The body utilizes three systems to provide this energy. The type of activity defines which of the systems will be used. The immediate energy source is from the one enzyme system. It provides energy for the first the first five seconds up to twenty seconds. The glycolytic pathway provides energy from five to twenty seconds up to two minutes.
Energy comes from the anaerobic breakdown of glucose.
This is a more complicated form of energy production involving multiple steps and enzymes. The third energy source is from oxidative metabolism. It starts approximately two minutes after the start of the physical exercise. It is the most complicated energy system. It can use various substrates and is the most efficient system.