When do I need to fuel?

This naturally depends on a number of factors: How long you will be exercising, how intense the effort is, what you have eaten beforehand and what your goal is for the training session or competition. Your fuel needs will vary depending on whether you are trying to win the Triathlon World Championships in Kona or doing a recovery session at chat pace with your best mate. 

 

When our glycogen stores are full and we perform physical activity at high intensity, our stores will last for approximately 2h. After this, muscle glycogen levels are so low that muscle efficiency drops drastically due to inhibited calcium handling in the muscle cells. That is why you should start consuming fuel early in the race or competition if you know you will be exercising for a longer period at moderate to high intensity. 

 

During high-intensity sessions, regular intake is recommended to consume approximately 90g of carbohydrates per hour. Intake may vary depending on how well your gut tolerates it and how much you have trained your gut to take in fuel. Some people can manage 60-70g/h, while others can consume 120-140g/h. However, these higher-end intakes mainly apply to competition and very high-intensity activity, and only when you know your gut can handle the intake.

 

 

In that case, you can instead aim for a lower fuel intake. One example is to consume just 30g of carbohydrates per hour. At low intensity, this is enough to keep going for 2-4h without being too worn out when the session is over, depending on how you fuelled with dinner the night before and breakfast.

 

Some people also choose to start on an empty stomach and then begin consuming carbohydrates after 90-120min. The aim is to improve fat adaptation, based on the training concept train low, compete high. However, bear in mind that if you go too low on carbohydrates during the session, you will become more fatigued, which may affect upcoming training, so plan when these sessions should be carried out.  

 

When training for under 60min, there is usually no reason to fuel at all. It is more important to have eaten properly before the session and to have full glycogen stores.

 
The table below provides useful guidance. One serving is 1 scoop of sports drink, one bar or one gel.

Recommended fueling plan by duration
< 30min	None, or a sports drink mouth rinse
30-60min at moderate to high intensity	1 serving/h (~30g of carbohydrates/h)
1-2h at moderate to high intensity	2 servings/h (~60g of carbohydrates/h)
2-4h at low intensity	2 servings/h (~60g of carbohydrates/h)
>2h during competition or high-intensity exercise	3 servings/h (~90g/h)