Energy Systems and Exercise

1. Energy Systems and Exercise Chapter 3 Nutrition for Sport and Exercise Dunford & Doyle

2. 3 major energy systems provide energy for exercise p67

3. Learning 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 replace ATP during exercise. • Describe the specific characteristics of the anaerobic glycolysis energy system, and explain how it is used to replace ATP during exercise.

4. Learning Objectives • Describe the specific characteristics of the oxidative phosphorylation (aerobic) energy system and explain how it is used to replace ATP during exercise. • Explain the process of aerobic metabolism of carbohydrates, fats, and proteins (amino acids), and the concept of measuring fuel utilization with the respiratory exchange ratio, and describe the factors that influence fuel utilization.

6. ATP Basics • ATP = adenosine triphosphate • Immediate source of energy in the body for activity and exercise • Found in all cells of the body • Stores potential energy in phosphate bonds • Releases energy when broken down to ADP, or adenosine diphosphate • Body must restore ATP from ADP after use through rephosphorylation

7. Hydrolysis of ATP

8. Rephosphorylation of ADP to ATP

9. ATP and Energy Use by Muscle

10. The Three Major Energy Systems • 3 major energy systems used to replenish ATP: • Creatine Phosphate • Anaerobic Glycolysis • Oxidative Phosphorylation • Each has advantages and disadvantages • All energy systems are active, but depending on the specific sport or exercise, one will be the predominate energy system used

11. The Three Major Energy Systems

13. 1. The Creatine Phosphate Energy System • Creatine Phosphate (CrP) • CrP is a high energy phosphate • Stored in muscle • Energy released when phosphate bond broken • This energy is used to rephosphorylate ADP into ATP • So, creatine phosphate stored in muscle acts as readily accessible reservoir of energy for re-formation of ATP

14. Creatine Metabolism • Creatine • Amine (nitrogen-containing compound) constructed from: • Arginine • Glycine • Methionine • Can be consumed in diet or produced by body • Major food sources are beef and fish • Creatine is a common dietary supplement that is in powder form and mixed with water to drink • Creatine monohydrate

15. Creatine Metabolism • Creatine (cont’d) • Synthesized by liver and kidneys • Transported in blood to tissues throughout body, which will take up creatine and store it • Approximately 1/3 as creatine and 2/3 as CrP • Excess creatine filtered by kidneys and excreted as creatinine • Average non-vegetarian not taking creatine supplements will consume and/or synthesize ~2g of creatine per day and body will excrete same amount

16. Creatine Metabolism

17. CK ATP + Cr CrP + ADP Creatine Phosphate Energy System • 1 Chemical Step • Catalyzed by Creatine Kinase (CK) • CK increases when ADP increases • Very fast reaction • 1 molecule of CrP molecule can rephosphorylate 1 molecule of ADP to ATP (1:1 ratio) • 5-10 seconds for CrP in muscle to be depleted

18. Creatine Phosphate Energy System • Anaerobic • Fatigue associated with CrP depletion • Predominant energy system in veryhigh intensity, short duration exercise when ATP is being used very rapidly • “power” events • Ex/ short and fast sprints, shot put, dunking a basketball, very heavy weight lifting

19. The Creatine Phosphate Energy System

20. Creatine Phosphate and ADP Rephosphorylation

21. ATP and Creatine Phosphate Use During Short-term Exercise – Hirvonen et al. (1987)

22. The Creatine Phosphate Energy System • The creatine phosphate system does not require oxygen (anaerobic) when CrP is used to replenish ATP from ADP • However, it requires oxygen (aerobic) to restore creatine to CrP (i.e. rephosphorylation) • Oxygen is needed to produce ATP in mitochondria • This process is known as the “Creatine Shuttle” • Takes about 1-2 minutes if exercise intense and long enough… • Body uses aerobic energy system to restore creatine, which is why athletes breathe hard for a time after short duration high-intensity events

23. The Creatine Shuttle

24. Question… • So, is the creatine phosphate system completely anaerobic? • NO! – oxygen is required to recover CrP from Cr

25. The Creatine Phosphate Energy System • Advantages: • Very rapid way to replace ATP • Disadvantages: • CrP stored in very limited amounts in the muscle, can be depleted rapidly, and has very short duration

26. Creatine Loading and Supplementation • Athletes competing in events that rely heavily upon the creatine phosphate energy system may supplement with creatine to improve performance • CrP concentration in the muscle can be increased up to ~ 20% with supplementation (Huffman et al, 1996) • Some people are non-responders to supplementation if CrP concentrations are already near maximum • For example, a vegetarian may respond better • Vegetarians increased 76% vs. nonvegetarians 36% (Watt et al. 2004)

27. Creatine Loading and Supplementation • No direct effect on performance except for power lifters or weightlifters (Volek & Rawson, 2004) • Indirect effect by allowing athlete to train harder, which may improve strength, speed, or power • Increases intracellular water in muscle cells • Weight gain may not be desirable for some athletes • Safe with some minor side effects • GI upset, cramps • Effective for strength and power athletes

28. Creatine Loading and Supplementation • Recommendations: • Dosage • Usual dose 3-5 g/day • Loading dose 20-25 g/day in 4-5 doses x 5-7 days • Keep in mind response may be r/t initial creatine levels • Do not use if kidney dysfunction or disease • Only effective with vigorous training • Consume with CHO to enhance uptake • Stay well-hydrated • Document any adverse effects and re-evaluate use

29. 2. The Anaerobic Glycolysis Energy System • Process of taking carbohydrate in the body and putting it through a series of chemical reactions that release enough energy to rephosphorylate ADP and re-form ATP • Breaks down glucose without the use of oxygen • Final product is lactic acid • Often called the “Lactic Acid Energy System” • “Glycolysis” = breakdown of glucose

30. The Anaerobic Glycolysis Energy System

31. Anaerobic Glycolysis System • 18 Chemical Steps/Reactions, 6 are repeated • 12 Chemical Compounds, 11 Enzymes • Rate-limiting enzyme is Phosphofructokinase (PFK) • Fast, not as fast as CrP system • 2 ATP’s via Glucose, 3 ATP’s via Glycogen • Anaerobic • 1-2 minute duration • Fatigue associated with pH (Metabolic Acidosis) • Predominant energy system in high intensity exercise or repeated exercise lasting 1-2 minutes • Ex/ repeated sprints, long sprints, 50-100m swim interval

32. Anaerobic Glycolysis System • Starts with glucose and ends with lactate • 1st reaction: ATP is added to glucose to form glucose-6-phosphate (G-6-P) • 6th reaction: ADP is rephosphorylated to ATP • This step is repeated, so 2 ATP are produced at this point • 9th reaction: 2 additional ATP are produced and pyruvate is produced • Final Reaction: Pyruvate then proceeds through to lactate • Glycolysis produces 4 ATP, but 2 ATP are used in the process, so net production is 2 ATP

33. Schematic of Anaerobic Glycolysis

34. Anaerobic Glycolysis System • Glucose – a sugar found in food and in the blood • Glycolysis – metabolic breakdown of glucose • Glycogen – large molecule composed of many glucose molecules linked together • Stored in liver and skeletal muscle • Broken down directly into G-6-P without the use of an ATP • Net ATP of 3 produced if glycogen used, since only 1 ATP is used while 4 are produced • Glycogenolysis – metabolic breakdown of glycogen

35. Anaerobic Glycolysis System • Advantage: Uses blood glucose and stored glycogen, so is rarely limited by depleted energy stores • Disadvantage: Increasing acidity, or decline in pH w/in the muscle cell that occurs when anaerobic glycolysis is used at a high rate • Metabolic acidosis • If acidosis occurs in exercising muscle, the drop in pH can decrease activity of key metabolic enzymes, interfere with force production and cause muscle fatigue • This occurs in 1-2 minutes

36. Anaerobic Glycolysis System • Uses only carbohydrate as fuel source • Becomes predominant energy system after 5-10 seconds when CrP system reaches its limit • Types of exercise: • Long sprints, such as 400-meter sprint • Repeated high intensity sprints, such as intermittent sprints by a soccer or basketball player • Repeated high-force activities, such as 10-15 repetitions of weight lifting • Regular/repeated intervals, such as 50-100 meter swimming intervals

37. Anaerobic Glycolysis System • During anaerobic glycolysis, lactate concentration increases • Lactate is transported out of exercising muscle into the venous circulation and is then distributed throughout body via arterial circulation • When concentrations of lactate are high, lactate can be converted back to pyruvate • Pyruvate can be converted to lactate anaerobically • Pyruvate can be taken into mitochondria of highly aerobic tissues (liver, muscle, heart) and be used to produce ATP via oxidative phosphorylation

39. Lactate Threshold • Lactate Threshold – the level of exercise intensity in which lactate production has increased to the point where it has overwhelmed the body’s lactate removal mechanisms • Significance – it is associated with an exercise intensity that can be sustained for long periods during endurance exercises • Ex/ LT correlates highly with the race pace for a distance runner • A pace too much faster results in fatigue and poor results • A pace too much slower results in less than optimal performance

40. Lactate Threshold • As exercise intensity and O2 consumption increase, initially the concentration of blood lactate does not change much b/c it is being removed from blood by aerobic tissues and oxidized as fast as the exercising muscles are releasing lactate into the blood • However, as exercise increases in intensity, the production of lactate exceeds its rate of removal and the lactate concentration continually increases

41. Lactate Threshold

42. 3. The Oxidative Phosphorylation Energy System • Used to supply ATP on a virtually limitless basis, as long as oxygen and fuel sources are available • Takes place in the mitochondria • 3 major phases • CHO, fat, protein metabolized aerobically • Krebs cycle • Electron transport chain

43. Oxidative Phosphorylation

44. Glycolysis, Krebs cycle, and electron transport chain

45. The Oxidative Phosphorylation Energy System

46. The Oxidative Phosphorylation Energy System

47. Oxidative Phosphorylation System • 124 Chemical Steps/Reactions • 30 Compounds, 27 Enzymes • Rate-limiting enzymes: • IDH – isocitrate dehydrogenase (Krebs Cycle) • COX – cytochrome oxidase (Electron Transport Chain) • PFK – phosphofructokinase (Anaerobic Glycolysis) • Slow • Pyruvate must be transported to mitochondria

48. Oxidative Phosphorylation System • 30 ATP’s via Glucose, 31 via Glycogen • Potentially limitless duration • Aerobic • Fatigue associated with fuel depletion • Predominant energy system in endurance exercise • Ex/ - long distance running, cycling long distance, dance aerobics, long distance swimming, walking

49. Krebs Cycle

50. Krebs Cycle – Appendix J (p. 576)