The mechanisms responsible for the
acute responses to exercise in the
muscular systems (Ms).
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
Exercise occurs when muscles contract and
movement occurs
The type of contraction, the force and the
speed of contractions are controlled by the
CNS
Increased
motor unit
& ms fibre
recruitment
Increased
lactate
Increased
ms temp
Ms
responses
Energy
substrate
depletion
Increased
blood flow
to ms
Increased
02 supply
and use
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We know that during exercise there is a significant
increase in the blood flow to working muscles.
Blood is directed away from non-essential organs to the
working muscles
Skeletal capillaries vasodilate allowing for the increase
in blood flow to:
◦ Increase surface area = increased diffusion rate
◦ Allow for increased total muscle blood flow
◦ Allows for increased blood volume with minimal
increase to blood flow velocity
As a result of the increase in blood flow to the
working muscles, allowing for greater delivery of
oxygen to meet the metabolic demands of exercise


Motor unit = a motor neuron and the muscle
fibres it stimulates
The means by which the CNS talks to the
muscles to control muscle contraction



During exercise, the brain recruits more
motor units or it can increase the frequency
of messages sent to activate the motor unit
So when the body requires more
strength/power/force there is an increase in
the number of motor units recruited
Increase the frequency of messages will
increase the force produced in the muscle

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It is important to remember the “all or none
law”
That is a motor unit either contracts fully or it
does not contract
A contraction that requires maximal force will
recruit more motor units than a contraction
that doesn’t require as much force
E.g. Compare holding a pen to lifting a full
suitcase


When we begin exercising the muscle stores
of the fuels we use to produce energy will
deplete
The following fuels deplete whilst exercising:
◦ ATP (adenosine triphosphate)
◦ PC (phosphocreatine) (can also be called CP
– creatine phosphate)
◦ Glycogen levels
◦ Triglyceride

ATP is the immediate source of energy for all
muscles
◦ However, ATP is relatively in short supply and when
it is used up, the muscles must then rely on energy
substrates to fuel metabolism


Glycogen is used in both anaerobic and
aerobic respiration to produce ATP
During exercise, phosphocreatine (PC)
donates a phosphate to ADP to resynthesize
ATP


High-intensity sprint events rely more on the
stored ATP and PC as a fuel for energy
productions
Endurance events use glycogen and fat

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When we begin exercising we are working
relying on the anaerobic systems (without O2)
and as a result large amounts of lactate is
released
It is not until 02 consumption = 02 demand
that these stops accumulating in the muscles
When O2 consumption increase to meet
energy demands, the lactate can then be
delivered to sites for removal


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At this point lactate is produced and removed
at the same time
The last point this occurs is the LIP (Lactate
inflection point)
After the LIP, the body is unable to clear
lactate at the same rate as being produced,
so it accumulates, which equals fatigue.
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Heat is a by product of energy production
When you begin exercising there is a rapid
increase in energy production, therefore an
increase in heat produced = leading to an
increase in body temperature
To accommodate these, increase in sweat
glands stimulation and the skin produces
sweat, which acts to cool the skin
Blood flow to the skin (as discussed) which
cools the blood also


During exercise more 02 is delivered and
extracted by the working muscles because of
the increased demand
This leads to an increase in A-V02 diff

Now that we know everything, please take the
time to update the definition sheet we started
at the start of that chapter. Write down
definition and any other important
information you may want to remember (like
formulas such as V = RR x TV or Q = SV x
HR)



Mechanisms responsible for the acute
responses to exercise in the cardiovascular
system.
Mechanisms responsible for the acute
responses to exercise in the respiratory
system.
Mechanisms responsible for the acute
responses to exercise in the muscular
system.

Participate in physical activities to collect and
analyse data relating to the range of acute
effects that physical activity has on the
cardiovascular, respiratory and muscular
system of the body.