Date Posted... 30th Jun 2019
HYPERPLASIA is an increase in the number of muscle fibers.
HYPERTROPHY is an increase in the size of the already existing fibers.
Hyperplasia. What evidence do we have?
Antonio, J. and W.J. Gonyea in 1993 (1) conducted a study where they added weights to a bird equal to 10% of its body weight, followed by increments of 15%, 20% 25% and 35% of its weight. Each weight increment was interspersed with a day rest. After just 28 days under strain, the bird increased muscle mass by 334% and a 90% increase in fiber number (hyperplasia!).
However, I know what you are thinking. What the actual F does a bird have to do with me? However, I also know you are very interested in increasing muscle mass by 334% for just 28 days of effort. Now whilst the bird does not show a direct correlation to humans it does show that hyperplasia can be possible with the right stimulus!
Rats have been used by Japanese researchers (2) to also study muscle growth. They made Rats squat through electrical stimulation (don’t try this on your mate that skips legs) and the results were a 14% muscle fiber count increase of the plantaris muscle.
Another point to raise that could strengthen the argument of Hyperplasia occuring is that, Researchers have frequently seen small fibers in enlarged muscles. Initially they thought this was to be a sign of Muscle atrophy, however it seems crazy that a muscle fibre could atrophy when the muscle as a whole hypertrophies. It is more likely that these small fibers are newly made fibers. Although the research is slightly in direct, this could be the reason as to why they saw these results.
Hyperplasia in humans?
The biggest problem with human studies is how dense human muscle is. For example, one study (3) found that the tibialis anterior (front of your lower leg) had 160,000 muscle fibers and your biceps will contain 3-4x the amount, that’s up to 640,000 muscle fibers just in one part of your arms! So, trying to find new fibers within 640,000 is more than an easy counting exercise. Because of this, we must look at indirect human studies to show that hyperplasia is possible. For example, Larsson and Tesch (4) found that bodybuilders possessed thigh circumference measurements 19% greater than the average person yet the general size of the muscle fibers were not different. This tells us that hyperplasia is taking place, as the thigh circumference was much greater with little change in fiber size.
On the other hand, contradictory studies would advise that bodybuilders tend to have LARGER muscle fibers rather than MORE of them when compared to a control population (23, 30, 36). It is argued that some bodybuilders will have muscle fibers that are similar if not smaller in size when compared with untrained individuals suggesting that fiber size is largely affected by other factors such as genetic endowment when compared to training.
I don’t know about you but that seems to be a rather weak conclusion? How can, historically, body builders be training as hard as they are and look like they do to with muscle fibers the same size as those who are untrained? It would be more plausible to suggest that the larger muscle mass found in body builders is as a result of both hypertrophy and hyperplasia.
But the question now is, when in humans can Hyperplasia occur?
There are two mechanisms in which fibers can be formed. The first is where a fiber splits and becomes two or more fibers or the second is when satellite cells can be activated. Satellite cells are myogenic stem cells that are involved with skeletal muscle. When you exercise, stretch or injure a muscle fiber, satellite cells are activated which creates myoblastic cells (new muscle cells). Their myoblastic cells then either fuse to existing muscle fiber to get bigger or they can form with each other to create a new muscle fiber. Thus achieving hyperplasia.
How to damage a muscle to the point of hyperplasia?
We have all read online, in magazines or books that eccentric contractions are vitally important to hypertrophy. We also know that eccentric contractions can cause greater injury compared to concentric or isometric contractions. Both in animal and human studies these facts have been proven (8,9,10).
However, in the real world in day to day life or even in the gym we do not perform pure concentric, isometric or even eccentric contractions! We do a combination of all three. So the most important take away from this is that all exercises should be performed with a controlled descent of the weight being lifted (if maximum muscle is the goal).
How do you achieve hyperplasia?
Can Joe Bloggs who lifts 4 times a week increase the number of muscle fibers in his biceps? Probably not, certainly not enough to notice.
However, if a bodybuilder is 250lbs, 5 foot 8 and shredded. It would be both ignorant and naïve to assume that this was gained only as a result of hypertrophy. But how exactly the bodybuilder managed it is truly unknown to them and science as there is no direct cause for hyperplasia at this time.