Sarcoplasmic versus Myofibrillar Muscle Growth Theory

Without the proper understanding of the link between CNS (central nervous system) and muscle it is impossible to fully comprehend the mechanism of developing muscular strength. (See the article on STRENGTH here)

Such lack of proper understanding probably lead to creation of a theory with a sophisticated name “Sarcoplasmic vs Myofibrillar muscle growth”.

The theory goes like this:

-Bodybuilders have large muscle mass but lack in strength (which is basically not true)

-Weight lifters and others have smaller muscle mass but more strength (also dubious)

-There has to be a difference in the structure of muscles typical for bodybuilders and that of weight lifters (this is probably true although in a different way that this theory proposes)

-The explanation is that while bodybuilder’s muscle fibers are mostly inflated by sarcoplasmic fluid (wrong) the muscle fibers of weight lifters are thick, comprising of more protein

It should be noted that the theory originated among coaches, not in academia. True, it sounds attractive to many, especially to athletes doing power sports who are sick and tired of the bodybuilder’s perceived egocentricity and lack of athletic performance.

Before we delve into details of scientific evidence (or absence of it) concerning the Sarcoplasmic vs. Myofibrillar theory let’s try to (shortly) explain the difference between the power training and muscle growth training.

In most power sports there are usually a limited number of exercises (typically 2 or 3) which must be mastered. Let’s take powerlifting as an example. The 3 events are squat, bench press and deadlift. There is a specific way how those events must be carried out. So if your aim is to maximize your bench press you must invest most energy in training the very specific movement that involves specific parts of some muscles.

You train the CNS (central nervous system) to involve as many muscle fibers as possible in this very specific movement and you train mostly the specific parts of muscles.

There is no reason losing much of your time on such muscles as biceps that are not directly involved in your events. And of course, investing time and energy in training parts of, say, shoulders that are not involved in bench press makes little sense too.

In bodybuilding you try to achieve a balance: every part of every muscle is trained and strength stemming from CNS coordination is ignored.

So when we discount the importance of CNS in proper performance of various exercises, the muscle size of trained muscle is not very different in bodybuilders and athletes involved in power sports.

Some little understood differences may exist but they do not confirm the theory of “inflated” muscle fibers.

Scientific evidence

Tesch and Larsson described the muscle fibers of bodybuilders and weight lifters (http://www.ncbi.nlm.nih.gov/pubmed/6890445 ). There were indeed some differences but not as one would expect if Sarcoplasmic vs. Myofibrillar theory was valid. The bodybuilders’ muscle fibers were not larger. On the contrary: “…the percentage of FT fibers was less, mean fiber area was smaller and selective FT fiber hypertrophy was not evident. Values for fiber type composition and fiber size were more similar to values reported for physical education students and non-strength trained individuals.”

More importantly, there is no evidence for the sarcoplasmic/myofibrillar theory in scientific literature. Although mentioned in a book by Zatsiorsky and Kraemer (Science And Practice of Strength Training, 2006) the authors neither explain it nor provide any reference to scientific studies. Careful reading of the mentioned book also shows that its authors sometimes rely on limited, dubious or unverified sources and make statements not supported by solid scientific evidence (eg when describing muscular hyperplasia).

Does sarcoplasmic growth exist at all?

Just like myofibrillar protein synthesis, sarcoplasmic protein synthesis is a measurable value. But as the research shows (for instance N.A. Burd & colleagues, 2010), sarcoplasmic protein synthesis is only achieved by protein ingestion and is not influenced by resistance exercise.