercise112 200 22.4
Trained Rest 105 58 6.1Trained Max
exercise126 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)
Conditions SV(mL/beat)
HR(beats/min)
Cardiac Output(L/min)
Untrained Rest 75 82 6.2Untrained Max
exercise112 200 22.4
Trained Rest 105 58 6.1Trained Max
exercise126 192 24.2
Cardiac OutputSubject SV HR QRESTUntrained male 70 x 72 = 5.0Untrained female 60 x 75 = 4.5Trained male 100 x 50 = 5.0Trained female 80 x 55 = 4.4MAX EXERCISEUntrained 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
Redistributed blood flow Vasodilation occurs with blood vessels
near the: Working muscles
Vasoconstriction occurs with blood vessels near the: Spleen Kidney Gastrointestinal tract Inactive muscles
Redistributed blood flow
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
Redistributed blood flow 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
Redistributed blood flow 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
Arteriovenous oxygen difference
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
Arteriovenous oxygen difference
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
Arteriovenous oxygen difference