Exercise Metabolism Lecture Notes PDF

Unit 3: Exercise Metabolism Exercise Metabolism the exact same Exercise Metabolism Unit Outline: Measuring Energy Expenditure: Indirect Calorimetry, RER and Fuel Use Energy Requirement at Rest (BMR and RMR) From Rest to Exercise (and beyond…)...

Unit 3: Exercise Metabolism Exercise Metabolism the exact same Exercise Metabolism Unit Outline: Measuring Energy Expenditure: Indirect Calorimetry, RER and Fuel Use Energy Requirement at Rest (BMR and RMR) From Rest to Exercise (and beyond…) o Energy Spectrum of Exercise o Fast Component and O2 deficit o ‘Steady State’ Exercise and the Slow Component Incremental Exercise - VO2max Incremental Exercise – Blood Lactate, Lactate Threshold and Critical Power Factors Affecting Fuel Use Special Topic: Glycogen Depletion and Carbohydrate Loading Recovery From Exercise (EPOC) Supplement: Quantifying Work  Measuring Energy Expenditure: Indirect Calorimetry, RER and Fuel Use calorimetry Indirect Calorimetry amnt.ofenergyittakestoraiselgofHzoi Indirect calorimetry involves the measurement pmeasuredviane.at of oxygen consumption as an estimate of metabolic rate rooms Foodstuffs + O2 ® Heat + CO2 + H2O Indirect Calorimetry Direct Calorimetry Open-circuit spirometry involves measuring the volume of inspired air and analysis of O2 and CO2 content of expired air identical TIME VO2 = O2 insp. – O2 exp. = (VI x FIO2 ) – (VE x FEO2) 798sÉallytallso VCO2 = CO2 exp. – CO2 insp.= (VE x FECO2) – (VI x FICO2) zero nearly represents breath in 21 Both are generally expressed in L/min rate breath out18 shouldbepresent everypt.in slide where did go 20.93everywhere on earth water of Oxygenbreathed in through air 3 VOMIT Respiratory Exchange Ratio (RER) Also referred to as the Respiratory Quotient or RQ RER = VCO2 / VO2 The chemical makeup of CHO and lipids dictates that different amounts of O2 are needed to oxidize them, which also affects the amount of CO2 produced o This ratio allows prediction of the fuel source being used during rest and steady state exercise Although often used synonymously, these two terms are not exactly the same o RQ reflects the VCO2/VO2 ratio in the cell o RER reflects the VCO2/VO2 ratio in the expired air RER and Fuel Use For glucose: C6H12O6 + 6 O2 → 6 CO2 + 6 H20 + 32 ATP RQ = 6 CO2/6 O2 = 1.00 For palmitic acid: C16H32O2 + 23 O2 → 16 CO2 + 16 H20 + 106 ATP RQ = 16 CO2/23 O2 = 0.70 RER and Fuel Use – The Zuntz Table (Powers) Karased very 7 important numbers I See: Table 8.1 in McArdle can go above 1 w lactic acid buildup Or Zuntz table in Lab 3 materials. will get buffered making us go above 1  AKA non protein RER p RER and Fuel Use Generally, protein is not considered in indirect calorimetry o Sometimes referred to as non-protein RER o RER for protein is approximately 0.82 protein not included b c it is so complicated At rest, RER is usually around 0.78 – 0.8 o With increasing exercise intensity RER approaches 1.0 The application of RER assumes that O2 and CO2 exchange at the lungs reflects actual gas exchange from nutrient use in the cell Carbohydrate Vs. Lipid The “Crossover Concept” 50 50 085 trainable Powers Fig.4.11 f intensity yes directly related to lactate OBLA graph RER and Fuel Use Arterial blood remains almost fully saturated (~98%) even during intense exercise, so we can assume O2 extracted from the air is is taken into cells and and consumed during oxidative phosphorylation CO2 exchange is less consistent o CO2 elimination increases during hyperventilation without any change in O2 consumption o RER can increase over 1.0 in high intensity exercise without any change fuel for oxidation o Consider increased blood lactate with intense exercise... w out breathing in more02 of RER assumes that 0 CO exchange the lungs reflects application what is happening cell as far as gasexchangefrom nutrient use RER and Fuel Use When H+ accumulates in the blood it is buffered: occurs in H+ + HCO3- H2CO3 H20 + CO2 theblood To producedfrom This non-metabolic production of CO2 causes an increase in RER metabolism o Can be 1.0 – 1.15 at maximal exercise Following exhaustive exercise, CO2 can also be retained to replenish bicarbonate that was used to buffer lactate o Reduction in expired CO2 can lower RER to 0.7 or lower Validity of Indirect Calorimetry Oxidation / Respiration Foodstuff trying to ATP + Heat predictheat produced Non-oxidative glycolysis, PCr, Myokinase For indirect calorimetry to be valid, production of ALL ATP must consume oxygen o Resting, submaximal and steady-state oxygen uptake (for the most part…) Energy from non-oxidative metabolic pathways during exercise CANNOT be accurately determined via indirect calorimetry o High intensity exercise, transitions in exercise intensity, etc. Energy Requirement at Rest Energy Requirement at Rest At rest, nearly all ATP required is produced by aerobic metabolism o Consider what the ATP requirements are o How much ATP is required? need 40kg ATP rest for 70kg individual Basal Metabolic rate (BMR) is the minimum level of energy required to sustain the body’s vital functions in a waking state o 12 hour fast with no activity o Must lay supine for 30-40 minutes and determine VO2 Resting metabolic rate (RMR) is measured under less controlled circumstances and yields only a slightly higher value than BMR Energy Requirement at Rest BMR and RMR are usually expressed in terms of daily energy expenditure: o VO2 = ~250-300 mL O2/min at rest o RER = ~ 0.8, therefore 4.8 kcal/LO2 o kcal/day = 0.3 L O2 X 24 h/day X 4.8 kcal/LO2 = 2,074 kcal/day BMR is usually around 1,200-2,400 kcal/day o This is 60-75% of the total daily energy expenditure o 10% thermic effects of feeding and 15-30% physical activity Normal daily energy expenditure is 1,800-3,000 kcal/day o Athletes will ‘burn’ much more than this, for example cyclists in the Tour de France will expend ~6000 kcal/day (~126,000kcal for the 21-day event!) Basal Metabolic Rate BMR is related to fat-free mass (or lean body mass) and is sometimes determined as kcal/kg/min or day o The more fat free mass, the higher the BMR BMR is also related to body surface area and is sometimes determined as kcal/m2/h or day o The greater the skin’s surface area, the more heat is lost, the higher the BMR Basal Metabolic Rate Effect of Sex on fat-free body mass Age, sex and FFM affect BMR McArdle Figure 9.3 Metabolic Equivalent The term Metabolic Equivalent (MET) is commonly used to express energy expenditure o One MET is equal to resting VO2 o 1 MET = 3.5 mLO2/kg/min Energy expenditure can therefore be expressed as VO2 or in multiples of METs, for example: o VO2 = 2.1 L/min for a 60 kg person (absolute VO2) o VO2 = 35 mL/kg/min (or mL.kg-1.min-1) (relative VO2) exercise o This is 10 METs intensity expressed as multiples of resting The MET is often used to prescribe exercise in a clinical setting o Light exercise 6MET From Rest to Exercise (and beyond….) The ‘Energy Spectrum’ of Exercise Powers Fig. 3.23 The ‘Energy Spectrum’ of Exercise glylolysis alitate Transition from Rest to Exercise The change in work rate required to …so, the ATP demand to accomplish perform exercise is instantaneous... the work is instantaneous. Time (min) Time (min) Powers Fig. 4.1 Transition from Rest to Exercise The immediate need to supply ATP is met by a blending of of the energy pathways Whyte to p all areinitiated thesecond exercia starts therate whichthey Time (min) Powers Fig. 4.1 re piprivate lactate anaerobic glycolysis This need is met primarily by PCr and glycolytic metabolism until oxidative metabolism can match demand (if O2 metabolism can match demand depending on intensity) Transition from Rest to Exercise Whole body VO2 is function of delivery and use of oxygen as defined by the Fick Equation: VO2 = Cardiac Output * Arterial – Venous O2 Difference Lblood delivered 0 how much min p At the onset of exercise, several factors play into how VO2 changes: 0 we have to o HR and CO increasecardiac output deliver o Ventilation increases duetogradien o Blood flow increases to exercising muscle po greater difference alsodictates o Oxygen extraction from blood must increase hemoglobin con o Mitochondrial respiration must increase venous oz These changes are not immediate, and so neither is the increase in VO2 DEBT Fast Component of VO2 Kinetics VO2 rises in an exponential fashion during the first few minutes of exercise (or following a change in intensity of exercise) o This is the fast component of oxygen uptake kinetics o The oxygen deficit created is meant to describe the non-oxidative contribution to meeting the immediate ATP demand After a few minutes, a steady-state is achieved and the VO2 curve plateaus o ATP requirement is met through aerobic ATP production o The ability to achieved steady-state is dependent on exercise intensity o Theoretically, steady-state exercise could continue indefinitely if fuel supply is maintained, and the subject has the willpower! Fast Component of VO2 Kinetics 02 deficit L O consumption 102 min increase V02 training of EffNN esuit in less deficit multiply getareaunder curve Powers Fig. 4.1 Subtractfrom blue to find volume we did not consume Fast Component of VO2 Kinetics The fast component is steeper with morework increasing intensity of exercise orconsumption o Reconsider the factors that establish VO2 18 may takes longer to reachsteady state Submaximal and steady-state oxygen uptake increases with increasing work rate o Higher steady-state to match energy demand Theoretical depiction of VO2 responses 0 MMG to increased intensity deficit Lot02 0 deficit ofOz L notconsumed Time (min.) how much 02would be needed to meet 0 demands that pt Fast Component of VO2 Kinetics Energy requirement: “Supra-maximal” can'taccuratley Ghostumed measure 0 consumption VO2max aerobic Ulesssteady state is reached can't have a slow component above max Energy requirement: 50% VO2max Brooks Fig. 10-6 Fast Component of VO2 Kinetics trained people have less or deficit reach steady fallmark of trained state quicker athlete faster V02 Kinetics See Powers Fig. 13.4 Or, McArdle Fig. 7.2 Why might this occur with exercise training? trainedindividualshave higherenzymeconc enzymes apart of oxidative metabolism better 0 delivery Usage more mitochondria get to aerobic Pcr metabolism faster greatercapacity for 0 metabolism less on Slow Component of VO2 Kinetics Expected Vs. Observed VO2 191radintensity slow monent Time (min.) Time (min.) Slow Component of VO2 Kinetics A steady-state VO2 can generally be maintained for light and moderate(maybe heavy?) intensity exercise o Light 85% g o Extreme >100% 5 capacity V0 Max roughly translate As exercise intensity increases, there can be a substantial “slow component” to the oxygen uptake kinetics o A steady-state is not achieved The slow component can be substantially higher than expected VO2 based on work rate Time (min.) o Can cause VO2 to rise to maximal values. moremetabolic work for loss of it you see slow samemechanicalwork efficiency component recruit more fast twi usemoreOz  dobhmewto.pe r VO ‘Drift’ 2 Environmental conditions and duration can affect the slow component p effects drift pefferts slow component intensity onstant both Jw component or risine body temp as resultofheat See Powers Fig. 4.6 The drift in VO2 represents and increase in metabolic rate which is not related to the absolute energy demand of the exercise – Increased body temperature – Increased catecholamines 7happens in both fiber transition unique to intensity recruit fast twitch Slow Component of VO2 Kinetics EEii slowing down Incremental Exercise – VO2max Incremental Exercise Incremental (or graded) exercise tests are used to examine a subject’s cardiovascular fitness o Ramp: continuous increase in work rate (e.g., 1 W increase every 5 seconds) o Stages: longer durations at each work rate (e.g., 50 W increase every 3 minutes) These test are used to determine maximal oxygen uptake (VO2max) o VO2max is the region where VO2 plateaus and shows no further increase (or only a very slight increase) with an additional workload VO2max quantitatively expresses a person’s capacity for aerobic synthesis of ATP o Obtained NOT sustained Specificity of exercise mode is important in interpreting the results of these tests o Bike vs running vs XC skiing, etc. maximum aerobic ATPproduction Incremental Exercise and VO2max McArdle Fig. 7.4 Incremental Exercise and VO2max realitywhen dealing w slow component See Powers Fig. 4.7 Time (min.) slowcomponenttells us about level of intensity VO2max VO2max quantitatively expresses a person’s capacity for aerobic synthesis of ATP o Probably the best single measure of cardiorespiratory capacity Can be expressed as an absolute value (L/min) nonweightbearing Since energy need varies with body size, it can also be expressed as a relative value (mL/kg/min) weight bearing Often, you will see L/min used for non-weight bearing activities and mL/kg/min for weight bearing activities VO2max Relative values allow us to better compare VO2max between individuals For example, who is more “fit”: o Subject 1: VO2max = 4.0 L/min, wt: 90 kg 400mL 90 o Subject 2: VO2max = 2.5 L/min, wt: 50 kg 250mL 50 5 o Subject 1: VO2max = 44.4 mL/kg/min o Subject 2: VO2max = 50.0 mL/kg/min Subject 2 is more fit! Factors Affecting VO2max Recall the Fick equation: VO2 = Cardiac Output * Arterial – Venous O2 Difference VO2 max demonstrates the ability to take up, transport and use oxygen and so it is affected by: 1. O2 Exchange at alveoli – Usually ~98% Hb.sat. Stroke preload 2. O2 delivery Volume contraltility – [Hb], stroke volume, heart rate, fibre capillarization, fibre [myoglobin] increasenumber 3. O2 utilization canttrain – Oxidative capacity of muscle all musclefibers types can increase – Distribution of fibre types (FT Vs. ST) their oxidative capacity fast slow twitch twitth Factors Affecting VO2max Some of these differences are due primarily to body size and not necessarily sex, but generally: o ♀ have smaller heart size o ♀ have lower blood volume o ♀ have lower fat-free mass (i.e., muscle) o ♀ also tend to have have lower [Hb] hemoglobin Yn ghemoglobindL If expressed per kg of lean mass, men and women have more similar VO2max values Factors Affecting VO2max Along with fibre type and capillarization, the oxidative capacity of muscle or (QO2) will influence VO2max o Assessed by characterizing activity of oxidative enzymes of the Krebs cycle such as citrate synthase and succinate dehydrogenase highly I correlated Factors Affecting VO2max The fibre-type composition of a whole muscle will impact VO2max o “Slow Twitch” myosinisoform specproteinresponsiblefor myosin cyclin occursslowly o Type I or Slow Oxidative (SO) lots of mitochondria ability to consume0 2 o “Fast Twitch” a o Type IIa or Fast Oxidative Glycolytic dif myosin isoform b o Type IIb, IIx/b/d or Fast Glycolytic D humans SDH Stain of Muscle Sample 189ha x soleus m almostentirelyoxidative b c always on forposturalreaso Gastrocnemius White notalways on Factors Affecting VO2max A greater % of ST/SO fibres is found in athletes with higher VO2 max values fibers can getbigger but can'tincrease of fibers Factors Affecting VO2max Examples of sport specific differences in fibre-type profiles from the vastus lateralis muscle Glycolytic Mitochondrial Enzymes Enzymes FG FOG SO Incremental Exercise – Blood Lactate, Lactate Threshold and Critical Power Lactate Threshold The lactate threshold (LT) indicates that lactate is being added to the blood at a greater rate than it is being cleared o Often also called the anaerobic threshold The onset of blood lactate accumulation OB.LA.ME (OBLA) is defined as the exercise intensity at which blood lactate reaches 4 mM 2mm painful mod Occurs at exercise intensities ~ 50-60% of heavy VO2max in untrained individuals o 65-85% or higher in trained Powers Fig. 4.8 muscles Coricycle ability to uptake lactate blood LT levels tells us abt balance Lactate Threshold Potential causes of LT: 1. Is there a ‘lack’ of oxygen in working muscles leading to an increase in anaerobic metabolism? lack of ability to use or that is present 2. Muscle fibre recruitment order? 11 13 11A o ST muscle fibres are recruited at lower intensity exercise, followed by FOG, then FG as exercise intensity increases o LDH isoform in FT fibres has greater affinity for pyruvate, promoting formation of lactate Lactate Threshold 3. Increased glycolytic rate? o Catecholamines show an increase around LT which may stimulate glycolytic rate o If the rate of glycolysis is high, then NADH production can exceed the capacity for the C shuttles that move it to the mitochondria Showsame shape as Bloodlactatelevels Lactate production will also be influenced by the rate at which the ETC can ‘accept’ these cytoplasmic NADH o FOG and FG fibers have less mitochondria...reconsider the recruitment order 4. Lactate is not being cleared from the blood o Recall that liver, heart and non-exercising (maybe even exercising) skeletal muscle will use lactate for metabolism o Does this rate of clearance drop with exercise? NO it goesup Lactate Threshold So, does lactate threshold mean we have stopped using aerobic metabolism? NI Lactate Threshold don'tgetturnedoff remain on in additionto I can't ever more utilize Powers Fig. 19.3 Lactate Threshold otentially Ty Powers Fig. 4.10 twoprimary causes Gas Exchange Threshold Gas exchange threshold (GET) or the ventilatory threshold (VT) correspond with the LT o Consider how changes in lactic acid might affect ventilation correlated due to pH Orimpactsblood decrease xygenation 102 420 Helo H H2O i i dEaf.it Ive Fig 14.5 McArdle z remains rightwardshiftlowers the same saturation fmae1 jq.fi shiftsdueto decreased Pehnaintempo  Yingrease clarify Exercise Intensity Domains GET and LT delineate the transition from the moderate to the heavy domain Extreme Severe OBLA Severe Heavy Heavy Moderate Moderate Exercise Intensity Domain Exercise Intensity Domains Above GET and LT, steady-state VO2 kinetics can be achieved o i.e., heavy domain Severe Domain Heavy Domain Lactate production is high, but oxidation of lactate continues to keep up with demand Severe Domain The severe domain is delineated by the inability to maintain steady-state VO2 Heavy Domain o Concomitant with rise in blood lactate Lactate Turning Point Blood lactate increases uncontrollably unsustainable beyond the lactate turning point (LTP) 12 sustainable LT LTP o At (or near) OBLA 10 [Blood Lactate] (mM) o LTP delineates the boundary between 8 Sustainable heavy and severe intensity domains 6 getbroughtto th o Oxidation of lactate can no longer keep up 4 intensityV02 Slowcomponent with production. 2 kicksinheavily o While debated, LTP occurs near the critical 0 power (or intensity) 12 10 LT LTP [Blood Lactate] (mM) 8 6 4 2 0 16 17 18 19 20 21 22 Treadmill Velocity (km/hr) Critical Power Critical Power (CP) is the highest sustainable Predictable work rate without appreciable fatigue (~40 min) o Corresponds to the highest rate of sustainable V oxidative metabolism o Also used to delineate the transition to the ‘severe’ domain i Work above CP (W’) is a finite work capacity o Predictable o Requires non-oxidative metabolic pathways to maintain work-rate (which is limited) o Blood lactate rises until exhaustion 99 agent o In the severe domain Redrawn from Jones et al., MSSE, 2010. o VO2 kinetics unavoidably rise to max Exercise Intensity Domains Summary Med Sci Sports Exerc. 2011 Nov;43(11):2046-62. avoid slow omponent Leep BLT under control Effect of Training Training can have a significant impact on LT (and GET, LTP, CP, W’) 1 o Deceased production of lactate a o ↑ Oxidative enzymes b o Fiber type recruitment 2 o Increased uptake of lactate o ↑ Oxidative enzymes o Increased mitochondrial MCT after V0 is tapped out you can train lactate increase critical power Also see Figure 7.1 in McArdle Factors Affecting Fuel Use Factors Affecting Fuel Use The two main factors affecting fuel use during exercise are: 1. Intensity 2. Duration Depletion of fuels is one of the potential mechanisms leading to fatigue during exercise o Fuel replenishment therefore becomes important for repeated bouts of exercise, especially with glycogen Factors Affecting Fuel Use - Intensity Effect of Intensity on Fuel Use Powers Fig. 4.11 Or Brooks Fig. 7-13 Why does use of CHO increase with intensity? – Fibre type recruitment All fibers are experiencing 2 – Glycogen phosphorylase activity signals to glycolytic rate as exercise intensity increase Glycogen use Glycogen use is influenced by glycogen phosphorylase activity intracellular calcium not directly proportional proportional to muscle contraction Effect of Intensity on Glycogen Use Powers Fig. 5.13 Or McArdle Fig. 11.5 Effect of Intensity on FFA Use I doesn't take into acnt energy cost of exercise Effect of Duration on Fuel Use There is a shift towards FFA use in prolonged exercise Why take in carbs on a runt Powers Fig. 4.12 Effect of Duration on Fuel Use I Steed so don't need to replenish comes fromliver long runs Powers Fig. 4.15 Special Topic: Glycogen Depletion and CHO Loading Glycogen Depletion As muscle glycogen decreases, the rate of perceived exertion increases The sensation of fatigue, or 'hitting the wall’ in long-term exercise is associated with decreased/depleted muscle glycogen Glycogen Depletion Recall the effect of intensity on glycogen depletion… Powers Fig. 5.13 Or McArdle Fig. 11.5 Pattern of Glycogen Depletion Muscle fibres are recruited in specific patterns o The depletion of glycogen follows a similar pattern If a critical number of fibres become depleted, the number of fibres capable of producing the force required to maintain exercise is reduced (i.e. fatigue!) Pattern of Glycogen Depletion e.g., glycogen depletion following a 30 Km run Slow oxidative fibres are almost completely depleted of glycogen o SO fibres are preferentially used during prolonged aerobic exercise requiring only moderate force Glycogen Depletion and Fatigue Glycogen depletion is one of many potential causes of fatigue in endurance (aerobic) events This occurs even though there is sufficient oxygen and lipid available o Blood glucose is the only (highly preferred?) fuel for the central nervous system, therefore may have experience ‘central fatigue’ as glucose availability become limited o Background glycogen metabolism is needed for use of lipid as a fuel o Rate of energy release from lipid may be too slow (especially in heavy domain near CP) Glycogen depletion and hypoglycemia (low blood glucose) can limit performance in activities lasting longer than 30 min. Can we prevent (or at least delay) this to increase performance? Diet and Training High CHO diet maintains muscle glycogen stores with daily bouts of exercise, while glycogen depletion is exacerbated with a low CHO diet Diet and Performance Amount of CHO in the diet is reflected in the amount of glycogen stored in the muscle In turn, higher muscle glycogen content leads to a delayed onset of fatigue Carbohydrate Ingestion For Exercise What type of CHO? How much? When? Simple CHOs Elevate blood glucose levels Rely on insulin to move them to cells When intake exceeds usage, stored as fat Complex CHOs Require more time to breakdown Produce smaller and slower rise in blood glucose Carbohydrate Intake During Exercise Effect of CHO ingestion every 15 min. throughout exercise on blood glucose ….And Power Output Carbohydrate Intake During Exercise Muscle glycogen is not necessarily spared when ingesting glucose throughout exercise o It does spare liver glycogen leaving it as a potential fuel source later in exercise CHO solutions empty from the stomach more slowly than water or even salt solutions o The higher concentration of CHO in solution, the slower the gastric emptying rate o This can have implications in deciding how much simple sugars to add to sports drinks and gels Carbohydrate Intake Prior to Exercise How about a pre-game Snickers or Clif bar? Although beneficial during exercise, CHO should not be consumed in the last hour (or so…) before exercise CHO (especially simple sugars) ingested in this time period will stimulate insulin secretion, leading to elevated insulin levels at the onset of exercise Carbohydrate Intake Prior to Exercise Effect of CHO ingestion 15-45 min prior to exercise on insulin levels As a result, muscles and adipose take up glucose quickly at the onset of exercise, leading to hypoglycemia in the first 10-15 min of exercise Carbohydrate Intake Prior to Exercise A larger demand is placed on glycogen stores for the remainder of exercise o May lead to fatigue faster than had CHO not been consumed just prior to exercise Caffeine Intake Prior to Exercise Caffeine is on the IOC’s list of banned substances at urinary levels >12 μg/mL At doses much lower than the acceptable limit, time to exhaustion can be increased 20-25% when exercising at 70-75% VO2max Appears to be due to increased mobilization of FFA, which (might?) leads to a decreased use of glycogen in the first 15-20 min of exercise o Revisit the ʻGlucose-Fatty Acid Cycleʼ Carbohydrate Loading It can be of obvious benefit to have higher glycogen stores prior to starting an event o Endurance-type event of intensity around 60-85% of VO2max There are a few different strategies to maximize the amount of glycogen stored in muscle o These strategies involve manipulating exercise intensity and diet in the days leading up to the event Carbohydrate Loading The simplest strategy is to consume a normal mixed diet, followed by a high CHO diet for 3 or 4 days prior to the event Carbohydrate Loading The amount of glycogen stored can be increased by first depleting the muscle of its glycogen prior to a high CHO diet Carbohydrate Loading For athletes, this can be taken advantage of by performing an exhaustive exercise bout 4-5 days prior to the event, followed by a high CHO diet Carbohydrate Loading A third strategy is to perform an exhaustive bout of exercise 7 days prior to the event For the next 3 days a high fat and protein diet is consumed to deprive the muscles of CHO and increase the activity of glycogen synthase In the last 3 days, a high CHO diet is consumed, and glycogen storage is maximized due to the increased activity of glycogen synthase Carbohydrate Loading Effect of different strategies of CHO loading on muscle glycogen Carbohydrate Feeding to Maximize Performance Maximizing glycogen stores by CHO loading leading up to the event Pre-event carbohydrate feeding should be reduced starting ~ 4 hr. prior to the start of the event CHO feeding should be limited in the last 30-60 min. before event Ingestion of simple sugars is beneficial during exercise Along with CHO, ingestion of sports nutrition products higher in lipid can also be beneficial for longer duration activities Recovery From Exercise (EPOC) Recovery From Exercise Just as with the O2 deficit seen at the beginning of exercise, VO2 does not necessarily match muscle activity during recovery I Following exercise VO remains elevated temporarily even though muscle activity 2 has stopped o i.e., little to no external work notusuallyused anymore This component of VO2 has been called O2 debt, but the more contemporary term is excess post-exercise oxygen consumption (EPOC) EPOC EPOC is the volume of O2 consumed above that which would normally be consumed at rest  Hypothesis that EDOC Or deficit are equal EPOC EPOC is generally greater than the O2 deficit Duration and intensity of exercise can both affect how much oxygen is consumed during EPOC as well as how long it takes to return to resting VO2 Variations in EPOC are related to specific metabolic and physiological processes involved in exercise of differing intensities EPOC Light Exercise probably more (a) O2 deficit is small 4.5 4 Subject’s highest attainable VO2 (VO˙ 2 max) ˙ moderate increases as intensity increases 3.5 graph EPOC following light exercise is nearly 3 ˙ 2 Steady-state VO ˙ 2 (L · min−1) 2.5 all ‘rapid componentʼ 2 O2 deficit Aerobic ATP Rapid component o Following light, primarily aerobic exercise VO supply meets 1.5 ATP demand Slow of short duration, EPOC is reduced by ½ 1 ˙ 2 Resting VO baseline EPOC component within ~30 seconds 0.5 o Recovery is complete within minutes −4 −2 0 2 4 6 8 10 12 14 lactate Pcr recovery Time (min) EPOC is approximately equal to O2 (b) 5 Powers Fig. 4.3 deficit 4.5 O2 requirement 4 O2 deficit End of exercise 3.5 Rapid Steady state acheived 3 ˙ 2 (L · min−1) component ˙ 2 Highest VO 2.5 attainable VO 2 EPOC Moderate to Heavy Exercise steadystateacheived (a) O2 deficit is larger 4.5 4 Subject’s highest attainable VO2 (VO˙ 2 max) ˙ 3.5 EPOC lasts longer and has two distinct 3 ˙ 2 Steady-state VO ˙ 2 (L · min−1) 2.5 phases 2 O2 deficit Aerobic ATP Rapid component o Rapid and Slow Components of EPOC VO supply meets 1.5 ATP demand Slow o Slow component can last hours 1 ˙ 2 Resting VO baseline EPOC component 0.5 EPOC is generally greater than O2 deficit −4 −2 0 2 4 6 Time (min) 8 10 12 14 Powers Fig. 4.3 b c slow component lasts so long (b) 5 O2 requirement 4.5 4 O2 deficit End of exercise 3.5 Rapid 3 ˙ 2 (L · min−1) component ˙ 2 Highest VO 2.5 attainable VO 2  3 ˙ 2 Steady-state VO ˙ 2 (L · min−1) 2.5 O2 deficit Rapid 2 Aerobic ATP component VO supply meets 1.5 ATP demand Slow EPOC component 1 ˙ 2 Resting VO baseline EPOC 0.5 Severe and Supramaximal Exercise significant −4 −2 0 2 4 6 8 10 12 14 Time (min) slow component (b) 5 Energy demand can exceed VO2max 4.5 O2 requirement o Steady-state VO2 cannot be achieved 4 O2 deficit End of exercise o O2 deficit is difficult to determine 3.5 Rapid 3 ˙ 2 (L · min−1) component ˙ 2 Highest VO 2.5 attainable VO Significant blood lactate accumulation 2 1.5 Slow component 1 ˙ 2 EPOC Resting VO Figure 4 baseline deficit 0.5 EPOC is large and can take a long time to post-ex sumpt moder return to baseline −4 −2 0 2 4 6 8 10 Time (min) 12 14 16 18 20 22 and du haustin magnitude and duration of this elevated post-exercise collected in Powers the 1920s Fig. 4.3 b and 1930s slow components are nearly directly metabolic rate are influenced by the intensity of the exercise (5, 51, 91). The reason(s) for this observation researchers in Europe and the Un gested that the oxygen debt could correlated between Or deficit EPOC will be discussed shortly. two portions: the rapid portion imm Historically, the term oxygen debt has been ing exercise (i.e., approximately two applied to the elevated oxygen uptake (above rest- post-exercise) and the slow portion ing levels) following exercise. The prominent Brit- for greater than 30 minutes after ex ish physiologist A. V. Hill (62) first used the term O2 portion is represented by the steep debt and reasoned that the excess oxygen consumed gen uptake following exercise, and (above rest) following exercise was repayment for is represented by the slow decline the O2 deficit incurred at the onset of exercise (see following exercise (Figs. 4.3(a) and ( A Look Back—Important People in Science). Evidence for the two divisions of the O2 de 70 Section One Physiology of Exercise Intensity Vs. Duration and EPOC 80 min. at various 70 % VO2max for various intensities duratiuons samepeople brought back 70 V02 Gipheople more linear gdemyg.ge pogamy Mitochondria more exponential longerduration moreEPOC that will be seen  I V13 1 Metabolic Causes of EPOC – A History Lesson The term ‘O2 debt’ was first described in the 1920’s by A.V. Hill in financial/accounting terms: o CHO stores were linked to energy ‘credits’ o If stored credits were expended during exercise, then a ‘debt’ was incurred o The greater the energy ‘deficit’ (i.e., use of energy credits), the larger the debt incurred useO2 consumption to pay back CHO stores The VO2 during recovery was thought to represent the metabolic cost of repaying this debt Metabolic Causes of EPOC – A History Lesson In more physiological terms, Hill and colleagues proposed that lactic acid produced during anaerobic exercise represented the use of glycogen, with the ensuing O2 debt serving 2 purposes: 1) Resynthesis of glycogen stores from ~80% of the lactate 2) Converting the remaining lactate to pyruvate and generating ATP through the Krebs cycle Presumably, 2) provided the energy necessary for 1) 2 powers 1 Theoryinthe 1920 s Metabolic Causes of EPOC – A History Lesson Later observations showed that the initial part of recovery VO2 occurred before any decreases in blood lactate, so… Whererapid slow component same about 2 phases of O2 debt were proposed: 1) Alactic O2 debt restoration of Pcr 2) Lactic acid O2 debt Metabolic Causes of EPOC – A History Lesson The alactic O2 debt was attributed to the restoration of ATP and PCr through fast component aerobic metabolism during recovery (fast component) alactic o ~20 % of O2 debt O2 debt or EPOC Recall….. Metabolic Causes of EPOC – A History Lesson The alactic O2 debt was attributed to the restoration of ATP and PCr through aerobic metabolism during recovery (fast component) alactic o ~20 % of O2 debt The lactic acid O2 debt was thought to represent the production of glycogen lactic from lactate (slow component) o ~80% of O2 debt O2 debt or EPOC Metabolic Causes of EPOC It turns out that no substantial replenishment of glycogen is observed in the 10 minutes following exercise, even with substantial reduction in blood lactate o A major portion of the lactate is oxidized for energy in other tissues o Although some lactate is converted to glycogen via glycogenesis, the main source for replenishing glycogen is dietary CHO Excretion Amino acids Glycogen synthesis Oxidized 0 10 20 30 40 50 60 70 % of Blood Lactate So, the traditional view of Hill et al. is not entirely accurate Metabolic Causes of EPOC not or consumed due to myoglobin doesn't go to mitochondria appears to be 02 consumption only happens for supramax exercise Powers Fig. 4.5 r Or McArdle Fig 7.10 higherintensity driven by catecholamines exercise drift Lactate Recovery lower intensity leads to quickerclearance b c oxidative tissues use lactate as a substrate for energyproduction stillproducinglactate Idifmodalities of recovery not producin notusing was good actate quicker McArdle Fig. 7.11 faster rate of clearance w active TMax using lactate ec s 1