The “natty limit” is an interesting concept. It is a way to determine what is possible without steroids and Peformance Enhancing Drugs (PEDs). Just because you are under this limit does not prove you are natty. There are a LOT of lazy, shortcut seeking gym goers in search of that quick “aesthetic” physique who are hardcore steroid users but yet dont even have the physique of someone who has done it naturally with hard work and clean nutrition. Also, just because you are over this line does not prove that you are using steroids, it just makes it very likely that you are lying about your “natty card”. In my experience, these natty limit charts are VERY hard to achieve except for the top 0.01% of the genetically gifted and I am personally only in the top 1%. I have always been 10-15lbs under the natty limit line. Remember, the natty limit line was based on research that simply looked at a bunch of bodybuilders before steroids were available and used these data points to try and determine equations which predict the natty limit. Today, our nutrition and exercise science has advanced beyond what was know in the 1950s. Also some ethnic makeups are genetically advantaged and some are genetically disadvantaged. In my experience, its far easier for a Scandinavian and some Africans to approach the natty limit than all Asians, Latinos, or Central Europeans. Again, this generalization means nothing as in every race there are outliers to the average curves. Here is the research that these “natty limit” curves are based on.
Natty Limit for Body Weight with Sixpack Abs (kilograms)