Module: Principles of Performance Session 2: Exercise Physiology James Fern Learning Outcomes LO1 - Understand the diverse requirements for ATP production and the different metabolic pathways that meet these demands. LO2 - Be able to explain the different demarcations that separate the exercise domains. LO3 - Be able to list the adaptations to training that lead to improved exercise performance. Biological Work In pairs discuss and create a list of tasks the body performs everyday that can be described as “biological work”? Muscle Contraction Digestion & Absorption Gland Function Establishment of Gradients Synthesis of New Compounds Energy First Law of Thermodynamics Conservation of Energy Energy can not be “Created” or “Destroyed” Our body simply transforms energy ATP What is ATP? o Adenosine molecule bound to three phosphate groups. o Chemical “fuel” for all processes in body o Food “energy” (kcals) used to “rebuild” ATP o Potential Energy o Phosphate bonds - “high energy bonds” 1. How much can we “store” in the human body? 2. Where do we store it? Aerobic vs. Anaerobic Energy Production Anaerobic: No O2 required/available for energy production Aerobic: O2required for energy production Metabolic pathways To maintain a constant supply of ATP several metabolic pathways are used. Some are located in the cytosol and some in the mitochondria. 1. Cytosol ATP production via the anaerobic breakdown of PCr, glucose, glycerol and carbon fragments of deaminated amino acids. 2. Mitochondria Aerobic ATP production via the Krebs cycle, β oxidation and the electron transport chain (ETC). Phosphocreatine (PCr) Acts as an energy reservoir to overcome the storage limitations of ATP. Fat and glycogen are the major sources for maintaining ATP synthesis. However some comes directly from the splitting of a phosphate from PCr. Speed of ADP phosphorylation from PCr considerably exceeds anaerobic energy transfer from glycogen, because of the activity rate of creatine kinase (CK). What happens if intense exercise exceeds ~10 seconds? Cellular oxidation Majority of energy for phosphorylation comes from the oxidation (burning) of dietary carbohydrates, lipids and proteins. This process continually provides hydrogen atoms from the catabolism of these macronutrients. The mitochondria contain carrier molecules that remove electrons from hydrogen (oxidation) and eventually pass them onto oxygen (reduction). ATP synthesis occurs during these oxidation-reduction reactions that take place in the ETC. Electron Transport Chain During cellular oxidation hydrogen atoms are not merely turned “loose” into intracellular fluid. Instead, dehydrogenase enzymes catalyze hydrogen’s release from the nutrient substrate. Co-enzyme NAD+ and FAD accept pairs of electrons (energy) from hydrogen. The substrate is oxidized by giving up its hydrogen - by gaining this hydrogen NAD+ and FAD reduce to become NADH and FADH2. The NADH and FADH2 formed from the breakdown of food provide energy-rich molecules as they are carrying electrons with high energy- transfer potential. Electron Transport Chain Located on the inner membrane of the mitochondria cytochromes pass along the electrons carried by NADH+ and FADH2. Substrate Phospharylation Catabolism of the macronutrients serves one vital function - to phosphorylate ADP to ATP. This involves 3 important stages: Stage 1. Digestion and absorption of large food molecules into smaller subunits for use in cellular metabolism. Stage 2. Degradation of amino acids, glucose and fatty acid and glycerol units into acetly-coenzyme A. Small amount of ATP produced at this stage. Stage 3. Within in the mitochondria acetly CoA degrades to CO2 and H2O with a large amount of ATP produced. Refer to handout 1 (Fig 6.9) Energy from food CHO is the only substrate who’s stored energy generates ATP anaerobically (vital for nervous tissue) Important implications for performances that require rapid energy release above levels supplied by aerobic metabolism. Aerobic hydrolysis of CHO occurs more rapidly than energy production from fatty acid breakdown, thus depleting glycogen reserves early during endurance performance significantly reduces power output in the later stages. List some common steps taken to prevent this. Energy from food Glycolysis (see handout 2, Fig 6.11) Occurs in the cytosol. A cells capacity for glycolysis is crucial for performances requiring max effort lasting upto 90 seconds. PFK vital role in: Conversion of fructose 6-phosphate to fructose 1, 6- diphosphate. 1 glucose (6 carbon) converts to 2 pyruvate (3 carbon). Fast Twitch fibres contain comparatively large quantities of PFK Glucose Anaerobic Energy H+ Pyruvic Acid (2) Lactic Acid (2) ATP Inter Cellular Fluid Mitochondria CO2 & H+ Fatty Acids Aerobic Acetyl Co-A (2) Amino Acids Energy ATP Krebs CO2 Cycle H+ To ETC ATP – CP Energy System Small amount of ATP stored 80-100 g in whole body, must be re-synthesized Enough for a few seconds of explosive all-out exercise CP: immediate energy source for ATP rebound CP stored in larger quantities Where and how much? 1. Stored in the cytosol 2. Up to 6 times more CP than ATP can be stored. Energy Transfer Systems and Exercise 100% % Capacity of Energy System Anaerobic Glycolysis Aerobic Energy System ATP - CP 10 sec 30 sec 2 min 5 min + Aerobic Capacity Capacity for aerobic resynthesis of ATP O2 uptake during exercise Oxygen Uptake: Use of oxygen by the cells for aerobic respiration. VO2 – Relative (ml/kg/min) and Absolute (l/min) VO2max = Max O2 uptake, transport and utilization possible by individual Quantification of Aerobic Capacity VO2max VO2max : Max Oxygen Uptake Further increases in exercise intensity (further energy requirement), results in NO increase in VO2. Additional energy is produced via anaerobic glycolysis Exercise of Increasing Intensity 60 Oxygen Consumption (ml/kg/min) 50 VO2max 40 30 20 10 0 Stage 1 Stage 2 Stage 3 Stage 4 Stage 5 Stage 6 What effects our capacity to produce energy? Nutritional status Training status Acid-base balance (cellular environment) Genetics Energy Systems and Exercise Anaerobic/Aerobic energy is always being produced. Exercise intensity/duration determines the ratio or relative contribution. How can we estimate the ratio between aerobic vs. anaerobic energy production during a given task? •Respiratory exchange ration: RER •VCO2/VO2 - ranges from 0.7~1.15 •Lipid = 0.7 •CHO = 1.00 Lactic Acid Byproduct of Anaerobic Metabolism. Glucose Energy H+ Pyruvic Acid (2) Lactic Acid (2) ATP Lactic Acid Causes Fatigue Irritation of local muscle contractile function Decreased pH of cellular environment & bloodstream Accelerated depletion of glycogen stores Training can increase lactate tolerance and decrease lactate formation for a given workload. How? Possibly by limiting the ability of the enzyme LDH (lactate dehydrogenase) to compete for pyruvate. (Wasserman et al., 1985) Blood Lactate Threshold (Tlac) The demarcation between the moderate and heavy exercise domains. 1st increase in blood lactate above resting value during incremental exercise. Exercise intensity at Tlac is associated with a non-linear increase in VE (Tvent). Blood Lactate Threshold (Tlac) Constant rate intensity exercise below Tlac Can be sustained without an appreciable increase in blood lactate. HR and ventilation reach an early steady state, subjects perceive the exercise to be relatively easy. Can be sustained for several hours. What factors will lead to termination? Blood Lactate Threshold (Tlac) If constant intensity 12 exercise is 10 Severe performed just 8 above the Tlac then blood lactate Lactate (mM) 6 Heavy increases above 4 resting levels and 2 Moderate eventually stabilizes 0 around 2-5mM. 0 10 20 30 Time (mins) 40 50 60 Effect of Training on Blood Lactate / Lactate Threshold [Blood Lactate] Untrained Trained LT LT 25% 50% 75% 100% Percent of VO 2 max What Effects Lactate Threshold ? GENETICS Aerobic capacity Fiber type Training Aerobic capacity Fiber type Adaptations Physiological Adaptations with Training in capillaries ( Density) aerobic enzymes mitochondria (# and size) Pain tolerance to lactic acid Blood Lactate Threshold Lactate appearance in the bloodstream Powerful predictor of aerobic exercise performance. Higher Tlac = Improved “performance” Lactate curve shifts to the right. Lactate Processing Cori Cycle Muscle Cell Liver Glucose Glucose / Glycogen Pyruvate Pyruvate Lactate Lactate References Skinner, J.S., McLellan, T.H., (1980), The transition from aerobic to anaerobic metabolism, Research Quarterly for Exercise and Sports, 51, 234-48. Wasserman, K., Beaver, W.L., Davis, J.A., (1985), Lactate, pyruvate and the lactate- to-pyruvate ratio during exercise and recovery, Journal of Applied Physiology, 59, 935-40. Recommended reading McArdle, Katch & Katch 5th Ed - Energy transfer in the body (Section 2, Ch6, pp. 132-155).
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