Why Some People Struggle to Build Muscle: Exploring the Genetic Factors

Building muscle mass is a goal for many individuals, but it can be more challenging for some than others. Understanding the biology behind skeletal muscle growth and the influence of genetics can shed light on this phenomenon.

The process of muscle growth occurs when muscle cells synthesize new proteins at a faster rate than existing proteins break down. Weightlifting and resistance exercises create tension on the muscles, triggering protein synthesis. Muscle damage during exercise can also stimulate growth, hence the popular saying “no pain, no gain.”

However, individuals who are new to exercise or engage in high-intensity training may experience excessive muscle damage. In such cases, the body uses a significant portion of protein synthesis to repair muscle fibers and reduce inflammation during rest, limiting muscle growth. To optimize growth while minimizing damage, focusing on concentric contractions (muscle shortening) rather than eccentric contractions (muscle lengthening) is recommended.

Within muscle fibers, proteins like mammalian target of rapamycin (mTOR) promote muscle protein synthesis in response to tension, while proteins like myostatin regulate muscle growth. Some animals, such as “bully” whippets, genetically suppress myostatin, leading to significant muscle growth. Regular resistance training in humans can decrease myostatin secretion over time, potentially accelerating muscle gains.

Muscle fibers are tubular cells containing multiple nuclei that cannot divide. Although protein synthesis contributes to muscle growth, the limited potential for division in these nuclei restricts overall muscle growth. Satellite cells, muscle stem cells, compensate for this by donating their nuclei to growing muscle fibers. Age-related decline in satellite cells can make it more challenging to regain muscle mass later in life, but exercise can stimulate satellite cell proliferation.

Genetics also play a role in muscle growth. Individuals have a mix of two muscle fiber types specialized for different exercises: fast-twitch and slow-twitch fibers. Fast-twitch fibers have a higher propensity for growth compared to slow-twitch fibers. Those who struggle to build muscle may have a smaller proportion of fast-twitch fibers. While this ratio is largely genetically determined, it can be influenced by focusing on weightlifting over endurance training.

Sex differences also impact muscle growth. Testosterone, a hormone more prevalent in males, enhances protein synthesis and activates satellite cells. This hormone disparity during puberty may explain why males generally have more muscle mass than females. However, when adults undergo similar weightlifting programs, their gains relative to size tend to be comparable between sexes.

Recent research has identified ribosomes, the molecular machines responsible for protein synthesis, as another potential genetic factor affecting muscle gains. Genetic variations in ribosomes can influence protein synthesis levels and the types of muscle proteins produced.

While genetic factors can make building muscle more challenging for some individuals, evidence suggests that everyone’s muscles can adapt and grow. By lowering myostatin, stimulating satellite cells, and focusing on specific training, individuals can optimize their muscle growth potential.