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The body’s response to physical activity

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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 Adenosine triphosphate
Back to chapter overview Adenosine triphosphate Page 125

6 ATP is broken down into adenosine diphosphate (ADP) (see Figure 4.3).
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.

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 of fuel Duration of system Cause of fatigue Efficiency of ATP production Anaerobic Alactacid system (ATP–PC) Phosphocreatine (PC) Up to 10 seconds Depletion of PC stores Rapid but limited Lactic acid system Glucose and glycogen Up to 3 mins Build-up of lactic acid in the muscles Aerobic Aerobic system Carbohydrates, glucose and glycogen, fats, protein Indefinite at low intensities Depletion of fuel sources Slow but unlimited Source: Adapted from ML Foss and SJ Keteyian, Fox’s Physiological Basis for Exercise and Sport, 6th edn, WCB/McGraw-Hill, Boston, 1998

17 1. Describe the contributing energy systems.
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
Duration of event 10 secs 30 secs 60 secs 2 mins 4 mins 10 mins 30 mins 60 mins 120 mins Anaerobic 90% 80% 70% 50% 35% 15% 5% 2% 1% Aerobic 10% 20% 30% 65% 85% 95% 98% 99% Event (run) 100 m 200 m 400 m 800 m 1500 m 5000 m m Marathon ATP–PC/LA ATP–PC/ LA/aerobic <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
Relative contribution of each energy system (%) Sport or activity ATP–PC and anaerobic glycolysis Anaerobic glycolysis and aerobic Aerobic 1 Aerobic dance 15–20 5 75–80 2 Baseball 80 15 3 Basketball 60 20 4 Hockey 50 5 Football 90 10 Negligible 6 Golf 95 7 Gymnastics 8 Rowing 30 9 Skiing a Slalom, jumping b Downhill c Cross-country 85

20 Various sports and their predominant energy systems
Relative contribution of each energy system (%) Sport or activity ATP–PC and anaerobic glycolysis Anaerobic glycolysis and aerobic Aerobic 10 Soccer a Goalie, wing, strikers b Halfbacks or sweeper 60 30 20 10 11 Swimming and diving a Diving b 100-m swim c 400-m swim d 1500-m swim 98 80 2 15 40 Negligible 5 70 12 Tennis 13 Walking 95 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
VO2 maximum Men Women Basketball 40–60 43–60 Cycling 62–74 47–57 Gymnastics 52–58 35–50 Rowing 60–72 58–65 Soccer 54–64 50–60 Swimming 50–70 Track and field – running 60–85 50–75 Source: Brian Mackenzie, UK Athletics Level 4 Performance Coach;

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
With active recovery With rest only Restoration of ATP–PC 2 minutes 5 minutes Increase in oxygen consumption 3 minutes 6 minutes Replenishment of muscle glycogen 10 hours (continuous exercise) 46 hours Replenishment of liver glycogen 5 hours 24 hours Reduction of lactic acid in muscles and blood 30–60 minutes 1–2 hours Restoration of oxygen stores 10–15 seconds 1 minute 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
Predominant energy system Likely causes of fatigue Types of recovery ATP–PC Fuel depletion, ATP and PC Rest recovery Lactic acid Accumulation of metabolic by-products • H+ (hydrogen ions • Pi (inorganic phosphates) NB: Lactic acid is no longer thought to contribute to fatigue. In fact, it is being regarded more as appositive performance enhancer rather than a negative. Non-dietary • Active recovery • Massage • Water-based therapies, e.g. contrasting via hot/cold baths Aerobic Fuel depletion • Glycogen stores, then fats • Elevated body temperature leading to : – dehydration – blood flow away from muscles Dietary • High GI foods • Rehydration via sports drinks: – Hypertonic to replace glycogen – Hypotonic to replace lost fluids 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 Immediate physiological responses to training
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 Long-term physiological effects of training
Back to chapter overview Long-term physiological effects of training Page 146

39 Long-term physiological responses to training
Increases Decreases Stroke volume and cardiac output Resting heart rate Oxygen uptake and lung capacity Haemoglobin level Muscle size Muscle fibre type being trained

40 Now that you’ve finished …
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 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.

51 7b. Explain how these adaptations lead to an improvement in performance.
Increasing the number of breaths per minute combined with a larger lung size, enables more oxygen to be breathed into the lungs and increased capillaries in the lungs combined with increased haemoglobin for carrying oxygen in the blood allows more oxygen to be absorbed into the bloodstream. Once in the bloodstream, the ability of the heart to pump this oxygen quickly to the working muscles can be improved by the increased size and strength of the heart causing stronger pumps of the heart. An increased number of capillaries in the muscles allows this oxygen-rich blood to be delivered more quickly and efficiently to the working muscles. By increasing the size of muscles, the strength of the muscles and their ability to carry out work will improve.

52 8. Predict three physiological adaptations that could occur from long-term strength training.
Muscle hypertrophy (increasing the size of the muscle) is a result of: An increase in the size of the muscle fibres due to an increase in the number of muscle fibrils. After strenuous exercise, muscle fibrils will split into two. Each half of the muscle fibril will grow to the size of the parent fibril, hence, an increase in size. Muscle fibres will also increase in size due to the increased storage of glycogen, adenosine triphosphate and phosphocreatine. Slow twitch and fast twitch muscle fibres cannot be changed, but each can take on the characteristics of each other through specific training. Muscle fibres can contract with greater force (an increase in the number of actin and myosin filaments which will have an increase in cross bridges required for contraction).

53 9. Explain the difference between sub-maximal exercise and maximal exercise.
Sub-maximal exercise is exercise performed at a level that leaves the heart rate in a plateau (a consistent rate for an extended period of time) below its maximum number of beats per minute. Generally, this level of exercise can be maintained for more than 20 minutes at a time. Maximal exercise, however, is activity that leads to a heart rate that approaches its maximum level and is hard to maintain for a long period of time.

54 10. ‘Elite athletes are born, not made
10. ‘Elite athletes are born, not made.’ Using your knowledge of muscle fibres, justify your opinion about this statement. There are 3 types of muscle fibres: red slow-twitch fibres, which contain a large number of capillaries and produce a large amount of ATP slowly; red fast-twitch fibres, which contain some capillaries and can rapidly produce ATP but fatigue faster than slow-twitch fibres; and white fast-twitch fibres, which contain few capillaries and rapidly generate ATP anaerobically. Although an increase in muscle fibre size and number can be a physiological adaptation to long-term training, an individual’s genetic make-up determines their proportion of muscle fibre type and consequently, their suitability to certain sports. An athlete, for instance, born with large proportions of white fast-twitch fibres will be more suited to sprinting.

55 Image credits Slide 1, Getty Images/Ian Walton
Slide 4, Getty Images/Jupiterimages Slide 25, Australian Sports Commission

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