How glycogen works

Learn · Energy systems · Explainer, Typed Supps

The carb store in your muscles and liver. It runs down, then refills.

Stage by stage

Intake (Carbohydrate to glucose): Carbohydrate is digested to glucose and absorbed into the blood.
Storage signal (Insulin drives it in): Insulin activates the enzyme that links glucose into branched glycogen chains, stored with about 3g of water per gram.
Two separate stores (Muscle vs liver): Muscle glycogen fuels only that muscle. Liver glycogen is the shared store that holds blood sugar steady between meals.
Depletion & refill (~5% per hour): Hard effort empties it; refilling takes around a day of adequate carbohydrate.

What the evidence supports

Carbohydrate availability limits high-intensity endurance performance — strong evidence. One of the most reproducible findings in sports science, going back to muscle biopsy studies in the 1960s.
Post-exercise carbohydrate speeds glycogen resynthesis — strong evidence. Well established, and dose-dependent.
A narrow post-workout "window" is critical for refuelling — limited evidence. It matters when you train again within about eight hours. For everyone else, total daily intake is what counts.
Low-carbohydrate diets improve endurance performance — insufficient evidence. Fat oxidation adapts upward, but high-intensity performance consistently suffers, because the fast anaerobic pathway needs glycogen.

Timing

Refuelling matters most when you are training hard again within 24 hours. If you train once a day or less, total daily carbohydrate matters far more than timing it around the session.

Time to effect

90 min: Roughly how long a full store lasts at hard effort.
20–24 hrs: Full resynthesis with adequate carbohydrate.

Common myth

“I lost 3kg in my first week of low carb.” In reality: Most of that is glycogen and the water stored alongside it — roughly 3g of water per gram of glycogen. It returns as soon as carbohydrate does.