Acute muscular responses to exercise The mechanisms responsible

Acute muscular responses to exercise The mechanisms responsible for the acute responses to exercise in the muscular systems (Ms).

Acute muscular responses � 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 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

Increased blood flow to the muscles

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 the working muscles, allowing for greater delivery of oxygen to meet the metabolic demands of exercise

Increased motor unit and ms fibre recruitment

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

Energy Substrate

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 sprint events rely more on the stored ATP and PC as a fuel for energy productions � Endurance events use glycogen and fat � High-intensity

Increase in lactate

Increase in lactate � When we begin exercising we are working relying on the anaerobic systems (without O 2) 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 O 2 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.

Increased body temperature

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 02 supply & use

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-V 02 diff

Now � 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)

Key Knowledge � 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 Skills � 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.