After 12 weeks of training, some participants' strength doubled and their muscles grew significantly, while others saw little or no change. Participants with the worst results lost 2% of muscle mass and did not increase strength at all, while the genetic lucky ones increased muscle mass by 59%, one-repetition maximum by 250%. And this is with absolutely identical loads.

Let's understand why the indicators differ so much and how genetics affects muscle growth.

In his research, Dr. Robert Petrella suggested that the difference in results with the same physical load depends on the number and efficiency of satellite cells - the stem cells of muscle tissue.

At the beginning of the experiment, the participants with the best indicators had an average of 21 cells per 100 muscle fibers, and by the 16th week of training, the number of satellite cells increased to 30 per 100 fibers.

Participants whose muscles did not grow during the experiment had about 10 satellite cells per 100 muscle fibers. This number did not change after training.

The dependence of sports results on genetics was confirmed by another study. As a result of the same training, 17 out of 66 participants increased the cross-sectional area of ​​the muscles by 58% (let's call them successful athletes), 32 participants - by 28%, and 17 genetic losers - by 0%.

The reasons for such a spread of results:

Another study showed that hypertrophs with high expression of key genes adapt to strength training faster than normal people.

In the past, genes that endowed humans with an economical metabolism were an evolutionary advantage, because it helped them survive in times of famine. Today, when our lifestyles include sedentary work and excess calories, these same genes cause health problems and obesity.

With the same diet, the results of the participants differed greatly and varied from 4 to 13 kilograms. People with the metabolic curse gained three times more weight than the lucky ones, accumulated 100% more calories and increased their visceral fat by 200%. The amount of visceral fat did not increase in the metabolic lucky ones.

Another study found that heredity accounts for 42% of subcutaneous fat and 56% of visceral fat. This means that genetics directly affects where your body stores fat.

Another study suggested that 40% of the variation in metabolic rate and energy expenditure for physical activity is genetic. Another study showed that body mass index is inherited by 40-70%.

A 1999 study found that genetics influence calorie intake. The same conclusion was reached by other scientists who studied the eating behavior of 836 participants. They found six genetic associations that increase calorie and macronutrient intake, including the gene for adiponectin, a hormone involved in glucose regulation and the breakdown of fatty acids.

The most well-known gene that increases physical performance is ACTN3, known as alpha-actinin-3. This gene is being studied to reveal a predisposition to certain sports.

There are two types of alpha-actinin protein - ACTN2 and ACTN3. ACTN2 is found in all types of muscle fibers, and ACTN3 in type IIb - fast and large muscle fibers that are activated by short-term loads and develop great force. Therefore, ACTN3 is associated with powerful force production.

Approximately 18% of people worldwide are ACTN3 deficient. Their bodies produce more ACTN2 to compensate for the deficiency. These people cannot perform explosive movements as quickly as those who have an abundance of this protein. For example, there are no people with alpha-actinin-3 deficiency among elite sprinters.

The angiotensin-converting enzyme (ACE) gene is also involved in sports performance. An increase in the frequency of the ACE D allele is associated with strong athletes and sprinters, while an increase in the frequency of the ACE I allele is more common in athletes with impressive endurance.

One study found that variants of the VNTR-1RN gene also affect physical development. This gene affects cytokines and enhances the inflammatory response and recovery processes after exercise.

After all these studies, one might think that a strong and beautiful body should be won in the genetic lottery. If you're not lucky, you can't do anything. In fact, it is not.

First, everyone has genetic issues that need to be worked on. Some people tend to accumulate fat, others find it difficult to increase muscle mass. Even among elite athletes, there are no people with perfect genetics, but they still work on their shortcomings and achieve their goals.

Secondly, these studies did not take into account the characteristics of specific people and did not select training and nutrition programs for each of them. Yes, with the same program, people with good genetics will show the best results, but if you choose the right load, even the worst genetics will not hinder you.

Strength, endurance, body composition, and training response are polygenic, multifactorial traits. A single ACTN3 or ACE variant—or a commercial “sports DNA test”—cannot reliably determine sport choice, talent, or future results.

It is more useful to monitor load tolerance, progress, sleep, injury, recovery, and available conditions. Genetic predisposition is neither destiny nor a guarantee; training should be adjusted to the person’s observed response.

Source: 2023 review of sports genomics.