PHYS-05 · Principle

Do I have to eat straight after training?

Only when the next hard session is within hours. Storage is fastest right after exercise, but with enough carbohydrate over the day the muscle refills within about a day either way.

How the body works, agreed across the reviews below; a study entry shows what one experiment measured.

established physiologyApplies to everyoneEstablished — a faster early rate (two reviews of small biopsy studies); well supported — refilling within about a day with enough carbohydrate (one review's figure for extreme depletion, REF-1336; single studies…

Practical Application

Do I have to eat straight after training? Only when the next hard session is within hours. Storage is fastest right after exercise, but with enough carbohydrate over the day the muscle refills within about a day either way.
What it means for training: with a short gap (under about 8 h in REF-1336), carbohydrate soon after at the consensus dose (REF-748); with a day or more, the day's total decides (SYNTH-69, SYNTH-85).
What it does not mean: that missing a 30-min "window" spoils the refill: eating early starts the refill; there is no brief gate (REF-1336); 7.7 vs 2.5 μmol/g/h in 12 cyclists is REF-056's number, not a law.

Mechanism

A rapid phase of 30-60 min needs no insulin, a slower one runs for hours, and low glycogen itself drives storage (REF-1337); synthesis stays low until carbohydrate arrives (REF-1336, REF-056).
From 4 to 24 h the total decides more than type or pattern; the reviewers' 20-24 h to normal stores is for extreme depletion (REF-1336); one high-carbohydrate rest day filled trained muscle (REF-891); alcohol in place of part of the carbohydrate cut 24-h storage, alcohol on top of it did not (REF-1013).
Storage plateaus past an adequate intake (REF-1336); protein adds only when carbohydrate is short (REF-1337, REF-151); after soccer matches glycogen was still low at 24 h (REF-1336).

Common misreading

"The window decides everything", "no shake within 30 min means a wasted session".

Backs

SYNTH-23 "fuel stores are assumed to refill faster than that (not from a study)" · SYNTH-69 "Timing matters when the next hard session is close" · SYNTH-85 "Name the gap first"

Sources

Burke, van Loon & Hawley 2017 REF-1336 (B+) · Paper ↗
Jentjens & Jeukendrup 2003 REF-1337 (B+) · Paper ↗
UCI position statement 2026 REF-748 · Paper ↗