The body's ability to produce energy comes down to three things:

  1. Energy system development (anaerobic and aerobic capacity)

  2. Muscular size and fibre type (bigger and stronger muscles need more energy and can also produce more energy)

  3. Nutrition (how your body is fuelled will dictate energy production)

Over the next few weeks, we are going to focus on energy systems.  Why is this important?  If you're an athlete or a highly active individual (training 3+ times per week) you can learn how to increase your performance by understanding how energy is produced in the body and therefore structuring your training and nutrition to improve energy metabolism.

The three energy systems (anaerobic alactic, anaerobic lactic, and the aerobic)  work together to sustain life and meet the energy demands of physical performance. Each sport/activity challenges energy production in different ways based on the power output (sympathetic driven) and the work to rest ratio. Every adaptation in the body is about meeting the demands of the environment while maintaining homeostasis (body temperature, fluid balance, blood sugar, oxygen saturation, blood pH, minerals levels, hormones and enzymes).  The human body priorities survival over both health and performance and hence energy management has a huge role to play in many different aspects of life and longevity.

The energy requirements of each sport/environment can be broken down into the following components:

  1. The rate of energy production - how rapidly energy is generated during the period of work (high power = high rate). Sports that require maximum power output over a short duration of time (Olympic weightlifting, powerlifting, sprinting, etc…) depend on the alactic energy system.

  2. Duration of energy production - how long the levels of energy production must be maintained. Sports that require sustainable power over long durations (triathlons, cycling, marathons, etc..) depend heavily on the aerobic energy system

  3. Work to rest ratio  - The time ratio between the length of work and the rest period.  Higher peak power and longer rest= greater anaerobic contribution.   Shorter rest periods and/or longer work periods = higher levels of aerobic contribution

Every cell in the body needs energy, not just during physical activity.  The brain requires significant levels of energy to function correctly (400-700cal per day).  Energy comes for the nutrients that you eat and it's important to make sure your body has the fuel it needs to survive and perform.  The body is designed to adaptable to the different environment and utilise different sources of energy including carbohydrates, fats and protein.

The body takes the foods you eat and turns them into the fuel source that cells, tissues, and muscle can use.  The nutrient density and volume of the food you eat has a critical role in your ability to produce energy to survive and perform both physically and mentally.

The currency of energy in the body is known as Adenosine Triphosphate (ATP).  The body can produce ATP in two different ways; with or without oxygen - i.e aerobically and anaerobically. Each energy system pathway is capable of producing ATP from different substrates, at different rates, and for different time duration. There is always an inherent tradeoff between the rate of ATP production and the duration a given power output can be sustained.

Trying to determine exact energy system contributions across different sports in a waste of time and can be misleading.  There is no exact way to quantify energy system percentages and each athlete is an individual with different movement quality, strengths, genetics, and abilities to deal with stress.  A simple rule of thumb would be:

  1. If the work period is less than 60seconds it largely anaerobic

  2. If the work period is greater than 60seconds is largely aerobic

  3. If the work is intermittent then it’s aerobic-alactic 

The intensity of the work period must also be taken into consideration as 60sec of twiddling your thumbs is demanding high levels of energy production. 


We can think of the energy systems as three separate engines in a car. The aerobic energy system is like a small engine that can produce low levels of power and be very fuel efficient.  When you put your foot down and the demand for power increase the aerobic engine can not produce enough power by itself, so it calls on the anaerobic lactic system to start burning fuel and producing more power.   If you continue to push your foot to the floor, both the aerobic and lactic system will not be able to produce maximum power and hence the alactic energy system will kick in to help increase power production.   At top speed, the alactic system can only last for 8-10second before it shuts down and the car starts to lose power.  The lactic system will continue to assist for 30-90seconds and then it will also run out of steam and the car will lose more power.  Finally, it's up to the aerobic system to keep the car moving.   

If you pull the car over to the side of the road and give it a chance to recover the aerobic energy system will help to recharge the lactic and alactic energy system.  The time taken to recharge them will depend on the power of the aerobic system and the quality of the fuel in the car (i.e nutrition).

In our next blog post, we will talk a little more about the most powerful engine, the alactic phosphocreatine energy system.