Cardiovascular and respiratory systems
Stroke Volume
The volume of blood pumped out of the left ventricle in each contraction. On average, resting stroke
volume is approximately 70ml, but this value is much bigger in elite performers. Stroke volume increases as
exercise intensity increases, but only up to 40-60% of maximum effort. Once a performer reaches this
point, stroke volume Plateaus because the ventricles do not have as much time to fill up with blood due to
an increased heart rate.
Heart Rate
Heart rate is the number of times the heart beats per minute. It increases with exercise – the higher the
intensity, the higher the heart rate. Maximum heart rate can be calculated as 220 minus the individuals
age.
A trained performer has a greater heart rate range because their resting heart rate is lower and maximum
heart rate increases. Regular exercise causes hypertrophy of the heart, resulting in an increase in stroke
volume and maximum cardiac output, and leading to bradycardia (a lower resting heart rate of below
60bpm)
(a) (b) (c)
^HR response to exercise of different intensities: (a) sub-maximal (aerobic), (b) maximal (anaerobic), (c.) fluctuating
intensities
Cardiac Output
Cardiac output (Q) is the amount of blood pumped out by the left ventricle per minute: Q = SV x HR
Cardiac output stays the same at rest for both trained and untrained performers. During exercise,
maximum cardiac output increases due to an increase in HR and in SV. Cardiac output will increase as the
intensity of the exercise increases until maximum intensity is reached and then it plateaus. During exercise
the increase in maximum cardiac output will have huge benefits for the trained performers as it will
increase the oxygen carrying capacity of the blood to the working muscles.
Cardiac Cycle
The cardiac cycle describes the process of the cardiac muscle contracting and the movement of blood
through the heart chambers. Each complete cardiac cycle takes approximately 0.8 seconds. There are two
phases: Cardiac Diastole is the relaxation of the cardiac muscle, and cardiac systole is the contraction of
the cardiac muscle.
Atrial Systole – atria contracts which forces blood into ventricles.
Ventricular Systole – ventricles contract which pushes blood away from the heart.
Diastole – the relaxation phase of the heart which allows blood to enter.
, Cardiac conduction system
The cardiac conduction system ensures that the rate of the cardiac cycle increases during exercise to allow
the working muscles to receive more oxygen.
SA node – generates electrical impulse causing atria walls to contract
AV node – collects impulses and delays by 0.1 seconds
Bundle of HIS – splits electrical impulse into 2
Bundle Branches – carries impulses to base of ventricles
Purkinje Fibres – distributes impulses through ventricle walls causing ventricular systole
Regulation of heart rate during exercise
The rate at which impulses are fired from the SA node can be controlled by neural, hormonal, and intrinsic
factors.
Neural control = receptors
1. 2. 3.
Chemoreceptors: Baroreceptors: Proprioceptors:
Detects an increase in CO2 Detects an increase in Detects an
increase in
and decrease in O2 blood pressure muscle movement
Cardiac control centre
Sympathetic nervous system Parasympathetic nervous system
Accelerator nerve SA node, increases HR Vagus Nerve
The Cardiac Control Centre (CCC) is located in the medulla oblongata of the brain.
Hormonal control
Adrenaline is a stress hormone that is released by the sympathetic nerves and cardiac nerves during
exercise. It stimulates the SA node, which results in an increase in both the speed and force of contraction,
therefore increasing cardiac output.
Intrinsic Factors
Venous return Temperature
More blood returns back to the right atrium Increased speed of nerve transmission
Right atrium stretch causing SA to increase increase blood viscosity
Firing rate
SA node
Blood is forced down into the ventricles
Increase ventricle stretch/contraction force
Increase stroke volume/ cardiac output
Changes in temperature will affect blood viscosity and the speed of nerve impulse transmission. In
addition, venous return will increase, which stretches the cardiac muscle, stimulating the SA node, which in
turn increases the force of ventricular contraction and therefore stroke volume.
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