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Carbohydrates for Training and Competition

What is a carbohydrate?

Carbohydrates are one of three macronutrients, and are the predominant fuel source for sub-maximal and high intensity endurance exercise. Carbohydrates are found in breads, cereals, rice and pasta as well as fruits, vegetables and dairy. Once consumed, carbohydrates are broken down in the body to their simplest form - glucose - which may either be used immediately as fuel or stored in the muscle and liver as glycogen.

 

How can carbohydrates help with performance?

Carbohydrates have been consistently shown to improve performance and reduce the effects of fatigue. Although the body has the ability to store glucose, this storage is limited and is enough to fuel only around 90-120 minutes of high intensity exercise. Once depleted, the body relies on exogenous (outside) sources of carbohydrates to fuel activity as endogenous (inside) sources become exhausted. Failure to do so can lead to hypoglycaemia which is thought to be a major contributor to the development of fatigue, and increased perception of effort.

 

What sort of carbohydrate should I be having and when?

This is entirely dependent on your training schedule and/or sport as well as your goals. However baseline recommendations for carbohydrates (for prolonged events) usually include:
1) Pre-exercise consumption (approximately 2 hours prior) of a high GI (glycaemic index) carbohydrate meal (which is low in fat, fibre and protein to avoid stomach issues),
2) A high GI, high carbohydrate “snack” within the hour prior to exercise in order to 'top up' glycogen stores and to help prevent a condition known as “Rebound Hypoglycaemia” (which is a rapid drop in blood sugar after the consumption of carbohydrates) from occurring,
3) The consumption of high GI carbohydrate during running (>90 minutes duration) with recent evidence suggesting an inclusion of 2:1 glucose and fructose may be useful in longer events, and finally
4) A carbohydrate (and protein rich) meal post exercise to help replenish glycogen stores and ensure optimal immune function.

 

What about carbohydrate loading?

Carbohydrate loading, contrary to popular belief, is not a bowl of pasta on the night prior to competition! Carbohydrate loading is the consumption of 10-12 g/kg body mass of carbohydrates per day for at least two days (which equates to around 700-840 g of carbohydrate per day in a 70kg athlete) and ensures optimum glycogen stores.

 

Aren’t whole grain carbohydrates better for me?

Although a refined, high GI carbohydrate would not be recommended for the general population as wholegrain carbohydrates have much better protective and health properties, a high GI/refined carbohydrate is the optimal fuel for athletes as they are more easily accessed than low GI/wholegrain carbohydrates (which may also cause stomach upset during exercise). In addition, given that some athletes require such high amounts of carbohydrate, the more fibre present in the diet will increase satiety (fullness), and may not allow for adequate consumption of carbohydrates. However, in saying this, it is still important that athletes consume adequate fibre in the diet (25-30 g/day).

 

Are supplements required?

Supplemental forms of carbohydrate may provide a more convenient way to ensure adequate consumption and are handy in events where you are required to carry your own food. They may also provide a palatable way that is easy on the stomach to consume carbohydrate during an event.

 

Rebekah Alcock
Accredited Practicing Dietitian
Recover Sports Medicine

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