Chemistry and the Gym

1. Chemistryand the Gym

2. Learning Objectives • Exercise can be aerobic (sustained physical activity with O2) or anaerobic (bursts of effort that do not have sufficient O2 to metabolize fuels). • The aerobic pathway is much more efficient than the anaerobic pathway at producing ATP to power muscle movement. • The rate at which oxygen is delivered to the muscles (VO2 max) is one of the limits to the level of aerobic activity.

3. Learning Objectives (cont) • Athletic training results in a number of adaptations that increase muscle efficiency and delivery of fuel and oxygen to the tissues. • Some individuals may have “thrifty genes” that result in decreased energy expenditure for basic life functions. Exercise can help increase energy output, even in the resting state. • Exercise lowers the risk of some chronic diseases.

4. Learning Objectives (cont) • Strategies to improve athletic performance include increasing delivery of fuel and/or oxygen to the muscles. • Illegitimate performance enhancers include anabolic steroids and human growth hormone to build muscle mass and erythropoietin and blood doping to improve oxygen delivery.

5. Outline • The Molecular Basis of Exercise • Aerobic vs. Anaerobic Activity • ATP, the Cell’s Energy Currency, is called adenosine triphosphate • Fuels that Power Exercise • Primarily fats and carbohydrates (glucose or glycogen).

6. EnergyRequirements Vary with Activity

7. FuelReserves for a Typical 70-kg Male

8. Many of the carbonatoms in glucose have ―OH substituents

9. Glycolysis 1st stage in the breakdown of glucose to produce ATP is glycolysis (greek words means sweet and splitting) Adenosine diphosphate ADP

10. Outline • The Molecular Basis of Exercise (cont) • Mobilization of Fuels • During glycolysis, glucose is oxidized to pyruvate and ATP is produced. • Pyruvate can be oxidized in the efficient aerobic pathway (cellular respiration) or converted to lactic acid in the anaerobic pathway (fermentation). • The rate at which oxygen is delivered to the muscles (VO2 max) dictates the level of activity that can be sustained under aerobic conditions.

11. Alternate Fates of Pyruvate Cellular respiration occurs in the mitochondria, the cell’s “powerhouse”. It traps the maximum amount of chemical energy stored within a molecule of glucose, generating an additional 30 molecules of ATP per pair of pyruvate molecules.

12. Gerty andCarl Cori, 1947 Nobel Prize winners In 1947, they shared the Nobel prize in Physiology or Medicine for their work on glucose metabolism, including characterizing the relationship between liver and muscle glycogen stores. Credit: Corbis

13. Path of glucose metabolism During anaerobic metabolism, muscle glycogen is converted to glucose and then to lactic acid, which circulates to the liver, where it is converted back to glycogen. When needed, the liver replenishes blood glucose, which is taken up by the muscles to form glycogen, completing the cycle.

14. Energy Sources forPowering Muscles During Exercise Credit: P. L. Greenhaff, E. Hultman, and R. C. Harris. In J. R. Poortmans (ed.), Principles of Exercise Biochemistry, 3rd. rev. ed. Basel: Karger, 2004, pp. 108–151.

15. VO2 max isdetermined by measuring oxygen exhaled VO2 max is determined in the laboratory by measuring the amount of oxygen exhaled, allowing the calculation of how much is consumed. Therefore determinants of VO2 max include the hematocrit (the percentage of red cells in a volume of blood) Credit: Photo Researchers, Inc.

16. Outline • The Chemistry of Muscles • Muscle Contraction • ATP powers muscle contraction, in which the thick filaments (made of the protein myosin) slide past the thin filaments (made of the protein actin). • Types of Muscle Fibers • Slow-twitch muscle fibers, which are enriched in myoglobin, are designed for aerobic activity. • Fast-twitch muscle fibers, which lack myoglobin, are designed for anaerobic activity.

17. Muscle Contraction Muscles are made up of the proteins myosin and actin. The muscle protein myoglobin picks up oxygen from hemoglobin and delivers it to the mitochondria for use in cellular respiration. 2 types of muscle fibers: Type I or slow-twitch muscle fibers are designed for aerobic activity because they contract slowly and steadily. Type II or fast-twitch muscle fibers are designed for anaerobic activity. They are stronger and larger than Type I

18. Outline • Physiological Aspects of Exercise • Endurance (Aerobic) Training • Slow-twitch muscles become larger. • Amounts of myoglobin and mitochondria in the muscles increase. • VO2 max increases. • Levels of key enzymes for fat metabolism increase. • Glycogen stores increase.

19. Outline • Physiological Aspects of Exercise (cont) • Anaerobic Training • Fast-twitch muscles become larger. • Stores of ATP, phosphocreatine, and glycogen increase. • Capacity for lactic acid increases. • Levels of key enzymes for glycolysis increase.

20. Outline • Physiological Aspects of Exercise (cont) • Depletion of Energy Reserves • When carbohydrate stores are exhausted, hypoglycemia (low blood sugar levels) set in. • Hormones • Chemical signals that mediate metabolic changes that occur during exercise; e.g., adrenaline prepares for “fight or flight”

21. Examples ofHormones Involved in Exercise

22. Outline • Physiological Aspects of Exercise (cont) • Runner’s High • Endorphins are natural painkillers (made by the body) produced during times of physical stress. • Sex Differences • Women generally have greater fat stores than men, making them well suited for aerobic endurance events.

23. Outline • Exercise and Weight Control • Energy Balance • Energy In = Food Consumed • Energy Out = Exercise, Basal Metabolism, Thermogenesis • The Thrifty Gene Hypothesis • “Thrifty genes” may allow some individuals to maintain life processes with very little food intake. • Thrifty gene effects may be related to the hormone leptin.

24. Effect of Leptin on Body Mass Leptin is a peptide hormone that mediates body weight, metabolism, and reproduction.

25. Outline • Exercise and Chronic Disease • The risk factors for many chronic diseases, including heart disease and diabetes are decreased by exercise.

26. Outline • Legal Performance Enhancers • Carbo-Loading • Increases glycogen stores, delaying the onset of hypoglycemia • Carnitine • Escorts fatty acids into the mitochondria for oxidation, maximizing fat burning and conserving glycogen.

27. Carnitine

28. Outline • Legal Performance Enhancers (cont) • Creatine • Increases stores of phosphocreatine, the muscle’s quickest energy source • Electrolyte-Replacement (Gatorade) • Provides water, essential electrolytes, and carbohydrates • Altitude Training • Increases the number of red blood cells (the hematocrit) and the amount of hemoglobin

29. Compositionof Various ERG Beverages Electrolyte replacement glucose (ERG) is a beverage that supplies water, electrolytes, and carbohydrates.

30. Outline • Illegal Performance Enhancers • Improving Oxygen Delivery • Blood Doping: red blood cells are removed several weeks prior to competition; body responds by making more red blood cells; right before competition, athlete receives a blood transfusion. • Erythropoietin (EPO): hormone that promotes the production of red blood cells

31. Effect of EPO (Erythropoietin) on Hematocrit

32. Outline • Illegal Performance Enhancers (cont) • Building Muscle Mass • Anabolic steroids (means building up): structurally similar to the male sex hormone testosterone • Human growth hormone (hGH) to achieve the same effects but without using Anabolic steroids. Side effects of hGH include enlargement of the extremities, such as hands and feet, diabetes, enlarged internal organs, and increased risk of cardiovascular disease, all of which may result in premature death.

33. Mark McGwire legallyused anabolic steroids in his record-setting 1998 season Credit: Getty Images

34. Anabolic Steroids

35. Aerobic Anaerobic ATP (adenosine triphosphate) Adipose tissue Glycolysis Cellular respiration Fermentation VO2 max Hematocrit Slow-twitch muscle fibers (Type I) Fast-twitch muscle fibers (Type II) Hypoglycemia Hormones Endorphins Leptin Hyperthermia Erythropoietin (EPO) Anabolic steroids Testosterone Human growth hormone (hGH) Key Words