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Friday, 11th December 2015 | By Bobby Garlington

Glucose the bodies favoured fuel source:

During exercise our bodies use a mixture of carbohydrates and fats for energy. When carbohydrates are consumed they are stored as glycogen (the storage form of glucose) in the muscles and liver. During exercise these glycogen stores are then converted to glucose which is used to provide energy. Glucose is the bodies preferred energy source especially when performing at a high intensity. This is because it is a more efficient energy source as it can be converted to energy quicker than fat. It is not only required by the working muscles but also by the brain and central nervous system.

The benefit of Carbo Loading

When fuel supplies are inadequate this will hinder performance and will result in fatigue occurring earlier. It is therefore beneficial to build up fuel supplies leading up to a race. This is done by increasing carbohydrate intake a few days before a race, as carbohydrates provide a large amount of the energy for endurance exercise. This is known as “carbo loading” and it helps build up glycogen stores within the body so that you have a greater supply of energy. The body is able to store enough glycogen to fuel 90-120mins of moderate intensity exercise (40-50% of VO2 Max), carbo loading will ensure these energy stores are maximised and this will delay the onset of fatigue. A study in 2005 found that carbohydrate loading improved cycling power output and time trial performance (Rauch et al, 2005).

Carbo Loading Strategies

Classic Approach:

The original carbo loading strategy was developed in the 1960’s and contained a 3-4 day depletion phase followed by a 3-4 day loading phase. The depletion phase aimed to deplete glycogen stores through combining hard training with a low carb diet. The loading phase consists of tapering training (gradually reducing volume of training) and consuming a high carbohydrate diet with the intention of increasing glycogen stores.
               The theory behind this classic approach is that the depletion of glycogen stores would cause the body to adapt and store more carbohydrate as glycogen rather than fat when carbohydrates are re-introduced into the diet. Whilst this depletion phase is still used by some athletes it is becoming increasingly less common. This is because it is extremely taxing both mentally and physically and therefore isn’t suitable when competing on a regular basis. 

Modern Approach:

A more modern approach to carbo loading doesn’t involve a depletion phase as it has been found that it isn’t necessary. This is beneficial for athletes as it removes the physiological stress caused by training hard on a low carbohydrate diet. This modern strategy involves increasing carbohydrate intake 3-4 days prior to a race whilst gradually tapering training. It is important that protein and fat intake are also maintained as these are also required to fuel performance and aid recovery.

Sample Diet

70kg athlete aiming to carbohydrate load

This sample plan provides ~ 3,500 kcal, 630 g carbohydrate, 125 g protein and 60 g fat


3 cups of low-fibre breakfast cereal with 1½ cups of semi-skimmed milk

1 medium banana,

250ml orange juice


3 scones with honey

500ml sports drink



2 sandwiches (4 slices of bread) with filling as desired

200g serving of low-fat fruit yoghurt

375ml can of soft drink


banana smoothie made with low-fat milk,

banana and honey,

cereal bar


1 cup of pasta sauce with 2 cups of cooked pasta

3 slices of garlic bread

2 glasses of cordial


3 scones and jam

500ml sports drink


Enjoyed this article? Head over to our nutrition guides for more nutrition and exercise related articles.


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