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Predicting How Much Muscle You Can Build

Updated: Feb 5

Last month I wrote about protein absorption, and how at least 100 grams of protein consumed orally in a single sitting can be absorbed and enter circulation, with little of it being oxidized. But that study neither informed the long-term impact on muscle growth nor the ability to predict and set realistic lean mass goals with athletes. So that’s what this article is all about.


Below, I’m going to review the following:

  • Defining muscle protein breakdown and synthesis.

  • Managing expectations when goal setting.

  • Evaluating if you can predict the rate of lean mass growth.

  • Dietary recommendations for calorie and protein intakes to support lean mass.



What is Muscle Protein Breakdown and Synthesis?

Muscle protein breakdown (MPB) and muscle protein synthesis (MPS) do not work in isolation, as if each were a light switch that you could turn off and on. For muscle hypertrophy, the goal is to have a net MPS effect, meaning over the course of a day (or any timeline), MPS outpaces MPB.



Muscle Protein Breakdown


This is the breakdown of muscle into its amino acid building blocks, which the body can then recycle for other purposes. When in the fasted state, MPB is higher than MPS. (1)



Muscle Protein Synthesis


MPS is the “metabolic process that describes the incorporation of amino acids into bound skeletal muscle proteins.” (2)


MPS increases with resistance training and/or a protein feeding, and is stimulated to a greater extent than MPB—upwards of 2.5-fold in healthy individuals. (2) Resistance training will increase MPS for greater than 24 hours and consuming dietary protein for 3-6 hours. That increase reflects the muscle cells being sensitized to a pro-building state. (1)

Fluctuating MPS and MPB curves.
The overall goal is for MPS to outpace MPB. The stimulus of resistance training and/or protein intake further increases MPS. (3)

MPS can be measured in multiple ways. One of which is the fractional synthetic rate (FSR), which represents the rate of amino acids being incorporated into muscle protein over time. (4) FSR is expressed as a percentage per hour (FSR %/hour) and the rate at which a muscle would take to rebuild itself entirely. (1) As an example, a skeletal muscle's FSR of 0.04% means that in three months, that entire muscle would be entirely replenished with new cells. (1)


When reviewing muscle hypertrophy research, it’s important to understand measurement methods and how they’re translated and interpreted into real world scenarios. Common FSR measurements are isotope-labeled amino acids (e.g., 13C6 phenylalanine, 1-13C leucine [used in the 100-gram study]) and deuterium oxide (D2O). Regarding the former, labeled amino acids provide insight into the acute environment after training and/or a protein feeding (i.e., researchers taking samples over a 12-hour time period in the laboratory). Regarding D2O, this is a measurement over hours to months and provides a better snapshot of not only an intervention over time, but of someone living their life, eating, and exercising beyond the lab. For studies using D2O, results are better suited for predicting resistance training’s effect on muscle hypertrophy. (2)



Setting Lean Mass Expectations: #1 Is the Athlete New to Resistance Training?


As a dietitian, one screening question I ask an incoming athlete is if they’ve lifted previously. Within the research, novice lifters (i.e., new to lifting and are considered untrained) initially respond differently than a trained lifter.


For the novice, and when compared to a trained lifter, MPS tends to peak later and remains elevated for a longer period of time. However, have you ever done a new exercise or workout class and felt sore? That’s a reflection of increased muscle damage experienced with any new activity. Even with that prolonged MPS, some of that increase is tending to damaged muscle cells—and isn’t solely directed to hypertrophy. As training progresses, the pattern of MPS begins to mimic that of a trained lifter, and more of that MPS is directed away from repairing damage and towards hypertrophy. (2) This adaptation from novice to trained has been proposed to be 10 weeks. (5)

Graphs showing myofibrillar and mixed muscle protein synthesis percent changes to resistance exercise in the trained versus untrained.
The untrained and trained responses to resistance exercise. (6)

Another consideration is the age and developmental stage the athlete is in. Especially for boys, who enter puberty later than girls, being mindful of the Tanner Stages is helpful. Measuring what stage an adolescent is in would require a pediatrician. For me, I ask all incoming athletes if they’ve grown in height the past year and, considering body type and composition holds a genetic factor, what their mother or father was like at their age. For instance, was the male athlete's dad delayed in gaining muscle into their early twenties, despite their best efforts?



Setting Lean Mass Expectations: #2 What Lifting Phase is the Athlete in?

Lean mass and hypertrophy goals are not simply, “eat X grams of protein per day.” There needs to be a conversation with the athlete and great consideration of the strength and conditioning coach’s plans (or at least some sort of planned workout regime for the average adult) that will produce desirable results, be it body recomposition, skeletal muscle hypertrophy, etc.

In the athletic setting, there are cycles of the year where hypertrophy is the goal and other times where weight and muscle retention are the goal. For instance, during a basketball season I don’t expect there to be lean mass increases and the goal is to maintain total body weight. This is because (a) the athletes can’t be lifting heavy and have sore muscles for game day and (b) traveling seems to be a risk factor for unintentional weight loss, as the athlete is without their fueling station for in between meals or their kitchen pantry for a late-night snack, among other reasons.

Understanding and integrating this into scheduling body weight and composition checks is important: Based on the training schedule and time of year (e.g., offseason versus preseason versus during season), will the changes, or lack thereof, in weight and composition match what you expect? How can you provide context of the results to an athlete and high-performance staff when, during season, they learn that zero muscle was gained?

Setting Lean Mass Expectations: #3 What Percentage Increase Does Research Predict?


So, what can you expect for lean mass goals? Predictions are “all over the place in the literature.” (7) Even in studies where body recomposition was measured (i.e., muscle gain concurrently with fat loss), there were still participants who failed to do so in the presence of a calorie deficit and high-protein diet. Authors noted that roughly “70% of subjects improve their overall body composition when implementing high-protein diets”—meaning 30% did not. (8)


A summary of research reviewing chronic resistance training over an 8-16-week period found a range of a 5-20% increase in skeletal muscle volume or mass in younger to middle-aged adults. (9) However, and given the importance of understanding (a) training status, (b) nutrition, (c) Tanner Stages, and (d) being sensitive to the wild card that is genetics, I picked apart the referenced studies:

A review of studies that have shown a 5-20% lean mass increase.


From a research perspective, the populations studied (age, gender, training background), short intervention timelines (2-4 months), and a near absence of dietary interventions makes it hard to translate the goal of a 5-20% lean mass prediction to the athletic population.



Setting Lean Mass Expectations: #4 What Does Real Life Predict?


Using the Fat-Free Mass Index (FFMI) could be a starting point, but in my many readings this has been used for body building, not team sport athletes. For “natural” lifters (i.e., no anabolic drug use), an FFMI of 25 is reasonable. (17) Here’s a link to the FFMI calculator.

Aragon (October 2022) wrote that for someone with a normal body fat level (normal was not defined, but was differentiated from overweight/obese), a fat mass loss goal of 0.5-1 pounds per week was proposed. For lean mass gains, novice lifters could reasonably aim for 1-2 pounds per month and trained lifters 0.5-1 pounds per month. (7)

If available, you could use professional league data as a comparison range, for instance, Combine data for men's American football (NFL), baseball (MLB), and basketball (NBA). Granted, it's not entirely fair to compare a freshman point guard (17-18 years of age) to a 22-to-24-year old NBA draftee with years of organized strength programming behind them. You can use Combine data as a starting point, but be ready to manage expectations with the athlete and high-performance team.

Dietary Recommendations for Calories and Protein

Whether someone is in a calorie deficit (often to lose fat mass), maintenance, or surplus (often to gain lean mass), skeletal muscle can still be built. (18)


However, if the goal is to maximize lean mass growth, a calorie surplus is best. Otherwise, anabolic (building) signaling and MPS will be suppressed. The systematic review and meta-analysis by Murphy and Koehler (2022) recommended that those individuals with the goal of lean mass gains and who are actively resistance training should avoid chronic energy deficits, going on to write that an energy deficit of even 500 kcal per day could prevent lean mass gains, but not strength gains. (19)

Of note, “the closer you are to your ultimate potential for muscle gain, the greater the proportion of fat gain will occur alongside muscle gain.” (7) The goal then would be to minimize fat gain with a proposed ratio of 0.5:1 (i.e., 0.5 pounds fat gained to every one pound of lean mass gained). (7)

For trained individuals, start with a ~500-calorie daily increase from carbohydrates. If fat mass gain is of concern, increase protein in place of the carbohydrates. For the novice, increasing up to 1,000 kcal per day may be necessary. (18)


For those in a calorie surplus, aim for a range of 1.6-2.2 grams per kilogram body weight per day (g/kg/d). (20-21) For those in a calorie deficit, that number may increase upwards of 2.4 g/kg/d. (22)

Take-Home Messages

Always keep in mind that your best intentions, research, and implementation as a dietitian, even when the athlete is 100% following your plan, may not meet the original goals as written. Athletics continues to drive towards individualization, so continue within that trajectory and individualize your approach.

My best advice is to:

  • Collect comprehensive baseline data: Complete a full nutritional intake, including validated body weighing and composition protocols (i.e., no DXA scans immediately after practice).

  • Evaluate any population data you do have, compare it to some of the ideas in section 4 above, and create a reasonable goal. Ranges are encouraged to provide flexibility.

  • Ensure the athlete and high-performance team are aware of the goal and understand any nuances, especially for younger athletes who are new to the program.

  • Create nutrition resources for an athlete, ensuring their voice and preferences are reflected throughout the process (i.e., create something realistic and actionable for them and one that they're bought into).

  • Send the athlete off, with clear follow-up plans for checkins, weigh ins, and body composition measurements, plus scheduled re-evaluation periods.

Your first plan will not be your best plan, and you, the athlete, and high-performance team must anticipate that.

Further Reading

What is the muscle full effect and what would a 100-gram of protein do?

Review what literature does exist and how to use them with athletes (if at all).

Gaining weight healthfully and understanding the concepts of NEAT and fiber.

Apply muscle protein breakdown to the timing and content of nutrient-dense calories before bed.

Witard, O.C., Bannock, L., & Tipton, K.D. (2022). Making sense of muscle protein synthesis: a focus on muscle growth during resistance training. IJSNEM,32(1):49-61. 

Trommelen, J. (2023, May 4). The ultimate guide to muscle protein synthesis. Nutrition Tactics.


(1) Trommelen, J. (2023, May 4). The ultimate guide to muscle protein synthesis. Nutrition Tactics.

(2) Witard, O.C., Bannock, L., & Tipton, K.D. (2022). Making sense of muscle protein synthesis: a focus on muscle growth during resistance training. IJSNEM,32(1):49-61.

(3) Burd, N.A., Tang, J.E., Moore, D.R., & Phillips, S.M. (1985). Exercise training and protein metabolism: influences of contraction, protein intake, and sex-based differences. J Appl Physiol,106(5):1692-701.

(4) Cross, K.M., Granados, J.Z., Ten Have, G.A.M., Thaden, J.J., Engelen, M.P.K.J., Lightfoot, J.T., & Deutz, N.E.P. (2020). Protein fractional synthesis rates within tissues of high- and low-active mice. PLoS One,15(11):e0242926.

(5) Damas, F., Phillips, S.M., Libardi, C.A., Vechin, F.C., Lixandrao, M.E., Jannig, P.R., ... & Ugrinowitsch, C. (2016). Resistance training-induced changes in integrated myofibrillar protein synthesis are related to hypertrophy only after attenuation of muscle damage. J Physiol,594(18):5209-22.

(6) Damas, F., Phillips, S., Vechin, F.C., & Ugrinowitsch, C. (2015) A review of resistance training-induced changes in skeletal muscle protein synthesis and their contribution to hypertrophy. Sports Med,45(6):801-7.

(7) Aragon, A. Strategic bulking & cutting cycles: realistic ceilings of potential, productive rates of muscle gain & fat loss. Alan Aragon's Research Review [Internet]. 2022 October 1 [cited 2024 February 4]. Available from:

(8) Barakat, C., Pearson, J., Escalante, G., Campbell, B., & De Souza, E. (2020). Body recomposition: can trained individuals build muscle and lose fat at the same time? Strength Cond J,42(5):7-21.

(9) Jorgenson, K.W., Phillips, S.M., & Hornberger, T.A. (2020). Identifying the structural adaptations that drive the mechanical load-induced growth of skeletal muscle: a scoping review. Cells,9(1658):1-32.

(10) Aargaard, P., Andersen, J.L., Dyhre-Poulsen, P., Leffers, A.M., Wagner, A., ... & Simonsen, E.B. (2001). A mechanism for increased contractile strength of human pennate muscle in response to strength training: changes in muscle architecture. J Physiol,534(Pt 2):613-623.

(11) Abe, T., Kojima, K., Kearns, C.F., Yohena, H., & Fukuda, J. (2003). Whole body muscle hypertrophy from resistance training: distribution and total mass. Br J Sports Med,37(6):543-545.

(12) Franchi, M.V., Atherton, P.J., Reeves, N.D., Fluck, M., Williams, J., ... & Narici, M.V. (2013). Architectural, functional and molecular response to concentric and eccentric loading in human skeletal muscle. Acta Physiol (Oxf),210(3):642-54.

(13) Mandic, M., Rullman, E., Widholm, P., Lilja, M., Leinhard, O.D., ... & Lundberg, T.R. (2020). Automated assessment of regional muscle volume and hypertrophy using MRI. Sci Rep,10(1):2239.

(14) Mitchell, C.J., Churchward-Venne, T.A., Parise, G., Bellamy, L., Baker, S.K., ... & Phillips, S.M. (2014). Acute post-exercise myofibrillar protein synthesis is not correlated with resistance training-induced muscle hypertrophy in young men. PLoS One,9(2):e89431.

(15) Mitchell, C.J., Churchward-Venne, T.A., West, D.W.D., Burd, N.A., Breen, L., ... & Phillips, S.M. (1985). Resistance exercise load does not determine training-mediated hypertrophic gains in young men. J Appl Physiol,113(1):71-77.

(16) Trappe, T.A., Carroll, C.C., Dickinson, J.M., LeMoine, J.K., Haus, J.M., ... & Hollon, C.J. (2011). Influence of acetaminophen and ibuprofen on skeletal muscle adaptations to resistance exercise in older adults. Am J Physiol Regul Integr Comp Physiol,300(3):R655-62.

(17) Kouri, E.M., Pope Jr., H.G., Katz, D.L., & Oliva, P. (1995). Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med,5(4):223-8.

(18) Aragon, A. (2021). Protein: all of your burning questions answered [eBook edition]. Self published.

(19) Murphy, C., & Koehler, K. (2022). Energy deficiency impairs resistance training gains in lean mass but not strength: a meta-analysis and meta-regression. Scand J Med Sci Sports,32(1):125-137.

(20) Morton, R.W., Murphy, K.T., McKellar, S.R., Schoenfeld, B.J., Henselmans, M., Helms, E., ... & Phillips, S.M. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med,52(6):376-384.

(21) Bandegan, A., Courtney-Martin, G., Rafii, M., Pencharz, P.B., & Lemon, P.W. (2017). Indicator amino acid-derived estimate of dietary protein requirement for male bodybuilders on a nontraining day is several-fold greater than the current recommended dietary allowance. J Nutr,147(5):850-857.

(22) Hector, A.J., & Phillips, S.M. (2018). Protein recommendations for weight loss in elite athletes: a focus on body composition and performance. Int J Sport Nutr Exerc Metab,28(2):170-177.


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