Macro partitioning
Ingesting 10–12.5 g carbohydrate per kg body mass per day for 1–7 days prior to competition increases muscle glycogen to 170–180 mmol/kg wet mass and enhances endurance performance in events lasting 90 minutes or more.
If you are competing in an event longer than 90 minutes, start eating 10–12.5 grams of carbohydrates per kilogram of your body weight daily for 1–7 days before the race. You do not need to do extreme exercise during this time; light activity is fine. This maximizes your muscle glycogen stores, which is the primary fuel for long endurance efforts.
Increased dietary carbohydrate intake in the days before competition increases muscle glycogen levels and enhances exercise performance in endurance events lasting 90 min or more.
Why this rating
Supported by multiple classic studies (Bergstrom, Sherman, Coyle) and consistent findings across decades.
Source
Pre-exercise carbohydrate and fat ingestion: effects on metabolism and performance
Mark Hargreaves et al. · Journal of Sports Sciences · 2003
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