MEDI/EXSC221 2023 Anaerobic Energy Systems & EPOC PDF

Metabolism: Anaerobic Energy Systems MEDI/EXSC221 Lecture Objectives Describe how energy is liberated from anaerobic pathways Describe triggers for the liberation of energy in anaerobic pathways Apply knowledge of anaerobic systems to a common assessment for anaerobic threshol...

Metabolism: Anaerobic Energy Systems MEDI/EXSC221 Lecture Objectives Describe how energy is liberated from anaerobic pathways Describe triggers for the liberation of energy in anaerobic pathways Apply knowledge of anaerobic systems to a common assessment for anaerobic thresholds 30-s Wingate Sprint Articulate the importance and fate of lactic acid Briefly describe EPOC/Oxygen deficit Reading Chapter 6 & 7. Energy Transfer During Physical Activity McArdle, W.D., Katch, F.I. and Katch, V.L. Exercise Physiology: Nutrition, Energy and Human Performance. Lippingcott, Williams and Wilkins, Sydney, NSW, 2014. ISBN/ISSN: 9781451191554. Why can’t I sprint forever? Fatigue? Why? Deplete energy stores (availability [speed] vs demand) Build up of metabolites (H+, K+ etc) Blood flow for removal, oxygen to metabolise, bicarbonate to buffer) ATP resynthesis inhibited / slow (breakdown>resynthesis) PH, feedback (to control flux through metabolic pathways) = inhibit enzyme activity What determines fuel use in exercise? 1. Exercise intensity (rate of energy demand) 2. Exercise duration (how long at that intensity)  Power = rate (how fast ATP can be created), Capacity = (how much ATP can be created) Changes in [ATP] and [PCr] during sprint exercise 1. ATP turnover -rapid especially in first few seconds 2. Decrease in phosphocreatine- using this to resynthesise in ATP 3. Increase in Inorganic phosphate- from release of phosphate bond when ATP is broken down and from the depletion of phosphocreatine. 4. Muscle ATP well-maintained because of point 2. Inorganic Phosphate is an important signalling molecule as it increases glycolysis. Energy system interplay = a continuum Phosphagen system (ATP-CP) Primary functions Provide ATP for high intensity activities (e.g., sprinting, weight training) Provides most of energy for up to ~10 s Active at the start of all exercise regardless of intensity! For example 100m sprint….. FIRST 3 Seconds (~20m of 100m sprint) Main energy system: Phosphagen system (ATP-CP) Fuel: stored ATP Up until ~8-10 sec PCr hydrolysis - resynthesises ATP 2 ADP molecules are combined to make one ATP molecule Phosphagen system First few seconds ATP ATPase ADP + Pi CP + ADP Creatine kinase C + ATP ~8 seconds When ATP is used it is broken down to ADP. ADP can then combine with CP to make more ATP, but only for a short period of time.  Creatine phosphate (CP) stores can decrease 50-70% Fuel use, 100m sprint in the first 5-30 seconds CP stores are virtually eliminated as a result of high intensity exercise ATP stores do not decrease more than 60% even with very intense exercise ATP stores replenished ~3-5 min CP stores in ~8 min Summary Phosphagen system Supplies energy for speed/power/sprint events 0-10s ~Stored ATP ~2-3s ~Stored PCr ~3-10s (resynthesise ATP by combining with ADP) Fast rate of ATP generation, but low capacity (Fuel depletion – use>replenishment) Amount of fuel stored and enzyme activity (ATPase and Creatine Kinase) important Phosphagen system (Power / Speed) 30 s Cycle Wingate Lab 5 What energy systems and fuel are being used during this 30-s Wingate Not just anaerobic Start ATP/PCr Primarily anaerobic glycolysis Large proportion from glucose from aerobic metabolism using CHO (oxidative phosphorylation)  Glycolysis (Anaerobic glycolysis / Lactate system) Primary functions Carbohydrate (CHO) (i.e., blood glucose and muscle glycogen) break down to produce ATP in the cytosol of a muscle cell Provides energy primarily for moderate to high intensity activities For 30 seconds up to 2-3 minutes of activity Hypoxic (anaerobic) cellular environment For example, a 100m Freestyle swim race….. 100m freestyle in 47.05 seconds Main energy system: Anaerobic glycolysis Main Fuel: Glucose and glycogen Glucose Glycogen Extra ATP from glycolysis if start with ATP Hexokinase Glycogen ATP G-6-P G-1-P PFK 2Pyruvate 4 ATP  Overview of Glycolysis blood glucose sarcolemma Cytosol ATP Glycogen glycolysis G-6-P glycogenolysis ATP PFK 4 ATP pyruvate mitochondria lactate acetyl CoA High intensity exercise Moderate to low intensity  high rate of exercise demand/flux  Slower demand/flux low O2  O2 available availability   When the FLUX (speed) Lactate  too great for mitochondria  lactate formation occurs.  The formation of LACTATE is actually preferred  Less energy  Any pyruvate not immediately entering the mitochondria is reduced to lactate  Not a waste product,  Preferred source of fuel  Lactic acid production from pyruvic acid  alkalinizing reaction  actually buffers acid production from glycolysis  Lactate  Does not cause fatigue  Single fibre studies  Lactic acid forms during anaerobic glycolysis. In the body, it dissociates to release a hydrogen ion (H+). The remaining compound is what we measure in the blood as lactate. Important note: The conversion of pyruvate to lactate is reversible Therefore, lactate can be used as an energy source Key Message: The formation of lactate regenerates NAD+ to allow glycolysis to continue! Lactic acid does not directly cause fatigue Lactic acidosis causes fatigue – but lactate itself isn’t the cause Acidosis (H+) causes fatigue Inhibits PFK (rate limiting enzyme) and energy production Inhibits actin-myosin cross bridges for muscle contraction Benefits of Lactic acid: Maintains redox potential (regenerates NAD+ allows glycolysis to continue) Can be converted to glucose and used for energy production (Cori cycle)  Figure 6.12 – Text book Cori Cycle – Lactate shuttle Where does lactate go? 1. Oxidised by muscle (type 1 fibers, resting tissue) 2. Used by the heart 3. Liver gluconeogenesis (making of new glucose) MCT transporters shuttle lactate in and out of muscle Lactate Accumulation Blood lactate does not accumulate at all exercise levels During light and moderate exercise (