Metabolic System and Exercise EXS 558 Lecture #4 September 21, 2005

Review Questions #1-3 What is the primary role of hormones? Maintain homeostasis Most hormone secretion is modulated through what biological process? Negative Feedback Why is this process effective? Self-limiting

Review Question #4 Name three mechanisms which affect circulating concentrations of hormones? 1.) exercise (physical stress) 2.) psychological stress 3.) fluid volume stress

Review Question #5 Exercise can induce alterations in the endocrine system other than changing the circulating concentrations of hormones. Give an example of how this is possible. Down-Regulation: the # of hormone receptors is decreased to reduce the possibility of contact between the “lock and key”

Review Question #6 What is one of the major differences between steroid and peptide hormones? Steroid hormones are lipid soluble allowing them to pass through the cell membrane to their intracellular receptors, while peptide hormones react with receptors housed in the cell membrane

Review Questions #7, 8 TRUE/FALSE TRUE/FALE A single training session has been shown to decrease peripheral testosterone levels above resting levels TRUE/FALE Type of training program affects circulating testosterone levels

Review Question #9 What would be the expected testosterone response to a 10 mile run (~70 minutes)? a.) no response, endurance activity has no effect b.) ↑ circulating testosterone levels c.) ↓ circulating testosterone levels d.) first it increases and then decreases

Review Question #10 Which of the following has the LEAST effect on influencing a growth hormone response? a.) sleep b.) nutrition c.) exercise d.) environment

Literature Review Techniques SUNY Cortland Memorial Library Databases http://library.cortland.edu/databases.asp Search Options 1.) By Subject: Exercise Science & Sport Studies a.) MEDLINE b.) SportDiscus c.) Physical Education Index 2.) Fulltext Database (.PDF available online)

Literature Review Techniques (continued) Find IT Button Reference  Save Citation Information (APA) Google Scholar http://scholar.google.com/advanced_scholar_search Cortland ESSS Librarian hollistera@cortland.edu

Literature Review Techniques (continued) Search for a recent REVIEW article close to your topic, if possible Print online abstracts of all articles you may include within your review of literature Use ILL early  it takes time to receive articles

Metabolic System & Exercise

Aerobic vs. Anaerobic Training Aerobic (endurance) training leads to w Improved blood flow, and w Increased capacity of muscle fibers to generate ATP Metabolic and Morphological Changes Anaerobic training leads to w Increased muscular strength, and w Increased tolerance for acid-base imbalances during highly intense effort. Metabolic Changes

Energy Systems Phosphagen Energy System (ATP-PC) Cytoplasm High-intensity: Up to 30 seconds Glycolytic Energy System High-intensity: 1-3 minutes Oxidative Energy System Mitochondria Activity > 3 minutes

ATP Adenosine triphosphate (ATP) common currency of useful (chemical) energy used by cells Principle function of ATP Energize synthesis of important cellular components Energize muscular contractions Synthesis of organic molecules used for structure and function Energize active transport

ATP (continued) Energy released from ATP caused by ATPase ATP + water  ADP + Pi + 7,000 cals/mol 1 mole of energy of ATP stores 12,000 cals, however, the real function of ATP is to transfer energy! - energy stored in ATP will sustain life for about 90 seconds

ATP-PC Energy Source ATP-PC (Phosphocreatine) stored within the muscle Immediate use PC is major storage depot for energy (13,000 cals/mol) It transfers phosphate group to ADP, so it can become ATP again Catabolic breakdown of food substrate leads to synthesis of ATP When subjects in study are brought to maximal exertion levels, ATP in muscles has not dropped much, but PC levels are way down

ATP-PC Energy Source (continued) PC supply exhausted in ~30 seconds PC levels decline rapidly during intense exercise (sprinting) Resynthesis of PC ½ recovered in 20-30 seconds Last ½ may take up to 20 minutes Most replenished within 3 minutes Implications for workout design

ATP and PC During Sprinting

Glucose Breakdown and Synthesis Glycolysis—Breakdown of glucose; may be anaerobic or aerobic Glycogenesis—Process by which glycogen is synthesized from glucose to be stored in the liver Glycogenolysis—Process by which glycogen is broken into glucose-1-phosphate to be used by muscles

Breakdown of Sugar (Glycolysis) 10 step pathway leads to synthesis of 2 pyruvate molecules and net production of 2 ATP molecules (or 3) All reactions in cytosol and none require O2 Fate of pyruvate depends on O2 If inadequate available (anaerobic), pyruvate converted to lactate If enough O2, converted to acetyl-CoA

Breakdown of Sugar (Glycolysis) Where does the glucose come from? From the blood (1) through CHO digestion or (2) from the breakdown of glycogen in the liver From glycogen broken down in the muscle Gluconeogenesis = process of metabolizing glycogen into glucose Glycogen metabolized = 3 ATP Glucose metabolized = 2 ATP

Role of Lactic Acid Nociceptors (pain receptors) are sensitive to changes in the cellular H+ levels ↑ lactic acid interfere with production of ATP Hinder binding of calcium to troponin (ECC) *The combined actions of the ATP-PC and glycolytic systems allow muscles to generate force in the absence of oxygen; thus these two energy systems are the major energy contributors during the early minutes of high-intensity exercise.

Oxidative Energy Source w Relies on oxygen to breakdown fuels for energy w Produces ATP in mitochondria of cells w Can yield much more energy (ATP) than anaerobic systems w Is the primary method of energy production during endurance events

Oxidative Production of ATP 1. Aerobic glycolysis—cytoplasm 2. Krebs cycle—mitochondria (byproduct = CO2) 3. Electron transport chain—mitochondria 1 molecule  39 ATP Oxidative energy system primarily uses CHO and FAT but during periods of CHO and prolonged exercise significant amounts of protein can be metabolized

Aerobic Glycolysis & Electron Transport Chain

Krebs Cycle

Oxidation of Fat Lipolysis = breakdown of fat for energy triglycerides metabolized into glycerol and 3 free fatty acids Free fatty acids used as primary energy source Free fatty acids enter the mitochondria and undergo β-oxidation Energy production from 1 molecule of fatty acid (palmitic acid C16H32O2) yields 129 ATP

Protein Metabolism w Body uses little protein during rest and exercise (less than 5% to 10%). w Some amino acids that form proteins can be converted into glucose. w The nitrogen in amino acids (which cannot be oxidized) makes the energy yield of protein difficult to determine.

Energy Source Interaction ALL three sources will supply a portion of the needed energy for exercise at all times One system will predominate depending on the intensity of the exercise

Oxidative Capacity Determined by: Oxidative enzyme activity within the muscles Fiber-type composition and # of mitochondria Oxygen availability and uptake in lungs Endurance Training What does training effect?

Review Ideas (continued) w The ATP-PCr and glycolytic systems produce small amounts of ATP anaerobically and are the major energy contributors in the early minutes of high-intensity exercise. w The oxidative system uses oxygen and produces more energy than the anaerobic systems. (continued) w Carbohydrate oxidation involves glycolysis, the Krebs cycle, and the electron transport chain to produce up to 39 ATP per molecule of glycogen aerobically.

Review Ideas (continued) w Fat oxidation involves b oxidation of free fatty acids, the Krebs cycle, and the electron transport chain to produce more ATP than carbohydrate, but it is O2-limited. w Protein generally contributes little to energy production (less than 5%), and its oxidation is complex because amino acids contain nitrogen, which cannot be oxidized. w The oxidative capacity of muscle fibers depends on their oxidative enzyme levels, fiber-type composition, how they have been trained, and oxygen availability.

Metabolic Adaptations to High Intensity Training ATP-PC Energy System No change to resting levels of ATP or PC Resting [ ] of enzymes may be positively altered Causes activity of ↑ creatine kinase and myokinase ADP + ADP  ATP + AMP AMP leaves muscle and acts as signal to slow down glycolysis Parra et al. (2000) 2 weeks of daily sprint training ↑ elevation of creatine kinase 6 weeks of daily sprint training with longer rest intervals no change of creatine kinase

Metabolic Adaptations to High Intensity Training (continued) Glycolytic Energy System ↑ glyoclytic enzymes (10-25%) Resistance training alone CAN NOT stimulate metabolic changes Implications “These studies suggest that athletes training for anaerobic sports need to include both resistance training and sprint or interval exercises in their conditioning programs in order to maximize their physiological adaptation for the sport” J. Hoffman

Metabolic Adaptations to High Intensity Training (continued) Oxidative Energy System High intensity training ↑ mitochondrial enzyme activity When duration of exercises exceeds 3 minutes Does not match gains from endurance training Implications An athlete who trains anaerobically may still generate some aerobic capacity improvements

Metabolic Adaptations to High Intensity Training (continued) Improvements to buffering capactiy Allows greater [ ] of lactic acid before effecting muscular output ↑ 12-50% from a 8 week high intensity training program ↑ 9.6% of blood lactate after 6 weeks of high intensity cycling program (Jacobs et al., 1987)