Energy systems

• Aerobic system - 180+ seconds

  used when exercise intensity is low and oxygen supply is high.

  • Glycolysis - Glycogen--glycogen phosphorylase-->glucose--phosphofructokinase-->pyruvic acid-->Acetyl CoA. 2 ATP yield. Sarcoplasm
  • Krebs cycle - Acetyl CoA+ oxaloacetic acid-->citric acid- energy+ hydrogen+ Co2. 2 ATP yield. Mitochondrial matrix
  • Electron transport chain - Hydrogen-->electron, hydrogen+ O2-->H2O. 34 ATP yield. Mitochondrial cristae
• Glycolytic system - anaerobic -

  Glycogen--Glycogen phosphorylase-->Glucose--Phosphofructokinase-->Pyruvic acid+ energy.

  Pyruvic acid--lactate dehydrogenase-->lactic acid.

  • sarcoplasm
  • 2 ATP yield
  • lactic acid - by-product
  • high intensity
  • 10-180 seconds
  • no need to wait for oxygen
  • build up of lactic acid
• ATP-PC system - anaerobic -

  Phosphocreatine--creatine kinase--> Phosphate+ creatine+ energy.

  Energy+ ADP+ Phosphate--> ATP

  • sarcoplasm
  • 1 ATP yield
  • very high intensity
  • 2-10 seconds
  • simple
  • limited stores of Phosphocreatine
• The energy continuum - Describing which type of energy system is used for different types of physical activity depending on intensity and duration of exercise.

  • very high intensity - less than 10 seconds - ATP-PC
  • High to very high - 8-90 seconds - ATP-PC and anaerobic glycolytic
  • high - 90 seconds - 3 minutes - Anaerobic glycolytic and aerobic
  • Low to medium - 3+ minutes - Aerobic
• Slow twitch fibres are used for low to medium intensity. They use aerobic respiration to receive fuel. Fast twitch are more suited to high intensity activities and use the anaerobic system as their main energy pathway.
• Oxygen consumption during exercise (submaximal and maximal oxygen deficit) -

  Oxygen consumption is the amount of oxygen we use to produce ATP and is usually referred to as VO2.

  When we start to exercise, insufficient oxygen is distributed to the tissues for all the energy to be provided aerobically, as it takes time for the body to respond to the increase in demand for oxygen. Energy is provided anaerobically to satisfy the increase in demand for energy until the body can cope. This is referred to as submaximal oxygen deficit.
• Breathlessness after exercise is known as post-exercise oxygen consumption (EPOC). And essentially is the amount of oxygen consumed during recovery above that which would have been consumed at rest during the same time. There are two components;

  • fast replenishment stage - restoration of ATP and phosphocreatine stores and the re-saturation of myoglobin with oxygen.
  • slow replenishment stage - oxygen consumed in this stage is important for: removal of lactic acid , maintenance of breathing and heat rates, glycogen replenishment and the increase in body temperature.
• Lactate accumulation - Lactic acid is a result of glycolysis during the anaerobic system. The higher the intensity, the more lactic acid that is produced. This quickly breaks down, releasing hydrogen atoms. Remaining compound combines with sodium ions or potassium ions to form the salt lactate. As lactate builds up in the muscles, there is more hydrogen ions and therefore an increased acidity. This slows down enzyme activity and affects the breakdown of glycogen, causing muscle fatigue.
• Lactate threshold and onset blood lactate accumulation - The crossing of the aerobic/anaerobic threshold is known as the lactate threshold and is the point where lactate rapidly accumulates in the blood. When unable to produce enough oxygen to break down lactate, the levels of lactate build up and this is known as OBLA (onset blood lactate accumulation).

  OBLA - the point where blood lactate levels go above 4 millimoles/litre.

  lactate threshold is expressed as a percentage of VO2 max.

  VO2 - the maximum amount of O2 that can be utilised by the muscles per minute
• ATP = Adenosine triphosphate - only useable form of chemical energy in the body. The energy stored in ATP is released when it is broken down. ATPase breaks down ATP into ADP and an inorganic phosphate. There are three systems that work to regenerate ATP and these are:

  • aerobic
  • ATP-PC
  • anaerobic
• Factors affecting the rate of lactate accumulation -

  • exercise intensity - higher = more demand for energy and faster OBLA occurs - lactic acid
  • muscle fibre type - Slow twitch breaks down glycogen faster in presence of oxygen and so less lactate production.
  • Rate of blood lactate removal - if removal is slower than production, lactate will accumulate in the blood until OBLA is reached.
  • Respiratory exchange ratio - when ratio is near 1.0, glycogen becomes the preferred fuel and there is a greater chance of the accumulation of lactate.
  • Fitness of performer - training regularly delays OBLA
• Measurements of energy expenditure -

  • indirect calorimetry - measures how much carbon dioxide is produced and how much oxygen is consumed at both rest and during aerobic exercise. precise calculations of VO2 + VO2 max.
  • Lactate sampling - accurate and objective measure of lactate in the blood and can also be used to measure exercise intensity.