Muscle Hypertrophy Explained – Myofibrillar and Sarcoplasmic

Last updated on August 29th, 2018

muscle hypertrophy

Muscle hypertrophy = the increase in size of skeletal muscle via growth of its component cells.

It’s important that you understand at least the basics of the two ways in which your muscle fibers grow. They are:

  1. Myofibrillar Hypertrophy
  2. Sarcoplasmic Hypertrophy

You’ve probably seen diagrams of muscle fibers in cross-section. Imagine a pipe with smaller cables running through it and you’re most of the way there.

The cables represent the myofibrils and the space between them represents the sarcoplasm.

What Are Myofibrils?

Myofibrils – the cables in our pipe metaphor – are long chains of contractile proteins. They are responsible for the actual contractions of muscle fibers, for example when you lift a weight in the gym.

Myofibrillar Hypertrophy is therefore the growth in size and quantity of the myofibrils within the muscle fibers.

It is often said that myofibrillar hypertrophy directly corresponds to increased strength and maximum force output.

Training specifically and regularly with heavy weight (near the one rep max – 1RM – weight) is known to trigger myofibrillar hypertrophy.

What is the Sarcoplasm?

Going back to the pipe visualization, the sarcoplasm would be the areas between the cable-like myofibrils, except that the sarcoplasm is not empty space.

It is in fact much like the cytoplasm of the cell, which is comprised largely of the gel like substance that surrounds the nucleus.

You can think of the sarcoplasm as the softer “gel-like” substance surrounding the tougher, “rope-like” myofibrils.

Sarcoplasmic Hypertrophy can therefore be thought of as the enlargement of the sarcoplasm, or growth of the sarcoplasmic volume.

It can be assumed that sarcoplasmic hypertrophy directly corresponds to increased size of muscle fibers, and thus whole muscles.

There have been different theories offered as to the main purpose of sarcoplasmic hypertrophy.

You will find one generally accepted theory is that it increases the volume for muscle glycogen storage. Glycogen is basically globs of glucose, and a major source of energy.

For experts, the glycogen storage theory doesn’t paint the whole picture. The sarcoplasm is also a protein reservoir.

Expansion of the sarcoplasmic protein reservoir is probably a more logical explanation for sarcoplasmic hypertrophy, with increased glycogen storage being a concomitant or resultant benefit.

Training specifically for enhanced muscle size involves a lot more sarcoplasmic hypertrophy, and thus “high volume” training.

This usually means employing lower weight than specific strength training, but with higher reps, or “volume” sets, often to muscle failure.

Bodybuilders strive for aesthetic perfection

Strength versus Size Argument

Training predominantly for muscle size, i.e. bodybuilding is regarded by many as involving the growth of a lot of non-functional muscle mass.

That is to say a bodybuilder has huge muscles but can’t lift as much as someone much smaller who has trained as a powerlifter or weightlifter.

Physique goals are different as well. Bodybuilders strive for aesthetic perfection, muscle balance and symmetry, whereas powerlifters, weightlifters and strongmen train almost purely for strength and increased force output.

As such, the latter group tend to build physiques functional to their discipline or multi-discipline sport.

It follows that a bodybuilder has more sarcoplasmic volume and less myofibril density than a pure strength athlete.

The Skill Component

Much of a strength athlete’s ability to lift heavier weights than a bodybuilder is actually down to practice, and hence skill.

Powerlifters are regularly lifting weights that are high percentages of their 1RM (one rep max – the maximum weight they can lift for one rep only).

Furthermore, they use less movements than a bodybuilder because they strive primarily for the functional necessities of the sport.

By contrast, a bodybuilder must train every muscle of their body in various ways to grow each one to its maximum size.

So, where a strongman will squat, deadlift, pull, press and bench heavy weight in big compound movements, a bodybuilder will do that with moderate weight as well as working on all the satellite muscles of the smaller muscle groups.

Basically, the skill of regularly lifting bigger weight has a huge effect on the ability to do so.

Here’s an excellent article on the science of sarcoplasmic vs myofibrillar hypertrophy if you don’t mind getting into the technical stuff.

Mutually Beneficial but Not Mutually Exclusive

It turns out that sarcoplasmic hypertrophy is probably an inevitable function of resistance training. Whether you’re particularly aiming for size or not, there will be some increase there no matter what – after all, powerlifters aren’t exactly small.

The same can be said for myofibrillar hypertrophy. Of course someone who wants to get massive has to increase their strength significantly.

Bodybuilders also find it very easy to switch to all-out strength when they want to. Using the earlier metaphor again; this could be because they’ve built their pipes bigger, and so they can pack more cables in by changing up their training style.

If sarcoplasmic hypertrophy expands the sarcoplasmic protein reservoir then it stands to reason that this would serve the myofibrils well, if not providing direct functional strength in and of itself.

The non-contractile proteins in the sarcoplasm are heavily involved in anaerobic metabolism, which bodybuilding training relies on to a large degree.

Volume sets where the muscle tissue is worked way past lactate threshold and into the pure anaerobic zone would benefit greatly from increased sarcoplasmic proteins.

Sets of 3 or 4 reps with heavy weight you’re mostly remaining in the aerobic zone and using muscle creatine and phosphocreatine stores for energy. The sarcoplasm therefore doesn’t need to be as expansive if strength sets make up the habitual training regimen.

Summary – How Can I Use This Information?

Most people reading this won’t want to compete for the Mr. Olympia title, or indeed become the strongest man in the world, anytime soon.

The differences between sarcoplasmic and myofibrillar hypertrophy are important to understand because it gives you an idea as to how you should train for specific physique and strength targets.

I recommend a mixture of strength and volume training in order to get best of both worlds: functional and aesthetic.

In my opinion, sarcoplasmic hypertrophy shouldn’t be viewed as non-functional muscle growth because it obviously provides an energy pool for the muscles to tap into during anaerobic exercise.

Personally, I put more emphasis on strength training for myofibrillar hypertrophy because it provides a platform of stability and functionality, while helping to prevent injury and chronic exhaustion as you progress.

To get really big, you will need to lift heavy weight regardless of the weight’s proportion to your maximal output. Bodybuilders might squat, press and bench less weight than a pure strength athlete, but they still lift ridiculously heavy weights compared to the average person.

My advice: don’t choose between size or strength. Take the best of both.

Click here to read about the different muscle fiber types and what you should know as a lifter

About Ross T 31 Articles
Ross is well versed on all things connected to the supplement industry. He is a former martial artist and iron man. He is now turning his attention to physical conditioning.

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