The 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

Ms responses Increased motor unit & ms fibre recruitment Increased ms temp Increased blood flow to ms Increased 02 supply and use Energy substrate depletion Increased lactate

 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

 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

 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

 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.

 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.