The factors that contribute to favorable bodybuilding genetics range from molecular-level dynamics to overall muscle shape. Since no one has ever performed tests to identify many of those factors in elite bodybuilders, what follows is speculation based on current science.
Your genetic potential is known as your genotype. That refers to the genes you were born with, and you can’t change it. What you can change is your phenotype, which is the specific physical characteristics created by the interaction between your genetic potential and the environment. The environment includes training, nutrition and mental outlook—in short, the controllable factors.
Your genotype is expressed in enzyme activities, hormone balance and muscle fibers. For example, while the average human musculature features a 50/50 balance of fast-twitch and slow-twitch muscle fibers, research has shown that elite long-distance runners have an abundance of slow-twitch fibers— up to 90 percent—which enables them to metabolize oxygen more effectively than the average person. Sprinters, who need power more than endurance, show the reverse: higher levels of power-producing fast-twitch muscle fibers.
For bodybuilding purposes, a higher level of fast-twitch fibers is more conducive to muscular growth. The length of a muscle belly offers some indication of fiber content. Longer muscle bellies foster greater potential for muscle growth. You can see that in trainees who have high calves, which is an example of a short muscle belly. They have a difficult time getting their calves to grow simply because they don’t have an abundance of fast-twitch fibers there.
Certain genetic attributes are considered highly desirable for bodybuilding success. Starting out with a mesomorphic structure, or being inclined to natural muscularity, is an obvious plus. Most people, however, are a combination of body structures, such as mesomorphic/endomorphic, which means muscular and fat. The majority of bodybuilding champions are mesomorphic/ectomorphic, which means muscular and thin. That’s evident when they quit training or lay off for any reason. They often appear to “shrink” and recede back to their natural skinniness.
While it’s possible for a meso/endo to become an elite bodybuilder, it’s more difficult. People with that combination often have a greater abundance—in both number and size—of fat cells. So they have an uphill battle in achieving the thin-skinned appearance of today’s successful competitors. It can be done, but it isn’t easy. That’s where mental toughness and discipline come into play.
Over the years certain bodybuilders have come close to perfection in shape and structure, including Steve Reeves, Sergio Oliva and Matt Mendenhall. That ideal structure is rare, and it isn’t related to the degree of muscular size the athlete achieves. Those who don’t have such ideal structures will be glad to know that most of the champs have succeeded without one.