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Written by Brad Schoenfeld, Ph.D., CSCS, FNSCA
26 September 2018

16NN202-WIND

The Post-Workout Anabolic Window

Science Proves It's Not As Narrow As Often Believed

 

 

For many years, the concept of a “post-workout anabolic window of opportunity” has been taken as gospel by those in the bodybuilding community. Simply stated, the “anabolic window” hypothesis postulates that a limited time exists after training to optimize training-related muscular adaptations— generally believed to be less than an hour after completion of an exercise bout.2,4,5 According to popular belief, consuming the proper ratio of nutrients during this critical time period not only facilitates muscle protein accretion, but it does so in a supercompensated fashion that maximizes the hypertrophic response to lifting— delaying protein intake by a matter of minutes after this time period is purported to seriously compromise muscular gains. Some researchers have proposed that the timing of nutritional intake is even more important to muscle growth than the absolute daily consumption of nutrients.2 Bold claims indeed!

 

What Does Research Say    

There is some evidence showing superior increases in muscle protein synthesis when amino acids are ingested in close proximity to the conclusion of exercise as opposed to delaying consumption. One such study found significantly greater acute protein accretion when beagle dogs consumed amino acids immediately following 150 minutes of treadmill running compared to two hours post-exercise.9 Although intriguing, we need to take these findings with a large grain of salt; an animal trial using aerobic training is not exactly indicative of the anabolic response of hard-training lifters. Another study carried out in human subjects by Levenhagen et al.7 showed that lower body and whole-body protein synthesis was increased significantly more when protein was ingested immediately versus three hours after exercise. Problem is, the training involved moderate intensity, long-duration aerobic exercise. This raises the distinct possibility that results were attributed to greater mitochondrial and/or sarcoplasmic protein fractions as opposed to synthesis of contractile elements. Let’s face it, long-duration aerobic exercise is not much of a muscle-building activity. Conversely, Rasmussen et al.10 investigated the acute impact of protein timing after resistance training— without question, a better indicator of synthesis of muscle contractile elements. In this study, no significant differences were seen in the protein synthetic response after consuming nutrients one versus three hours post-exercise. It should be noted that measures of acute muscle protein synthesis do not necessarily correlate with muscular gains achieved from consistent lifting8, so results from these studies need to be interpreted with caution. Ideally, the effects of protein timing can best be determined by long-term training studies that measure actual muscle growth.

 

A number of longitudinal training studies have endeavored to determine the effect of protein timing on muscle growth over the long term (more than six weeks of consistent resistance exercise). The study that nutrient timing proponents often cite in support of an anabolic window of opportunity was carried out by Esmarck et al.3, who randomly assigned 13 elderly men (average age 74) to perform a resistance-training protocol three days a week for 12 weeks. The only variation in the protocol was that subjects consumed 10 grams of protein (a combination of skimmed milk and soy protein) either immediately following or two hours after the training bout. Results showed that muscle cross-sectional area and mean fiber area of the quadriceps increased by seven and 22 percent respectively for the group that received protein immediately post-exercise, while the group that delayed protein intake showed no increases in fiber hypertrophy. On the surface, these findings would appear to provide compelling evidence for a narrow anabolic window of opportunity. Nail-in-the-coffin evidence, right?

 

Not so fast.

The study had several notable limitations and inconsistencies. For one, the sample size was very small, with only seven subjects in the group that received immediate protein supplementation, and six in the group where supplementation was delayed. Such a small number of subjects ultimately compromises statistical power, hindering the ability to find probable effects. For another, the dose of protein was well below the amount needed to maximize protein synthesis in an elderly population, estimated to be about 40 grams.12 What’s more, it’s highly curious that the delayed-intake group saw no gains in muscle growth over a period of 12 weeks of regimented resistance training simply because they waited two hours to consume protein. Zilch! Considering that virtually every resistance-training study ever conducted shows significant hypertrophy in untrained subjects after three months of regular lifting, these results must be viewed with skepticism. On top of all this, the timed group achieved gains similar to the growth experienced in other studies that did not provide immediate protein supplementation. All told, this study raises more questions than providing answers.

 

When looking at the body of literature as a whole, the results of longitudinal studies have been decidedly conflicting: some show a benefit to protein timing, while others don’t. In an attempt to achieve clarity on the topic, our lab recently conducted a meta-analysis that pooled data on all relevant protein-timing studies.11 Inclusion criteria required that studies were randomized controlled trials, where one group received protein within one hour post-exercise and the other delayed consumption by at least two hours after completion of the workout. A total of 23 studies qualified for inclusion, comprising 525 subjects. A basic analysis showed a small effect for protein timing on hypertrophy, seemingly indicating that there is in fact a fairly short anabolic window of opportunity. However, we then carried out a technique called regression analysis that accounted for potential confounding variables that unduly influenced results. Lo and behold, it was found that virtually the entire effect was explained by greater protein consumption in subjects receiving immediate protein provision! The issue here is that most studies gave a placebo to the subjects where provision was delayed, so that those in the group receiving supplementation immediately post-exercise consumed ~1.7 grams per kilogram versus only 1.3 grams per kilogram in the control condition. Given that research indicates hard-training lifters need a daily protein intake of at least 1.7 grams per kilogram to maximize muscular adaptations1, the subjects who received immediate protein supplementation were necessarily at an advantage from a hypertrophy standpoint.

 

The meta-analysis had several limitations. Notably, only five studies matched protein intake; two showed an effect and three did not. Moreover, only two studies evaluated trained subjects with matched intake; one showed and effect and one did not. It’s therefore difficult to draw definitive conclusions from the current research. What can be extrapolated with a high degree of confidence is that any effect of protein timing on muscle hypertrophy, if in fact there is one, is relatively small. That said, for serious lifters, particularly those competing in physique-oriented competitions, any small benefits that might exist would be potentially meaningful— perhaps even critical.

 

Here’s the Take-Home

First and foremost, total protein intake is paramount to muscle building— make sure you consume at least ~1.7 grams per kilograms a day, preferably more. That said, nutrient timing potentially can be a beneficial strategy for maximizing muscular gains, but the “window of opportunity” is not as narrow as often believed. Rather, the window exists on a fairly wide continuum, and its effects on muscle growth ultimately depend on when you ate prior to the training bout. Research indicates that the anabolic effects of an individual meal last up to six hours.6 Thus, provided that a protein-rich meal is consumed within about three to four hours prior to a workout (or possibly even longer, depending on the size of the meal), you don’t have to stress about chowing down a post-workout meal the moment you finish training. For those who train partially or fully fasted, on the other hand, consuming protein immediately post-workout becomes increasingly more important to promote anabolism. Although research is somewhat equivocal, it seems prudent to consume high-quality protein (at a dose of ~0.4-0.5 grams per kilogram of lean body mass) both pre- and post-exercise within about four to six hours of each other depending on meal size.

 

Brad Schoenfeld, Ph.D., CSCS, FNSCA is widely regarded as one of the leading authorities on training for muscle development and fat loss. He has published over 80 peer-reviewed studies on various exercise- and nutrition-related topics. He is also the author of the best-selling book, The M.A.X. Muscle Plan, andruns a popular website and blog atwww.lookgreatnaked.com.

 

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