T Nation

The Anabolic Window - Fact or Fiction?

Hi Christian, Firstly thanks for your recent article on “the key to continuous growth” I’ve ready it about 5 times and it’s really insightful.

I’m after your executive view on the “Anabolic Window” - the idea that post training you have a period of time where your body is more willing to absorb nutrients.

  • Is it real?
  • How long does it last after training?
  • If it is real, what % of total calories should we be aiming to consume in this window?

Thanks for your help,


You could actually describe the “anabolic window” as two different things.

Traditionally the “anabolic window” is seen as the period immediately following a workout, where the uptake of nutrients by the muscle is increased (nutrients can more rapidly and easily get into the muscle). But in light of what we now know, we could actually include the workout period itself as part of this anabolic window, since the muscle contractions do enhance nutrients uptake by the working muscles.

The main reasons for this “window” are:

*Increase in GLUT4 translocation and expression. This occurs during muscle contractions and increases nutrients transport to the muscles. The GLUT4 stays “active” for some time at the conclusion of the workout.

*You use up muscle glycogen when training, “freeing-up” storing space in the trained muscle. This increases muscle insulin sensitivity which makes it easier to store ingested carbs inside the trained muscles.

There are studies showing that you replenish muscle glycogen faster when you consume carbs right after a workout than if you wait a few hours. That’s for the above reasons.

However, protein synthesis doesn’t spike and come down making protein ingesting within the first hour post-workout more effective.

Really, that first type of “anabolic window” really is an extrapolation of research done on muscle glycogen replenishment post-exercise. And yes, it is a part of the recovery process, but for us it is not a make or break thing because we will not use up as much muscle glycogen as an endurance athlete and even if we miss the “anabolic window”, if you consume sufficient carbs throughout the day we will still be able to replenish muscle glycogen.

That brings us to the second possible “anabolic window”: the elevation of protein synthesis following a workout. As I mentioned in a few articles, protein synthesis in a trained muscle stays elevated above baseline for up to 36 hours. But the period of highest elevation is from post-workout to 24h after the session concluded. From 24h to 36h post-workout it gradually comes down.

In that regard, as long as you have a sufficient protein intake during those 24-36h you wil not have an issue. And having more frequent meals of 25-35g of protein seems to be better than less frequent meals with more protein.

That having been said, consuming protein around the workout could still have benefits by helping increase mTOR activation, which in turn will increase protein synthesis. If your protein is high in leucine it’s even better.

The “anabolic window” does exist, but it relates mostly to glycogen replenishment. To build muscle, it’s more about protein intake over the 24h post-workout period. Having a rapidly absorbed protein (ideally rich in leucine) around the workout can be beneficial though, not by avoiding missing the magical anabolic window but rather by increasing protein synthesis.