What is the genetic potential for muscular development?

Question

I've heard the concept of "genetic potential" thrown around when referring to bodybuilding. They say that people are hardwired to reach certain size. I have the following questions regarding this elusive concept.

Scientific validity

Have scientists singled out the gene that determines the genetic potential a person's muscles? Or is the concept purely based off observation from the bodybuilding community?

Plateau

How can you differentiate between hitting a plateau and hitting your genetic potential? Should a person who's been unsuccessfully trying to break a plateau for over a year give up because it's not really a plateau but rather a genetic brick wall?

Hard Limit?

Is the limit a hard limit? For example, the gene says one person's upper arm circumference will not exceed 26 inches no matter what. Or is it a ballpark limit? That is, a person will struggle to get past the suggested limit, but will have an exponentially harder time going past that limit.

Answer 1

Based on what I've read, we do have a genetic potential, but what exactly that is for any person is nearly impossible to determine.

Scientific Validity - Dr. Casey Butt did a study based on the top bodybuilder athletes that provided some formulas to estimate your genetic potential. Now, as he describes in the article, the study was based on observing the body building community, and the numbers are not hard limits. However, you would have to train harder than the people he used in the study. The formulas are fairly accurate when applied back on the complete population that the formulas were generated from.

Plateau - Plateaus are an indication that either the type of stress you are applying is not enough to cause adaptation, or that you do not have enough recovery to allow adaptation to complete. As you become more and more of an advanced athlete, you will have to vary the types of stress (endurance rep ranges, strength rep ranges, and changing assistance exercises) to stimulate the type of adaptation you want. Practical Programming for Strength Training by Dr. Kilgore and Rippetoe have a lot to say about that--whether you are interested in strength or physique the same principles apply.

Hard Limit - Using the same reference in the last bullet point (Practical Programming), there are some graphs that help illustrate what you suspect. Essentially, the graph of results over effort is logarithmic. In short as a beginner, your adaptation is quick and you can make incredible gains very quickly. The closer you get to your genetic potential (the limit in calculus terms), the more work you have to put in and the more carefully you have to manipulate all the variables to help you progress. An elite lifter will only be able to make an increase once or twice a year.

Sarcopenia - Getting old sucks, and one of the reasons for people who use weights is Sarcopenia. Essentially the older you get the more muscle mass you lose. For sedentary people it can be up to 15% per decade after 30-35. For weightlifters (and by extension bodybuilders) will slow the loss down to 5% per decade (per Practical Programming). Theoretically, if you hit your genetic peak before turning 30, the capacity of what you can do will diminish as you get older. Lifting weights is one way of slowing down those changes.

Answer 2

I'll answer point by point.

Scientific Validity - I doubt there's any single gene that controls one's maximum physical ability. When people use the term, they are referring to the fact that if someone worked out the ideal amount, with an ideal schedule, ideal nutrition, and everything else perfect, their genetic makeup would still cause them to experience diminishing returns in terms of performance and hypertrophy.

Plateau - unless you're an elite athlete or national-level bodybuilder, you have not reached or come near your genetic potential. If you are, then it's still the case that you'll experience diminishing returns instead of a brick wall.

Hard Limit - as you might surmise, it's my understanding that while there are physical limits due to physics and the human form, people are referring to a rather amorphous thing here. Your "exponentially harder" theory seems correct.