New Findings on the ‘Anabolic Window’

As many of you are aware, there is a prevailing notion among fitness enthusiasts that a narrow window of opportunity exists following a training session where protein must be consumed to stimulate muscle growth.

Many people are in agreement that this window of opportunity only lasts 45 minutes, and that the absence of protein consumption within this time period will impair muscle growth.

It should go without saying that such an extreme notion would be highly unlikely to be true.

Thankfully, a well designed study by Schoenfeld and colleagues was recently carried out to determine the possibility of this ‘anabolic window of opportunity’.

Specifically, the researchers wanted to determine if immediate consumption of protein post-workout would have a superior effect on strength and muscle growth over a long time period.

Here’s what went down.

 

STUDY DESIGN

  • A group of resistance trained young men were split into two groups: PRE-SUPP and POST-SUPP.
  • Both groups carried out a supervised resistance training regimen, consisting of a full body workout performed 3 days per week for a duration of 10 weeks.
  • The PRE-SUPP group consumed 25 g of whey protein immediately prior to resistance training, however they refrained from eating anything for at least 3 hours after the training bout.
  • The POST-SUPP group did not eat anything for at least 3 hours prior to training, however they consumed a matched amount of protein immediately following the workout.
  • All subjects were instructed to maintain a calorie surplus of 500 kcal, however contrary to this instruction, most of the subjects reduced their calorie intake during the intervention.
  • In regard to protein intake, the subjects were appointed to consume 0.8 grams of protein per pound of bodyweight, the amount that is commonly recommended in the current research (study, study).

 

RESULTS

  • Both groups achieved a modest reduction in body fat, with no significant differences between groups.
  • There were little changes in lean mass gains across groups, with no significant differences between groups.
  • There were significant gains in 1RM squat at the end of the study in both groups, however there were no significant differences between groups. Gains in bench press 1RM approached significance in both groups, again with no differences between groups.

 

PROS OF THE STUDY

Given that this study was carried out by some of the best researchers in the field of exercise science, it is no surprise that this study was very solid in design.

Not only did the researchers equate protein intake between groups (which is a rarity in studies that analyze the anabolic window), they also measured actual muscle growth over a long time period.

This is in contrast to most studies that simply measure protein synthesis rates, and falsely correlate it to long-term muscle growth.

Furthermore, the participants in the study all had previous training experience, thus eliminating possible confounding factors related to novel training stimuli.

 

CONS OF THE STUDY

Now, while this study was very well done in design, it did have some notable limitations, as the authors point out in the Discussion section.

The most glaring one was the sample size, which was particularly small at just 21 participants.

Second, the participants in the study (for whatever reason) went against instruction to maintain a calorie surplus, and instead maintained a calorie deficit.

It is unclear if the results would have been different during an energy surplus, which would be far superior for muscle-building than an energy deficit.

Furthermore, it should be noted that food intake was monitored through self-report, which is obviously not the most reliable method of tracking food consumption in individuals (study).

 

WHAT TO TAKE AWAY FROM THIS?

All in all, this was a very good study.

Not to my surprise, it provides further evidence against the ludicrous notion of a 45 minute window of opportunity post-exercise.

As the authors state in the Discussion section:

The primary and novel finding of this study was that, consistent with the research hypothesis, the timing of protein consumption had no significant effect on any of the measures studied over a 10-week period. Given that the PRE-SUPP group did not consume protein for at least 3 h post-workout, these findings refute the contention that a narrow post-exercise anabolic window of opportunity exists to maximize the muscular response and instead lends support to the theory that the interval for protein intake may be as wide as several hours or perhaps more after a training bout depending on when the pre-workout meal was consumed.”

Given the results, this study further buffers the point that total daily protein intake is the overriding factor during a resistance training regimen (study), and that protein timing has a far lesser effect on muscle gains than we once thought.

See you next time.