The energy systems

The body can produce energy for movement using 3 energy systems:

  1. The primary (ATP-CP) system
  2. The secondary (anaerobic) system
  3. The tertiary (aerobic) system

A detailed physiological explanation of these systems is not needed but the systems are important to consider when investigating the demands of the game. Some sports are very dependent on one system, but the stop and start nature and alternating intensity of rugby means that all three systems are often used during a game.

To simplify, we will use rugby-based examples of when each energy system might be dominant:

  • When a winger goes sprints a maximal level following an interception, they are mainly using the primary system because they require energy at a very high rate to maintain the sprint. The primary system can produce energy very quickly but not for a long duration (only about 10 seconds). This is why players cannot sprint at maximum speed for long periods.
  • Players forming a maul is a good example of when the secondary energy system is used as the players are pushing as hard as they can for a prolonged period (20-40 seconds). This system supports the high intensity efforts that last longer than the 10 second duration of the primary system. The secondary energy system can still supply energy quickly but importantly can supply over a longer duration than the primary system.
  • During low intensity efforts like jogging, the tertiary system dominates as it cannot produce energy very quickly but it can produce a lot of energy for a long duration. During low intensity efforts (where players have time to produce energy more slowly) this energy system is dominant. As much of the time on the pitch during a rugby game is spent at these lower intensities it is an important energy providing system.

While the game of rugby challenges all the energy systems it can be concluded that the high intensity efforts are often what determine the outcome of the game and are therefore the most important. This could mean the primary and secondary systems are the most important to develop, however, a well-developed tertiary energy system increases the speed of recovery from the high-intensity bouts. Consequently, it remains important to develop this system.

A basic understanding of the energy systems gives us the knowledge of what energy system we are trying to improve through our training and gives the training specificity.