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Interaction of the energy systems

The energy system used depends upon a number of factors including the type of activity or sport, its duration and intensity, the standard or level of the sport and individual factors such as fitness levels. The energy systems rarely work alone; at any one time, two or more systems may be interacting, for example during the 1500m the lactic acid system may be used for the first 90 seconds of the race until the aerobic system comes into play, and during the 400m the ATP-PC system may be used for the first 10-12 seconds of the race until the lactic acid system kicks in.

To see how the systems interact see the graph below:

The interaction of energy systems over time.[D]