Physiological responses to physical activity. Acute responses to exercise.

KEY KNOWLEDGE Know the mechanisms responsible for the acute responses to exercise in the cardiovascular, respiratory and muscular systems 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 systems of the body

What is meant by acute physiological responses to exercise? How do acute responses to exercise differ from chronic adaptations to exercise?

Acute responses to exercise RESPIRATORY MUSCULAR CARDIOVASCULAR Oxygen Consumption Ventilation Temperature a-vO2 difference Motor unit recruitment Diffusion Cardiac Output Energy substrates Venous return Blood pressure Lactate Redistribution of blood flow

Acute Respiratory responses to exercise What is the Respiratory System responsible for?? Ventilation (V) – how much air is breathed in or out in one minute. Measure in Litres per minute. Diffusion – the movement of molecules from an area of higher concentration to one of lower concentration.

V (L per minute) = TV (litres) x RR (breaths per minute) Ventilation Ventilation - How much air is breathed in or out in one minute.  in ventilation is result of an Tidal Volume (TV) and Respiratory Rate (RR). V (L per minute) = TV (litres) x RR (breaths per minute) Tidal Volume - How much air is inspired or expired in one breath Respiratory Rate - the number of breaths taken in one minute Increases volume of O2 in lungs, can now be transported to working muscles. At rest depending on body size and gender in can be anywhere from 4-15L. During exercise it can be anywhere from 15-30L. How can body size and gender impact on Ventilation? Watch: ‘What happens to your lungs when you exercise?’

Ventilation When exercise begins, there is a rapid increase in Ventilation increasing the volume of O2 in the lungs , which can then be transported to the working muscles. Why might we see an increase in Ventilation immediately before exercise? Sub maximal exercise - Ventilation rapidly at start of exercise 4-5mins. But continues more slowly until reaches plateau. What does a plateau look like? Linear relationship b/w ventilation and oxygen consumption. TV and RR increase proportionally to increase ventilation.

Ventilation Maximal exercise - Continues to  until exercise has stopped. High intensity exercise - No longer linear relationship b/w ventilation and O2 consumption, meaning that when TV plateau but RR will continue to increase. Why would we see a plateau in TV? Ventilatory Threshold the point where ventilation increases at a non-linear rate. Occurs approx. 65-75% max O2 consumption. When exercise stopped, ventilation  suddenly, then gradually return to resting levels. Familiarise yourself with Table 4.1 page 99 and Figure 4.1 page 100

Diffusion Refer to Figure 4.2 page 101 Diffusion occurs from an area of high pressure to an area of low pressure In the lungs – O2 concentration is high, so O2 diffuses from the alveoli into the bloodstream CO2 levels in the blood are high, so CO2 moves from the blood into the alveoli At the muscle – the opposite occurs Blood O2 levels are high and muscle O2 levels are low – O2 is diffused into the muscle CO2 is removed by moving it out of the muscle (high concentration) and into the bloodstream (low concentration) During exercise - Diffusion capacity is increased – increased SA of the alveoli and the muscle tissue Greater amounts of O2 and CO2 can be exchanged Greater amounts of O2 available at muscle, greater amounts CO2 removed.

Acute Cardiovascular responses to exercise What is the main focus of the Cardiovascular System? Oxygen consumption (VO2) – the volume of O2 that can be taken up and used by the body Arteriovenous Difference (aVO2 Diff) – difference in O2 concentration in the arterioles compared with the venules Cardiac Output – the amount of blood pumped out of the heart in one minute Venous Return – the bodies ability to return blood back to the heart Blood pressure – the pressure exerted by blood against the walls of the blood vessels Redistribution of blood flow – During exercise blood is redirected away from inactive muscles and less important organs to the working muscles

Q (litres per minute) = HR (bpm) x SV (litres per beat) Q, SV & HR Cardiac output - the amount of blood pumped out of the heart in one minute. Q (litres per minute) = HR (bpm) x SV (litres per beat) Stroke volume - the amount of blood ejected by the left ventricle per beat. Heart rate - the number of times the heart beats in one minute. Familiarise yourself with table 4.2 page 102 At the beginning of exercise both SV and HR  = in Q A lower HR and a larger SV indicates an efficient circulatory system What part of the heart is the blood ejected from to move to the working muscles? At rest the heart will eject only 40/50% of the blood in the ventricle

Q, SV & HR Heart rate – Sub maximal - will increase until O2 demands met, then levels off as we have reached steady state (O2 supply = O2 demand) During Sub maximal exercise, SV reaches a maximum. Further increase in Q is a result of an increase in HR Maximal - increases linearly until max heart rate is reached Exercise beyond 30mins HR will continue to increase but SV will decrease – Q remains unchanged. Explain why this may be?

Test your understanding Draw and explain the relationship between heart rate and exercise intensity. How does cardiac output compare between trained and untrained athletes during rest, sub-maximal and maximal exercise?

Blood Pressure  in Q Blood pressure Systolic blood pressure - pressure in the arteries following contraction of ventricles as blood is pumped out of the heart (top number) – A good systolic pressure is under 120mm Hg Diastolic blood pressure - pressure in the arteries when the heart relaxes and ventricles fill with blood between heart beats (bottom number) – A good diastolic pressure is under 80mm Hg Blood pressure and exercise - Exercise using large muscles - running or swimming Greater changes in the systolic pressure and minimal changes in the diastolic pressure - arterioles supplying the working muscles vasodilate meaning more blood drains from arterioles into muscle capillaries. Strength exercises – weight lifting greater increases in systolic and diastolic, changes in Q and HR are less 1o mmHg

Which line depicts the systolic blood pressure and which is the diastolic blood pressure?

Venous Return Venous return by muscle pump, respiratory pump and venoconstriction Muscle pump - Muscles contract- veins squashed together- blood in them are forced towards heart Valves in veins prevent blood from flowing backwards Muscle relaxes - veins fill with blood until next contraction Process continues - ‘pumping’ action Respiratory pump - Inspiration (breathing in) diaphragm increases abdominal pressure, veins in thorax and abdomen emptied towards heart. Expiration (breathing out) - process is reversed. Veins fill with blood When RR increases venous return also increases – more effective pump Venoconstriction - constriction of veins Reflex controlled by central nervous system Reduces capacity of venous system, forcing blood to be pushed out towards heart

Redistribution of Blood Flow During exercise blood flow is redirected away from spleen, kidneys etc. To the working muscles so that these are receiving greatest % of Q Familiarise yourself with figure 4.7 page 105 Mechanisms responsible: Vasoconstriction - a decrease in diameter of a blood vessel, results in decrease in blood flow (inactive areas) Vasodilation - increase in diameter of blood vessel, results in increase in blood flow (working muscles) Blood flow to heart and brain maintained during exercise Blood supply to heart increases during exercise Blood flow to skin increases as exercise intensity increases WHY???? When exercise intensity approaches maximum, blood flow to skin decreases WHY????

VO2 & aVO2 Difference Oxygen consumption (VO2) - volume of blood that can be taken up and used by the body. Increase in exercise intensity = an increase in O2 consumption Direct result of increase in Q and an increase in the arteriovenous oxygen difference Arteriovenous oxygen difference (a-vO2 diff) - difference in oxygen concentration in the arterioles compared with the venules. During exercise working muscles extract greater amounts of O2 from blood, increases a-vO2 difference. At rest arterial blood releases 25% of its O2 to tissues. What happens to the remaining 75% ? Watch: ‘Arteries, Arterioles, Venules & Veins’

What affects VO2 max? Body size - a larger heavier person requires more oxygen than a smaller person Gender – females have a lower oxygen uptake compared to males of similar age and athleticism Genetics – significant evidence suggest that aerobic capacity is genetically determined. Can be 25-50% of the variance seen between individuals Age – declines with age by approx 1% per year after the age of 25 Training status – aerobic training increased o2 uptake

Test your understanding! What is a-VO2 difference? How does a-VO2 difference change during exercise and explain why this is the case? What is the relationship between VO2 and exercise intensity? Why is VO2 max expressed relative to body weight?

Acute Muscular responses to exercise Temperature – increase in the rate of metabolism which produces heat and an increase in body temperature Motor Unit Recruitment – the brain can increase the number of motor units recruited to produce more force Energy Substrates – the bodies fuel source for exercise to occur Lactate – released by the working muscle when O2 is not present

Increased blood flow Blood is directed away from non-essential organs to working muscles Skeletal capillaries open up and serve three main purposes: Allow increases in total muscle blood flow Deliver large blood volume with minimal increase in blood flow velocity Increase the surface area to increase diffusion rates Results in an increased blood flow to working muscles, allows greater delivery of oxygen to meet metabolic demand of exercise.

Which of the bars and why would represent blood flow to the working muscles during exercise?

Motor Unit Recruitment Motor unit - A motor neuron and the muscle it stimulates The CNS talks with the muscle to control muscular contractions. During exercise - increase in force developed by the working muscle. To do this the brain can increase frequency of messages sent to activate motor unit or increase number of motor units recruited. Motor unit will contract maximally or not all, depends on strength of stimulus. (all-or-nothing principle.) The number of motor units that are recruited and the rate at which they are recruited can be adjusted and depend on required strength and speed for contraction. Maximal force - will recruit as many motor units as possible, increase frequency of messages.

Energy Substrates ATP - a chemical compound made up of adenosine and three phosphate molecules ADP - a chemical compound made up of adenosine and two phosphate molecules PC - a chemical fuel consisting of a bound of phosphate and creatine molecule ATP is the immediate source energy for all muscular contractions - Stored in muscle Small supply once used up, must rely on substrates to fuel metabolism. Glycogen - both anaerobic and aerobic respiration to produce ATP During exercise - PC donates a phosphate molecule to ADP to resynthesise ATP Exercise = decrease in all fuel levels within the muscle (ATP, PC, muscle glycogen and intramuscular triglycerides) Glycogen decreases more rapidly in endurance activities High intensity sprint- rely more on stored ATP and PC as a fuel Endurance- use glycogen and fats Familiarise yourself with Figure 4.9 page 108

Lactate Start of exercise - large amounts of lactate released WHY??? Body takes time to respond to increased demands of exercise Until O2 supply can meet demand, energy to continue produced anaerobically. Sub maximal exercise - Sharp increase in lactate Until O2 consumption can meet demand Can be delivered to sites for removal At this point, lactic acid is produced and removed at equal rates so no accumulation of lactic acid Greater exercise intensities - Blood lactate levels increase Body continue to produce and remove lactic acid Done so at a higher rate than sub maximal levels

Lactate Lactate Inflection Point – (LIP) The exercise intensity beyond which lactate production exceeds removal, sometimes referred to as the lactate threshold. At this point - production of lactate exceeds clearance. Increases- result of removal mechanisms being unable to cope with the increase in lactate produced. What would you expect to occur to the blood lactate levels during a marathon during a 400 metre sprint? Apart from lactate what are two other by products that would accumulate?

Temperature Heat is a by-product of process of converting chemical energy (fuel) to mechanical energy (movement) Increase in rate of reactions accompanied by increased in heat production, causes body temperature to increase Accommodates changes by stimulating sweat glands to produce sweat. Works to maintain relatively constant body temperature. At higher intensities - Blood vessels vasoconstrict which hinders heat transfer to skin and increases rick of heat- related injuries WHY does this occur?? SUMMARY – Familiarise yourself with Table 4.4

Test your understanding Outline how one acute muscular response contributes to exercise performance. During exercise, blood flow is diverted from some organs. Which organs are likely to receive less blood flow during exercise? The skeletal muscles and the brain The small intestine and the kidneys The skin and the skeletal muscle The heart and the brain When an athlete begins to exercise, the body’s need for oxygen increases and a number of immediate changes occur to help increase the supply of O2 to the working muscles. What name is given to these immediate changes that occur in response to exercise? One of these cardiovascular responses to exercise is an increase in aVO2 diff. What is meant by the term aVO2 difference? Outline why aVO2 difference increases during exercise. Explain the relationship between body temperature and redistribution of blood flow in the body as a result of continuous exercise.