Ask the Muscle Doc: Is Sarcoplasmic Hypertrophy Real?

Q: Is sarcoplasmic hypertrophy a real thing and, if so, is it affected by the type of training that I perform?

The sarcoplasmic hypertrophy theory has been around for decades and continues to be a source of controversy. The key to understanding it begins with a little muscle physiology.

Skeletal muscle is made up of approximately 75 percent water, with myofibrillar proteins (i.e., actin and myosin) and non-myofibrillar (i.e., sarcoplasmic) proteins comprising the balance. The fluid surrounding these proteins is the sarcoplasm, and it is critical for maintaining proper muscular function. The myofibrillar proteins are the ones responsible for carrying out muscle contraction.

It is generally accepted that lifting weights increases myofibrillar hypertrophy, which is a primary reason that building muscle is said to make you stronger.[1] During myofibrillar hypertrophy, there is a corresponding expansion of the sarcoplasm in which the ratio between myofibrillar protein and water remains relatively constant, thereby maintaining the integrity of the muscle cell. Still, it has been theorized that under certain conditions, growth of the sarcoplasm and increases in cellular components other than myofibrils can outpace that of the myofibrils—a phenomenon known as “sarcoplasmic hypertrophy.” The theory originally stemmed from research showing that differences exist in the composition of muscle fibers between bodybuilders and powerlifters, conceivably attributed to differences in training methodology.[2]

Initial work from McMaster University found that training-induced muscle fiber growth of the triceps involved an increase of the sarcoplasmic fractions with a corresponding slight decrease in myofibrillar area, providing early evidence that resistance exercise may indeed promote preferential sarcoplasmic growth.[3] More recent research by Cody Haun and colleagues offers further insights that the phenomenon may be training specific.[4]

The researchers put resistance-trained men on a six-week very-high-volume lifting program and then performed biopsies on the subjects’ vastus lateralis. The results showed a substantial increase in muscle fiber size (greater than 20 percent) that was accompanied by a roughly 30 percent reduction in the proportion of myofibrillar proteins. Those findings suggest that the hypertrophy was due to an increase in sarcoplasmic components (likely a combination of fluid and proteins related to metabolic stress).

What’s really interesting is that follow-up work from the same lab found that a heavier-load, lower-volume protocol resulted in type 2 fiber hypertrophy, but the changes occurred without significant increases in sarcoplasmic proteins and fluid.[5] Collectively, these studies suggest that bodybuilding-type training routines, with higher volume and moderate loads, produce greater increases in sarcoplasmic growth, whereas powerlifting-type programs, with lower volume and heavier loads, may generate greater myofibrillar gains.

The take-home is that sarcoplasmic hypertrophy can in fact occur, and it’s likely influenced by the type of training performed. The more relevant question is whether this phenomenon has meaningful practical implications.

Although the research is still preliminary, the short answer is: it depends on your goals. The increased sarcoplasmic bulk would certainly be beneficial for anyone looking to improve aesthetics, as any increase in muscle size is a plus, regardless of functional implications. The increases in sarcoplasmic proteins may even help to improve performance in bodybuilding-type training, enhancing muscle-building potential.

On the other hand, sarcoplasmic hypertrophy would be of no benefit to an athlete looking for improvements in strength, and it may be detrimental in sports that have weight classes, like powerlifting. In that case, it’s advisable to focus primarily on heavier-load, lower-volume lifting to limit sarcoplasmic gains, as they would increase your weight without improving performance.

References

1. Taber, C. B., Vigotsky, A., Nuckols, G., & Haun, C. T. (2019). Exercise-induced myofibrillar hypertrophy is a contributory cause of gains in muscle strength. Sports Medicine, 49(7), 993-97.
2. Tesch, P. A. (1988). Skeletal muscle adaptations consequent to long-term heavy resistance exercise. Medicine & Science in Sports & Exercise, 20, S132-4.
3. MacDougall, J. D., Sale, D. G., Elder, G. C., & Sutton, J. R. (1982). Muscle ultrastructural characteristics of elite powerlifters and bodybuilders. European Journal of Applied Physiology and Occupational Physiology, 48(1), 117-126.
4. Haun, C. T., et al. (2019). Muscle fiber hypertrophy in response to 6 weeks of high-volume resistance training in trained young men is largely attributed to sarcoplasmic hypertrophy. PLoS One, 14(6), e0215267.
5. Vann, C. G., et al. (2020). Skeletal muscle protein composition adaptations to 10 weeks of high-load resistance training in previously-trained males. Frontiers in Physiology, 11, 259.