Is the "Anabolic Window" Real?

If you're well informed in the fitness industry, you've likely heard of the anabolic window an know that old school train of though stated "nutrient timing is everything, if you want to build muscle!" However you've likely also learned that more recent research has somewhat debunked this "anabolic window" theory, in favour of simply meeting total daily nutrient requirements.

If you're not optimizing your post-workout nutrition properly, you may very well be missing out on some potential gains. If you really want to know the truth about the "anabolic window" and post-exercise nutrition, you want to read this article...

Consuming adequate nutrients, such as protein and carbohydrates, are essential to optimize muscle growth. This much is undisputed. The data are very clear on the benefits of enhancing protein synthesis, attenuating protein breakdown and ultimately contributing to muscle hypertrophy, but the timing of supplementation has been a topic of heated debate. In some cases, the timing of nutrient ingestion is thought to be more important than what the nutrients are. In a nutshell, proper nutrient timing is optimizing the delivery of nutrients to the muscle during a time when the muscle is primed to use them most effectively.

Nutrients and Exercise

Resistance exercise training is a reference point commonly used as a basis for the timing of nutrient ingestion due to the metabolic effects of exercise. The time frame immediately prior to and during exercise is the phase primarily devoted for consuming energy to improve the quality of the workout. However, this period of time is not consistently associated with enhancing muscle growth after exercise. An article explaining supplementation during the energy phase can be found here.

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During exercise and immediately after exercise, the body is in a catabolic state. Blood insulin is low, while cortisol and other catabolic hormones are high. Liver glycogen levels are reduced, or in some cases depleted, and rates of muscle protein breakdown is at it’s highest. While resistance exercise itself is known to be an activator for protein synthesis, the absence of any post-exercise nutrition will leave the body in a net catabolic state. This is because the increase in protein synthesis is offset by the high rates of protein breakdown. This catabolic state can prevail for many hours until nutrients are consumed. Therefore, exercise without any post-exercise nutrition is not a favorable situation for muscle growth.

The consumption of protein and carbohydrates initiates the shift to anabolism by simultaneously reducing all the catabolic factors and amplifying the effects of protein synthesis. One possible mechanism is that muscle is particularly sensitive to insulin post-exercise, which ensures the rapid transport of glucose and amino acids into muscle and subsequently promotes muscle glycogen synthesis, protein synthesis as well as inhibits the pathways governing protein breakdown. Since the insulin sensitivity declines with time, the effectiveness of nutrient intervention will also decline. Although the muscle sensitivity is known to be elevated for up to 48 hours post-exercise, the relative decline has been established during that time-course. The muscle sensitivity is greatest within the first 3 hours and then progressively declines (sensitivity at 3 hours is greater than at 24 hours, which is greater than at 48 hours).

Protein Post-exercise

The ingestion of protein post-exercise primarily serves to augment the rates of protein synthesis with only a minor role in the attenuation of protein breakdown. Surprisingly, there are very few studies that have analyzed the protein synthetic response of various time-points post-exercise. One study focused on protein synthesis, observed a 66% lower rate when protein ingestion was delayed by 3 hours. Other studies indicate that between 1 and 3 hours results in a similar acute response. The general consensus is that there is a clear additive effect of protein synthesis when protein is ingested within the first few hours post-exercise. Thinking logically however, the sooner the muscles transition from catabolism to anabolism, the greater the potential for muscle growth. For this reason, while there may not be a clear narrow window when nutrient ingestion is required, most exercise studies clearly support protein supplementation sooner rather than later for the optimal stimulation of protein synthesis and muscle accretion over time.

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Carbohydrate Post-exercise

Most weight-lifting athletes primarily focus on protein supplementation post-exercise, with concern mostly on protein synthesis, and with little regard to the need for carbohydrates. As previously mentioned, protein supplementation focuses on pathways to stimulate protein synthesis and does not have a major affect on protein breakdown. However, the ingestion of carbohydrates post-exercise makes a major impact on the attenuation of cellular pathways involving protein breakdown. The inclusion of carbohydrates during post-exercise nutrition, therefore, plays a prominent role in the transition from muscle catabolism to anabolism. Furthermore, research suggests that the glycogen level of muscle influences the activity of a number of metabolic activities including glucose transport and protein metabolism. The restoration of muscle glycogen, therefore, is paramount in the exercise recovery process. Clinical studies indicate that the combination of carbohydrates with protein results in greater gains in muscle hypertrophy after 12 weeks of resistance exercise training when compared with a protein-only supplement.

The timing of carbohydrate supplementation appears to be more stringent than it is for protein. Post-exercise muscle glycogen synthesis occurs more rapidly when carbohydrates are consumed immediately after exercise as opposed to waiting several hours. In fact, delaying supplementation for two hours can reduce the rate of muscle glucose uptake and glycogen synthesis by up to 50%. Otherwise, if carbohydrates are not adequately supplied post-exercise, the rate of muscle glycogen synthesis can be extremely low despite normal increases in blood glucose and insulin levels later in the day.


Protein and carbohydrate supplementation post-exercise is a vital component to optimizing post-exercise muscle recovery. This includes not only maximizing muscle hypertrophy, but also minimizing muscle soreness and optimizing muscle recovery time. The combination of these nutrients increases the efficiency of muscle recovery when compared to either carbohydrates or protein alone. While it may have been previously believed that this nutrition is imperative during a narrow window of time to be effective, the evidence shows that the muscles may be sensitive to these nutrients up to 48 hours post-exercise. However, any delay in supplementation is still not recommended, as the muscle remains in a catabolic state until nutrients are delivered to them. Furthermore, the sensitivity of muscle is highest soon after exercise. Therefore, although the concept of an anabolic window may be debunked, if getting the most out of a workout is crucial, then consuming nutrients soon after exercise should be considered equally as important.

So as you can see, most of the myth-busting about the anabolic window focuses on protein supplementation alone for post-exercise and that's where most people get it wrong. As you read above, carbohydrates post-exercise are perhaps even more important for muscle recovery and growth due to increased muscle glycogen synthesis.

This is why Blue Star Nutraceuticals™ Post-Factor™ is formulated with an optimal 2:1 carb to protein ratio and includes other key ingredients such as CherryPURE® and L-Carnitine L-Tartate for maximum recovery and muscle growth.

Create your "anabolic window" and find out more about Post-Factor™ on the next page:
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