There are many people who train for several months at a gym then become disheartened because they realize how their body responds to lifting is not the same as others. While everyone has an equal opportunity to workout, not everyone has an equal starting point.
This unequal starting part is based off genetics. The two main ways that genetics impact how well you can build muscle are through genes that affect hypertrophy and your unique muscle insertions.
There are other ways that your natural genes can affect muscle building such as your levels of testosterone and wether you have health issues, but the genes which primarily affect building muscle are the ones relating to hypertrophy and how your muscles are naturally shaped.
How Genetics Affect Hypertrophy
There are many genetics which impact how the body builds muscle in response to the stimulus of training.
This study was able to identify 47 different genes which play a role in muscle hypertrophy. For those interested, the most highly impactful genes for muscle hypertrophy are Asb15, Klf10, and Tpt1.
Since everyone has a unique set of genes, each individual will have an overall cumulative advantage or disadvantage based off the expression of these genes in their cells. Just because you have an ideal or non-ideal combination of these genes does not mean your body can not or can build muscle however. Poor genes just means that the response of muscular growth following lifting will not be as quick and dramatic as it is in other people.
You should know after the first 4-5 months of consistent training how well your body responds to working out and be able to tell where you fall in terms of genetics.
It is important to remember that these genetics just make it easier or harder to build muscle but they certainly do not limit you entirely. Weak genetics can be made up by having on point nutrition and training. Genetic advantages only matter if someone puts in the work and if you enjoy lifting and doing the work, the competitive advantage in building muscle is in your favor.
How Genetics Affect Muscle Insertions
A second way genetics can affect your physique in addition to hypertrophy is through muscle insertions.
Common muscle insertions that are easy to notice are where your abs are, the shape of your chest, and where your bicep attaches to the tendon. All of these are things which can impact how you look. For example, if your bicep attaches to the tendon higher up, the bicep will be closer to the shoulder and less long. If it attaches further down, the bicep will be fuller, longer, and may have a slightly more appealing shape.
Muscle insertions can not be changed without surgery so they are something which you have to own with pride. Testosterone can be elevated with supplements, lifestyle, and exogenous hormones, training volume can be elevated by working out more, but your muscle insertions are mostly immutable so it is best to accept and appreciate how your own muscles develop.
Where your muscle insertions are will not limit your ability to build muscle, they will just impact how the muscle looks after you build it. A common problem many people have is that they work out with the goal of building the physique someone else has. Since everyone has unique muscle lengths and insertions, you will never look exactly like another person.
The insertions and lengths of your muscles really only matter if you want to compete in bodybuilding, otherwise having the exact symmetry and perfect muscle bellies is barely even noticed by most people and rarely is significant enough to have an effect on training.
Can You Build Muscle Without Good Genetics?
While good genetics can allow some people to coast and build muscle without needing to exert themselves as much as others, good genetics can not replace mindset, discipline, and drive.
Regardless of your muscle insertions and genetic makeup, if you love lifting and do it with more passion and discipline than other people, you will have much more of an advantage than if you had amazing genetics.
If you do have amazing genetics, you will be able to notice after 4-5 months of lifting and this will be from how quickly you get results and how your physique is developing. If not, you probably are average in terms of genetics but this of course can be overridden by how you use them.
Genetics play a role in how your body responds to training and how physique looks.
There are 47 different genes which can be expressed differently in different people that all affect hypertrophy. There are also an infinite combination of muscle insertions you could have which will affect how your physique looks from training.
Overall, how good or bad your genetics are for building muscle is much less important than how consistent and disciplined you are with working out. A weightlifter with bad genetics who follows a program, has good nutrition, and is consistent will always surpass a weightlifter with good genetics who does the bare minimum and lacks passion for lifting.
Unless you are limited by serious disabilities or have medical problems that restrict your ability to train, the progress and results you get from working out are your own responsibility and genetics should not be an excuse for a physique to not be up to the standards you have for yourself.