Presentation on theme: "Exercise Metabolism Chapter 4. Timing, Energy Use, and Control What are the steps that occur going from rest to exercise back to rest? How do we know."— Presentation transcript:
Timing, 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?
Fuel During Exercise Limited or unlimited? Can we add more? How do we get access?
Sources of Fuel During Exercise Carbohydrate –Blood glucose –Muscle glycogen Fat –Plasma FFA (from adipose tissue lipolysis) –Intramuscular triglycerides Protein –Only a small contribution to total energy production (only ~2%) May increase to 5-15% late in prolonged exercise Blood lactate –Gluconeogenesis via the Cori cycle
Estimation of Fuel Utilization During Exercise First - need to understand oxygen uptake.
Oxygen Uptake Ventilation - moving air into and out of the lungs – breathing –Stimulated by CO 2 in the blood Air exhaled from the lungs is missing some oxygen and has new CO 2 added
Oxygen Uptake Respiration – movement of gasses – oxygen and carbon dioxide –Pulmonary – lungs to blood, blood to lungs –Cellular – blood to tissues, tissues to blood Tied to metabolism –O 2 needed for metabolism –CO 2 made from metabolism
Oxygen Uptake VO 2 – rate volume of oxygen used by the body each minute –Absolute units = liters/min –Relative units = ml/kg/min VCO2 – rate volume of carbon dioxide produced by the body each minute –Absolute units = liters/min –Relative units = ml/kg/min VE – rate volume of air exhaled each minute –Absolute units = liters/minute...
Estimation of Fuel Utilization During Exercise During steady state exercise –VCO 2 and VO 2 reflective of O 2 consumption and CO 2 production at the cellular level..
Estimation of Fuel Utilization During Exercise Respiratory exchange ratio (RER or R) –RER = VCO 2 VO 2 –Indicates fuel utilization 0.70 = 100% fat 0.85 = 50% fat, 50% CHO 1.00 = 100% CHO..
Estimation of Fuel Utilization During Exercise Fat Oxidation (metabolism) C 16 H 32 O 2 + 23 O 2 16 CO 2 + 16 H 2 O RER= VCO 2 / VO 2 = 16 CO 2 / 23 O 2 = 0.70..
Estimation of Fuel Utilization During Exercise Glucose Oxidation (metabolism) C 6 H 12 O 6 + 6 O2 6 CO 2 + 6 H 2 O RER = VCO 2 / VO 2 = 6 CO 2 / 6 O 2 = 1.0..
Exercise Intensity and Fuel Selection Low-intensity exercise (<30% VO 2max ) –Fats are primary fuel High-intensity exercise (>70% VO 2max ) –CHO are primary fuel..
Effect of Exercise Intensity on Muscle Fuel Source
Exercise Intensity and Fuel Selection “Crossover” concept –Describes the shift from fat to CHO metabolism as exercise intensity increases –Due to: Recruitment of muscle fibers that need fuel quickly Increasing blood levels of epinephrine that stimulates glycogenolysis
Exercise Duration and Fuel Selection During prolonged exercise there is a shift from CHO metabolism toward fat metabolism Increased rate of lipolysis –Breakdown of triglycerides into glycerol and free fatty acids (FFA) –Stimulated by rising blood levels of epinephrine
Shift From CHO to Fat Metabolism During Prolonged Exercise
Interaction of Fat and CHO Metabolism During Exercise It is not all one or all the other Carbohydrate is a key material Carbohydrate is the brain’s fuel source –Run low = physical fatigue –Run low = mental stress (BONK)
Interaction 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.
Interaction of Fat and CHO Metabolism During Exercise “Fat burns in the flame of carbohydrates” When glycogen is depleted during prolonged high-intensity exercise –Reduced rate of glycolysis and production of pyruvate –Reduced Krebs cycle intermediates –Reduced fat oxidation Fats are metabolized by Krebs cycle
Effect of Exercise Duration on Muscle Fuel Source
Rest-to-Exercise Transitions Light switch & energy example
Rest-to-Exercise Transitions Oxygen uptake increases –Reaches steady state within 1-4 minutes Oxygen deficit –Lag in oxygen uptake at the beginning of exercise –Suggests anaerobic pathways contribute to total ATP production After reaching steady state, ATP requirement is met primarily aerobically
Recovery From Exercise: Metabolic Responses EPOC (formerly known as oxygen debt) –Excess post-exercise oxygen consumption –Elevated VO 2 for several minutes immediately following exercise –Aerobic metabolism provides the energy to recycle ADP to ATP.
Recovery From Exercise: Metabolic Responses “Fast” portion of EPOC –Resynthesis of stored PC –Replacing muscle and blood O 2 stores
Recovery From Exercise: Metabolic Responses “Slow” portion of EPOC –Elevated body temperature and catecholamines –Conversion of lactic acid to glucose (Cori Cycle - gluconeogenesis)
Oxygen Deficit and Debt During Light-Moderate and Heavy Exercise
Metabolic Response to Exercise: Incremental Exercise = Incremental increase in intensity
Metabolic Response to Exercise: Incremental Exercise Oxygen uptake increases linearly until VO 2max is reached –No further increase in VO 2 with increasing work rate..
Changes in Oxygen Uptake With Incremental Exercise
Fate of Lactate Where does it go? -During anaerobic metabolism -During aerobic metabolism -After exercise
Fate of Lactate Anerobic metabolism -Lactate can stay in the cell and build up -Hydogens inhibit PFK – slow glycolysis -Fatigue and discomfort -Decreased performance -Lactate can leave the cell and go into the blood -Measurable in millimoles per liter (mM/liter) -Lactate can be used by “aerobic” cells – reconvert to pyruvate, etc.
Lactate Threshold The point at which blood lactic acid suddenly rises during incremental exercise –Also called the anaerobic threshold –Also called OBLA – onset of blood lactic acid
Lactate Threshold Practical use as a marker of exercise intensity –High intensity needs anaerobic metab =OBLA –The intensity cannot last for long inhibit PFK with lactic acid – high intensity run out of glycogen/glucose – high inten. + duration
Lactate 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
Other Mechanisms for the Lactate Threshold Failure of the mitochondrial hydrogen shuttle to keep pace with glycolysis –Excess NADH in sarcoplasm favors conversion of pyruvic acid to lactic acid Type of LDH –Enzyme that converts pyruvic acid to lactic acid –LDH in fast-twitch muscle fibers favors formation of lactic acid
Effect of Hydrogen Shuttle and LDH on Lactate Threshold
Questions: Can lactate be removed faster? What does training do to OBLA / lactate threshold? Where does the lactate ultimately go?
Training Effect on OBLA Endurance Training –“Grow” more mitochondria Use aerobic metab. to supply ATP at higher intensities (less lactate produced) More places for lactate to go Greater and thus faster LA removal / use
Lactate as Fuel for the Heart Heart is the ultimate “aerobic” muscle –Converts lactate to pyruvate easily –LDH in slow-twitch muscle fibers favors formation of pyruvate –Makes ATP through aerobic metabolism with pyruvate as the substrate
Fat as fuel Why is fat an economical fuel source?
Comparing CHO and FAT 1g of CHO = 4kcal 1g of CHO needs 3 g H2O for storage 1g of fat = 9kcal 1g of fat needs no H2O for storage So the energy equivalent of CHO in 1g of fat requires 2g CHO and 6g H2O This is 8g of weight
So…….. To gain the energy equivalent of 1 lb of fat it would take 2 lb CHO + 6 lb H2O = 8 total lb of weight
So…….. A 5 lb fat gain would equal a 40 lb CHO gain 1. WOW !!!! 2. Energy efficient?
Note: Too much of a good thing is never good, however.