2 Cardio-Respiratory responses to exercise VO 2 max –Anaerobic hypothesis –Noakes protection hypothesis Limits of Cardio-Respiratory performance Is Ventilation a limiting factor in VO 2 max or aerobic performance? Cardio-respiratory adaptations to training Outline
4 Cardio-Respiratory Responses to Exercise
5 Cardio-Respiratory System Rest vs Maximal Exercise Table 16.1 (Untrained vs Trained vs Elite athletes) Rest Max Ex Rest Max Ex Rest Max Ex UTUT TT E E HR(bpm) SV(ml/beat) (a-v)O 2 (vol%) Q(L/min) VO 2 ml/kg/min SBP(mmHg) Vent(L/min) Ms BF(A) ml/min CorBFml/min
6 With exercise of increasing intensity, there is a linear increase in O 2 consumption VO 2 = Q * (a-v)O 2 (Fick Equation) Cardiovascular response determined by –rate of O 2 transport (Q) –amount of O 2 extracted (a-v)O 2 Fig 16-2,3,4 –O 2 carrying capacity of blood (Hb content of blood) –Changes in Q and (a-v)O 2 important when moving from low to moderate intensities –changes in HR become more important when moving from moderate to high intensity Oxygen Consumption
7 important factor in responding to acute demand HR inc with increasing intensity is due to; –Sympathetic stimulation (fig 9-11) and Parasympathetic withdrawal –Mechanical (stretch) and chemical (metabolites) feedback to CV control center –HR response influenced by anxiety, dehydration, temperature, altitude, digestion –estimated Max HR age (+/- 12) Steady state - leveling off of heart rate to match oxygen requirement of exercise (+/- 5bpm) –Takes longer as intensity of exercise increases, may not occur at very high intensities Cardiovascular drift - HR may increase with prolonged exercise at steady state –may be due to inc skin blood flow with temp –may be due to decreased stroke volume with dehydration or breakdown of sympathetic blood flow control Heart Rate
8 HR response : –Is higher with upper body - at same power requirement Due to : smaller muscle mass, increased intra-thoracic pressure, less effective muscle pump, feedback to control center –Is less significant during strength training Inc with ms mass used Inc with percentage of MVC (maximum voluntary contraction) Rate Pressure Produce - RPP –HR X Systolic BP –Good estimate of the workload of the heart, myocardial oxygen consumption, with Heart Rate
9 Stroke Volume - volume of blood per heart beat –Rest ml ; Max ml Fig SV increases with intensity to ~ 25-50% VO 2 max - then plateaus Fig Factors affecting SV during exercise –Pre load - end diastolic pressure (volume) Affected by changes in Q, posture, venous tone, blood volume, atria, muscle pump, intrathoracic pressure. Frank Starling Mechanism (fig 14.8) –After load - resistance to ventricular emptying –Contractility - inc by sympathetic stimulation (fig 14-10) SV biggest difference when comparing elite athletes and sedentary population ~ same max HR - double the SV and Q Stroke volume
13 Difference between arterial and venous oxygen content across a capillary bed –(ml O 2 /dl blood -units of %volume also used) (dl = 100ml) (a-v)O 2 difference - depends on –capacity of mitochondria to use O 2 –rate of diffusion –blood flow (capillarization) (a-v)O 2 difference increases with intensity –fig rest max 16 (vol %) (ml/100ml) –always some oxygenated blood returning to heart - non active tissue –(a-v) O 2 can approach 100% extraction of in maximally working muscle 20 vol % (a-v)O 2 difference
14 Blood Pressure fig 16-5 –BP = Q * total peripheral resistance (TPR) –dec TPR with exercise to 1/3 resting cue to vasodilation in active tissues –Q rises from 5 to 25 L/min –systolic BP goes up steadily with intensity –MAP - mean arterial pressure 1/3 (systolic-diastolic) + diastolic –diastolic relatively constant Rise of diastolic over 110 mmHg - associated with CAD Blood Pressure
16 With exercise - blood is redistributed from inactive to active tissue beds the priority for brain and heart circulation are maintained Skeletal muscle blood flow is influenced by balance between metabolic factors and the maintenance of blood pressure Fig 17.3 a,b Exercise Physiology, McCardle, Katch and Katch Circulation and its Control
19 Metabolic (local) control is critical in increasing O 2 delivery to working muscle –sympathetic stimulation increases with intensity Causes general vasoconstriction in the whole body brain and heart are spared vasoconstriction –Active (exercise) hyperemia - directs blood to working muscle - flow is regulated at terminal arterioles and large arteries –vasodilators decrease resistance to flow into active tissue beds adenosine, low O 2, low pH, high CO 2, Nitric Oxide(NO), K+, Ach, Figs 9.3 and 9.4 (Advanced cv ex physiology Human Kinetics) –Increases capillary perfusion –Increases flow in feed arteries through conducted vasodilation Vasodilation in distal vessels spreads proximally through cell to cell communication between endothelial cells and smooth ms cells Circulation and its Control
22 maintenance of BP priority “cardiovascular triage” –Near maximum exercise intensities, the working muscle vasculature can be constricted –This protective mechanism maintains blood pressure and blood flow to the heart and CNS –This may limit exercise intensity so max Q can be achieved without resorting to anaerobic metabolism in the heart Experimental Eg - changing the work of breathing alters blood flow to active muscle Circulation and its control
23 Experimental Eg. Altitude study fig observe a reduction in maximum HR and Q with altitude –illustrates protection is in effect as we know a higher value is possible Cardiovascular Triage
24 Experimental Eg - –one leg exercise - muscle blood flow is high –two leg exercise - muscle blood flow is lower –to maintain BP, vasoconstriction overrides the local chemical signals in the active muscle for vasodilation Cardiovascular Triage
25 Large capacity for increase –( ml/min) –due to metabolic regulation –flow occurs mainly during diastole –Increase is proportional to Q warm up - facilitates increase in coronary circulation Coronary blood flow
26 Maximal rate at which individual can consume oxygen - ml/kg/min or L/min long thought to be best measure of CV capacity and endurance performance –Fig 16-7 VO 2 max
27 Criteria for identifying if actual VO 2 max has been reached –Exercise uses minimum 50% of ms mass –Results are independent of motivation or skill –Assessed under standard conditions –Perceived exhaustion (RPE) –R of at least 1.1 –Blood lactate of 8mM (rest ~.5mM) –Peak HR near predicted max VO 2 max
28 Traditional Anaerobic hypothesis for VO 2 max –After max point - anaerobic metabolism is needed to continue exercise - we observe a plateau (fig 16-7) –max Q and anaerobic metabolism will limit VO 2 max –this determines fitness and performance Tim Noakes,Phd - South Africa (1998) –Protection hypothesis for VO 2 max –CV regulation and muscle recruitment are regulated by neural and chemical control mechanisms –prevents damage to heart, CNS and skeletal muscle –regulates force and power output and controls blood flow –Still very controversial - not accepted by many scholars What limits VO 2 max ?
29 Q dependant upon and determined by coronary blood flow –Max Q implies cardiac fatigue - ischemia -? Angina pectoris? - pain does not occur in healthy subjects Blood transfusion and O 2 breathing –inc performance - many says this indicates Q limitation –But still no plateau, was it actually a Q limitation? DCA improves VO 2 max without changing muscle oxygenation –Stimulates pyruvate dehydrogenase altitude - observe decrease in Q (fig 16-6) –This is indicative of a protective mechanism Discrepancies between performance and VO 2 max –Elite athletes, changes with training, blood doping Inconsistencies in Anaerobic hypothesis
30 regulatory mechanisms of Cardio Respiratory and Neuromuscular systems facilitate intense exercise –until it perceives risk of ischemic injury –Then prevents muscle from over working and potentially damaging these tissues Therefore, improve fitness / performance by; –muscle power output capacity –substrate utilization –thermoregulatory capacity –reducing work of breathing These changes will reduce load on heart –And allow more intense exercise before protection is instigated CV system will also develop with training Practical Aspects of Noakes Hypothesis
31 Endurance performance - ability to perform in endurance events (10km, marathon, triathlon) General population - VO 2 max will predict endurance performance - due to large range in values elite - ability of VO 2 max to predict performance is poor –athletes all have values of ml/kg/min –world record holders for marathon –male 69 ml/kg/min female 73 ml/kg/min - VO 2 max –male ~15 min faster with similar VO 2 max Observe separation of concepts of VO 2 max / performance –Lower VO 2 max recorded for cycling compared to running –Running performance can improve without an increase in VO 2 max –Inc VO 2 max through running does not improve swimming performance VO 2 max versus Endurance Performance
32 other factors that impact endurance performance –Maximal sustained speed (peak treadmill velocity) –ability to continue at high % of maximal capacity –lactate clearance capacity –performance economy –Thermoregulatory capacity –high cross bridge cycling rate –muscle respiratory adaptations mitochondrial volume, oxidative enzyme capacity VO 2 max versus Endurance Performance
33 Relationship between Max O 2 consumption and upper limit for aerobic metabolism is important 1. VO 2 max limited by O 2 transport Q and Arterial content of O 2 ? or protection theory 2. Endurance performance limited by Respiratory capacity of muscle (mitochondria and enzyme content) Evidence Fig restoration of dietary iron –hematocrit and VO 2 max responded rapidly and in parallel –muscle mitochondria and running endurance - improved more slowly, and in parallel VO 2 max versus Endurance Performance
35 Table Correlation matrix –VO 2 and Endurance Capacity.74 –Muscle Respiratory capacity and Running endurance.92 –Training results in 100% increase in muscle mitochondria and 100 % inc in running endurance –Only 15% increase in VO 2 max –VO 2 changes more persistent with detraining than respiratory capacity of muscle –Again illustrating independence of VO 2 max and endurance VO 2 max versus Endurance Performance
36 Ventilation (VE) does not limit sea level VO 2 max or aerobic performance in healthy subjects There is sufficient ventilatory reserve to oxygenate blood passing through the lungs The following evidence comes from investigating the rate limiting factor in the processes of oxygen utilization 1. Capacity to increase ventilation is greater than the capacity to increase Q or oxygen consumption 2. Alveolar surface area is extremely large compared to pulmonary blood volume. 3. Alveolar partial pressure of O 2 (PAO 2 ) increases during exercise 4. arterial partial pressure of O 2 (PaO 2 ) is maintained 5. Alveolar - arterial O 2 gradient widens during max effort 6. Ventilatory capacity may not even be reached during max exercise Is Ventilation a limiting Factor?
37 1. Capacity to increase ventilation is greater than the capacity to increase Q or oxygen consumption Fig 13-2 VO 2 /Q Q rest 5L/min - ex 25 L/min VO 2 /Q ratio ~.2 at rest and max –Oxygen use and circulation increase proportionally with exercise Ventilation perfusion Ratio - VE/Q –VE rest 5 L/min - exercise 190 L/min –VE/Q ratio ~1 at rest - inc 5-6 fold to max exercise –Capacity to inc VE much greater than capacity to increase Q Is Ventilation a limiting Factor?
38 Ventilatory Equivalent VE/VO 2 –Fig linear increase in vent with intensity to ventilatory threshold - then non linear VE rest 5 L/min - exercise 190 L/min VO 2.25 L/min - exercise 5 L/min –VE/ VO 2 : rest 20 (5/.25) ; max 35(190/5) Ventilation as a limiting Factor to performance?
39 3,4,5. PAO 2 (alveolar) and PaO 2 (arterial) –Fig 11-4 –PAO 2 - rises –PaO 2 well maintained Ventilation as a limiting Factor to performance?
40 6. Capacity of Ventilation MVV - maximum voluntary ventilatory capacity –VE at VO 2 max often less than MVV –athletes post exhaustive exercise can still raise VE to MVV, illustrating reserve capacity for ventilation MVV tests –With repeat trials - performance decreases while fatigue is possible in these muscles, it may not be relevant –If VE does not reach MVV during exercise, fatigue and rate limitation is less likely Ventilation as a limiting Factor?
41 Fig observe decline in PaO 2 with maximal exercise in some elite athletes Elite Athletes
42 may see ventilatory response blunted, even with decrease in PaO 2 –may be due to economy –extremely high pulmonary flow, inc cost of breathing, any extra O 2 used to maintain this cost –? Rise in PAO 2 - was pulmonary vent a limitation, or is it a diffusion limitation due to very high Q ? Elite Athletes
43 Cardiovascular Adaptations with Endurance Training Table 16.2 Rest Submax Ex Max Ex (absolute) VO Q 0 0 HR 0 SV (a-v)O 2 0 SBP 0 0 0 CorBFlow Ms Bflow(A) 0 0 BloodVol HeartVol 0 = no change
45 O 2 consumption improvements depend on –prior fitness, type of training, age –can inc VO 2 max ~20% –Performance can improve much more than 20% –Impacts are sport specific Cardiac Output (Q) –Same for a given absolute submaximal workrate (VO 2 ), –Q increases dramatically at maximal exercise due to increased stroke volume CV Adaptations
46 Heart Rate –training-decreases resting and submax HR –Increased Psympathetic (vagal) tone to SA node Observed after 4 weeks of brisk walking faster recovery of resting HR evidence of improved PS tone –Max HR may decrease ~3 bpm with training (not significant) Stroke volume - 20% increase -at rest, sub and maximal after training –End Diastolic Volume increases with training - inc blood volume (20-25%) - increases venous return slower heart rate - increases filling time inc left vent volume and compliance –Myocardial contractility increases Better release and reuptake of calcium at Sarcoplasmic Reticulum Shift in isoform of myosin ATPase to V1 Improves Q by about 15 to 20% –increased ejection fraction CV Adaptations
48 (a-v)O 2 difference –inc slightly with training due to ; –right shift of Hb saturation curve –mitochondrial adaptation –Hemoglobin mass increases 25% –muscle capillary density CV Adaptations
51 Heart Endurance training (increased pre load) –small inc in ventricular mass - sarcomeres added in series –triggered by volume load resistance training (increased after load) –pressure load - larger inc in heart mass –Sarcomeres added in parallel- increased relative wall thickness CV Adaptations
52 Blood pressure - Fig 10.2 Advanced CV Ex Phys (2011) –decreased resting and submax Systolic BP –Increase in maximal systolic pressure –Slight decrease in Diastolic BP CV Adaptations
54 Blood flow –training - dec coronary blood flow rest and submax (slight) inc SV and dec HR dn BP - decreases O 2 demand –inc coronary flow at max –Changes in myocardial vascularity depend on study Muscle Blood Flow –Selective increase in perfusion of high oxidative fibers –dec vascular resistance - improved release of vasodilators Inc eNOS expression and activation –Inc Nitric Oxide production in endothelial cells –Larger arterial diameter in trained limbs –Angiogensis - capillary growth –10 % inc in muscle blood flow at max CV Adaptations