energy systems

• Adenosine Triphosphate (ATP)


  • The food we eat is stored in the body as glycogen, which is converted into ATP
  • ATP is the body's universal energy currency
  • When ATP is broken down it releases energy that can be used for muscle contraction, nerve transmission, digestion
• ATP Resynthesis


  ADP + P + Energy = ATP
• 3 energy systems


  • ATP-PC System
  • Glycolytic Energy System
  • Aerobic Energy System
• ATP-PC System

  • Used during high intensity exercise
  • Lasts for 2 seconds
  • As ATP is used quickly, ADP + P stores build up
  • This triggers the enzyme creatine kinase to be released
• ATP-PC System

  1. We start with phosphocreatine (P + C)

  2. Creatine Kinase breaks down PC into P + C + Energy

  3. The energy is used to resynthesise the phosphate with ADP
• ATP-PC System


  • Type of reaction: Anaerobic
  • Site of reaction: Sarcoplasm
  • Food fuel used: PC (Phosphocreatine)
  • Enzyme: Creatine Kinase
  • ATP yield: 1 PC = 1 ATP
  • By-products: None
  • Activity intensity: Very High Intensity
  • Duration of system: 2-10 seconds
  • Strengths: No delay for O2, PC readily available, Quick resynthesis of ATP, No fatiguing by-products, Fast recovery, Provides energy for high intensity activities
  • Weaknesses: Low ATP yield, Small PC stores lead to rapid fatigue, after 8-10 seconds
• Glycolytic Energy system


  1. Glycogen

  2. Glucose

  3. Pyruvic Acid

  4. Lactic Acid

  5. Energy + 2p + 2ADP = 2ATP
• Glycolytic Energy system


  1. Glycogen

  2. Glucose

  3. GPP

  4. PFK
• Glycolytic Energy system


  1. Glucose

  2. Pyruvic Acid

  3. Energy + 2P + 2ADP = 2ATP
• Glycolytic Energy system


  1. Pyruvic Acid

  2. Lactic Acid

  3. LDL
• Glycolytic Energy system


  • Type of reaction: Anaerobic
  • Site of reaction: Sarcoplasm
  • Food fuel used: Glycogen / glucose
  • Enzyme: GPP, PFK, LDH
  • ATP yield: 1 Glycogen = 2 ATP
  • By-products: Lactic acid
  • Activity intensity: High intensity activities
  • Duration of system: Up to 3 minutes (depending on intensity)
  • Strengths: No delay for O2, large fuel stores, Fast fuel breakdown for ATP synthesis, Lactic acid can be recycled into fuel for further energy production, Lasts 3 minutes
  • Weaknesses: Fatiguing by-product such as lactic acid reduces pH and enzyme activity, Relatively low ATP yield, Can be lengthy recovery
• Aerobic glycolysis


  1. PFK catalyses the conversion of glucose into pyruvic acid, releasing energy to resynthesise 2 ATP

  2. GPP converting glycogen into glucose, making more glucose available

  3. The presence of O2 prevents pyruvic acid being converted into lactic acid. Instead, it goes through a link reaction catalysed by coenzyme A, which produces Acetyl CoA, allowing access to the mitochondria
• Mitochondria


  A structure within the cell where aerobic respiration and energy production occur
• Krebs Cycle


  1. Acetyl CoA combines with oxaloacetic acid to for citric acid

  2. The citric acid is oxidised through a cycle of reactions, known as the Krebs Cycle

  3. The Krebs Cycle releases CO2, Hydrogen and enough energy to resynthesise 2 ATP

  4. All this occurs in the matrix of the mitochondria
• Electron Transport Chain (ETC)


  1. The Hydrogen atoms are carried through the ETC in the mitochondrial cristae, carried by NAD and FAD (hydrogen carriers)

  2. They are split into ions (H+) and electrons (H-)

  3. The H+ are oxidised and released as H20

  4. The H- are carried by NAD and FAD (NADH2 / FADH2)

  5. NADH2 release energy for 30 ATP, while FADH2 release enough energy for 4 ATP (34 ATP in total)
• Aerobic Energy System


  • Type of reaction: Aerobic
  • Site of reaction: Sarcoplasm. Matrix and cristae of mitochondria
  • Food fuel used: Glycogen / glucose and triglycerides (Free Fatty Acids)
  • Enzyme: GPP, PFK, CoA, Lipase
  • ATP yield: 1 glycogen = 38 ATP
  • By-products: CO2 and H2O
  • Activity intensity: Low - Moderate
  • Duration of system: 3 minutes +
  • Strengths: Large fuel stores (glycogen, glucose, FFA's, triglycerides etc...), High ATP yields, no fatiguing by products
  • Weaknesses: Delay for O2 delivery, complex series of reactions, slow energy production limits to only submax exercise, more O2 needed to break down triglycerides / FFA's
• The Aerobic System and Free Fatty Acids (FFA)


  1. Glycogen is the main fuel for endurance performers

  2. Triglycerides or fats can also be metabolised aerobically as FFA's, allowing us to conserve glycogen / glucose stores

  3. The enzyme lipase is released, which catalyses the breakdown of fats, which are converted into FFA's and glycerol

  4. FFA's are converted into Acetyl CoA and follow the path through the Krebs cycle and ETC
• Energy Systems


  INTENSITY & DURATION can help indicate which energy system is being used by an athlete at a given time
• Energy Systems


  • ATP-PC System
  • Glycolytic System
  • Aerobic System
• Energy Continuum


  • The relative contribution of each energy system to overall energy production depending on intensity and duration of activity
  • Although one energy system is predominant at one time, all 3 will contribute to all activities performed
• Energy Continuum


  1. Intensity Very High: Duration <10 seconds: ATP-PC system predominant

  2. Intensity High: Duration 10 seconds - 3 minutes: Glycolytic energy system predominant

  3. Intensity low-moderate: Duration >3 minutes: Aerobic energy system predominant
• Intermittent Exercise


  • Where the intensity alternates, either during interval training or between rest and work intervals during a game
  • This can lead to the athlete switching between the 3 energy systems during the same game
  • The point where an athlete moves from one energy system to another is known as a Threshold
• Recovery Periods: (ATP-PC)


  1. PC replenished: 50% in 30 seconds & 100% in 3 minutes

  2. The O2 stored in myoglobin can also be restored fully within 3 minutes
• Recovery Periods: (Glycolytic)


  Some lactic acid is removed during periods of low intensity exercise / active recovery (creating the zigzag line on the graph)
• Recovery Periods: (Aerobic)


  Endurance athletes often have breaks in play, providing the chance to rehydrate and replenish glycogen / glucose levels through drinking water, glucose tablets, gels, bananas, isotonic drinks
• Additional factors affecting the energy system usage


  • Position of the player
  • Tactics
  • Level of competition
  • Structure of the game