Acute muscular responses to

exerciseThe mechanisms responsible for the acute responses to exercise in the

muscular systems (Ms).

Exercise occurs when muscles contract and movement occurs

The type of contraction, the force and the speed of contractions are controlled by the CNS

Acute muscular responses

Ms response

s

Increased motor unit & ms fibre recruitmen

t

Increased ms temp

Increased blood flow

to ms

Increased 02 supply and use

Energy substrate depletion

Increased lactate

Acute muscular responses

Increased blood flow to the muscles

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 theworking muscles, allowing for greater delivery ofoxygen to meet the metabolic demands of exercise

Increased blood flow to the muscles

Increased motor unit and ms fibre recruitment

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

Increased motor unit and ms fibre recruitment

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

Increased motor unit and ms fibre recruitment

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

Increased motor unit and ms fibre recruitment

Energy Substrate

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

Energy substrate

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

Energy substrate

High-intensity sprint events rely more on the stored ATP and PC as a fuel for energy productions

Endurance events use glycogen and fat

Energy substrate

Increase in lactate

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

Increase in lactate

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.

Increase in lactate

Increased body temperature

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

Increased body temperature

Increased 02 supply & use

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

Increased 02 supply & use

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)

Now

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.

Key Knowledge

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.

Key Skills