Your Anaerobic energy system can be be thought of as your V6 engine. It is very powerful, but it doesn’t produce quite as much ATP, or as quickly, as your Immediate system does. It is however more sustainable. Through a process called ‘Glycolysis’, glycogen is broken down into glucose, which is then broken down by enzymes to produce ATP, Pyruvate and Hydrogen ions. The production of Hydrogen ions increases the acidity of your muscles, which will eventually cause an intense burning sensation.
As the Glycolysis occurs anaerobically, there isn’t oxygen available to break down the pyruvate to produce more ATP. This results in pyruvate binding with some of the hydrogen ions and converting them into a substance called lactate (this is not 'lactic acid'). This lactate acts then as a temporary buffering system to reduce the sensation of acidosis, allowing you to exercise at high intensity for longer.
Becoming a significant contribution after about 10 seconds of exercise, glycolysis is responsible for supplying the majority of your ATP for a maximum effort between approximately 30 and 60 seconds. After this time, it is your Aerobic system that becomes the primary energy producer.