THE BLOG

Post Exercise Protein Shakes - Is the Anabolic Window a Myth?

16/05/2013 13:52 BST | Updated 15/07/2013 10:12 BST

The concept of the post-exercise 'anabolic window' has become so engrained in the resistance training community that it is practically dogmatic. It refers to a limited time period where, post resistance training, skeletal muscle is primed for growth as long as a suitable protein source is consumed. With just a small window of opportunity to provide this protein source to your muscles, supplement companies have gleefully pointed out the benefit and convenience of the rapidly digested whey protein shake.

This begs the question, is there merit to such a claim or is it yet another example of an overhyped marketing ploy?

The Case for the Post Workout Window

It is well established that a higher than average protein intake is necessary to reap the full extent of benefits from resistance training. Dietary protein is a must for achieving positive nitrogen balance post training; enhancing post-exercise muscle protein synthesis and inhibiting muscle protein breakdown [1-3]. This allows increased muscle protein accretion during the post-exercise recovery period. Academic consensus is that strength and power athletes require at least twice the protein intakes of sedentary individuals [4], and a recent meta analysis found significant augmentation of the adaptive response of our muscles (increased skeletal muscle mass and strength) when weight training individuals, already habitually consuming 90-100g of protein daily (the British Dietetic Association recommends levels of 55 grams a day), upped their daily protein intake by 50 grams [5].

Anabolism is raised for 48 hours post exercise, but it is not at a steady rate - with a 112% increase observed after 3 hours, dropping to 65% at 24 hrs and 34% at 48hrs [6]. Along with this the post-exercise increased blood-flow to the worked muscles will likely enhance amino acid uptake, as well as the possible effect of anabolic priming from altered hormonal mediators [7]. So, it all seems to suggest that we need protein and as soon as possible after a workout.

Let's get a bit technical and delve a little deeper. Resistance training elevates levels of a chemical called AMP-activated protein kinase (AMPK) - raised in times of metabolic stress [8]. When activated, AMPK switches on catabolic pathways while switching off biosynthetic pathways, including glycogen and muscle synthesis. Normally it takes an hour, post-training, for raised AMPK levels to start to fall back to baseline, and for the desired anabolism to commence [8]. But, by consuming glucose and protein (essential amino acids) we attenuate this AMPK rise, lessening its effects, promoting anabolism sooner [9].

Thus it seems that post-workout we really do have a valid window of opportunity, not to provide nutrients to our muscles primed for growth, but to provide nutrients so our muscles can become primed for growth.

Can We Improve On This?

We have to ask, have we missed a step? Instead of trying to suppress the rise in AMPK after training, can we simply prevent it from occurring in the first place? AMPK is a sensor of cellular fuel (glucose) and energy status, increased when cells energy (ATP) levels fall, and thus it is plausible that the consumption of nutrients pre-training - acting as a fuel reserve throughout the training - will prevent exercise induced rises in AMPK, and the corresponding delay in post exercise anabolism.

A study investigated the consumption of 35g of sugar and 6g essential amino acids in liquid form immediately before or after resistance training [10]. In the group consuming the liquid pre-training, it was found that amino acid delivery and uptake was far greater during training and for one hour after; the critical period when it comes to AMPK elevation. It is noteworthy that this study was conducted in a lab setting on fasting individuals. Thus, it is not evidence to support the need to consume supplement shakes immediately before training, but instead to illustrate the importance of ensuring the presence of nutrients in the blood to promote positive nitrogen balance and prevent the AMPK rise. With resistance training sessions usually limited to an hour or under, this is just as easily achieved by ingesting a carbohydrate and protein-containing-meal circa two hours before training. Switching from the lab to a real world setting this is aptly illustrated in a study of resistance trained individuals, which demonstrated that those already on a high protein diet who consume protein supplements directly before and after training see no extra benefit compared to those who took it morning and evening [4].

Recommendation

It appears that the anabolic window as it is traditionally perceived is fabled. It is, however, paramount to ensure you have ingested protein and carbohydrates in a timely manner before training. The timing of this consumption is important; giving long enough that the meal is ingested before commencing training and preventing stomach distress, yet, being close enough to ensure that the nutrients are still in the blood to prevent the exercise induced AMPK rise. Whether this is achieved through diet or supplements is the choice of the user.

If we decide to supplement, users should follow the amounts used in the studies, i.e. circa 35g of glucose/carbohydrates and 6g of essential amino acids. One standard serving of a good quality whey protein will more than provide the 6g of essential amino acids used in the studies, ensuring you are maximising your recovery potential.

Further nutrients will be needed again post-training, to maximise the increased anabolic response, but the concept of a confined window of opportunity, and the need for rapidly ingested and digested protein, appears nonexistent.

1. Biolo G, Maggi SP, Williams BD, Tipton KD, Wolfe RR. Increased rates of muscle protein turnover and amino acid transport after resistance exercise in humans. Am J Physiol 1995;268:E514-20.

2. Biolo G, Tipton KD, Klein S, Wolfe RR. An abundant supply of amino acids enhances the metabolic effect of exercise on muscle protein. Am J Physiol 1997;273:E122-9.

3. Tipton KD, Ferrando AA, Phillips SM, Doyle D, Jr., Wolfe RR. Postexercise net protein synthesis in human muscle from orally administered amino acids. Am J Physiol 1999;276:E628-34.

4. Hoffman JR, Ratamess NA, Tranchina CP, Rashti SL, Kang J, Faigenbaum AD. Effect of protein-supplement timing on strength, power, and body-composition changes in resistance-trained men. Int J Sport Nutr Exerc Metab 2009;19:172-85.

5. Cermak NM, Res PT, de Groot LC, Saris WH, van Loon LJ. Protein supplementation augments the adaptive response of skeletal muscle to resistance-type exercise training: a meta-analysis. Am J Clin Nutr 2012;96:1454-64.

6. Phillips SM, Tipton KD, Aarsland A, Wolf SE, Wolfe RR. Mixed muscle protein synthesis and breakdown after resistance exercise in humans. Am J Physiol 1997;273:E99-107.

7. Suzuki M, Doi T, Lee SJ, et al. Effect of meal timing after resistance exercise on hindlimb muscle mass and fat accumulation in trained rats. J Nutr Sci Vitaminol (Tokyo) 1999;45:401-9.

8. Dreyer HC, Fujita S, Cadenas JG, Chinkes DL, Volpi E, Rasmussen BB. Resistance exercise increases AMPK activity and reduces 4E-BP1 phosphorylation and protein synthesis in human skeletal muscle. J Physiol 2006;576:613-24.

9. Fujita S, Dreyer HC, Drummond MJ, et al. Nutrient signalling in the regulation of human muscle protein synthesis. J Physiol 2007;582:813-23.

10. Tipton KD, Rasmussen BB, Miller SL, et al. Timing of amino acid-carbohydrate ingestion alters anabolic response of muscle to resistance exercise. Am J Physiol Endocrinol Metab 2001;281:E197-206.