Introduction

Anaerobic simply means without oxygen, it can therefore be assumed that it must be exercise of a fairly short duration. Up to 60 seconds would be considered to be anaerobic.
Most power sports are considered to be anaerobic, examples of which include short sprints, weight training, jumping, and throwing events such as those in athletic field events.
These exercises or sports can be performed without the body's energy providing systems requiring any oxygen.

Aerobic exercise on the other hand means with oxygen and is generally longer in duration, possibly even as long as several hours, e.g. a triathlete.
Aerobic exercise is generally less intense (lower in heart rate) and therefore oxygen can be supplied fast enough to the aerobic energy systems.

In practice most activities are unlikely to be purely aerobic or anaerobic, although one of the energy systems will be dominant.
It is important to note that it is not the exercise that determines whether it is anaerobic or aerobic but the energy system that provides the fuel.

Aerobic & Anaerobic Energy Systems

Q. So do we have different energy systems for different types of exercise?
No, but the presence of oxygen determines the amount of energy yielded and the by-product at the end of it. (see Fig 1 below)
During anaerobic activity, carbohydrate must be converted into energy very quickly in order to meet the requirements placed on it by the muscles to be used. Such demands occur when you lift, jump, sprint or throw - movements included in many sports.
In order to meet these sudden huge demands of energy glucose (from carbohydrates) bypasses the energy producing pathways that would normally use oxygen, and follows a different route that does not use oxygen.
Although this is a very fast method of energy production, it is not very efficient and only produces two molecules of ATP rather than the 38 produced when oxygen is present.
Think of it as a candle that provides heat and light. If that candle is in a room with no air the flame will only burn for a few seconds. If air is present in the room the candle will burn for much longer and provide heat and light for a greater period of time.

Fig.1 show the main difference between an Aerobic and an Anaerobic energy system.
Let us first take a look at the diagram of the Aerobic system on the left. The food that you have eaten is broken down and stored in the body as glycogen. Whether you ate a meal of fats, carbohydrates or proteins, the body energy systems use only glycogen.
Through the various processes of the digestive system, glycogen is produced (excess stores of energy will be discussed later).
As long as there is sufficient glycogen and oxygen the Aerobic system will continue to function with muscle fatigue likely to set in before fuel runs out.
The pyruvic acid or the ashes from the fire are carbon Dioxide and Water can be removed from the body.
Looking at the diagram for the Anaerobic system on the right, the only difference is the fact that there is an insufficient amount of oxygen at the final process to convert the waste to carbon dioxide and water. The system instead creates Lactic acid, which prevents the muscles from contracting rather than the system itself failing. If during exercise or even running for the bus you have felt that burning sensation in your calves or other muscles that is an accumulation of lactic acid and it will prevent you from performing any further exercise or movement. The lactic acid buildup in your muscles prevents any further muscle contraction and you will therefore have to stop what you were doing to allow recovery and the body to remove this lactic acid.

What is the difference?

Anaerobic simply means without oxygen, it can therefore be assumed that it must be exercise of a fairly short duration. Up to 60 seconds would be considered to be anaerobic.
Most power sports are considered to be anaerobic, as are most short distance sprints.
These exercises or sports can be performed without the body's energy providing systems requiring any oxygen.

Aerobic exercise on the other hand means with oxygen and is generally longer in duration, possibly even as long as several hours, eg a triathlete.Aerobic exercise is generally less intense (lower in heart rate) and therefore oxygen can be supplied fast enough to the aerobic energy systems.
In practice most activities are unlikely to be purely aerobic or anaerobic, although one of the energy systems will be dominant. It is important to note that it is not the exercise that determines whether it is anaerobic or aerobic but the energy system that provides the fuel.