The body has two main energy systems (aerobic and anaerobic energy system). Energy is needed for maintenance, growth, everyday activities and exercise. The amount of energy required during exercise by the body depends on the intensity and duration of exercise.
Put simply exercising harder for longer periods requires more energy.
The aerobic energy system is usually the first to be used, when you’re active the demand for energy increases, as does the demand for more oxygen by the muscles. This extra demand for oxygen is met by an increase in the rate and depth of breathing and an increase in blood supply due to increased heart rate.
When the oxygen required by the body cannot be met, the body will switch to a different energy system (the anaerobic energy system), which produces energy without the use of oxygen.
Muscle fatigue (tiredness) happens when you’ve burned all the energy sources you have (ATP-PC, glycogen and blood glucose) and you have a build up of lactic acid. In short if you have no energy ( If you haven’t eaten the right types of food) you’ll not be able to be active for very long.
Sorry its getting a bit technical, but for those of you who are interested there is a description of the two energy systems below!
Aerobic energy system Energy taken during the breakdown of food manufactures Adenosine triphosphate (ATP). The energy required for exercise can be obtained by burning food stores with oxygen (obtained by breathing). This aerobic system works by the breakdown of carbohydrate, fatty acids and some amino acids. This system uses slow twitch fibres and as it requires oxygen it can run for longer.
Anaerobic energy system This system relies on the release of energy from food stores in the body without the use of oxygen. This type of energy system is used in short bursts of intensive activity and results in the accumulation of a waste product called lactic acid, which results in muscle fatigue.
There are two types of anaerobic systems: (1)The ATP-PC system (Alactic) (2)The anaerobic gycolysis (Lactic) from degradation of glucose/glycogen.
The ATP-PC system is found in both muscle fibre types, it doesn’t require oxygen and doesn’t produce oxygen. It is used for dynamic quick actions e.g. a tennis serve. The anaerobic glycolysis (Lactic) system doesn't require oxygen but does produce lactic acid and is normally used for activities that last between 10 seconds and a minute.
