There are limits to a person's natural ability to build muscle, a genetic limit. Although there's no definitive method for determining the precise amount of muscle an individual can build without resorting to the use of performance enhancing drugs, there are formulas that give a range of potential that is applicable to most people.
One such model was proposed by Martin Berkhan, a well-known online fitness consultant who developed a modified intermittent fasting method for gaining lean mass while losing fat that he calls Lean Gains. Martin's article.
According to Martin, the resulting number range represents the max potential body weight range for a stage-ready male bodybuilder at 5-6% body fat. According to Martin's formula, at 183 centimeters (6 feet) tall, my maximum weight at 5-6% body fat would be 178.5 - 187 pounds. What Martin's formula doesn't take into account is those genetically gifted outliers who are able to build more muscle, sometimes even much more.
Another individual, name Eric Helms, did his own research into maximum muscle building potential. Specifically, he looked at research performed in 1995 that examined the fat free mass index (called the FFMI) of 83 steroid using bodybuilders against that of 74 non-users. Based on his research, he came up with his own formula to determine a number that indicated the level of fat free mass. In order to use this formula, you need to know your percentage of body fat so you can determine your fat free mass:
FFMI = fat free mass in kilograms/(height in meters)2
In the study, the average FFMI of steroid users was 25, while that of the non-users was 22 - although it should be noted that there were a few non-users who approached a FFMI of 25. The max FFMI in the steroid users group was 32; in the non-users it was 25. Based on this research, a FFMI of 25 was suggested as the max for a natural body builder.
Fat Free Mass Index Interpretaton for Men
16 - 17: below average
18 - 19: average
20 - 21: above average
23 - 25: superior
26 - 27: scores considered suspicious but still attainable naturally
28 - 30: highly unlikely scores to be obtained naturally without steroid usage
Dr. Casey Butt is life-long student of natural bodybuilding. He has degrees in physics with an applied math minor, pure math with a biochemistry minor, electrical engineering, a Masters in mechanical engineering and a Ph.D. in controls engineering. His formula takes into consideration an individual's bone structure, determining frame size as measured by the circumference of the ankle and wrist:
Casey also came up with formulas to predict maximum muscular measurements:
Lastly, Casey also offers us a formula for predicting your maximum total body weight at different body fat levels:
Max Body Weight = (Lean Body Mass/(100-Bodyfat%))x100
Enter your values below to see result according to all of the above formulas: