Bioenergetics of Exercise and Training

1. Bioenergetics of Exercise and Training

2. Objectives • Defining essential terminology • The role of ATP • Three basic energy systems to replenish ATP in skeletal muscle: • Phosphagen, Glycolysis, and Oxidative • How substrates are used and broken down for energy production • Contribution of each energy system to physical activity

3. Energy • The ability or capacity to perform physical work • Chemical: • Work for synthesizing cellular molecules • Mechanical: • Work of muscle contraction • Conversion of chemical into mechanical is necessary for movement to occur

4. Bioenergetics Defined • Conversion of food • Chemical energy in carbohydrate, protein, and fat molecules is converted into mechanical energy • The breakdown of chemical bonds in these molecules releases energy to perform: • Muscular activity • Digestion and absorption of food nutrients • Glandular functions that secretes hormones • Maintenance of electrochemical gradients across cell membranes • Synthesis of new chemical compounds and tissues

5. Catabolic and Anabolic • Catabolic: • Breakdown of large molecules into smaller molecules to release energy • Carbohydrates = Glucose • Fat = Fatty Acids and Glycerol • Protein = Amino Acids • Anabolic: • The synthesis of larger molecules from smaller molecules • Formation of proteins from amino acids

6. Metabolism • Metabolism: • Total of all catabolic and anabolic reactions in the body (build up and break down of food in the body) • Michael Phelps consumes 12,000 calories per day in order to swim six hours a day, six days a week. He swims 50 miles per week (a little over 8 miles per training day).

7. ATP • ATP is Adenosine Triphosphate • It contains a large amount of chemical energy stored in its high-energy phosphate bonds • It releases energy when it is broken down (hydrolyzed) into ADP (or Adenosine Diphosphate).

8. ATP • ATP is produced in the mitochondria to power muscular activity • Muscle cells only store a limited supply of ATP and activities require a constant supply of ATP for muscle contraction • Three basic energy systems exist in muscle cells to replenish ATP: • The Phosphagen System • Glycolysis • The Oxidative System

9. Aerobic vs. Anaerobic • Aerobic: • ATP synthesized With Oxygen • Anaerobic: • ATP generated rapidly for short durations Without Oxygen

10. Three Energy Systems to Replenish ATP • Phosphagen System: • Anaerobic, synthesizes ATP without oxygen • Glycolysis: • Two types: Fast (Anaerobic) and Slow Glycolysis (Aerobic) • Oxidative: • Aerobic, requires oxygen

11. Energy Systems • Fat and Glycogen are the major sources for ATP resynthesis • Some ATP comes from Creatine Phosphate • Carbohydrates are the only macronutrient that generate ATP anaerobically • All three systems are active at a given time • The fuel mixture that powers exercise depends on the Intensity and Duration of effort, and the exerciser’s fitness and nutritional status

12. Creatine Phosphate (CP) • Can be stored in the muscle and is made from ATP during periods of rest • During periods of high activity CP is broken down quickly and its energy converted to ATP • But this source of ATP can only supply a cell for 8to 10 seconds during the most strenuous exercise • Creatine released during muscle activity shows up in the urine as creatinine • Training can increase the amount of creatine phosphate stored, but this alone does not increase the strength of a muscle, just the length of time before it runs out of CP

13. Enzymes • ATPase breaks down ATP for form ADP and P and release energy • Creatine Kinase regulates the breakdown of Creatine Phosphate • These reactions provide energy at a high rate; however ATP and CP are stored in the muscle in small amounts • The Phosphagen System cannot supply enough energy for continuous long duration activities

14. Phosphagen System • At the beginning of exercise, ATP is broken down into ADP releasing energy for muscle contraction • An increase in ADP activates creatine kinase to form ATP from creatine phosphate • Creatine kinase remains elevated if exercise continues at a high intensity • If exercise is discontinued or continues at a lower intensity Glycolysis or the Oxidative Systems supply ATP

15. Phosphagen System • Phosphagen concentration in muscle is more rapidly depleted as a result of high intensity anaerobic activity (plyometrics) • Creatine phosphate is decreased and can almost be eliminated as a result of very high intensity

16. Phosphagen System • Creatine phosphate can decrease (50-70%) during high-intensity exercise (5-30 seconds) and can be almost eliminated as a result of very intense exercise to exhaustion • Complete ATP resynthesis can occur within 3-5 minutes of rest • Complete creatine phosphate resynthesis can occur within 8 minutes of rest • Resistance training shows an increase in phosphagens • Type II fibers contain more phosphagens than Type I

17. Phosphagen System ATP ATPase ADP + Pi + Energy ADP + Creatine Phosphate Creatine Kinase ATP + Creatine

19. Phosphagen System • Volleyball • Gymnastics • Shot Put • Long Jump • High Jump • Pole Vault • Discus Throw • Javelin Throw • Hammer Throw • Figure Skating • Baseball • Diving • Olympic Weight Lifting (Snatch and Clean and Jerk) • Football • Fencing • Sprinting • Tennis • Golf

20. Glycolysis • Glycolysis is the breakdown of carbohydrates from glycogen stored in the muscles or liver or glucose delivered in the blood to produce ATP • Does not produce much ATP in comparison to aerobic metabolism, but it has the advantage that it doesn't require oxygen • It occurs in the Sarcoplasm of the muscle cell, not the mitochondria • For intense exercise of 1 to 2 minutes (e.g., jumping rope) duration, glycolysis provides the primary source of ATP

21. Glycolysis • The process of Glycolysis occurs in two ways • Fast Glycolysis • Slow Glycolysis

22. Glycolysis • ATP must be supplied at a high rate (e.g., resistance training) • The End Result of Glycolysis is Pyruvate • Pyruvate comes from the breakdown of carbohydrates • Pyruvate can proceed in Two directions: • Pyruvate can be broken down into Lactic Acid and then Lactic Acid is broken down into Lactate (Fast Glycolysis) OR • Pyruvate is shuttled to the mitochondria (Slow Glycolysis)

23. Fast Glycolysis • Lactic Acid: • A waste product of glucose and glycogen metabolism produced in the muscles during intense exercise • As lactic acid accumulates there is an increase in hydrogen ion concentration which interferes with muscle contraction: • Inhibiting calcium binding to troponin • Interfering with actin-myosin cross bridge formation

24. Fast Glycolysis • Results in the formation of Pyruvate and Hydrogens Ions (H+) • A build up of H+ will make the muscle cells acidic and interfere with their contraction so molecules called Nicotinamide Adenine Dinucleotide (NAD+), remove the H+ • The NAD+ is reduced to NADH which deposit the H+ in the mitochondria to be combined with oxygen to form water (H2O).

25. Fast Glycolysis • The presence of Hydrogen Ions, not lactate, makes the muscle acidic which will eventually halt muscle function • As hydrogen ion concentrations increase, the blood and muscle become acidic • This acidic environment will slow down enzyme activity and ultimately the breakdown of glucose itself • Acidic muscles will aggravate associated nerve endings causing pain and increase irritation of the central nervous system (“The Burn”) • An individual may become disorientated and feel nauseous

26. Fast Glycolysis • Lactic acid is converted to a salt called Lactate in the muscle and blood • Some of the Lactate diffuses into the blood stream and takes some H+ with it as a way of reducing the H+ concentration in the muscle cell • Lactate can be transported in the blood to the liver, where it is converted to glucose. • This process is referred to as the Cori Cycle

28. Lactate Threshold (LT) • The intensity at which lactate accumulates in the blood or Onset of Blood Lactate Accumulation (OBLA) • Begins at 50-60% of VO2 in untrained individuals and 70-80% VO2 in trained individuals • Aerobically and anaerobically trained individuals have a faster lactate clearance rate than untrained people • The clearance of lactate from the blood indicates a person’s ability to recover • Lactate can be cleared within the muscle it was produced

30. Fast Glycolysis • Basketball • Boxing • Wrestling • Football • Ice Hockey • Soccer • Skiing

31. Slow Glycolysis • If oxygen is present in sufficient amounts Pyruvate is not converted to Lactic Acid but transported to the Mitochondria • When pyruvate enters the mitochondria it is converted to Acetyl-CoA • Acetyl-CoA: • A form of acetic acid or vinegar • Acetyl CoA can then enter the Krebs Cycle (Citric Acid Cycle) • A chemical cycle which completes the metabolic breakdown of glucose molecules to carbon dioxide; occurs within the mitochondria

33. Glycolysis • Energy Yield of Glycolysis • Glycolysis from one molecule of blood glucose yields a net of two ATP molecules • Glycolysis frommuscle glycogen yields a net of three ATP molecules.

34. Oxidative System • Primary source of ATP at Rest and during aerobic activities • Uses primarily Carbohydrates and Fats as fuels • Protein is not metabolized except during long-term starvation and long bouts of exercise (90 minutes or more)

35. Oxidative System • Metabolism of blood glucose and muscle glycogen begins with glycolysis and leads to the Krebs cycle • Recall: If oxygen is present in sufficient quantities, the end product of glycolysis, Pyruvate, is not converted to lactate but is transported to the mitochondria, where it is taken up and enters the Krebs cycle

36. Oxidative System • Krebs Cycle: • A chemical cycle involving a series reactions by which fragments from any of the energy nutrients (carbohydrates, fats, and protein) are completely broken down to carbon dioxide and water, releasing energy for the formation of adenosine triphosphate (ATP) • The result is 38 molecules of ATP are produced from 1 molecule of glucose • It is the final common pathway for all nutrient metabolites involved in energy production

37. Oxidative System • Fat Oxidation • Triglycerides stored in fat cells can be broken down by hormone-sensitive lipase. This releases free fatty acids from the fat cells into the blood, where they can circulate and enter muscle fibers. • Some free fatty acids come from intramuscular sources • Free fatty acids enter the mitochondria, are broken down, form acetyl-CoA and hydrogen, and then enter the Krebs cycle

38. Oxidative System • Protein Oxidation • Protein is not a significant source of energy for most activities • Protein is broken down into amino acids, and the amino acids are converted into glucose, pyruvate, or various Krebs cycle intermediates to produce ATP

39. Oxidative System • Cross country skiing • Long distance running • Long distance swimming • Rowing • Walking

40. Energy Capacity • The Phosphagen System, does not require oxygen to produce ATP • High Intensity Short Duration Activities • Fast Glycolysis uses glycogen stores in the muscle and liver to produce ATP without oxygen • Slow Glycolysis uses muscle and liver glycogen to produce ATP and occurs in the presence of oxygen • Both Fast and Slow: Moderate-to-High Intensity Short to Medium Duration Activities • Oxidative: uses carbohydrates and fats stored in the body to produce ATP and requires oxygen • Low Intensity Long Duration Activities

41. Energy Capacity

43. Energy Capacity • The extent to which each of the three energy systems contributes to ATP production depends primarily on the Intensity of muscular activity and secondarily on the Duration. • At no time, during either exercise or rest, does any single energy system provide the complete supply of energy

44. Interval Training • Interval training is a method that can emphasize the energy systems by using predetermined intervals of exercise and rest periods • Much more training can be accomplished at higher intensities • Difficult to establish definitive guidelines for choosing specific work-to-rest ratios

46. Combination Training • Combination Training adds aerobic endurance training to the training of anaerobic athletes in order to enhance recovery (because recovery relies primarily on aerobic mechanisms). • May reduce anaerobic performance capabilities, particularly high-strength, high-power performance • Can reduce the gain in muscle girth, maximum strength, and speed- and power-related performance • May be counterproductive in most strength and power sports

47. Carbohydrates • A carbohydrate-deficient diet rapidly depletes muscle and liver glycogen • Low carbohydrate levels profoundly affect both anaerobic capacity and prolonged, high intensity aerobic exercise • A low carbohydrate diet makes it difficult to engage in vigorous physical activity • Exercise in a carbohydrate-depleted state causes significant protein catabolism

48. Carbohydrates • Repletion of muscle glycogen during recovery is related to post-exercise carbohydrate ingestion • Repletion appears to be optimal if 0.7 to 3.0 g of carbohydrate per kg of body weight is ingested every 2 hours following exercise

49. Fats • Stored fat represents the body’s most plentiful source of potential energy • Fatty acid catabolism requires oxygen • Rate of fat oxidation is slower than carbohydrate • Enhanced fat oxidation spares glycogen • You need carbohydrates to burn fat efficiently • Aerobic training increases fatty acid oxidation, particularly the fatty acids derived from active muscle during moderate intensity exercise

50. Protein • Protein catabolism accelerates during exercise as carbohydrate reserves deplete • Individuals who train vigorously must maintain optimal levels of muscle and liver glycogen to minimize lean tissue loss and deterioration in performance • Regular exercise training enhances the liver’s capacity to synthesize glucose from non-carbohydrate compounds