You know carbs are the endurance athlete’s best nutrition friend, but do you fully understand why?

Firstly carbohydrate is more oxygen-efficient than fat. Oxygen is needed to fuel aerobic activity (and to a limited and finite extend longer anaerobic activity). In doing so it releases more ATP (adenosine triphosphate) per oxygen molecule – ATP is the body’s universal energy donor and fires muscle contractions.

Fat, although it can fuel endurance activity, releases less ATP per oxygen molecule. Also carbs can be broken down by glycolysis to provide extra ATP energy. This is important for all running distances up to ultras, as 10kms and half marathons, for example, are usually run at anaerobic threshold; and it’s stored carbs (in the form of muscle glycogen and more limited liver glycogen that supplies the additional fuel (albeit in a limited capacity).

At 70% of VO2max glycogen provides 75% of energy needs, for example. We possess about 90-180 minutes of glycogen capacity (depending for example on our trained-state and the amount of pre-stored glycogen and racing/exercising pace).

Carb loading (coupled with the right training) can extend endurance performance by 20%. Consuming 2.5 grams of carbs/kg of bodyweight 3 hours before exercise will optimally stock your carb cupboard.

On the go drinking and eating extends your endurance capacity. Carbs are generally oxidised at a rate of around 1g/min which would supply 250 extra calories over an hour. However, not all carbs are created equally and it seems that glucose and fructose, will do the best job at pushing your endurance frontier.

It’s recommended you have 60-80g of carbs per hour from a 2:1 glucose to fructose source. This ratio will spare your precious glycogen stores.

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