How are body produces energy in accordance with our position in Rugby

Sports scientists classify team sports like rugby as ‘intermittent sprint sports’ because, in the course of a match, players will alternate between fast running or sprinting, walking, jogging and standing. Rugby matches are a bit like random interval workouts – except that they also involve non-running activities, such as rucking, mauling and scrums. These are game-specific tasks, during which groups of players push against the opposition; and, like fast running and sprinting, they are high-intensity activities.

When rugby players perform these high-intensity activities, their anaerobic systems provide the required energy, while the aerobic system predominates during the low-intensity activities.
If the high-intensity periods are short (less than 10 seconds) and recovery times between efforts are relatively long (60 seconds-plus), then the phosphocreatine (PCr) system will be the key source of anaerobic energy. This is the simplest and most rapid means of energy production, in which phosphate (donated by phosphocreatine) and ADP combine to make ATP – the body’s primary energy currency and supplier to all cells. During the low-intensity periods, the aerobic system will replenish PCr stores, ready for the next high-intensity effort.

However, PCR stores can provide energy for only about 10 seconds of activity. So, if the high intensity periods are of intermediate length (10-45 seconds) or the recovery times are relatively short (20-40 seconds), then the glycoltic system of anaerobic energy production, involving the breakdown of carbohydrate within muscle cells to release energy, comes into play. Similarly, short periods of high-intensity work, interspersed with recovery times that are too brief for complete replenishment of PCR stores, also bring the glycoltic system into play.

From the physiological point of view, there are two interesting questions about rugby:
1. What is the ratio of high-intensity to low-intensity activity?
2. Does the work/rest ratio vary with player position?

The answers to these questions should help you to understand the key physiological demands on each individual player.

This research data leads to the following conclusions about the key differences between forwards and backs:

• Forwards have to complete more high-intensity activity than backs, with shorter periods of low-intensity activity between them, which means the anaerobic glycoltic system is of prime importance for them.
• The type of high-intensity activity forwards perform tends to be ‘physical work’, e.g. pushing.
• Backs perform less high-intensity activity than forwards, with sufficient rest between efforts for the PCr system to predominate.
• Running and sprinting are the commonest high-intensity activities for backs.

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