B2 - Recovery of Energy Systems

• After taking part in any type of exercise, the body has to recover and return the energy systems back to their pre-exercise state
• Excess post-exercise oxygen consumption (EPOC) is also referred to as Oxygen debt
• EPOC is the total oxygen consumed after exercise in excess of a pre-exercise in excess of a pre-exercise levels. It occurs when the exercise performed is totally or partially anaerobic
• When the person stops exercising, their breathing rate remains elevated so that extra oxygen is breathed in to break down lactic acid into carbon dioxide and water, to replenish ATP, phosphocreatine and glycogen, and to pay back any oxygen that has been borrowed from haemoglobin and myoglobin
• After a bout of vigorous exercise, five events must happen before the muscle can operate again:

  1. ATP must be replaced
  2. Phosphagen stores must be replenished
  3. Lactate must be removed
  4. Myoglobin must be replenished with oxygen
  5. Glycogen stores must be replenished
• The replacement of ATP and phosphagen takes around 3 minutes. The aerobic energy system is used to produce the ATP required to replenish the PC stores and ATP stores in the body:

  ADP + P + oxygen = ATP

  ATP + C + P = PC + ADP

  Around 50% of the replenishment occurs during the first 30 seconds, while full recovery occurs at about 3 minutes
• Replacement of Muscle ATP and Phosphagen:

  • The amount of oxygen required during this process ranges between 2 to 3.5 litres of oxygen
  • The fitter you are, the greater the debt, because training increases the PC content within the muscle cells
  • However, the recovery time of a fitter person is reduced because they have enhanced methods of oxygen delivery, such as increased capilliarisation and in improved cardio-respiratory system, which will increase the rate of ATP production from the aerobic energy system
• The removal of lactate takes around 20 minutes to 2 hours after stopping exercises, depending on the intensity of the exercise
• Removal of lactate involves oxygen, which is required to break down the lactate produced during anaerobic glycolysis into pyruvate.

  Pyruvate can then enter the aerobic energy system and eventually be broken down into carbon dioxide and water
• Lactate + Oxygen = Pyruvate
• Removal of Lactate:

  • Lactate can also be converted in the liver to glycogen and stored either in the liver or in muscle tissue
  • Research has shown that an active recovery increases the rate of removal of lactate, so walking or slow jogging after a bout of exercise will help to decrease the time it takes to rid the body of lactic acid
  • An active recovery keeps the heart and breathing rate up, which has the effect of increasing the rate of delivery of oxygen to the working muscles, which will then help to rid the body of lactate
  • Therefore, cool-down is very important after any form of exercise
• Replacement of Glycogen Store and Resaturation of Myoglobin:

  • The oxygen replenishment of myoglobin and refilling the glycogen stores take between 2 and 48 hours.
  • If the exercise bout was a very high intensity then it will take longer to recover; however, the higher the aerobic fitness of a person the faster they will recover
  • Muscle glycogen stores must also be restored through a high carbohydrate diet and rest, and can take several days to recover, depending on the intensity of the exercise
  • The oxygen intake after exercise is used to replenish these stores of oxygen
• Myoglobin is used to store oxygen in muscle tissues which is used up during long periods of aerobic exercise
• Nutritional intake is important to help a person to recover from exercise as how long the person has exercised for will determine what sort of nutritional strategy will be best in order to help with recovery from the exercise
• Carbohydrate Intake:

  • A person who takes part in sports that are of a relatively high intensity and last longer than around 30 minutes would be classed an as endurance athlete
  • An example of these sports are: jogging, cycling, swimming, football, rugby and netball
  • An endurance athlete needs to have the energy in order to compete and train
  • Carbohydrate is the body's preferred source of fuel; however, carbohydrate stores in the body are relatively small so it is vital that these athletes are taking in sufficient quantities of this nutrient every day in order to meet their energy demands
• Carbohydrate Intake:

  • The amount of carbohydrate a person should consume is based upon the activity level of the individual in terms of length and intensity
  • If you only take part in low levels of activity you will need less energy and consequently need to consume lower levels of carbohydrate. This would be places in category A
  • However, an endurance athlete would be training or competing for longer periods of time and therefore require greater amounts of carbohydrate and fall into category E
• Activity Level/Category and recommended amount of carbohydrate per kilogram:

  A/Light (less than 1 hour a day/3-5 hours per week) - 5g

  B/Light to moderate (1 hour a day) - 6g

  C/Moderate ( 1-2 hours a day) - 7g

  D/Moderate to heavy (2-3 hours a day) - 8g

  E/Heavy (4 hours a day) - 10g
• Carbohydrate Intake:

  • During the 2 hours immediately after exercise or competition, your body is able to convert carbohydrate into glycogen at a very fast rate
  • Therefore, in order to help maximise your body's store of carbohydrate, you should eat foods high in carbohydrate as soon as possible post-exercise
  • You should aim to eat around 1-1.2g of carbohydrate per kg of your body weight
  • However, most people do not feel like eating a large carbohydrate meal after exercise, so many prefer to eat a series of carbohydrate snacks and sports drinks instead. Energy gels are also a popular choice
• Protein Intake:

  • Athletes that require high levels of protein during recovery take part in sports that last for a very short period of time and require strength and sometimes speed
  • Examples of these sports are: weightlifting, sprinting, shot put and long jump
  • In order for an athlete to perform well in power sports, they usually need to increase their muscle size, as larger muscles are able to produce more force which makes the athlete stronger and therefore more powerful
• Protein Intake:

  • In order for the muscle tissue to heal and grow, the athlete must rest and supply the body with sufficient quantities of protein
  • The amount of protein recommended depends upon how much activity a person does, the more they break down muscle tissue and consequently the more protein they need in order to repair the muscle tissue
• Activity Level/Category: Recommended protein per kg:

  A/Sedentary Adult 0.8g

  B/Recreational Exerciser 0.8-1.5g

  C/Endurance Athlete 1.2-1.6g

  D/Speed/Power Athlete 1.7-1.8g

  E/Adult Building Muscle(Hypertrophy) 2g
• Protein Intake:

  • Research has found that protein is best utilised if it is taken in amounts of 30-35g at a time
  • If a person was to eat more than this then the excess would be excreted or converted to fat and stored in the body
  • Therefore, athletes should aim to spread out their consumption of protein into a number of different meals and snacks
• Protein Intake:

  • Some athletes may find it difficult to consume all their protein requirements from their daily food
  • Therefore, a range of protein supplements have been devised that deliver high concentrations of protein
  • These supplements are usually made out of powdered milk, eggs and/or soya
  • Protein shakes are a popular choice with many power athletes as they contain plentiful supplies of amino acids and are quick and convenient to use
  • Protein bars are also available which deliver high concentrations of protein and low levels of carbohydrates with very little fat
• Rehydration:

  • Dehydration causes a significant loss of performance.
  • This is because dehydration will cause a loss of blood plasma affecting blood flow and the ability to sweat
  • Temperature starts to increase steadily
  • When we sweat it is predominantly blood plasma that is lost and so cardiac output is reduced
  • Rehydration is important to improve the circulation of the blood and body's ability to control temperature
  • While plain water is a good drink for an athlete to consume, there are now a huge array of sports drinks available that help to quench thirst, supply carbohydrates/electrolytes
• Isotonic:

  • These drinks are the most popular type of sports drink
  • They are used to help the body rehydrate and also contain some carbohydrate
  • The drink is termed 'isotonic' because they have a similar concentration of dissolved solids as out blood, which results in the drink being absorbed very quickly into the body so that we can rehydrate at a much faster rate then is we were to drink water alone
  • The drinks contain 6mg of carbohydrate per 100ml of fluid, which provides energy which is beneficial to endurance athletes
• Hypotonic:

  • The main aim of these sports drinks is to hydrate the athlete after exercising
  • These types of sports drinks are low calorie drinks and have a lower concentration of dissolved solids than blood
  • They are absorbed by the body at a faster rate than isotonic drinks
  • They contain no more than 2g of carbohydrate per 100ml of fluid, so they provide little energy to the athlete during exercise
  • They are a relatively poor source of energy
• Hypertonic:

  • The main purpose of these drinks is to supply the body with energy after exercise or during endurance events that last longer than 90 minutes
  • These drinks have a higher concentration of dissolved solids than blood and are absorbed relatively slowly
  • They contain 10g of carbohydrate per 100ml and are a very good source of energy but are relatively poor for hydration
  • These drinks will also contain the correct amounts of the electrolytes which ensure optimum speed of absorption
  • They often contain additives such as sweeteners and colourings which have a negative effect on health