Energy Systems Week 3 - Anaerobic Lactic - Glycolytic

Last week we explored the ATP-PC system, hopefully you got to grips with its role in high power physical activities and how taxing it can be if overtrained. In week 3 of this energy system blog series we are taking a look at the second most powerful energy system; the anaerobic lactic energy system, also known as the glycolytic energy system.

As the name suggests the anaerobic lactic system runs without requiring oxygen and uses glucose as its preferred fuel source. Although not as powerful as the ATP-PC system, it can produce a relatively high proportion of ATP for around 30 second. Energy production decreases between 30-90 seconds as a result performance will begin to plateau.

The primary role of the lactic system is to generate higher levels of force and power over slightly longer periods than the phosphocreatine system.

It's probably the most misunderstood energy system of the three, people associate the anaerobic lactic energy system with high levels of fatigue and lactate production. Simply training to fatigue doesn't train the anaerobic lactic system to improve. Continued anaerobic metabolism will lead to fatigue due to the large changes in the cellular environment that impairs energy production and muscle contractility, but this is not the only contributing factor, there will be a range of causes for fatigue depending on the sport.


Many Factors contribute to a process called glycolysis which significantly impacts energy production. The lactic energy system produces ATP by breaking down glycogen. This can be done through:

Anaerobic glycolysis or Aerobic Glycolysis. An individual's aerobic fitness levels will impact on glycolytic energy production. Lactate is always produced as a by-product of carbohydrate metabolism, both aerobically and anaerobically, but lactate only accumulates when the aerobic energy system can not keep up with the rate at which lactate is being produced.

There are four key steps involved in the anaerobic glycolytic system:

1: Initially, stored glycogen is converted into glucose. Glucose is then broken down by a series of enzymes. (Investment phase)

2: 2 ATPs are used (Investment phase) to fuel glycolysis and 4 ATPs are created (Payoff phase) so the body gains 2 ATPs to use for muscular contraction.

3: The breakdown of glucose to synthesise ATP results in the creation of a substance called ‘pyruvate’ and hydrogen ions. Without aerobic input, the muscle becomes increasingly acidic as more hydrogen ions are created.

4: Because this system is ‘anaerobic’ there isn’t enough oxygen to break down pyruvate and synthesise more ATP, the changes in the cellular environment that impairs energy production.

As a result of the anaerobic glycolytic process pyruvate binds with hydrogen ions converting them into a substance called lactate, this is different to lactic acid but often both are used in the same breath.A by product of ATP Pyruvate can be used to fuel further aerobic metabolism or it can be used to produce lactate. When the aerobic energy system is functioning at a high level relative to anaerobic demands lactate can be quickly oxidised back to pyruvate which can be used to fuel further anaerobic metabolism.

This highlights the importance of the aerobic capacity of an individual when training the anaerobic lactic system. An athlete who doesn't have a well developed aerobic energy system will not be able to maximise the energy production power of the anaerobic lactic system. Meaning the duration that they require to recover between rounds of lactic intervals will be greater than those with a well developed aerobic system.

Lactate build up in the muscle is an indication that the aerobic energy system can not recycle pyruvate as quickly as the anaerobic lactic system producing it. The body does try to shuttle lactate around to other working muscles in an attempt to convert it and utilise it.

Training the Anaerobic Lactate energy system:

Training the lactic system must be aimed at increasing lactate tolerance, improving the rate of lactate clearance and improving the rate at which glycolysis produces ATP.

Work to rest ratios will vary dependent on the desired outcome of a session. For near complete recovery and clearance of lactate between intervals to be able to repeat you would use a ratio of 1:6. So 30s of High effort to 3Mins of rest, this will help condition the body to clear lactate.

Where as if you were looking to improve lactate tolerance you would half the rest period 1:3. The shortened rest periods wont allow for lactate to clear the muscle and so it will begin to accumulate through the rounds.


The anaerobic lactic pathway prefers carbohydrates as fuel, both fats and proteins cannot be converted into energy without oxygen. The aerobic system supports the anaerobic lactic system and oxidised proteins and fats can be used as fuel to support the ATP production, but this chemical process requires more steps and is slower than anaerobic glycolysis.

Example Session:

  • 5 to 8 × 250m Ski fast - 45 seconds recovery - until pace significantly slows.

  • 150m Run intervals at 400-metre pace - 20 seconds recovery - until pace significantly slows

  • 1min Max Effort Assault Bike - 6 minutes recovery (lactate recovery training)


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