2Timing, Energy Use, and Control What are the steps that occur going from rest to exercise back to rest?How do we know what’s happening inside the body - external indicators?How are the energy demands supplied in the time necessary?What are the limitations that prevent us all from being world record holders?
3Fuel During Exercise Limited or unlimited? Can we add more? How do we get access?
4Sources of Fuel During Exercise CarbohydrateBlood glucoseMuscle glycogenFatPlasma FFA (from adipose tissue lipolysis)Intramuscular triglyceridesProteinOnly a small contribution to total energy production (only ~2%)May increase to 5-15% late in prolonged exerciseBlood lactateGluconeogenesis via the Cori cycle
5Estimation of Fuel Utilization During Exercise First - need to understand oxygen uptake.
7Oxygen UptakeVentilation - moving air into and out of the lungs – breathingStimulated by CO2 in the bloodAir exhaled from the lungs is missing some oxygen and has new CO2 added
8Oxygen UptakeRespiration – movement of gasses – oxygen and carbon dioxidePulmonary – lungs to blood, blood to lungsCellular – blood to tissues, tissues to bloodTied to metabolismO2 needed for metabolismCO2 made from metabolism
9Oxygen Uptake.VO2 – rate volume of oxygen used by the body each minuteAbsolute units = liters/minRelative units = ml/kg/minVCO2 – rate volume of carbon dioxide produced by the body each minuteVE – rate volume of air exhaled each minuteAbsolute units = liters/minute..
10Estimation of Fuel Utilization During Exercise During steady state exerciseVCO2 and VO2 reflective of O2 consumption and CO2 production at the cellular level..
11Estimation of Fuel Utilization During Exercise Respiratory exchange ratio (RER or R)RER = VCO2VO2Indicates fuel utilization0.70 = 100% fat0.85 = 50% fat, 50% CHO1.00 = 100% CHO..
12Estimation of Fuel Utilization During Exercise Fat Oxidation (metabolism)C16H32O O CO H2ORER= VCO2 / VO2 = 16 CO2 / 23 O2= 0.70..
13Estimation of Fuel Utilization During Exercise Glucose Oxidation (metabolism)C6H12O6 + 6 O CO2 + 6 H2ORER = VCO2 / VO2 = 6 CO2 / 6 O2= 1.0..
14Exercise Intensity and Fuel Selection .Low-intensity exercise (<30% VO2max)Fats are primary fuelHigh-intensity exercise (>70% VO2max)CHO are primary fuel.
15Effect of Exercise Intensity on Muscle Fuel Source
16Exercise Intensity and Fuel Selection “Crossover” conceptDescribes the shift from fat to CHO metabolism as exercise intensity increasesDue to:Recruitment of muscle fibers that need fuel quicklyIncreasing blood levels of epinephrine that stimulates glycogenolysis
18Exercise Duration and Fuel Selection During prolonged exercise there is a shift from CHO metabolism toward fat metabolismIncreased rate of lipolysisBreakdown of triglycerides into glycerol and free fatty acids (FFA)Stimulated by rising blood levels of epinephrine
19Shift From CHO to Fat Metabolism During Prolonged Exercise
20Interaction of Fat and CHO Metabolism During Exercise It is not all one or all the otherCarbohydrate is a key materialCarbohydrate is the brain’s fuel sourceRun low = physical fatigueRun low = mental stress (BONK)
21Interaction of Fat and CHO Metabolism During Exercise Some carbohydrate must be present in order for fat to be metabolized.Physiologic strategy: do what is necessary to “spare” carbohydrate.
22Interaction of Fat and CHO Metabolism During Exercise “Fat burns in the flame of carbohydrates”When glycogen is depleted during prolonged high-intensity exerciseReduced rate of glycolysis and production of pyruvateReduced Krebs cycle intermediatesReduced fat oxidationFats are metabolized by Krebs cycle
23Effect of Exercise Duration on Muscle Fuel Source
24Rest-to-Exercise Transitions Light switch & energy example
25Rest-to-Exercise Transitions Oxygen uptake increasesReaches steady state within 1-4 minutesOxygen deficitLag in oxygen uptake at the beginning of exerciseSuggests anaerobic pathways contribute to total ATP productionAfter reaching steady state, ATP requirement is met primarily aerobically
27Recovery From Exercise: Metabolic Responses EPOC (formerly known as oxygen debt)Excess post-exercise oxygen consumptionElevated VO2 for several minutes immediately following exerciseAerobic metabolism provides the energy to recycle ADP to ATP.
28Recovery From Exercise: Metabolic Responses “Fast” portion of EPOCResynthesis of stored PCReplacing muscle and blood O2 stores
29Recovery From Exercise: Metabolic Responses “Slow” portion of EPOCElevated body temperature and catecholaminesConversion of lactic acid to glucose (Cori Cycle - gluconeogenesis)
30Oxygen Deficit and Debt During Light-Moderate and Heavy Exercise
31Metabolic Response to Exercise: Incremental Exercise = Incremental increase in intensity
32Metabolic Response to Exercise: Incremental Exercise Oxygen uptake increases linearly until VO2max is reachedNo further increase in VO2 with increasing work rate..
33Changes in Oxygen Uptake With Incremental Exercise
34Fate of Lactate Where does it go? -During anaerobic metabolism -During aerobic metabolism-After exercise
35Fate of Lactate Anerobic metabolism Lactate can stay in the cell and build upHydogens inhibit PFK – slow glycolysisFatigue and discomfortDecreased performanceLactate can leave the cell and go into the bloodMeasurable in millimoles per liter (mM/liter)Lactate can be used by “aerobic” cells – reconvert to pyruvate, etc.
36Lactate ThresholdThe point at which blood lactic acid suddenly rises during incremental exerciseAlso called the anaerobic thresholdAlso called OBLA – onset of blood lactic acid
38Lactate Threshold Practical use as a marker of exercise intensity High intensity needs anaerobic metab =OBLAThe intensity cannot last for longinhibit PFK with lactic acid – high intensityrun out of glycogen/glucose – high inten. + duration
39Lactate Threshold Practical uses in prediction of performance High threshold compared to max capacity = ability to remain at “low intensity” when others might be at “high intensity”Ex. Top marathoners remain “aerobic” while running faster than 5 min/mile
41Other Mechanisms for the Lactate Threshold Failure of the mitochondrial hydrogen shuttle to keep pace with glycolysisExcess NADH in sarcoplasm favors conversion of pyruvic acid to lactic acidType of LDHEnzyme that converts pyruvic acid to lactic acidLDH in fast-twitch muscle fibers favors formation of lactic acid
42Effect of Hydrogen Shuttle and LDH on Lactate Threshold
43Questions: Can lactate be removed faster? What does training do to OBLA / lactate threshold?Where does the lactate ultimately go?
45Training Effect on OBLA Endurance Training“Grow” more mitochondriaUse aerobic metab. to supply ATP at higher intensities (less lactate produced)More places for lactate to goGreater and thus faster LA removal / use
47Lactate as Fuel for the Heart Heart is the ultimate “aerobic” muscleConverts lactate to pyruvate easilyLDH in slow-twitch muscle fibers favors formation of pyruvateMakes ATP through aerobic metabolism with pyruvate as the substrate
48Fat as fuelWhy is fat an economical fuel source?
49Comparing CHO and FAT 1g of CHO = 4kcal 1g of fat = 9kcal 1g of CHO needs g H2O for storage1g of fat = 9kcal1g of fat needs no H2O for storageSo the energy equivalent of CHO in 1g of fat requires 2g CHO and 6g H2OThis is 8g of weight
50So……..To gain the energy equivalent of 1 lb of fat it would take2 lb CHO + 6 lb H2O = 8 total lb of weight
51So……..A 5 lb fat gain would equal a 40 lb CHO gain1. WOW !!!!2. Energy efficient?
52Note:Too much of a good thing is never good, however.