Anabolic window: Fact or Fiction?

One of the most controversial topics within the field of protein nutrition concerns the appropriate time frame for consuming protein after a workout in order to promote muscle anabolism and ultimately muscle growth. A popular idea is that a 60-minute post-exercise “anabolic window of opportunity” time frame exists, within which protein must be consumed in order to achieve muscle anabolism [1]. Indeed, some advocates of the “anabolic window” have narrowed this window to only 45 minutes post workout. However, the practical relevance and validity of this “anabolic window” theory has been questioned and requires a balanced perspective. Whilst there might be some merit behind the “anabolic window” with regards to maximising muscle growth, a strong argument can be made that the importance of protein intake within such a short time-frame following exercise is not as critical as is often publicised [2, 3]. Instead, it can be argued that the “anabolic window” for protein intake should be extended beyond only the first 45-60 min post workout [4].

What does the scientific evidence tell us?

Taken literally, the “anabolic window” implies that delaying protein intake by 1 hour or more after exercise will reduce –or worse still – prevent muscle anabolism during recovery. So, according to this theory, consuming protein “say” 65 minutes after a workout may be considered worthless, or at best minimally beneficial for muscle growth. However, the scientific evidence behind this rather extreme idea is weak. Therefore, the importance of immediate post-exercise protein ingestion for muscle growth remains open to debate. Advocates of the “anabolic window” theory often cite the findings from a resistance training study in young men that was performed over a 10 week period [5]. In this study, the group of volunteers that consumed protein immediately before and after each workout gained more muscle mass than volunteers that consumed protein early in the morning and late at night. However, these findings have not been replicated by other follow-up training studies [6, 7]. For example, researcher failed to show any benefit of timing protein supplementation immediately before and after workouts versus morning and evening supplementation on changes in body composition following 10 weeks of training. As a note of caution, the interpretation of findings from any protein timing and training study must be considered in light of other “uncontrollable” factors (e.g. overall diet, physical activity levels) that, in addition to protein timing, may potentially influence the outcome (e.g. muscle growth) of interest. Collectively, these findings cast into doubt the importance of immediate post-exercise ingestion of protein for the purpose of muscle growth. In addition, high quality muscle biopsy studies report similar muscle building effects after consuming an essential amino acid mix 1, 2 or even 3 hours post exercise [8, 9]. This research clearly demonstrates that skeletal muscle remains responsive to protein ingestion during time periods outside the limits usually defined by the “anabolic window”. Indeed, it appears that this “anabolic window” extends to 24 hours post workout, or perhaps even longer [10]. Clearly, the appropriate timeframe to consume protein after exercise for muscle growth should not be restricted to a 45-60 min post-exercise window.

A risk-benefit approach

Whilst there is no scientific evidence that protein intake immediately post exercise promotes greater muscle anabolism than delaying protein intake 2 or 3 hours post exercise, taking a risk-benefit approach seems sensible. At present, given the lack of available scientific evidence, it is impossible to make solid conclusions about the optimal timing of protein intake for muscle growth. However, it is safe to assume that protein intake immediately post workout is unlikely to impair muscle anabolism and could feasibly improve it. There is therefore no reason to recommend against protein intake within the first hour of recovery if the goal is to maximise muscle anabolism. Plus, from a purely practical perspective, protein intake within 1 hour post workout is likely a convenient time for an athlete to consume protein in the natural scheme of things anyway.


Key Take Away

Whereas the theoretical “anabolic window of opportunity” remains open for longer than a 1 hour period after exercise, it is safe to recommend that athletes interested in maximizing muscle building consume ~25 grams of protein as soon after a workout as is practical.

Author: Dr. Oliver Witard is a Senior Lecturer in Nutrition and Exercise Metabolism at The University of Stirling. Oliver’s research focus is protein nutrition for maximising muscle adaptation to exercise training. His publications focus on establishing the optimal dose, source and timing of dietary protein for maximising gains in muscle mass, function and performance.

Disclaimer: The exercises, training and/or nutritional information and recommendations presented in this article/video are to be followed at your own risk and do not substitute personal and/or individual advice. Medical advice should be obtained beforehand by anyone under 18 years of age, by individuals with health restrictions (especially orthopaedic or internal complaints/conditions), and by women who are pregnant or breastfeeding. If problems are encountered when applying the training and nutritional methods, a doctor should always be consulted immediately. No liability is assumed by Active Nutrition International GmbH.


  1. Ivy, John., et al. “The future of sports nutrition: Nutrient timing.” In: Basic Health Publications.
  2. Witard, Oliver C., Tipton, Kevin D. “Defining the anabolic window of opportunity.” Agro food industry hi-tech 25.2 (2014): 10-13.
  3. Aragon, Alan., et al. “Nutrient timing revisited: is there a post-exercise anabolic window?” International society of sports nutrition 10.5 (2013).
  4. Tipton, Kevin D., Witard, Oliver C. “Post exercise nutrient timing with resistive activities.” In: Nutrient Timing: Metabolic Optimization for Health, Performance, and Recovery (2012): 163-176.
  5. Cribb, Paul J., Hayes, Alan. “Effects if supplement timing and resistance exercise on skeletal muscle hypertrophy.” Medicine and science in sports and exercise 38 (2006): 1918-1925.
  6. Hoffman, Jay R., et al. “Effect of protein supplement timing on strength, power and body composition changes in resistance trained men.” International journal of sport nutrition and exercise metabolism 19: (2009) 172-185.
  7. Burk, A., et al. “Time-divided ingestion pattern of casein-based protein supplement stimulate an increase in fat-free body mass during resistance training in young untrained men.” Nutrition research. 29: (2009) 405-413.
  8. Rasmussen, Blake B., et al. “An oral essential amino acid-carbohydrate supplement enhances muscle protein anabolism after resistance exercise.” Journal of applied physiology. 88: (2000) 386-392.
  9. Witard, Oliver C., et al. “Increased net muscle protein balance in response to simultaneous and separate ingestion of carbohydrate and essential amino acids following resistance exercise.” Applied physiology, nutrition and metabolism 39.3 (2014): 329-39.
  10. Burd, Nick A., et al. “Enhanced amino acid sensitivity of myofibrillar protein synthesis persists for up to 24 h after resistance exercise in young men.” Journal of nutrition 141.4 (2011) 568-573.