Glossary

Glycogen Loading

Updated April 3, 2026

Glycogen loading is a short-term high-carbohydrate strategy used before long endurance events to raise stored carbohydrate in muscle before the start. It matters when your event is long enough that late-stage pace, power, or decision-making starts to fall as fuel runs down. Endurance Athlete Fueling covers the full race-fuel picture. This page focuses on the part that happens before the gun goes off.

What changes during a loading phase

Muscle glycogen is stored carbohydrate. Loading works by combining reduced training stress with a very high carbohydrate intake for a short window before competition. Bergstrom and Hultman showed in 1967 that exhaustive exercise followed by a carbohydrate-rich diet could push muscle glycogen above baseline.¹ That supercompensation effect still defines modern loading practice.

The numbers are clearer now. A 2025 systematic review and meta-analysis pooled 30 studies with 319 participants and found that 3 to 5 days of high-carbohydrate eating increased muscle glycogen by 269.7 mmol/kg dry weight after cycling protocols and 156.5 mmol/kg dry weight after running protocols.² The size of the increase depended partly on how depleted the athlete was beforehand and how carbohydrate-dense the diet became. In the cycling studies, mean glycogen content after loading reached about 700 mmol/kg dry weight, and six studies exceeded 800 mmol/kg dry weight.²

Water moves with glycogen storage, so body weight often rises during a loading block. That shift usually reflects stored fuel and water, not fat gain. If scale noise creates confusion, read the number beside hydration, sodium intake, and the demands of the event week.

When glycogen loading is worth doing

Loading earns its keep in events that last longer than about 90 minutes or in sports with prolonged high-intensity intermittent work. The 2016 Academy of Nutrition and Dietetics, Dietitians of Canada, and American College of Sports Medicine position statement placed carbohydrate loading at 10 to 12 g/kg/day for the final 36 to 48 hours before events lasting more than 90 minutes.³ The GSSI review by Podlogar and Wallis carried that same practical target forward and noted that aggressive loading is usually unnecessary for events shorter than 90 minutes.⁴

Podlogar and Wallis note that performance benefits are less consistent in shorter events around half-marathon duration than in longer events where glycogen depletion is more likely to become performance-limiting.⁴ That matters because many athletes load for any race that feels important. Duration and glycogen cost decide whether the strategy is useful.

Practical protocol

The modern approach is simpler than the old depletion-first model. Training volume comes down as the race approaches. Carbohydrate rises sharply for the final 36 to 48 hours. Protein stays steady. Fat and fiber often come down a bit because they make it harder to reach the carbohydrate target comfortably.

Food choice matters because gastrointestinal comfort matters. A loading phase built from very high-fiber meals, large salads, and slow-digesting foods can leave the athlete full without actually clearing the carbohydrate target. Lower-fiber staples such as rice, potatoes, oats, bread, cereal, pancakes, fruit, juice, sports drink, and familiar snack foods usually work better. Carbohydrate sources and pre-workout nutrition matter here because the loading window and the pre-race meal need to fit together.

The final meal before the event still matters. The same sports-nutrition guidance recommends about 1 to 4 g/kg of carbohydrate in the final 1 to 4 hours before exercise.³⁴ Loading fills the tank. The pre-event meal tops off liver glycogen after the overnight fast.

Common mistakes

Using loading to fix chronic under-fueling usually fails. A two-day carbohydrate push cannot repair weeks of low energy availability or poor post-workout nutrition. The strategy works best when the athlete already has a stable daily fueling pattern and is only trying to maximize short-term storage before a demanding event.

Scale gain also gets misread very easily. Glycogen pulls water into storage, so body mass often rises during the loading block. That extra mass is part of the fuel package when the event is long enough for stored carbohydrate to matter.

Food choice can also ruin the plan. Race week is a bad time to test giant pasta dinners, heavy restaurant meals, or large fructose loads that your gut has never rehearsed. Gut Training for Race Nutrition matters because the athlete still has to absorb pre-race and in-race carbohydrate under stress.

Glycogen loading is most useful when the event is long, the taper is real, and the carbohydrate target is high enough to change stored fuel. If you need the next layer after this page, keep glycogen, pre-workout nutrition, and carb cycling together because they shape how much carbohydrate you store, when you deploy it, and how well the next hard effort holds up.