Energy & Work Capacity 3: The Systems

Whilst there is a significant amount of research on bioenergetics and the different energy systems of the body it is easy to get confused amongst all the information. A good way to understand the energy systems is to use different sporting activities and understand where energy is being derived from. It is important to note that as humans we are capable of deriving energy for work both aerobically (with oxygen) and anaerobically (without oxygen).

The anaerobic system is capable of producing energy rapidly, resulting in large but brief power outputs. However, this system is limited in the total amount of energy it can produce as a result of a depletion of phosphocreatine (key substrate) and the build up of lactate due to lack of oxygen for removal.

The aerobic system is quite the opposite, with an ability to produce large amount of energy. Unfortunately for the human race we are unable to produce energy through this system rapidly due to a limitation in the body's ability to break down carbohydrates and fats with the help of oxygen.

But do not get confused as to thinking energy systems are black and white, it is not so simple. Obviously, we know that we can't exercise maximally for very long, but there are a lot of different intensities between sprinting a 50m dash and jogging a marathon. The energy systems of our body work on a continuum so that when we can't maintain maximal output we will gradually slow down rather than automatically stop. An example of this is a 400m run whereby most people will be unable to attain and maintain maximum speed so we see a decline in performance before the end of the race.

Below are a couple of diagrams to help understand the energy continuum and its relevance to different sports:

Hopefully what is clear is that in power/strength sports which rely on short periods of maximum intensity the supply of energy will be anaerobic with ATP and PCr as the main sources. On the other end of the spectrum we have sports of a significantly lower intensity that require efficiency of our aerobic energy system to break down lipids (fats) and carbohydrates into ATP as fuel for energy.

HOWEVER, most sports sit somewhere in the middle, and this is one of the most basic start points when designing any sort of training program - identify the energy systems used in your sport.

Take boxing for example, in a professional bout lasting 10rounds of 3 minutes there is 100% going to be an aerobic element in place as it wouldn't be physically possible to exercise for 30 minutes anaerobically (without sufficient oxygen). But it VERY IMPORTANT to note that boxing is very much an explosive sport, with punchers relying on the transfer of power through the body to land knockout punches. Below is a breakdown of a fight to help understand when different systems are being used:

KO PUNCHES = ATP/PCr to provide maximal force rapidly.

LONGER COMBOS = ATP/PCr and Lactic Acid systems to sustain high intensity for longer period

DEFENSE & BETWEEN ROUNDS = Aerobic to repay any oxygen debt and restore other systems

As athlete's and coaches it is important to understand the needs of your sport, identify the time spent working a different percentages of maximum intensity and what the most important factors in winning are. For the purpose of organising training and classifying the demands of work, it is important to understand some terms:

1. Aerobic Capacity - Maximum amount of oxygen the body can consume in a minute

2. Aerobic Power - Percentage of the aerobic capacity that can be used

3. Anaerobic Capacity - Maximum amount of lactate a person can produce

4. Anaerobic Power - Percentage of anaerobic capacity that can be used

Energy systems are very much INTENSITY dependent, over time it has become a misconception that energy systems function as a set of timed switches that sequentially turn on as duration increases. But, this isn't true, as all three energy systems are turned 'on' at the beginning of exercise. Instead the contribution of each energy system will vary with the intensity of effort and duration of time the intensity is required to be maintained.

When training for sports performance you should ideally focus on the interaction between energy systems than any single component, for example in rugby there is no point having high anaerobic power if you have a shitty anaerobic capacity and are unable to recover between high intensity bursts. Those who want to win, need to understand themselves, their capabilities and the necessities of the competition they are involved in.