Let’s Talk Hyperplasia.

What is Hyperplasia?   

Hyperplasia is an increase in the number of muscle fibers.   

What is Hypertrophy?   

Hypertrophy is an increase in the size of already existing muscle fibers.   

Stretching to cause Hyperplasia  

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!  

Exercise to cause Hyperplasia  

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.   

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 part of one 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, Hygaard and Neilsen did a cross-sectional study (4) and they found that swimmers had smaller Type I and IIa fibers in the deltoid muscle when compared to controls even though the overall size of the deltoid was greater.   

Other studies have demonstrated that bodybuilders have larger fibers (5,6,7), not more fibers when compared to the control population. However other scientists suggest that bodybuilders and other athletes have a greater genetic endowment of muscle fibers. If this was true, then intense training over decades has produced the best average size of muscle fibers but this cannot be true as this would mean that some people just train their muscle fibers from below average to average. From a logical perspective, this does not work, and it makes more sense that both hypertrophy and hyperplasia does occur in humans.   

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 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 of vital 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.  


(1) Antonio, J. and W.J. Gonyea. Progressive stretch overload of avian muscle results in muscle fiber hypertrophy prior to fiber hyperplasia. J. Appl. Physiol., 75(3): 1263-1271, 1993.  

(2) 39. Tamaki, T., S. Uchiyama, and S. Nakano. A weight-lifting exercise model for inducing hypertrophy in the hindlimb muscles of rats. Med. Sci. Sports Exerc. 24(8): 881-886, 1992  

(3) 37. Sjöström, M., J. Lexell, A. Eriksson, and C. C. Taylor. Evidence of fiber hyperplasia in human skeletal muscles from healthy young men? Eur. J. Appl. Physiol. 62: 301-304, 1992.  

(4) Nygaard, E. and E. Nielsen. Skeletal muscle fiber capillarisation with extreme endurance training in man. In Eriksson B, Furberg B (Eds). Swimming Medicine IV(vol. 6, pp. 282-293). University Park Press, Baltimore, 1978  

(5) Häggmark, T., E. Jansson, and B. Svane. Cross-sectional area of the thigh muscle in man measured by computed tomography. Scand. J. Clin. Lab. Invest. 38: 355-360, 1978  

(6) MacDougall, J. D., D. G. Sale, S. E. Alway, and J. R. Sutton. Muscle fiber number in biceps brachii in bodybuilders and control subjects. J. Appl. Physiol. 57: 1399-1403, 1984.  

(7) Schantz, P., E. Randall Fox, P. Norgen, and A. Tyden. The relationship between mean muscle fiber area and the muscle cross-sectional area of the thigh in subjects with large differences in thigh girth. Acta Physiol. Scand. 113: 537-539, 1981.  

(8) Hather, B. M., P. A. Tesch, P. Buchanan, and G. A. Dudley. Influence of eccentric actions on skeletal muscle adaptations to resistance training. Acta. Physiol. Scand. 143: 177-185, 1991.  

(9) Wong, T. S. and F. W. Booth. Protein metabolism in rat gastrocnemius muscle after stimulated chronic concentric exercise. J. Appl. Physiol. 69(5): 1709-1717, 1990.  

(10) Wong, T. S. and F. W. Booth. Protein metabolism in rat tibialis anterior muscle after stimulated chronic eccentric exercise. J. Appl. Physiol. 69(5): 1718- 1724, 1990.  

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