How concept//fuel calculates your intake
A transparent breakdown of the algorithm behind your fuelling plan.
We think you should understand exactly how your fuelling plan is generated. Here is the logic behind every number, with the research it is based on.
Carbohydrate targets by duration and effort
The algorithm uses a three-tier model based on the work of Jeukendrup, adapted for practical application:
- //Under 75 minutes: 30 to 45g per hour. Glycogen stores are unlikely to be fully depleted in most athletes at this duration. Carbohydrate is still beneficial at race effort, but the ceiling is lower and the gut tolerance window is wider.
- //75 to 150 minutes: 45 to 75g per hour. The range where fuelling makes a measurable difference to performance, and where multi-transporter sources (glucose and fructose combined) become important.
- //Over 150 minutes: 75 to 90g per hour for race efforts, 60 to 75g per hour for training. Ultra distances are calculated individually based on field data.
Effort level (easy, moderate, race, race simulation) modulates the target. Race efforts produce higher demand and a narrower absorption window because splanchnic blood flow reduction is greater at intensity.
Caffeine timing
The 60-minute pre-start recommendation is drawn from Graham (2001) and subsequent meta-analyses showing peak plasma caffeine concentration at 45 to 75 minutes post-ingestion. The dose range (3 to 6mg per kilogram of bodyweight) reflects the performance-relevant window in the research, with upper limits set conservatively for individual variation and sleep sensitivity.
Sodium bicarbonate
Bicarb targets (300mg per kilogram bodyweight, 60 to 90 minutes pre-start) follow the ISSN position stand on buffering agents. The algorithm flags this as race-specific because the GI risk profile is meaningful and the benefits are primarily relevant to sustained high-intensity efforts over 60 seconds in duration.
Hydration scaling
Sweat rate estimates use bodyweight as a proxy for individual variation. The algorithm applies standard population ranges from field studies. If you know your actual sweat rate from sweat testing, use that number directly and adjust fluid targets accordingly.
The numbers are grounded in evidence, but they are starting points. Real performance comes from applying them consistently in training, reading your body, and refining over time.
Graham (2001) Appl Physiol; Jeukendrup (2010) Nutrition Reviews; Spriet (2014) Sports Medicine; Antonio et al. ISSN Position Stand on Caffeine.
Put it into practice
Apply this to your own training.