Energy systems

• Adenosine Tri-Phosphate (ATP)


  All actions in the body require energy and it can only come from ATP
• ATP


  • Stored in the muscle and only lasts 2-3 seconds during exercise
  • ATP breaks down to ADP + P + ENERGY
  • ATP must be rebuilt in order to continue activity
• Sources to rebuild ATP

  • Carbohydrates
  • Fats
  • Protein
  • Creatine Phosphate (PC)
• Anaerobic


  Without O2
• Aerobic


  With O2
• ATP-PC system


  1. Uses Creatine Phosphate (CP or PC) without the presence of O2

  2. PC breaks down easily to rebuild ATP very fast, but runs out very quickly

  3. 1 PC molecule rebuilds 0.7 of an ATP
• PC is the main fuel used to rebuild ATP for up to 10 seconds of high intensity (95+% MHR)
• Anaerobic glycolysis system


  1. Uses glycogen (comes from carbohydrates) without O2

  2. Glycogen breaks down fast, but because there is no O2, it produces lactic acid

  3. Lactic acid is made up of lactate and H+ (Hydrogen ions)

  4. 1 glucose molecule produces enough energy to rebuild 2 ATP
• Anaerobic glycolysis system is increased when exercising above 85% MHR
• Anaerobic glycolysis (cont)


  1. Lactate can be used to rebuild more ATP or converted back to glycogen

  2. When H+ accumulates, it causes fatigue by inhibiting muscle contraction

  3. H+ reaches muscle inhibitive levels around 40 seconds at maximal intensity

  4. If the intensity is below 85% MHR, then H+ may not reach fatigue levels, due to adequate O2
• Fat metabolism


  • Fats are the main fuel source in low intensity aerobic activities along with glycogen (below 70% MHR)
  • Fats are the slowest to rebuild ATP and require more O2 than glucose/glycogen
  • When glycogen is depleted, we rely heavily on the breakdown of fats
• In a marathon this depletion is called "hitting the wall". Mental and physical stress occurs because the brain needs glucose
• Protein metabolism


  • Protein repairs muscle but is an energy source for the body as a last resort
  • This happens to Anorexic or starving people, their body breaks down to survive
  • This causes enormous stress on the liver and kidneys which makes toxins build up
  • This can lead to brain damage and/or death
• Energy systems vs. food fuels at various exercise intensities & durations


  • Intensity
  • Total event duration
  • Dominant Energy system
  • Main Food / Chemical Fuel
• When an activity commences, all 3 energy systems start contributing to energy production
• At any point, only one of them will rebuild the most ATP (dominant). The intensity and duration of the activity will dictate which energy system is dominant
• The energy systems don't activate in sequential order but work together to supply ATP to varying amounts
• Steady state


  Oxygen supply equals oxygen demand. Heart rate should plateau
• Oxygen deficit


  Oxygen demand exceeds oxygen supply. Heart rate climbs
• Oxygen debt/EPOC


  The period after exercise stops when heart rate remains above resting levels. Heart rate slowly drops. Fast part replenishes PC stores, slow part oxides H+
• VO2 maximum


  The maximum oxygen that can be taken up, transported and used by working muscles
• Lactate Inflection Point (LIP)


  • Defined as the highest point at which lactate and H+ production = removal. This is the highest steady state where O2 demand still = O2 supplied to the muscles. The Aerobic system does virtually all the ATP rebuilding
  • Occurs at 85% maximum heart rate
  • Above this point, lactate and H+ production is greater than what can be removed and they begin to accumulate in the blood. This is due to insufficient O2 supplied to the muscle and therefore the Anaerobic glycolysis system has to increase the amount of ATP it rebuilds