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 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 Improved blood flow, and Increased capacity of muscle fibers to generate ATP

Anaerobic training leads to Increased muscular strength, and

Increased tolerance for acid-base imbalances during highly intense effort.

Metabolic and Morphological Changes

Metabolic Changes

Energy Systems

Phosphagen Energy System (ATP-PC) Cytoplasm High-intensity: Up to 30 seconds

Glycolytic Energy System Cytoplasm 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

Relies on oxygen to breakdown fuels for energy

Produces ATP in mitochondria of cells

Can yield much more energy (ATP) than anaerobic systems

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

Oxidative energy system primarily uses CHO and FAT but during periods of CHO and prolonged exercise significant amounts of protein can be metabolized

1 molecule 39 ATP

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

Body uses little protein during rest and exercise (less than 5% to 10%).

Some amino acids that form proteins can be converted into glucose.

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

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.

The oxidative system uses oxygen and produces more energy than the anaerobic systems.

(continued)

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)

Fat oxidation involves oxidation of free fatty acids, the Krebs cycle, and the electron transport chain to produce more ATP than carbohydrate, but it is O2-limited.

Protein generally contributes little to energy production (less than 5%), and its oxidation is complex because amino acids contain nitrogen, which cannot be oxidized.

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)