Energy Systems and Exercise PDF

Energy Systems and Exercise Dr Gregory Peoples [email protected]...

Energy Systems and Exercise Dr Gregory Peoples [email protected] 1 1 Introduction This lecture focuses on the connections between food, the energy found in food, and the transformation of that energy into ATP. There are few situations encountered by the human body that utilize ATP at a faster rate than exercise, so sport and exercise are excellent models to study the energy systems that lead to the restoration of ATP. Inadequate food intake can lead to a lack of fuel and substrates that the body needs to restore ATP, and this can affect speed, distance, power, strength, or stamina. How have you seen your physical capabilities (in sports, exercise, or daily activities) hampered in the past due to a lack of proper fueling? 2 2 1  Introduction 3 3 Lecture Objectives Describe the rephosphorylation of ATP and the general characteristics of the creatine phosphate, anaerobic glycolysis, and oxidative phosphorylation energy systems. Describe the specific characteristics of the creatine phosphate energy system, and explain how it is used to replenish ATP during exercise. Describe the specific characteristics of the anaerobic glycolysis energy system, and explain how it is used to replenish ATP during exercise. Describe the specific characteristics of the oxidative phosphorylation (aerobic) energy system, and explain how it is used to replenish ATP during exercise. Explain the process of aerobic metabolism of carbohydrates, fats, and proteins (amino acids), the concept of measuring fuel utilization with the respiratory exchange ratio, and describe the factors that influence fuel utilization. Describe the response of oxygen consumption to steady state and submaximal exercise, and explain the concept of maximal oxygen consumption (VȮ 2max). Explain the concept of the ‘oxygen slow component’ as it relates to the energy systems and therefore the maximal work capacity according to duration of time. 4 4 2  Overview of Energy Systems 5 5 Overview of Energy Systems 6 6 3  Overview of Energy Systems 7 7 Overview of Energy Systems 8 8 4  Overview of Energy Systems During an maximum effort exercise test over 30s there is a inverse contribution of the PCr/Glycolysis contribution with that of oxidative metabolism. The 15-30s time period is dominated by oxidative phosphorylation. 9 9 Overview of Energy Systems 10 10 5  Characteristics of the Three Energy Systems Speed of action Amount of ATP Duration of action replenished Creatine phosphate Very fast Very small Very short Anaerobic glycolysis Fast Small Short Oxidative phosphorylation Very slow Large Very long ATP = adenosine triphosphate 11 11 The Creatine Phosphate Energy System 12 12 6  What Is Creatine Phosphate (CrP)? High-energy phosphate compound similar to ATP Stored in muscle and other tissues May also be referred to as phosphocreatine, PC, PCr, and CP Serves as a readily accessible reservoir of energy 13 13 Creatine Phosphate Energy System 14 14 7  Creatine Phosphate Energy System 15 15 Creatine Metabolism 16 16 8  Dietary Creatine Whole Foods Supplements 17 17 Creatine absorption in the gut Mesa, J.L.M., Ruiz, J.R., González-Gross, M.M. et al. Oral Creatine Supplementation and Skeletal Muscle Metabolism in Physical Exercise. Sports Med 32, 903–944 (2002). https://doi.org/10.2165/00007256-200232140-00003 18 18 9  Creatine uptake into skeletal muscle 19 19 Utilisation of ATP and Creatine Phosphate during Short, High-Intensity Exercise 20 20 10  Overview of the Creatine Phosphate System One chemical step Anaerobic Catalyzed by creatine kinase (CK) Fatigue associated with CrP depletion Very fast reaction Predominant energy system in very 1 ATP per CrP molecule high intensity exercise; e.g., “power” events 10-second duration 21 21 The Creatine Shuttle 22 22 11  The Anaerobic Glycolysis System 23 23 The Anaerobic Glycolysis System 24 24 12  Schematic of Anaerobic Glycolysis Energy in the form of two ATP is needed to allow the reaction to proceed Sufficient energy is released in subsequent chemical reactions to re-form four ATP When the process commences from stored glycogen, it is called glycogenolysis 25 25 Overview of the Anaerobic Glycolysis System 18 chemical steps/reactions; 6 are Anaerobic repeated 1- to 2-minute duration 12 chemical compounds, 11 enzymes Fatigue associated with decreased pH (metabolic acidosis) Rate-limiting enzyme: phosphofructokinase (PFK) Predominant energy system in high- intensity exercise; for example, Fast, but not as fast as the creatine sustained, repeated sprints phosphate (CrP) system 26 26 13  Plasma Lactate is an unreliable marker of exercise intensity A: 60% and B: 110% of peak aerobic power result in the excess production of H+ ions. However, released from the muscle is an exponential conc of H+ compared to lactate (especially for 5 min) 27 27 The Fate of Lactate Lactate shuttling occurs in many physiological and pathological conditions, where in lactate is exported by one cell type and imported by another cell type. The well-known Cori cycle involves lactate shuttling between skeletal muscle and the liver. Therefore, due to both release and uptake rates impacting the actual concentration of La, it is non-precise in terms of its relationship to energy systems per se. 28 28 14  The Oxidative Phosphorylation System 29 29 Oxidative Phosphorylation 30 30 15  Schematic of Oxidative Phosphorylation Glucose follows the steps of glycolysis, except that rather than being converted to lactate, pyruvate is transported into a mitochondrion for aerobic metabolism. Pyruvate goes through the Krebs cycle, a series of chemical reactions that oxidize, or remove, the electrons from the intermediate compounds in the process. The electrons are transported to the electron transport chain where they participate in a series of reactions that release sufficient energy to phosphorylate ADP to ATP. Oxygen is the final electron acceptor and forms water. 31 31 The Oxidative Phosphorylation System 32 32 16  Summary of the Oxidative Phosphorylation System 124 chemical steps/reactions Slow 30 compounds, 27 enzymes Potentially limitless duration Rate-limiting enzymes: Aerobic phosphofructokinase Fatigue associated with fuel (PFK), isocitrate dehydrogenase depletion (for example, muscle (IDH), cytochrome oxidase (COX) glycogen) 30 ATP via glucose, 31 ATP via Predominant energy system in glycogen (in skeletal muscle) endurance exercise; for example, long-distance running 33 33 Fuel Utilisation 34 34 17  Substrates and exercise intensity Relative contributions of carbohydrate and fat fuel sources during exercise. Trained cyclists exercised at increasing intensities, and the relative contributions of fuels for contracting skeletal muscle were measured with indirect calorimetry and tracer methods. An increasing contribution of carbohydrate fuels, notably muscle glycogen, is observed at higher exercise intensities 35 35 Oxidation of Carbohydrates, Proteins, and Fats Carbohydrates are metabolized as glucose via glycolysis to pyruvate and produce 30 ATP through oxidative phosphorylation in skeletal muscle. Fats are metabolized in a variety of ways; the fatty acid palmitate is shown. The process of b-oxidation converts two-carbon portions of palmitate to acetyl CoA where it enters oxidative phosphorylation, eventually producing 113 ATP. Metabolism of alanine and isoleucine are two examples of protein metabolism. After removing the nitrogen group, alanine can enter the metabolic pathway as pyruvate, producing 10.5 ATP, whereas isoleucine enters as acetyl CoA, resulting in the production of 34 ATP. 36 36 18  Respiratory Exchange Ration and Energy Percentages from Carbohydrates and Fats RER Percent CHO Percent fat 1.00 100 0 0.95 83 17 0.90 66 34 0.85 49 51 0.80 32 68 0.75 15 85 0.70 0 0 RER = respiratory exchange ratio; CHO = carbohydrate The RER calculated from measured VO ̇ 2 can be used to determine the percentage of energy that is being derived ̇ 2 and VCO from carbohydrate and fat oxidation.The full table can be seen in Appendix H. Source: Carpenter, T. M. (1964). Tables, factors, and formulas for computing respiratory exchange and biological transformations of energy (4th ed., p. 104). Washington, DC: Carnegie Institution of Washington. 37 37 Metabolic Pathways Favored Liver Muscle Adipose tissue Central nervous system (CNS) Fed (absorptive) Glucose used as energy, stored as glycogen, Glucose used for energy or Fatty acids are stored as Glucose from food used to state and converted to fatty acids if energy intake is stored as glycogen triglycerides (three fatty acids provide energy greater than expenditure; amino acids 1 glycerol) metabolized; fatty acids transported to adipose tissue for storage as triglycerides Postabsorptive Glycogen broken down to provide glucose; Glucose used for energy, Triglycerides are broken down Glucose comes predominantly state manufacture of glucose from lactate and some glycogen storage to provide fatty acids to from liver glycogen alanine (provided by muscle) and glycerol continues; lactate and alanine muscle and liver; glycerol to (provided by the breakdown of fat from released to liver to make liver to be used for glucose adipose tissue) begins glucose; fatty acid uptake (provided by the breakdown of fat from adipose tissue) for use as energy Fasting (18 to Liver glycogen is depleted; glucose made Muscle protein degraded to Triglycerides are broken down Glucose provided by the liver 48 hours without from lactate and amino acids provided by provide amino acids to liver; to provide fatty acids to (from lactate and amino food) muscle; red blood cells also provide some lactate to liver for glucose muscle and liver; glycerol to acids) lactate Synthesis liver to be used for glucose Starvation (>48 Liver continues to manufacture glucose, Muscle depends Triglycerides are broken down CNS depends primarily on hours without predominantly from glycerol (from adipose predominantly on fatty acids to provide fatty acids to ketones produced by the liver food) tissue) to prevent muscle from providing and ketones for energy muscle and liver; glycerol to for energy amino acids and lactate; fatty acids broken liver to be used for glucose down to produce ketones (for use by CNS and muscle) 38 38 19  Triglyceride and fat oxidation The ‘Normal’ responses when taking 8481 steps/day the day before was a high rate of fat oxidation and a low level of plasma triglyceride concentration during the postprandial test. On the contrary, when taking either Low (2675 steps/day) or Limited (4759 steps/day) exercise, the postprandial triglyceride was significantly elevated (A) and fat oxidation significantly reduced (B) compared to Normal (P < 0.05). ∗Low and Limited are significantly different from Normal (P < 0.05). 39 39 Critical Power Profile – insight to metabolism 40 40 20  Functional Threshold Power FTP over 20 mins Power profile over 16.1 km 41 41 Functional Threshold Power 42 42 21  Oxygen Consumption 43 43 Maximal Energy Consumption (𝐕̇ O2max) 44 44 22  Submaximal Exercise 45 45 Oxygen slow component 46 46 23  Oxygen slow component 47 47 Oxygen slow component 48 48 24  Oxygen slow component Little effect (as shown by direct infusion studies). Very little effect. Strong effect shown Little effect (as shown both in animal, single by animal studies). limb and exercise studies 49 49 Oxygen slow component – Nutrition CHO depleted versus CHO restored conditions Type I fibres, which are low in glycogen, are unable to continue the same contribution to the work Type II fibres are recruited at an earlier stage, and these fibres are less efficient (O2) in the resynthesis of ATP. Evident higher oxygen consumption that is also drifting by minutes 15-20. 50 50 25  Oxygen slow component – Nutrition Dietary nitrate is classed in Group A (performance enhancing) Increased nitrate contributes to nitric oxide synthase production (NOS) which in turns promotes vasodilation of blood vessels L-arginine also stimulates NOS activity in the same way Beetroot juice Both pathways promote blood flow especially at the commencement of muscle contractions This repeated muscle contraction study (left) shows a reduction in the slow component of the oxygen consumption and less disturbance of PCr in the muscle, following the ingestion of beetroot juice. Time to exhaustion is also increased. The increased, rapid blood flow is thought to provide the contracting skeletal muscle with a more immediate oxygen supply, and therefore Type I efficiency (and less requirement to recruit Type II fibres). 51 51 Oxygen slow component – Nutrition Dietary sodium bicarbonate loading is classed in Group A (performance enhancing) More time was spent in the rapid component and then there was a blunting of the slow component Reasoning was levelled at the changed metabolic factors (H+), however, these are not the full explanation. 52 52 26  Summary Provision of energy is dependent on multiple factors, no less so the intensity and duration of the exercise stimulus. Even short duration exercise will require aerobic based metabolism, especially if there is a multiple bout effect The intensity of exercise (relative to the peak aerobic power) influences the mix of substrates used to fulfill the ATP re-synthesis rate, according to muscle fibre type. Oxygen consumption is observed to undergo a ‘slow component’ best described as a rise in the metabolic rate, despite the external work remaining relatively constant The presence and extent of the ‘slow component’ is high influenced by the training status of the individual, and most likely underpinned by the muscle fibre type contribution to the exercise. 53 53 27