The body’s response to physical activity

1. The body’s response to physical activity

2. Chapter overview Energy • Adenosine triphosphate page 125 • Energy systems page 127 • Fatigue and recovery page 142 Training effects • Immediate physiological responses to training page 146 • Long-term physiological effects of training page 146 Now that you’ve finished … answers

3. Back to chapter overview Energy Page 125

4. Humans obtain chemical energy from the food that we eat, and energy from food is measured in kilojoules • The energy gained from the breakdown of food is used to make a chemical compound called adenosine triphosphate.

5. Back to chapter overview Adenosine triphosphate Page 125

6. When ATP is broken down, releasing the final phosphate group in the chain, it releases energy. • ATP is broken down into adenosine diphosphate (ADP) (see Figure 4.3). • A great deal of energy is released when this bond is broken and this provides the energy that powers the human body. It provides energy for all processes, from breathing and digestion through to muscle movement. Figure 4.2 Figure 4.3

7. Carbohydrates Carbohydrates are broken down by the body into glucose. The glucose is then stored in the muscles and liver as glycogen, which is a ready source of energy. Chemical reactions involving the breakdown of glucose (glycolysis) or glycogen (glycogenolysis) then produce ATP.

8. Fats • Fat is stored as triglyceride in both adipose tissue (fatty tissue) and the muscles. • Triglycerides are broken down in a process called lipolysis. • Free fatty acids are the primary energy source when fat is used for energy. • Adipose triglycerides are used if exercise is prolonged at a low intensity.

9. Proteins Under normal conditions, protein is not used to produce ATP. During extreme conditions (for example, starvation or prolonged exercise), protein will be used as a fuel source to produce ATP.

10. Back to chapter overview Energy systems Page 127

11. ATP is produced using one of three energy systems: • the alactacid system (also called the phosphagen or ATP–PC system) • the lactic acid system (also called the anaerobic glycolysis system) • the aerobic system. The alactacid and lactic acid systems resynthesise ATP anaerobically, whereas the aerobic system resynthesises ATP aerobically.

12. Alactacid System • High intensity activities lasting for less than 10 seconds use this system as the primary source of energy. • The amount of PC in muscles is limited. After about 5–10 seconds of strenuous work, it runs out.

13. Lactic Acid System • The energy released in the breakdown of glucose is used to fuel the recombination of ADP and P to form ATP. • If the body continues to use the lactic acid system, as the glucose is broken down to form energy, lactic acid is produced. • The lactic acid system provides a relatively quick supply of ATP, and is an important energy source for intense, short bursts of activity (usually 30–60 seconds, but can be up to 3 minutes).

14. <insert fig 4.9> Personal reflection Have you ever experienced lactic acid build-up? If so, how did your body respond and how long did it take to recover?

15. Aerobic System The aerobic system allows the body to use carbohydrates, fats and proteins as the fuel to produce ATP aerobically. • Carbohydrates are broken down in a process called aerobic glycolysis. Carbohydrates are the preferred fuel as their breakdown requires the least amount of oxygen. • The breakdown of fats (oxidisation) requires significantly more oxygen to produce the same amount of ATP than the breakdown of carbohydrates. Fats are the preferred fuel only during low-intensity exercise. • Protein will usually be used as an energy store only in extreme situations.

16. A comparison of the three ATP-replenishing energy systems Source: Adapted from ML Foss and SJ Keteyian, Fox’s Physiological Basis for Exercise and Sport, 6th edn, WCB/McGraw-Hill, Boston, 1998

17. Integration Consider the energy systems contributing to the physical activity you are currently participating in. 1. Describe the contributing energy systems. 2. Justify how and in what order energy is provided for the duration of the activity.

18. Energy systems in practice • <insert table 4.2> Source: Adapted from ML Foss and SJ Keteyian, Fox’s Physiological Basis for Exercise and Sport, 6th edn, WCB/McGraw-Hill, Boston, 1998 and SK Powers and ET Howley, Exercise Physiology: Theory and Application to Fitness and Performance, 3rd edn, Brown and Benchmark, Madison, 1997

19. Various sports and their predominant energy systems

20. Various sports and their predominant energy systems Source: Adapted from ML Foss and SJ Keteyian, Fox’s Physiological Basis for Exercise and Sport, 6th edn, WCB/McGraw-Hill, Boston, 1998

21. How the body obtains and uses oxygen • Highly trained endurance athletes have efficient respiratory and cardiovascular systems.

22. How the body obtains and uses oxygen • Oxidative capacity refers to the muscles’ ability to obtain and use oxygen. • Athletes with a high proportion of muscles will be better able to produce energy from ATP aerobically as greater muscle mass = greater mitochondria.

23. Steady state • A ‘steady state’ is when the oxygen supply meets the body’s demands.

24. VO2 max • An individual’s highest possible oxygen consumption during exercise is known as the volume of maximum oxygen (VO2 max). • The body’s ability to deliver and use oxygen is the main factor determining VO2 max. • Other factors determining an individual’s VO2 max include: • Genes • Age • Gender

25. VO2 max comparisons by sport and by gender Source: Brian Mackenzie, UK Athletics Level 4 Performance Coach; www.pponline.co.uk

26. Anaerobic and aerobic training thresholds • During exercise, heart rate, ventilation and blood lactate all increase in proportion to the exercise. • The anaerobic threshold can be defined as that workload intensity (or level of oxygen consumption) when lactic acid starts to accumulate in the blood and muscles. • The threshold is the maximum speed or effort that an athlete can maintain and have no increase in lactic acid.

27. The aerobic training threshold is the intensity at which an athlete needs to work to produce an aerobic training effect or a physiological improvement in performance. • This occurs at about 70 per cent of the person’s maximum heart rate, or at approximately 50–60 per cent of that person’s VO2 max.

28. Back to chapter overview Fatigue and recovery Page 143

29. Fatigue • Three areas of the body can account for the physical fatigue: the central and peripheral nervous systems, muscle fibres and energy systems. • Fatigue can also be caused by psychological and environmental factors.

30. Recovery • Rest recovery is a period of no movement. • Active recovery includes performing light tasks, such as slow running, walking, stretching and minor games. • After an all-out exhaustive effort, an active recovery is recommended to restore ATP–PC stores and to remove lactic acid.

31. Recovery times for various physiological functions Source: Adapted from ML Foss and SJ Keteyian, Fox’s Physiological Basis for Exercise and Sport, 6th edn, WCB/McGraw-Hill, Boston, 1998

32. Fuel depletion and recovery Source: R Malpeli and A Telford, A+ Phys Ed Notes: VCE Physical Education Units 3&4, Nelson Australia, Sth Melb., 2008

33. Oxygen deficit • The lactic acid energy system accumulates lactic acid that has to be broken down. • Breaking down lactic acid and resynthesising depleted PC requires oxygen during recovery. • The difference between the amount of oxygen the body uses when truly at rest and the amount of oxygen used when exercise has just stopped is called the oxygen deficit. Oxygen deficit is also referred to as ‘oxygen debt’, ‘recovery oxygen’ and ‘excess post-exercise oxygen consumption’ (EPOC).

34. Personal reflection Have you ever been short of breath after exercise? What did it feel like? At what level of intensity were you working?

35. Back to chapter overview Training effects Page 146

36. Back to chapter overview Immediate physiological responses to training Page 146

37. Immediate physiological responses to training • Heart rate, ventilation rate, ventilation depth, stroke volume, cardiac output and lactate levels increase. • Muscles contract and different muscle types are recruited.

38. Back to chapter overview Long-term physiological effects of training Page 146

39. Long-term physiological responses to training

40. Back to chapter overview Now that you’ve finished … Answers

41. 1. Explain how ATP provides energy for muscle contractions. The energy in ATP is stored between the phosphate bonds. When a muscle needs to contract, a phosphate bond is broken off from the ATP molecule, releasing the energy it needs to make that contraction.

42. 2. Describe the relationship between the breakdown of each of the nutrients and the intensity and duration of exercise. • Carbohydrates are broken down easily and can be used to provide energy in high intensity exercise for moderate durations. • Fats are more difficult to break down but produce more energy. This makes them suitable for lower intensity exercise that does not require energy to be produce quickly. Due to the large amount of energy that is produce from each fat molecule, exercise can be prolonged using this fuel source. • Proteins are only used in times of starvation or after prolonged exercise where fats and carbohydrate stores are depleted. It is difficult to break down proteins so the intensity and duration of exercise using this fuel source is minimal.

43. 3. Identify the by-products of energy production for the lactic acid and aerobic energy systems The lactic acid energy system produces lactic acid as a fatiguing by-product. The by-products of the aerobic energy system include heat, carbon dioxide and water which are easily removed from the body without fatigue.

44. 4. Distinguish the energy system contributions for athletes in the following sports, events and positions: a. hockey mid-fielder A hockey mid-fielder would require a combination of all three energy systems. The predominant system used would be the alactacid system. There are many short, high intensity sprints involved in this position with some time given for recovery of the phosphocreatine which would enable this system to be used on and off for the entire game. When mid-fielder is given inadequate time to replenish PC, the lactic acid system would provide the energy needed to fuel the athlete. This would occur when high intensity effort is prolonged or repeated with very short rest breaks. At times when there are stops in play or when the ball is moved to an area of the field not controlled by a mid-fielder, the intensity of effort would be reduced considerably, enabling the body to access the aerobic system for energy.

45. 4. Distinguish the energy system contributions for athletes in the following sports, events and positions: b. pole vault As pole vault is an event requiring high intensity effort lasting less than 8 seconds, the energy system used by such an athlete would be the alactacid system. The rest period between attempts would use the aerobic system and during this time, the phosphocreatine stores would be replenished allowing for repeated maximal effort.

46. 4. Distinguish the energy system contributions for athletes in the following sports, events and positions: c. equestrian  The dominant energy system for equestrian events would be the aerobic system. The rider needs to stay calm and let the horse do the work. Even though muscular strength is required, the major energy system is aerobic. Equestrian events can range from 5 minutes in dressage and show jumping, to 24 hours in enduro events. During enduro events, there is a small contribution of the lactic acid system when the rider needs to dismount and run up hills to conserve the horse’s energy.

47. 4. Distinguish the energy system contributions for athletes in the following sports, events and positions: d. 200-metre freestyle. The lactic acid system would be the predominant system for this event, although all three systems would contribute. As this event requires a maximal, all out effort, the alactacid system would be used at the beginning of the race until the phosphocreatine is depleted after about 8 seconds. The lactic acid system would supply the energy where intensity is high but PC is not available. Once lactic acid begins to accumulate in the muscles (anaerobic threshold) the swimmer would be forced to slow down and the aerobic system would be able to supply the energy. When each of these systems is used would vary depending on the race strategy of the swimmer.

48. 5. Outline the factors affecting an individual’s oxygen consumption and delivery. An athlete’s heart and lung function impact upon oxygen consumption and delivery. Oxygen uptake is dependent upon the stroke volume (how much blood is pumped from the heart each beat), lung capacity (the amount of oxygen that can move in and out of the lungs each breath) and the amount of haemoglobin (oxygen-carrying molecules) in the blood.

49. 6. Explain the concept of VO2 max. VO2 max is the maximum volume of oxygen an individual can consume in any one minute.

50. 7a. Outline the adaptations that can occur as a result of aerobic training. Increased number of breaths per minute, increased size of the lungs, increased number of capillaries in the lungs, increased size of heart, ventricles and ventricle walls, increased blood volume, increased haemoglobin, increased muscle size, increased number of capillaries in muscle fibres.