Energy Systems Used When Running

Details of the major energy systems and their use while running

Whether we are at rest or running our body needs to create energy for our muscles and to allow our living systems to power chemical reactions required to maintain the body's functions.

The single unit of energy which is used for these reactions is adenosine triphosphate. (Often referred to as ATP), Adenosine triphosphate is the energy currency the body uses to pay for such reactions.

The key energy systems for running

There are three key energy pathways for running. These are often described as energy systems

  1. The Aerobic System
  2. The Anaerobic / Lactic Acid System
  3. The Creatine Phosphate System (ATP-CP)

What energy systems are you using while running?
What energy systems are you using while running? | Source

How does adenosine triphosphate create energy for running?

Adenosine triphosphate creates energy for the body while running through splitting. It is made up from three molecules of phosphate (hence the 'tri') held together tightly together by high-energy bonds. By breaking part of this bond a large amount of energy can be released to provide energy for muscular contractions and other body systems while running. The reaction removes one phosphate molecule to leave Adenosine diphosphate (ADP) and a separate phosphate molecule

Unfortunately the body does not have an unlimited supply of adenosine triphosphate. In fact only about 4 seconds worth of ATP is stored at any one point within the body and therefore resynthesis has to occur. The harder you run the more ATP is required and the more resynthesis has to occur.

The reaction of creating energy from ATP for running occurs in the mitochondria of muscle cells

The aerobic energy pathway for running

Aerobically the body can create energy for running through the use of glucose and fats in the presence of oxygen. This is known as aerobic glycolysis.

The aerobic energy system is primarily used in distance running. Typically running events such as the 10km to ultra-marathon events are run aerobically.

Creating aerobic energy for running using glucose

Aerobic glycolysis allows the body to produce 38 molecules of ATP for every molecule of oxygen through the use of glucose in the presence of oxygen. The downside of this is that glucose is taken from the body's glycogen stores. The body slowly moves away from solely creating energy using glycogen to using fat as well as this is more abundant in the body.

Creating aerobic energy for running using fat

After several minutes of exercise the body begins to use it's fat stores to create the energy required for running. In the presence of glucose and oxygen the body is able to create energy from our fat stores in the mitochondria of muscle cells

Sadly the body does not have an endless supply of glucose and our stores can deplete rapidly as shown by marathon runners hitting the wall as they can no longer effectively create the energy required to power their running muscles.

The below video clip shows the importance in maximising your glycogen stores prior to a marathon event or an ironman triathlon. You can also consider taking in additional carbohydrates on long distance runs to top up and maintain your glycogen stores.

Runners hitting the wall after glycogen store depletion

The anaerobic energy system for running

The anaerobic energy system (sometimes known as the Lactic Acid system) uses the body's glucose stores, however without the presence of oxygen.

At moderately high intensiies the body is unable to take in enough oxygen to maintain aerobic energy production and therefore has to switch to anaerobic energy production for running.

The anaerobic energy system creates energy for running while producing a waste product in the form of Lactic Acid which can lead to inhibited muscle contraction. Therefore the lactic acid pathway can only be maintained for short periods of time of up to 3 minutes.

The Anaerobic Energy system for running is primarily used in events such as the 400 and 800 meters.

The creatine phosphate energy system and running

Often known as the ATP-CR system, PCr System and the phosphocreatine energy system.


As our stores if ATP (adenosine triphosphate) can only last for a few seconds the body needs a back-up system which can resynthesize ATP from ADP almost immediately.

The creatine phosphate system creates energy for running without the presence of oxygen or glucose through the use of the phosphate molecules from creatine phosphate. The downside of this is that one molecule of ATP is produced from every one molecule of creatine phosphate.

In terms of running events the creatine phosphate energy system is used within the 100m sprint as we can only maintain this energy system for around 10 seconds

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