Rugby is a sport which requires a variety of actions. As players, you need to be able to sprint 10m, make repeat tackles, and get yourself around the pitch efficiently. It’s no surprise then, that there are a few different types of fitness at play to help us do all these things.

We have THREE Energy Systems

1) Anaerobic ATP-PC

2) Anaerobic Glycolysis

3) Aerobic

All of these are systems which help the body produce energy in the form of adenosine triphosphate (ATP) via the breakdown of different fuel sources. It is the differences in speed of ATP utilisation and the variety of fuel sources which helps us design conditioning sessions for rugby.

Anaerobic ATP-PC - Our BURST system

During very fast and short-term activities, such as that 10m dash, we utilse the ATP that’s immediately available - the ATP which is stored in the muscles. Once the muscle ATP is depleted, another compound comes into play; Phosphocreatine (PC) which is also stored in the muscle helps to resynthesise ATP.

There is a finite capacity for this supply of ATP before another energy system takes over, the Glycolytic System.

Glycolytic System - Our BOOST system

This is the system which takes over from the Burst system if we are forced to work beyond the capacity that stored muscular ATP and CP can provide for; activities lasting between 10-40s. Now we’re talking about activities like back-to-back tackles - explosive work but longer duration.

This energy system works by the breakdown of glycogen which is stored in muscle cells and the liver. Glycogen is created through the breakdown of carbohydrates (one very good reason we need to eat carbs!).

Lactic acid is produced as a by-product and accumulates in the muscles causing them to feel that burning sensation. This is the thing which ultimately becomes the reason we can’t continue the activity any longer.

Aerobic - Our BREEZE system

This is the energy system which helps us work at low-moderate speeds for long durations. This system relies predominantly on oxygen to create ATP for activity by breaking down fats and glycogen. Unsurprisingly our breathing rate increases with this type of work in order for oxygen to be transported to the muscle cells and keep replenishing ATP.

The reason we can work for long durations at this pace is because our energy supply can be replenished at a quick enough rate. The low level aerobic work uses fat predominantly as it’s fuel source whereas glycogen (carbohydrates) is used for activities of moderate intensities.

*Table1: Timing and % of energy usage across the three energy systems*

All these energy systems are interchangeable and some might be working at the same time. The lactic system and the aerobic system often join up to give us a hybrid energy system which helps us sustain longer periods of lactic acid build up - aka our anaerobic threshold or tolerance to being in a lactic state.

How to train each system

For training session design, work:rest ratios are used to determine which energy system is being targeted optimally. Generally speaking, the more intense the activity, the longer rest we require.

These ratios are set out as follows:

ATP-PC - 1:12 - 1:20

Work time = 5-10s

Glycolytic - 1:3 - 1:5

Work time = 10s-30

Glycolytic/Aerobic Hybrid - 1:2 - 1:4

Work time = 30s-90s

Aerobic - 1:1 - 2:1

Work time = >2 mins

Based on the time of year and your goals, it's important to decide which energy system you want to work on in a given block/session. There might be a mixture of systems at play at one go, but the target system needs to be highlighted.

Here’s an example of how we train our BOOST system for rugby.

Energy systems - a guide to conditioning for rugby