Nutrient Timing: A Review Study By Aragon And Schoenfeld (2013)


Getting In The Essentials For Optimal Performance

When you go to the gym and have an intense training session, two main things will happen: energy will be utilised (derived from glycogen and amino acid stores) and, muscle fibres will be damaged. This is pretty standard. You go to the gym, energy is used for lifting weights, and lifting those weights will tax your muscles and cause damage (the good damage!).

This is exactly the chain of events you need, in order to make progress in size and strength over time. In terms of optimising these chain of events for maximum development, it’s logical to assume then that timing your nutrition around your workouts is essential in this. It does make sense why nutrient timing would play an important role in size and strength gains.

Energy: If we are talking about energy provision and replenishment, then having something around your workouts (probably a combination of carbohydrates and proteins) would 1) provide the needed glycogen stores to successfully fuel your workouts 2) rapidly replenish these lost stores after your workout 3) spare vital amino acids, thus reducing potential catabolism (muscle breakdown). 

Muscle Fibre Repair: Since lifting weights with progressive amounts of volume and intensity  puts incredible stress on your muscles, they can become damaged during your workouts (micro-tears in the muscle fibres). The reparation of these muscle fibres allows the muscle to come back stronger and bigger. However, nutrients are needed to fuel the repair processes and thus it seems plausible that an intake of nutrients around your workout would provide the necessary ‘building blocks’ needed for the repair processes. 

So, the question to ask is:

Is there a case for timing nutrients pre- and post-workout and if so, is there a period of time in which to take them (anabolic window)?

Glycogen Repletion, Protein Breakdown And, Protein Synthesis

•Glycogen Repletion• 

During exercise, energy is provided in the form of ATP. In order to fuel optimal performance during resistance training, ATP is needed, and approx. 80% comes from glycolysis. Glycolysis is simply a conversion process that converts glucose into pyruvate in order to produce ATP. Glycogen acts as a store of glucose (glycogen can be broken down, and glucose released), which can then be used in the process of glycolysis to produce the needed ATP for your workouts. During resistance training protocols, it has been shown that single set exercises carried out can lead to significant depletions in muscle-glycogen. Furthermore, as the volume of these exercise are increased, further depletions in muscle-glycogen occur. (You can check out the full study here: Robergs et al, 1992). Although an old study, it does make the point that, particularly with HIGH-VOLUME workouts, a significant depletion in local glycogen stores would be expected



Why is this so important? Well, interestingly there have been a number of studies published over the impact that changing glycogen stores on signalling processes can have. These signalling processes have been implicated in control of hypertrophic responses, muscle protein synthesis (MPS) and, regulation of anabolic and catabolic processes (a collection of studies can be read here Aragon and Schoenfeld, 2013).

There are also studies to show that exercise enhances post-exercise glucose intake into muscle cells, thus facilitating rapid replenishment of lost glycogen stores (check out Aragon and Schoenfeld, 2013 with more precise details on the mechanisms). 

The bottom line: Changes in muscle-glycogen levels as a result of resistance training are likely to impact performance in following sessions if glycogen is not replenished. This in turn could effect further muscular hypertrophy development over time. This is likely to occur through a range of diverse signalling mechanisms (that are regulated in response to changes in glycogen) that modulate hypertrophy, MPS and anabolic and catabolic processes. It’s therefore possible that nutrient timing around workouts could play an important role in overall size and strength development over time, through glycogen-store replenishment.

It’s important to note that this is all mostly theoretical. Ok, we know that changes in the levels of glycogen stores occur in response to resistance training, and this can lead to changes in many signalling processes (many of which are involved in hypertrophy). But, there has been no substantial research done to identify what the practical significance of replenishing glycogen stores is, in the context of nutrient timing.

Furthermore, as Aragon and Schoenfeld highlighted, glycogen replenishment is not likely to be a concern even with higher training volume and intensities or, in the presence of complete glycogen depletion. Aragon and Schoenfeld pointed out that with recovery intervals of 24 hours between training sessions (provided the training sessions don’t have absurd amounts of volume), glycogen stores are replenished to PRE-training levels regardless of significantly delayed post-exercise carbohydrate intake. 

•Protein Breakdown•

Following a hard resistance training session, your muscles are tired, damaged and depleted. But, that is the job of resistance training! To tax them beyond their current capabilities. Essentially, all this new training stress on the muscle during resistance training can lead to an increase muscle protein breakdown (MBP). Now, muscle mass is maintained in a fairly constant state through a continuous balance between MPS and MPB. But, factors such as nutrition, fasting, exercise, stress etc can lead to a change in the balance between MPS and MPB. When MPB is greater than MPS, then the muscle is in a catabolic state (breakdown). However, when MPS is greater than MPB, the muscle is in a anabolic state (build up). In line with this, it has been demonstrated that MPB increases significantly after exercise and in a post-exercise fasted state, the magnitude and duration of the post-exercise MPB can further increase for up to 24 hours (further insight to the studies can be read here: Aragon and Schoenfeld, 2013).


As Aragon and Schoenfeld point out, post-workout nutrient timing may have a benefit on the attenuation of post-exercise MPB through elevations in insulin. Insulin is believed to modulate a range of signalling pathways implicated in MPB. When insulin is elevated, this is supposed to lead to a down-regulation in these pathways responsible for MPB. This reduction in MPB would likely tip the balance in favour of MPS thus allowing for a greater accretion in muscle building proteins.

The bottom line: MPB is increased following resistance training and the magnitude and duration is increased in a post-exercise fasted state. insulin is implicated in the down-regulation of pathways responsible for MPB. Thus, in the absence of post-workout nutrition, insulin is going to be low and these MPB pathways are likely going to be up-regulated, sending the muscle tissue into a catabolic state (MPB greater than MPS). It’s likely then that a post-workout meal comprising of protein + carbohydrate* would provide the insulin spike necessary to reduce the extent of MPB post-exercise.

*It has been shown in studies that protein and carbohydrates together lead to a greater elevation in insulin levels in comparison to carbohydrates alone. 

There are a few important things to note:

Firstly, Aragon and Schoenfeld highlighted a few studies in which it was found that following a meal (consisting of proteins, fats and carbohydrates) or ingestion of whey protein isolate, insulin levels remained significantly elevated (above fasting levels) for 5 hours and 2 hours respectively after ingestion. This suggested that with a properly constructed pre-workout meal, the timing of post-workout nutrition might not be necessary to consider. Only in the absence of pre-workout nutrition might post-workout timing be necessary.

Furthermore, another study was highlighted by Aragon and Schoenfeld, in which post-exercise consumption of protein and carbohydrate was found to influence MPS with only a minor effect on MPB (regardless of levels of circulating insulin). This brings into question whether insulin does indeed have positive effects on muscle growth post-exercise.  

•Protein Synthesis•

Protein breakdown is associated with an increase in MPB relative to MPS

Protein synthesis is associated with an increase in MPS relative to MPB.

As Aragon and Schoenfeld point out, a series of studies have been conducted on the effects of nutrient timing around exercise and it’s effects on the magnitude and duration of MPS post-exercise. However, the results from several studies are rather mixed and provide no conclusive answer on what the ideal timing would be (if any) of post-workout nutrition on maximising MPS. I

In one study in their review paper, positive benefits in consuming a post-workout supplement (consisting of carbohydrate, protein and fats) 1 hour after post-workout, in comparison with 3 hours post-workout were demonstrated. It was found that post-workout supplementation 1-hour after exercise resulted in greater MPS than supplementation 3 hours post-workout.

In another study, no differences in MPS were found between those that took a post-workout supplement (essential amino acids with carbohydrate) at 1 OR 3 hours post-exercise. 


The bottom line: Conflicting studies make it difficult to determine precisely what effect (if any) post-workout supplementation has on MPS and if there is an ‘effective time window’ for post-workout nutrition in order to maximise MPS. 

An important point to note: Most studies measure MPS following an acute bout of resistance training and in untrained individuals. As a result, this is not likely to tell us what the long-term implications are for hypertrophic responses following post-workout nutrition or, the nature of the post-exercise MPS in trained individuals. 

So What Do These Studies Tell Us?

Simply put: it’s not clear if there is an optimal post-workout window for nutrient intake in order to maximise hypertrophic gains (ANABOLIC WINDOW).

As pointed out by Aragon and Schoenfeld, there are a lot of conflicting studies making it difficult to determine if there is a definitive post-workout window of opportunity in which to maximise MPS. In a fasted state, it’s likely that immediate POST-workout nutrition is needed, due to MPB being significantly elevated over MPS (thus putting the muscle tissue in a catabolic state). Immediate post-workout nutrition is likely then to provide the necessary protein and carbohydrates needed to promote increased post-exercise MPS, thus reducing the influence of MPB. This is likely to switch the muscle into a net anabolic state after exercise.

Interestingly, Aragon and Schoenfeld bring up a study on pre-workout nutrition, in which it was found that ingestion of essential amino acids IMMEDIATELY before exercise, elevated blood and muscle amino acids for 2 hours AFTER the exercise.

This suggested that a sufficient pre-workout meal immediately before exercise is likely to provide the necessary nutrients needed to sustain recovery in the post-exercise period.

The bottom line: whether an anabolic window or not truly exists, is still up for further debate. At the moment, there are too many conflicting studies to derive a clear answer. However, it seems that for individuals who train fasted, or wait too long after a meal to exercise, might benefit from immediate post-workout protein and carbohydrate nutrition in order to support the recovery period. However, for those individuals who have had sufficient protein and carbohydrates immediately before exercise, something post-workout might not be needed. But, more still needs to be done before a conclusive answer can be given! 

Any questions, ask away! 


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