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The Anabolic Window: Fact or Fiction?

Do you rush to guzzle down a protein shake immediately after your workout? Or give yourself indigestion squeezing in a meal before your next work meeting?

If so, you’re not alone. Many people still believe that the post-workout ‘anabolic window’ is the be-all and end-all that will make or break your gains in the gym.

However, while there are undoubtedly times when you will make better use of certain nutrients, as usual, there’s no one-size-fits-all approach you absolutely ‘must’ follow to achieve great results.

In the second edition of our Male Fitness Myths series, we explore the science and thinking around the ‘anabolic window’ and how you can use nutrient timing to maximise the results you get from your workouts.

What is the ‘anabolic window?’

Over the past 20 years, alongside the ongoing development and interest in sports science, there has been increasing academic focus on nutrient timing, sparking numerous research studies and reviews.

The term ‘anabolic window’ centres on timing specific nutrients – most often protein and carbohydrates – around an exercise or training session. The purpose of this approach is to maximise exercise-induced adaptations and improve the recovery of damaged tissue[1]. It has been suggested that specific nutrient timing strategies provide several positive outcomes concerning improvements in body composition and, in some instances, may even be more important than overall calorie intake[2],[3].

This ‘anabolic window of opportunity’ has been defined as a limited period post-training to optimise training-related muscular adaptations[4]. And the scientific basis for this claim isn’t completely unfounded. We know, for instance, that intense resistance training depletes stored fuel in the form of muscle glycogen and amino acids. It also results in damage to muscle fibres. Therefore, it makes sense that consuming a particular ratio of nutrients in the post-workout window helps repair damaged tissue, restore energy reserves, and improve body composition and performance. However, several confounding factors mean that the application and utility of nutrient timing around the ‘anabolic window’ are not always black and white.

The Science Behind Post-Workout Nutrient Timing

1. Glycogen Replenishment

One of the key scientific bases behind the hypothesised importance of post-exercise nutrient timing is glycogen replenishment. When we eat carbohydrates, the body breaks them down into a storable form of glucose, known as glycogen, stored primarily in muscle tissue. This process, known as glycolysis, provides up to 80% of ATP during high-intensity exercise, such as resistance training[5]. By this same premise, high-volume, bodybuilding-style workouts involving multiple exercises and sets for the same muscle group should theoretically deplete the majority of local glycogen stores[6].

However, the research shows that real-world effects only apply in a narrow range of cases. For instance, in endurance sports, such as triathlon or high-level athletics, where the duration between exercise bouts is less than eight hours, it may be beneficial to speed up the rate of glycogen resynthesis[7]. Equally, suppose you were following a training split that required you to train multiple times per day, such as training the same muscle groups in the morning and evening. In that case, it may also be beneficial to focus efforts on maximising this post-workout window[8].

But when we look at the type of exercise that most gym trainees perform, which often includes between six to nine sets per muscle group, glycogen stores only deplete moderately by around 36-39%[9],[10]. So, while glycogen replenishment may be a priority for competitive bodybuilders, if your goal is simply trying to look and feel better, it probably isn’t worth sweating over.

2. Muscle Protein Synthesis

A continued focus of study in sports science has been whether post-workout nutrient timing improves outcomes for muscle protein breakdown. The mechanism behind this supposed benefit is through post-workout nutrient intake of carbohydrates to spike insulin levels rather than through increasing amino acids (through eating protein, for example)[11],[12]. Through doing so, insulin can, in theory, rapidly transport proteins and amino acids to target tissues, thereby initiating the recovery process sooner.

However, this hypothesis fails to consider that it takes several hours to eat, digest and break down food to the point where it hits your bloodstream. It is only then that insulin spikes to transport it to various tissues around the body. As a result, it’s likely not the foods you eat immediately before or after your workout that directly influence insulin levels at that time[13], [14]. Equally, post-exercise muscle protein breakdown only plays a small role in protein balance and muscle growth[15]. This means that it’s likely to be your food intake several hours prior and post your workout window that has the biggest effect on growth.

3. Muscle Hypertrophy

Various studies have sought to determine whether there is an advantage to muscle hypertrophy from post-workout nutrient timing. While several analyses have found slight advantages from post-workout consumption of protein, it’s not clear in many cases whether this is as a result of timing or simply increased protein intake[16],[17].

Part of the problem with overestimating the importance of post-exercise nutrition intake is that it largely assumes that training always occurs in a fasted state[18]. When you train in a fasted state, there is an increase in muscle protein breakdown that results in a net negative balance of amino acids, the building blocks for muscle growth that provide the parts for recovery[19]. So, if you train first thing in the morning before eating, it makes sense to time your first meal in this post-workout window, ideally containing some carbohydrates and protein. Over time, this could result in increased gains[20].

However, there are plenty of people who don’t like training fasted. Let’s say you eat one to two hours before training. Depending on the size of the meal, it’s likely that this would count as both a pre- and post-meal given the time required to digest and absorb it[21]. Further evidence also shows that consuming even minimal amounts of essential amino acids beforehand is sufficient to last through the training window and into the post-exercise period. This indicates that anything consumed post-workout will do little to prevent catabolism (muscle breakdown).[22] If this period were further extended, say if you train 4-6 hours after your last meal, post-exercise intake of carbohydrates and protein may be beneficial if muscle growth is your goal[23].

Of course, in all three scenarios, a final caveat is training age, which reflects an individual’s training history and potential for continued improvement. For the majority of people when they first start training, the stimulus is so new that nearly anything they do will produce gains. However, over time, this scope decreases, and as a result, protein timing and quality may become more important in advanced trainees[24].

Maximising the window of opportunity

So, with these three considerations in mind, what recommendations can we give regarding post-workout nutrition?

1. A post-workout shake probably isn’t a bad idea for most people.

A post-workout protein shake provides the amino acids required to prevent catabolism or muscle protein breakdown. While you probably won’t need one if you ate immediately before training, if you train fasted in the morning or after several hours without eating, an immediate protein hit post-workout is likely beneficial from a muscle growth perspective. However, remember that total daily protein intake is the catalyst for hypertrophy rather than specific timing[25].

2. You are most insulin sensitive in the post-workout window.

Scientific research shows us that exercise, specifically muscle contraction activates the transport and uptake of glucose, a process that triggers an increase in insulin sensitivity[26]. As a result, if improved body composition is your goal, you are likely to make the best use of any carbohydrates during this time. So, if you often train with around 4-5 hours since your last meal, a post-workout shake with a fast-acting form of carbohydrate, such as cyclic-dextrin could give you a slight edge.

3. A post-workout protein shake could be beneficial if you don’t have time for a solid meal.

In most instances, it’s better to make time for a solid meal that prioritises high-nutrient density from single-ingredient sources within around one or two hours of training. However, the reality is that not everyone’s lifestyle will allow for this. If you’re often short on time post-workout, a high-quality protein shake will help maximise your returns.

4. A post-workout meal can help support performance if you exercise multiple times each day.

If you exercise multiple times a day, the post-workout window becomes more important. Let’s say you weight train in the morning, but you play sports in the evening. In this instance, you’re likely to improve your performance and recovery on those days by timing a meal containing some carbs and protein after each exercise bout[27].

Closing the windows

While a post-workout serving of protein and carbs certainly won’t hurt your gains, it’s probably not as important as most people believe either. From the perspective of glycogen depletion, muscle protein synthesis and hypertrophy, most of the benefits of post-workout nutrition seem to stem primarily from your last meal prior to training. Total daily protein intake is generally of greater importance than specific meal timing, so find a post-workout strategy that works for your lifestyle and personal preferences.

Need some protein shake inspiration? Whether you want to enhance the flavour or up the nutritional value, here are 4 ways to switch up your shake, so you never get bored.

Key Takeaways

  • The term ‘anabolic window’ refers to timing specific nutrients – most often protein and carbohydrates – around an exercise or training session.
  • Glycogen is the dominant substrate used during high-intensity exercise, but this is often only an issue for endurance sports or those training twice a day.
  • Insulin plays a role in shuttling nutrients to cells but, given that it takes time for food to digest and absorb, the foods you eat immediately around your workout probably don’t make that much difference.
  • There may be a slight edge to post-workout feeding from a hypertrophy perspective if you train fasted or several hours after your last meal.
  • A post-workout shake or meal certainly won’t harm your gains, but it’s your overall nutritional intake that makes the biggest overall difference to your gains.


[1] Kerksick, C., et al. (2008). International Society Of Sports Nutrition Position Stand: Nutrient Timing. Journal of the International Society of Sports Nutrition, 5, pg. 17.

[2] Ivy, J., Portman, R. (2004). Nutrient Timing: The Future of Sports Nutrition. North Bergen, NJ: Basic Health Publications.

[3] Candow, D.G., Chilibeck, P.D. (2008). Timing of creatine or protein supplementation and resistance training in the elderly. Applied Physiology, Nutrition, and Metabolism, 33 (1), pp. 184–90.

[4] Hulmi, J.J. et al (2010). Effect of protein/essential amino acids and resistance training on skeletal muscle hypertrophy: A case for whey protein. Nutrition and Metabolism, 7, 51.

[5] Lambert, C.P., Flynn, M.G. (2002) Fatigue during high-intensity intermittent exercise: application to bodybuilding. Sports Medicine, 32 (8), pp. 511–22

[6] Schoenfeld, B.J., Aragon, A.A. & Krieger, J.W. (2013). The effect of protein timing on muscle strength and hypertrophy: a meta-analysis. Journal of the International Society of Sports Nutrition, (10)53.

[7] Jentjens, R., Jeukendrup, A. (2003). Determinants of post-exercise glycogen synthesis during short-term recovery. Sports Medicine, 33(2), pp. 117–44.

[8] Schoenfeld, B.J., Aragon, A.A. & Krieger, J.W. (2013) The effect of protein timing on muscle strength and hypertrophy: a meta-analysis.

[9] Robergs, R.A. et al. (1991). Muscle glycogenolysis during differing intensities of weight-resistance exercise. Journal of Applied Physiology, 70 (4), pp. 1700–6.

[10] Roy, B.D., Tarnopolsky, M.A. (1998). Influence of differing macronutrient intakes on muscle glycogen resynthesis after resistance exercise. Journal of Applied Physiology, 84 (3), pp. 890–6.

[11] Biolo, G., et al. (1997). An abundant supply of amino acids enhances the metabolic effect of exercise on muscle protein. American Journal of Physiology. 273(1).

[12] Kumar, V. (2009). Human muscle protein synthesis and breakdown during and after exercise. Journal of Applied Physiology, 106 (6), pp. 2026–39.

[13] Koopman, R., et al. (2007) Coingestion of carbohydrate with protein does not further augment postexercise muscle protein synthesis. American Journal of Physiology, Endocrinology, & Metabolism. 293(3).

[14] Aragon, A. A., & Schoenfeld, B. J. (2013). Nutrient timing revisited: is there a post-exercise anabolic window? Journal of the International Society of Sports Nutrition, 10(1), 5.

[15] Glynn, E.L., et al. (2010) Muscle protein breakdown has a minor role in the protein anabolic response to essential amino acid and carbohydrate intake following resistance exercise. American Journal of Physiology-Regulative, Integrative, and Comparative Physiology, 299 (2).

[16] Willoughby, D.S., et al. (2007). Effects of Resistance training and Protein plys amino acid supplementation on muscle anabolism, mass and strength, Amino Acids, 32 (4), pp. 467-77.

[17] Hulmi, J.J., et al. (2009). Acute and long-term effects of resistance exercise with or without protein ingestion on muscle hypertrophy and gene expression, Amino Acids, 37 (2), pp. 297-308.

[18] Aragon, A. A., & Schoenfeld, B. J. (2013). Nutrient timing revisited: is there a post-exercise anabolic window?

[19] Kumar, V., (2009). Human Muscle Protein Synthesis and Breakdwon during and after exercise, Journal of Applied Physiology, 106 (6), pp. 2026-39.

[20] Aragon, A. A., & Schoenfeld, B. J. (2013). Nutrient timing revisited: is there a post-exercise anabolic window?

[21] Aragon, A. A., & Schoenfeld, B. J. (2013). Nutrient timing revisited: is there a post-exercise anabolic window?

[22] Tipton, K.D., et al. (2009). Stimulation of Muscle Anabolism By Resistance Exercise and Ingestion of Leucine plus Protein, Applied Physiology Nutrition Metabolism, 34 (2), pp. E197-206.

[23] Aragon, A. A., & Schoenfeld, B. J. (2013). Nutrient timing revisited: is there a post-exercise anabolic window?

[24] Aragon, A. A., & Schoenfeld, B. J. (2013). Nutrient timing revisited: is there a post-exercise anabolic window? Journal of the International Society of Sports Nutrition, 10(1), 5.

[25] Aragon, A. A., & Schoenfeld, B. J. (2013). Nutrient timing revisited: is there a post-exercise anabolic window?

[26] Holloszy, J.O., (2005). Exercise-induced increase in muscle insulin sensitivity. Journal of Applied Physiology, 99 (1), pp. 338-43.

[27] Haff, G.G., et al. (1999) The Effect Of Carbohydrate Supplementation On Multiple Sessions And Bouts Of Resistance Exercise. Journal of Strength & Conditioning Research.13(2).

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