Learn how genetics, muscle fiber types, hormones, and techniques impact muscle growth. Adapt and maximize gains with science-backed insights.
Why is building muscle more challenging for some individuals compared to others? What happens within muscle cells after a workout? Additionally, how are genetic factors intertwined with the journey of a gym enthusiast?
A quick online search often highlights the importance of following a high-calorie, high-protein diet, progressively increasing resistance, and incorporating rest to support muscle mass development.
However, diving deeper into how these practices influence skeletal muscle at the cellular level can provide a better understanding of the growth process.
Weight training offers benefits for all, regardless of whether the primary goal is significant muscle gain. With age, muscle mass gradually declines, making it increasingly challenging to reverse the process as frailty sets in, according to Kevin Murach, a researcher specializing in muscle growth at the University of Arkansas.
“You lose muscle mass with age, and it becomes exceedingly difficult to reverse course the frailer you become.”
Growth occurs when muscle cells synthesize new proteins faster than the breakdown of existing ones.
Resistance from weightlifting or similar exercises stimulates this synthesis, while muscle damage that causes soreness also contributes to the process. This supports the well-known saying, “no pain, no gain.”
However, if physical activity is unfamiliar or if high-intensity training is performed, excessive muscle damage may occur. In such cases, much of the synthesis during rest is redirected toward repairing fibers and reducing inflammation rather than building additional mass. Focusing on concentric contractions, where muscles shorten as resistance is applied, rather than eccentric ones, which involve muscle lengthening, may help maximize tension while minimizing damage.
The Science of Muscle Building
Within individual muscle fibers, certain proteins, such as the mammalian target of rapamycin (mTOR), become activated by tension and contribute to growth by promoting muscle protein synthesis. Others, like myostatin, act as regulators that limit excessive muscle growth.
In some animals, genetic suppression of myostatin allows for significant muscle gains. This is observed in certain muscular racing dogs, known as “bully” whippets. As noted by Kevin Murach, “The breaks are taken off of muscle growth, so the muscle becomes very large.” In humans, consistent resistance training gradually reduces the secretion of myostatin by muscle cells, potentially facilitating faster muscle growth over time, he explained.
Muscle fibers, which are tubular muscle cells, differ from other cell types due to the presence of multiple nuclei, none of which are capable of division. While protein synthesis supports muscle mass increases, the inability of these nuclei to divide imposes a limit on growth potential. Muscle stem cells, referred to as satellite cells, help overcome this limitation by donating additional nuclei to growing muscle fibers.
The number of satellite cells decreases with age, which may explain why muscle recovery and growth become more difficult later in life. However, this decline can be partially mitigated through exercise, which stimulates the proliferation of satellite cells and supports ongoing muscle development.
How is muscle growth influenced by genetics?
The challenge of building muscle can vary widely and is partly controlled by genetic factors. Efforts such as increasing protein intake and intense strength training may not yield the same results for everyone due to these underlying influences.
Muscle fiber types
Muscle fibers consist of two main types, each specialized for different activities:
- Fast-twitch fibers support powerful, explosive movements and are more likely to grow in size.
- Low-twitch fibers are better suited for endurance and joint stabilization.
A lower proportion of fast-twitch fibers may contribute to difficulty in gaining muscle mass. While the ratio of fiber types is largely determined by genetics, Kevin Murach noted:
“It can shift — you’re not stuck with what you have.”
Resistance training, rather than endurance-based exercise, can encourage fast-twitch fibers to dominate, although these adaptations remain specific to the trained muscles.
Sex related factors
Testosterone, often referred to as a “male” hormone, plays a role by boosting protein synthesis and activating satellite cells. Higher testosterone levels during puberty could explain why males generally have more muscle mass than females at baseline. However, when adults engage in the same weightlifting programs, gains relative to body size are equivalent across sexes.
The transient testosterone increases caused by exercise do not significantly contribute to growth.
Genetic variations in ribosomes
The molecular structures responsible for protein synthesis represent another factor affecting muscle growth. Differences in ribosome types and quantities may influence protein synthesis rates and the specific proteins produced in muscle tissue.
Summary
- These genetic elements can make muscle growth more challenging for some, creating disparities in results.
- Despite this muscle adaptation and growth remain possible for all.
- Reducing myostatin levels, increasing satellite cell activity, and influencing muscle fiber ratios increase muscle development.
