Each muscle fiber is made up of sarcoplasm and myofibrils. The sarcoplasm is a fluid that contains things like glycogen (stored carbohydrates), water, ATP (energy source), minerals (like calcium), fats, and oxygen-binding proteins (called myoglobin).
Although the sarcoplasm is needed for muscle function, it does not directly generate the force/tension that can move a resistance.
On the other hand, the myofibrils are chain-like structures made up mostly of two proteins (called actin and myosin) that can contract in a muscle fiber. This just means these proteins work together to generate force/tension to move a weight.
The majority of space inside a muscle fiber is also filled with the myofibrils (usually 75% or more) and a single muscle fiber may have 1,000 myofibrils or more. Things like the sarcoplasm fill the small remaining area in the muscle fiber.
Myofibrillar hypertrophy causes the size and number of myofibrils to increase making the muscle larger and stronger since it can generate more force/tension.
During Sarcoplasmic Hypertrophy the myofibrils don’t change at all but the amount of sarcoplasm fluid increases instead.
Since the muscle is now bigger but not any stronger, Sarcoplasmic Hypertrophy is typically called non-functional hypertrophy because the muscle cannot generate any more force.
Just like myofibrillar hypertrophy, Sarcoplasmic Hypertrophy would also cause a muscle to become bigger since the muscle fibers are made up of both the myofibrils and sarcoplasm.
Is Sarcoplasmic Hypertrophy a Myth?
Yes, no, umm maybe, probably not…I don’t know.
There is some debate if Sarcoplasmic Hypertrophy can even occur.
Of course that doesn’t make it so.
Even if you look at the many studies on Sarcoplasmic Hypertrophy as Greg Nuckols has, there isn’t conclusive scientific agreement one way or another.
Part of the problem is the difficulty in actually being able to directly measure the amount of myofibrils vs. sarcoplasm in a muscle fiber.
The more direct method involves removal of some muscle tissue, which many people seem reluctant to do (I wonder why).
The indirect method such as predicted vs. actual force development from a known muscle size have a lot of possible errors leading to inaccurate conclusions.
Strength is very dependent on muscle size but is also a skill that needs to be developed. Just because you have the muscle doesn’t mean you fully use all of its available strength.
So is Sarcoplasmic Hypertrophy a myth?
In the end you will have to come to your own conclusions and the internet could make that very confusing and difficult.
Just remember, the sarcoplasm is needed for muscle function.
During any myofibrillar hypertrophy the sarcoplasm will also increase as necessary to support the new/larger myofibrils. Again, the myofibrils need the sarcoplasm to function.
How much the sarcoplasm will increase is influenced by genetics/nature and possibly the type of training used.
The sarcoplasm is also made up of things determined mostly from diet like glycogen, water and minerals so there will be natural fluctuations in the amount present. Increases in these things could increase the size of the sarcoplasm without changing the myofibrils.
Myofibrillar vs. Sarcoplasmic Hypertrophy
Now the real debate and myth is that the type of training you use can cause Sarcoplasmic Hypertrophy and myofibrillar hypertrophy to occur totally separate from each other.
The myth goes that a bodybuilder’s training causes just Sarcoplasmic Hypertrophy (using lighter weights with high reps and volume). That is supposedly why they are weaker but bigger than the powerlifters and Olympic lifters that train for myofibrillar hypertrophy (heavy weights for low reps and volume).
Since the sarcoplasm is not actual muscle fibers, bodybuilders are also said to have fake or puffy muscles unlike the supposedly dense muscles of strength athletes.
But if the muscles on bodybuilders were 100% Sarcoplasmic Hypertrophy, bodybuilders would not be any stronger than if they never lifted weights since the sarcoplasm doesn’t generate force. Following the same logic, endurance athletes would have the largest muscles from all the reps and volume they do.
Of course that’s not the case.
There are many things to consider but primarily that bodybuilders are concerned with muscle isolation not just the amount of weight used. Strength athletes just want to lift more weight, regardless of the muscles used. They don’t care if they “feel” the muscle work.
Bodybuilders also train and develop more muscle fiber types, especially Type I fibers, by using a wider variety of weights and reps than strength athletes do.
When a muscle is sufficiently stressed to cause hypertrophy (muscle growth), both myofibrillar AND Sarcoplasmic Hypertrophy will occur. They are dependent on each other, it’s just how the body works.
The amount each increases can be influenced by the type of training used since the body adapts as needed to its stress environment.
A strength athlete will definitely provide enough stress from heavy weights to trigger myofibrillar hypertrophy. But there will also be some Sarcoplasmic Hypertrophy to support the new/larger myofibrils.
A bodybuilder must also use sufficiently heavy weights to trigger muscle growth (both myofibrillar and sarcoplasmic). Although the weights used might be somewhat lighter, muscle fatigue with heavy loads can still cause the necessary triggers for muscle growth.
A bodybuilder that uses higher volume in their training may cause their sarcoplasm to grow even larger than in a strength athlete because they need more energy as glycogen and ATP, both of which are stored in the sarcoplasm.
In the end if a muscle is properly stressed, BOTH myofibrillar and Sarcoplasmic Hypertrophy will occur. Bodybuilders don’t just cause Sarcoplasmic Hypertrophy to occur completely by itself.
In general, the heavier weights are needed for myofibrillar hypertrophy while higher volume favors more Sarcoplasmic Hypertrophy.
Sarcoplasmic Hypertrophy Workout and Training
Unlike myofibrillar hypertrophy that comes when the myofibrils are sufficiently stressed, additional Sarcoplasmic Hypertrophy must be triggered by forcing the sarcoplasm to further increase in size.
Knowing that the sarcoplasm is made up primarily of glycogen, water, ATP, and non-contractile proteins, we must use training (and diet) to try and increase those things.
One way is by forcing the muscle to do more work with sub-maximal loads.
One of the most common bodybuilding training programs used is 3X10 (3 sets of 10 reps all to muscular failure using around 75% of maximum weight).
These higher workload volumes and reps help to use up the muscle glycogen and ATP.
After using up the glycogen and ATP, the GOAL is to then trigger super-compensation so that extra glycogen and ATP can be forced into the sarcoplasm.
As we saw with myofibrillar hypertrophy, a muscle fatigued with heavy weights will also trigger protein synthesis.
Protein synthesis will cause both myofibrillar hypertrophy (increase in contractile proteins) and Sarcoplasmic Hypertrophy (increase in non-contractile proteins) to occur.
Now the important part is that when glycogen is stored in the body, additional water is stored along with it as well.
How much water? It’s generally reported about 3 grams of water for every one gram of glycogen (although this study disputes that number).
Creatine intake may also help as it has been shown to be effective at increasing both ATP and water storage inside a muscle.
In theory all of this would increase the size of the sarcoplasm causing Sarcoplasmic Hypertrophy, assuming your diet provides enough carbohydrates (glycogen), protein, and water.
Again, Sarcoplasmic Hypertrophy and myofibrillar hypertrophy will not occur completely on their own.
BUT your training may help cause more Sarcoplasmic Hypertrophy over what occurs with traditional strength training (heavy weights for low reps and volume).