What is the anabolic window (post-workout eating time)?

In one line

The anabolic window is the idea that you must eat within a short time right after exercise for your muscles to grow best.

What is the anabolic window (post-workout eating time)?
Why are you told to eat right after training?
At the gym you often hear that you should grab a protein shake the moment your workout ends. The phrase that comes with it is "the anabolic window." What is this window, and how wide is it really?
In short
A short time after exercise when eating supposedly builds the most muscle
The anabolic window is the idea that you must eat nutrients within a short time right after exercise to get the most out of your workout. Once that time passes, the chance is thought to shrink, like a window closing. The "post-workout eating time" in the title is simply a plain-language version of the term.
What "anabolic" means
The side that builds big things from small pieces
When the body joins small pieces together to build a larger substance, it is called "synthesis," and this building side of the body's work is called "anabolic." The opposite, cutting a large substance into small pieces, is called "breakdown." So the anabolic window means "the window for building."
Muscle is always being built and broken down
Muscle grows when building beats breakdown
The protein in muscle is made of small pieces called amino acids, linked like a chain. Even at rest, muscle protein is constantly being built and broken down at the same time. Muscle protein increases when building is greater than breakdown.
Right after exercise
Building rises, but without food breakdown rises too
Weight training sharply raises muscle protein synthesis. But if you have not eaten anything, breakdown rises as well, so breakdown still outweighs building after the workout. Eating protein after exercise pushes synthesis higher, so building overtakes breakdown.
Where the window idea came from
Eating right away refilled glycogen faster
Muscle stores carbohydrate as "glycogen" and uses it during exercise. In an experiment where people ate carbohydrate after a long bike workout, eating right after exercise refilled muscle glycogen almost twice as fast as eating 2 hours later. Results like this became the basis for the idea that right after exercise is the chance.
The real size of the window
Muscle protein synthesis was still high the next day
After heavy weight training, the rise in muscle protein synthesis did not end within minutes. It was still above normal the next day, a full day later. So the rise in muscle protein synthesis from exercise lasted not just briefly but into the next day.
The pre-workout meal carries over
Food eaten before exercise is still being used afterward
The anabolic window idea mostly assumes you train on an empty stomach. If you ate a meal 1 to 2 hours before training, that food keeps being digested and entering the blood until after the workout ends. So the pre-workout meal also works as a post-workout meal.
When hurrying matters
When you train again a few hours later
Eating quickly after exercise matters at specific times. The International Society of Sports Nutrition names one: when there are less than 4 hours before the next session and glycogen must be refilled fast. Training the same muscles twice in one day is close to this case.
Common myth
If you can't eat right after training, is the workout wasted?
No. When studies comparing protein eaten within an hour before or after training were pooled, and total daily protein was taken into account, there was no difference in muscle or strength. What best explained muscle gain was not when people ate but how much protein they ate per day.
Summary
The building window is wider than you think
The anabolic window is the idea that you must eat within a short time right after exercise for your muscles to grow best. In reality, muscle protein synthesis stayed high for a day, and muscle gain followed total daily protein more than timing. Related terms: muscle protein synthesis, glycogen, protein.