Almost every muscle building article or blog post you see today seems to make at least some reference to myofibrillar hypertrophy and/or sarcoplasmic hypertrophy.
You’ll read about how the two are different, if they can be targeted/trained for separately, and if so, how.
However, there does seem to be some contention regarding these topics, depending on whose work you’re reading.
This article will take a brief look at the myofibrillar hypertrophy side of things.
What Is Myofibrillar Hypertrophy?
You’ve most likely read that myofibrillar hypertrophy is the dense-looking, “hard” muscle that’s built as a result of lifting heavy weights.
While that’s a more “broscience” description, it’s not too far off.
If you look at the anatomy muscle tissue, you’ll see that it’s essentially multiple strands of muscle fibers bunched together, encased in a sort of sheath called the perimysium.
The muscle fibers are then essentially made up of even smaller strands bunched together called myofibrils.
The gel-like substance between myofibrils is called sarcoplasm.
Simply stated, myofibrillar hypertrophy refers to increasing the thickness and overall number of myofibrils in muscle fiber.
Why Does it Matter?
While the muscle fiber is made up of both myofibrils and sarcoplasm, it’s the myofibrils that actually contract.
The more myofibrils your muscle tissue contains and the thicker they are, the more strength you can produce.
On the other hand, sarcoplasm can’t contract, therefore does not contribute to strength improvements.
The reason this matters to bodybuilders is because of the commonly held belief that an increase in myofibril number/thickness (i.e. – myofibrillar hypertrophy) leads to a more dense-looking muscle, while an increase in sarcoplasm leads to a softer, more “puffy” looking muscle.
“Broscience” vs Actual Science vs Anecdotal Evidence
Continuing with commonly held beliefs, it’s generally thought that myofibrillar hypertrophy occurs when lifting heavier weights for lower reps per set and moderate overall volume.
A typical example would be to use 80% of your one-rep max for sets of 5 reps or less for 20-25 total reps per exercise.
For the most part, science seems to back this up.
The question is if the general thought that lighter weight for higher reps and more total volume leads to an significant increase in sarcoplasm in the muscle (i.e. – sarcoplasmic hypertrophy).
There does seem to be some debate on this topic.
Depending on what you read, some will say that regardless of how you train, both myofibrillar hypertrophy and sarcoplasmic hypertrophy will occur at your own personal genetically predisposed rate.
When the idea that powerlifters tend to be way stronger for their size than bodybuilders arises, some say it’s not a question of myofibrillar hypertrophy vs sarcoplasmic.
Rather, it’s because powerlifters spend more time lifting heavy than lifting for volume, and simply practice the powerlifts more often.
Others still contend that while an increase in sarcoplasmic volume is possible, it’s not as long-term as myofibrillar hypertrophy is.
Should You Care?
Your best bet is to just train for whatever your physical demands are.
If you’re a powerlifter or an athlete, then strength is likely more important to you.
As a result, you’ll want to spend most of your time training heavy with lower reps.
If you’re a bodybuilder, you know that you need more volume, and that certain isolation movements don’t lend themselves to heavy weight and low reps, anyway.
So split your training between heavier weight/low reps and lighter weight/high reps.
Doing this can then allow you to monitor progress on a more quantifiable level – weight used, reps performed, effort level needed, etc.
Then you can just let the myofibrillar hypertrophy vs sarcoplasmic improvements happen on their own without you worrying about if you’re “properly” targeting either one.