Muscle growth generally occurs through the process of breaking down and repairing your muscle fibers. This process occurs in two ways: hypertrophy and hyperplasia. Although they both play a role in the growth of your muscles, they function slightly differently in hypertrophy vs hyperplasia.
Hypertrophy occurs when the muscle fiber cells increase in size, while hyperplasia occurs when the number of the cells themselves increases. In simpler terms, hypertrophy refers to cell size, and hyperplasia refers to cell quantity.
There is a dispute in modern science over muscle growth and how it occurs. Many believe that human muscle growth occurs purely through hypertrophy, while many believe hyperplasia also plays an important role.
How Exactly Do My Muscles Grow?
As any gym buff will tell you, muscle growth is key to your success for any of your workouts and weight loss goals. There are three different types of muscle tissue in your body:
Smooth Muscle Tissue: These muscles are not consciously controlled and do not have the same striation patterns the other forms of muscle tissue have. They are generally found in your internal organs and are particularly common in your gastrointestinal tract.
Cardiac Muscle Tissue: These are striated muscles but are also not something we consciously control. As the name would suggest, these muscle tissues are found along the walls of your heart.
Skeletal Muscle Tissue: These muscle tissues are striated and consciously controlled and tend to be the muscles in question when we discuss strength training or exercise.
Your muscles are constantly synthesizing and breaking down muscle proteins throughout the day. Whenever you synthesize more proteins than you break down, it is called hypertrophy, and whenever you break down more proteins than you synthesize, it is referred to as atrophy. When you are trying to gain muscle during your workout sessions, your goal is to achieve optimal hypertrophy.
Hypertrophy occurs when your muscles grow more because your muscle component cells grow. If your muscles are over-stimulated during workout sessions, this may cause disturbances in the muscle system that can spur specific signaling pathways to increase muscle cell size. Within the muscle system, the two forms of hypertrophy are myofibrillar and sarcoplasmic hypertrophy.
Myofibrillar Hypertrophy occurs when your muscle contraction parts (ex. myofibril) increase the size of your muscles. Since it triggers your contractor muscles, this form of hypertrophy is key to improving your strength and speed in the gym.
Sarcoplasmic Hypertrophy occurs when the volume of the sarcoplasmic fluid in your muscle component cells increases the size of your muscles. This form of hypertrophy does not provide you with any additional strength or speed but can cause your body to store glycogen in your muscles, which can improve your energy and endurance.
Check out this shoulder blasting workout for maximum hypertrophy.
Hyperplasia is the process wherein your skeletal muscles grow as your muscle fibers multiply. This is a slightly controversial topic since the evidence of hyperplasia in humans is slim. Many experts formerly believed that it does not exist in humans since we have no concrete evidence that it occurs during a controlled resistance training protocol.
However, while evidence of hyperplasia in humans is still a bit slim, we do have ample knowledge of its occurrence in similar animals such as birds, dogs, and mice.
Most experiments in the past observed hyperplasia as a process that may occur through the stretch. In 1973, a famous experiment attached a weight to a bird’s wing to stretch its back muscles for an extended period. The subsequent findings showed that the added weight increased the number of muscle fibers on the wing where it was attached.
Those who support the theory of human-based hyperplasia believe that there are roughly two ways it can occur in your muscles. Your satellite cells can spur the development of new muscle fibers, or your bigger muscle fibers may split into smaller muscle fibers.
One of the reasons it is somewhat challenging to examine hyperplasia in humans is that it is difficult to calculate the number of independent muscle fibers rather than simply measuring hypertrophy by observing muscle cell growth.
Does Exercise Lead to Hypertrophy or Hyperplasia?
Most scientific research indicates that exercise primarily results in muscular hypertrophy. This may be due in part to the ample research available on hypertrophy wherein scientists have measured the muscle’s cross-sectional area.
In 1986, Sports Medicine published a review that critiqued some studies that overemphasized hypertrophy in their work. The review claimed that the use of cross-sectional muscle measurements and the overestimation of longitudinal fiber growth showed a degree of methodological bias. This review claimed multiple studies had failed to correctly calculate the number of the muscle fibers because of their flawed hypertrophy-based methodology.
Today there are now a plethora of studies that show that muscle growth also occurs due to hyperplasia. The methodology for observing hyperplasia usually involves calculating the number of muscle fibers after the nitric acid digestion of the muscle.
Many of these studies compare bodybuilders to individuals who live a sedentary lifestyle to see how hyperplasia impacts muscle growth. Many of these subsequent findings did prove that these bodybuilders have more muscle fibers than those who live an inactive lifestyle.
However, one of the problems with these findings is that they do not account for any confounding variables that may have contributed to the increased muscle fibers in bodybuilders compared to other individuals. It can be intuitively true that a bodybuilder would grow more muscle fibers than the average individual, but the research on this subject is still somewhat inconclusive.
However, if you wish to target hyperplasia instead of hypertrophy in the gym, some workout experts believe that you should use stretch-based position exercises to spur the growth of more muscle fibers.
As the research with birds indicates, stretching your muscles with added weight may impact the number of muscle fibers in your body over a period of time. This may be a worthwhile strategy for some people but will only spur 5% of your overall muscle growth.
While the research on hyperplasia is starting to indicate that it does occur in humans, it is not as important for muscle growth as hypertrophy. Even the most generous studies indicate that hyperplasia may account for about 5% of your gains in the gym.
As such, it would not prove prudent to engage in any hyperplasia-inducing exercises for most of your training. However, if you want to work some hyperplasia-specific training into your daily regimen, then stretch-pause reps may be a good bet and doing four sets a week could be enough to induce your hyperplasia muscle fiber growth.
You could even do similar workouts with your calf muscles if they do not seem to be growing. But you should know that hyperplasia may take a long time to occur and likely will not be feasible unless you consistently use stretch-based position training for an extended period of time.
On the other hand, hypertrophy will occur whenever you train in the gym since the continual breakdown of your muscles will spur further muscle fiber synthesis and growth.