Learning Objectives: 1. To understand how the two anaerobic energy systems work. 2. To understand lactate threshold and its effect on performance. 3. To know which energy system is predominant in various sports.

Anaerobic Energy Systems When the body is unable to provide the oxygen required to resynthesise ATP it must start to work anaerobically. There are two anaerobic energy systems: 1. Phosphocreatine (PC) energy system (or ATP-PC system) 2. Lactate anaerobic energy system Anaerobic energy systems

Phosphocreatine (PC) Energy System (or ATP-PC system) PC → P + C + Energy AND Energy + P + ADP = ATP For every molecule of PC broken down, one molecule of ATP can be resynthesised. No oxygen is required. Energy is released very rapidly and there are no waste products. Stores only last for 5-8s of high intensity exercise. It is therefore excellent for very high short intensity activities (e.g. 100m sprint) but not for anything longer. PC can be resynthesised quickly. 50% in 30s, 100% in less than 4 mins (this requires O2 so intensity must be reduced).

Lactate Anaerobic Energy System This system involves the partial breakdown of glucose (oxygen is required for full breakdown). 2 molecules of ATP are produced (18 times less than aerobic!). Lactic acid is produced as a by-product. This system can therefore only be sustained for between 10 seconds and 3 mins. Few chemical reactions involved so energy can be produced quickly. summary of anaerobic energy systems

Lactic Acid Hydrogen is released during both glycolysis and the Kreb’s cycle. These H ions combine with oxygen (in the electron transport chain). At some point there becomes too many H ions for the amount of O2 available. Excess H ions combine with pyruvate to form lactic acid. This point is the lactate threshold (2 mmol per litre of lactic acid above resting levels). The build up in lactate acid is a contributing factor for fatigue. It produces an acidic environment which slows down enzyme activity and stops the breakdown of glucose. It also effects nerve endings causing some pain.

What happens to Lactic Acid? Lactic acid is often seen as a ‘waste product’ but can be a useful energy source. During recovery (when O2 is available) lactic acid can take the following routes: 1. conversion to water and carbon dioxide (after being converted back to pyruvate and entering the Kreb’s cycle) 2. conversion into glycogen and stored in liver / muscles 3. conversion into protein 4. conversion into glucose 5. conversion into sweat and urine

Lactate Threshold / OBLA Onset of blood lactacid accumulation (OBLA) is the point at which lactic acid starts to accumulate in the blood (above 4 mmol per litre). This occurs when there is insufficient O 2 available to break down lactic acid. As exercise intensity increases, O 2 consumption increases until VO 2 max is reached. Any increase in intensity will then cross the lactate threshold. Predominantly aerobic ATP resynthesis switches to anaerobic when there is insufficient oxygen in the mitochondria to combine with the H released when glucose is broken down. OBLA shows fitness levels as the longer a performer can hold off lactate accumulation, the fitter they are.

Exam Question Elite games players require high levels of fitness and psychological preparation, therefore regular fitness testing and after-match performance analysis are common. Figure 1 illustrates the relationship between the concentration of blood lactate and the workload. a) Use Figure 1 to identify the workload level at which lactate threshold occurs, and explain why lactate (lactic acid) tends to be produced when a player is exercising. (3 marks) (b) Explain how lactate is removed from the blood by the body. (4 marks)

a) 1.Lactate threshold correctly identified as between 500 and 800 Watts; 2. Lactate from anaerobic (glycolosis)/lack of oxygen (O2)/high demand/lack of supply; 3. High intensity/workload exercise/equiv. b)1 Used as respiratory substrate/for respiration / energy / using oxygen (O2)/ lactate to replenish ATP; 2 Converted to pyruvate/pyruvic acid; 3 then to Carbon Dioxide (CO2) and water; 4 In inactive muscle and various tissues/organs; 5 Converted to glycogen/glucose; 6 In liver; 7 Some excreted in sweat/urine/conversion to protein

Energy System Continuum There are three energy systems that can regenerate ATP: the ATP–PC system (anaerobic) the lactic acid system (anaerobic) the aerobic system The use of each of these systems depends on the intensity and duration of the activity: If the activity is short duration (less than 10 seconds) and high intensity, we use the ATP–PC system. If the activity is longer than 10 seconds and up to 3 minutes at high intensity, we use the lactic acid system If the activity is long duration and submaximal pace, we use the aerobic system.

Fatigue Muscle fatigue is the inability to maintain muscle contractions. There are numerous causes including: An increasingly acidic environment caused by the build up of lactic acid and excess H ions results in a breakdown in chemical reactions. Glucose stores being depleted. A change in the balance of chemicals that instigate muscle contraction. Dehydration causing increased blood viscosity (leading to increased HR, overheating etc.). The cause of fatigue depends on the type of activity being performed and is still very much being researched and more fully understood. What would be the cause of fatigue during the latter stages of a marathon compared to those during 100m sprint or a 400m race?

VO 2 Max Differences A higher VO 2 max means a higher lactate threshold. Several factors affect an individuals VO 2 max: Age – VO 2 max decreases with age. Gender – woman have a 20% lower VO 2 max. Training Genetic inheritance

Lactate Threshold / VO 2 Max and Exercise When an athlete crosses their lactate threshold fatigue will quickly set in. Pacing themselves to work near, but not over, their lactate threshold is key to success. As an individual becomes fitter they will be able to work at a higher percentage of their VO 2 max before crossing the lactate threshold (and moving to anaerobic energy systems).

Exam Question Many elite swimmers use blood lactate sampling during training as a means of establishing their training load. (i) What do you understand by the term lactate threshold ?(2 marks) (ii) How is lactate threshold related to VO2 max? (2 marks) (iii) Explain how knowing blood lactate levels during a swim might assist an elite performer. (2 marks) i) 1 Levels at which lactate; 2 Lactic acid accumulates in blood; 3 Exercise has become anaerobic. (ii) 1 Lactate threshold is some proportion/percentage of VO2 max; 2 Proportion/percentage increases as fitness increases. (iii) 1 Accurately measures intensity of training; 2 Elite performers need to train close to their Lactate threshold/VO2 max; 3 Accuracy in determining Lactate threshold/VO2 max is difficult.

Lactate Tolerance The ability to withstand the effects of lactic acid accumulation. This may be related to the amounts of bicarbonate in the blood (which can combine with lactic acid to reduce its acidity). May just be down to motivation/determination levels.

After Exercise To recover from intense exercise the body needs to: Restore ATP levels Restore phosphocreatine levels Deal with excess lactic acid (either by oxidating lactic acid into pyruvate, or by converting lactic acid into glycogen in the liver – both create ATP) Reloading myoglobin with oxygen Restoring muscle glycogen levels (high carb diet) All, but the last of these requires oxygen as energy is required from the complete breakdown of glucose.

Aerobic or Anaerobic? During nearly all activities both systems will be involved at the same time, the one which is more predominant depends on: The level of intensity The duration Your level of fitness energy systems used - youtube clip See p28/29 of textbook

Exam Question Successful track and field performance is dependent upon an effective energy supply. Figure 3 shows how the supply of each energy system varies according to the duration of a task. 1. Identify each of the energy systems A, B and C. (2 marks) 2. Explain how the differing energy sources of these systems are used during: (i) a series of javelin throws; (2 marks) (ii) a long-distance run of increasing intensity. (4 marks) 1. A- ATP-PC/phosphocreatine system/ATP system/alactic system; B – lactate/lactic acid system/anaerobic glycolytic system; C – aerobic/oxidative system. 2. (i) Immediate energy supplied/ATP system; PC/CP (broken down); (credit equation) Energy for ATP formation; Aerobic system used for recovery/restoration of PC levels. (ii) Low intensity – aerobic systems/oxidation; Fats/glucose/glycogen/carbohydrates (CHO’s); Krebs cycle/mitochondria; Carbon dioxide (CO2) produced; Increasing/high intensity – lack of oxygen (O2)/anaerobic; ATP produced by glycolosis/lactic acid system; Lactate accumulates/Hydrogen ions (H+)/acidity; Fatigue.