Anaerobic respiration is when the body produces energy for exercise without oxygen. The anaerobic energy system kicks in in the first few minutes of all exercise, before there is suffiecient oxygen available at the muscles for aerobic metabolism. It is also used for fast, powerful bursts of energy, for which the aerobic system is insufficient. There are two systems within Anaerobic metabolism, which are the ATP-PC system and the lactic acid system.
ATP is a high energy molecule which is broken down to form ADP and release energy. PC or Phosphocreatine is another high energy molecule, found in the Sarcoplasm of muscle fibres. The breakdown of ATP and increase in volume of ADP triggers an enzyme known as Creatine Kinase to initiate the breakdown of PC into Phosphate and Creatine. Being an exothermic reaction, this provides the energy required to resynthesise ATP at a fast rate.
We only have 120g of Creatine within our bodies and so this repeated breaking down of PC in order to produce energy to resynthesise ATP is temporary and can only last a maximum of 10 seconds. Therefore the ATP-PC system is used mainly for bursts of speed.
What are the advantages of the ATP-PC system?
- It does not require oxygen
- Phosphocreatine is stored in the muscle cell itself ready to be used immediately for energy.
- Being a small compound it reacts quickly to produce immediate energy.
- There are no biproducts produced by the reaction which cause fatigue (we simply run out of fuel rather than have any substance inhibit it).
- PC can be quickly resynthesised so we are ready to sprint or throw again after a short recovery period.
What are the weaknesses or disadvantages?
- Only small amounts are stored in the muscle so it runs out quickly (about 8 to 10 seconds).
Lactic Acid System
Sometimes also known as Anaerobic Glycolysis due to the initial process being the same as aerobic glycolysis (as mentioned above), only without oxygen. So, as before 10 chemical reactions occur within the Sarcoplasm which turn Carbohydrate into Pyruvic acid and 2 molecules of ATP. The difference now being the lack of oxygen meaning the carrier molecule NAD+ cannot offload the Hydrogen (H+) by-product of glycolysis causing a build up in the cell.
To try to prevent an increase in acidity the pyruvic acid accepts the H+, forming Lactic acid. If oxygen was present the H+ would be transported to the Mitochondria for use in the Kreb's cycle. Lactic acid is thought to interefere with muscle contraction due to disrupting the binding of Calcium to Troponin. Acidity also stimulates free nerve endings within the muscle, causing pain. Due to lactic acid production, this energy system can only be predominant for up to 2 minutes.
Following anaerobic exercise, despite the metabolic process used not requiring oxygen, your body will be in Oxygen Debt and so your respiration rate will be very high.
Anaerobic Respiration Equation:
Glucose = Ethanol + Carbon Dioxide + Energy
C6H12O6 = 2C2H5OH + 2CO2 + Energy
Which sports use the lactic acid system most?
Any sport or event requiring a sustained burst of high intensity exercise will use the lactic acid system and cause the body to go into oxygen debt. For example 400m Sprinting, Speed Skating, Crossfit competitions & Cicuit training.
What are the advantages of the lactic system?
- There is a huge amount of glycogen stored in the muscles and liver which can be made available for energy.
- It is more efficient - resynthesises two molecules of ATP as opposed to just one that the ATP-PC manages.
- Fewer reactions than the aerobic energy system are needed to produce energy so it is faster (but not as fast as the PC system).
- Provides more sustained high intensity energy for between 10 and 180 seconds.
- Can work both anaerobically (without oxygen) and aerobically (with oxygen).
What are the disadvantages?
- It is not as quick as the PC system.
- Lactic acid is produced which causes fatigue (and discomfort!)
- Causes pain by stimulating the pain receptors (telling the body to slow down and known as lactic acid buiild up).
- In the end it stops working because of muscle fatiugue and pain.