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Physical Education
Unit 3, Outcome 2 (Part 2): Acute responses to exercise
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Foundation
Acute Cardiovascular Responses
Increased heart rate: Heart rate increases when the body begins exercise due to a lack of oxygen in the blood
picked up by receptors, an increased heart rate means more oxygen is getting to the working muscles.
Increased stroke volume: Stroke volume increases at exercise to a point but then plateaus at the heart can
only pup so much blood at a certain speed. This is said to be caused by the Frank-Starling mechanism, which
states that there is an increase in stroke volume as there is more blood returning to the heart which causes the
heart walls to stretch causing a more forceful contraction and neural stimulation for increased stroke volume.
Increased cardiac output: As cardiac output is calculated by Heart rate X stroke volume, as both of these
factors are increased cardiac output will also increase.
Increased blood pressure: As there is a greater amount of blood returning to the heart, the heart walls are
more stretched this causes a more forceful contraction. Therefore blood pressure during the systolic (contraction
phase) is increased but during the diastolic (relaxation) phase blood pressure remains the same.
Increased redistribution of blood flow: During exercise blood is redistributed from organs and other areas
that do not require immediate blood flow to the working muscles increase oxygen supply.
Increased endocrine action: Hormones such as adrenaline and noradrenaline are produced to stimulate an
increase in heart rate, stroke volume and force of contraction.
Acute Respiratory Responses
Increased respiration rate: The number of breathes per minute increases. This is caused by a decrease in the
level of oxygen within the blood.
Increased tidal volume: Is the amount of air breathed per breath, during exercise a person will take in more air
to get more oxygen to the working muscles.
Increased ventilation: Is the amount of air inspired and expired per minute and is calculated by respiration rate
X tidal volume.
Increased oxygen uptake: Is the volume of oxygen transported to, taken up and utilised by the body for
energy. Is increased due to increased respiration rate and tidal volume.
Increased diffusion: Diffusion is the movement of molecules across a membrane, during exercise this occurs
predominately in two places from the lungs (aveoli sacs) to the blood vessels and then again in the muscles. This
simply means there is an increase of oxygen getting into the body and muscles and an increase in carbon dioxide
being expelled.
Aspects of oxygen uptake during exercise
(image from Live it up 2: VCE physical education Units 3 & 4)
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Oxygen deficit: Is the ‘oxygen debt’ that you accumulate at the beginning of exercise when the acute responses
are not yet in place to accommodate the increase in oxygen demands brought about by exercise. As a result the
body relies on anaerobic pathways for energy which creates harmful metabolic by-products that will need to be
broken down with oxygen later on.
Steady State: Is the state when oxygen demand is the same as the amount of oxygen being supplied.
Exercise post oxygen consumption (EPOC): Is the excess oxygen that the body consumes after exercise is finished.
This excess oxygen is used to breakdown the metabolic by-products produced by the anaerobic pathways in
oxygen deficit.
Acute Muscular response
Increased motor unit recruitment: During exercise there is increased demand on the muscles to produce a
forceful contraction to do this more muscle fibres are activated to contract producing a more powerful contraction.
Increased blood flow to muscles: Due to changes in the cardiovascular system and vasodilation of blood
vessels to the working muscles there is an increase in blood flow.
Increased AVO2 difference: AVO2 difference is the difference in oxygen concentration of the arteries
compared to the veins, this provides an indication of how much oxygen is being taken up by the muscles. At
exercise the muscles are utilising a far greater volume of oxygen than at rest hence they extract more oxygen from
the blood creating a large difference in oxygen concentration between the blood coming into the muscles and that
of the blood leaving the muscles.
Increased muscle enzyme activity: To produce more energy for the working muscles enzyme activity is
increased that reactions occur at faster rates and energy is produced quickly.
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