The Myth of Training for Sarcoplasmic Versus Myofibrillar Hypertrophy

Contrary to the claims of many bodybuilders, trainers, and coaches, you can not selectively train for sarcoplasmic versus myofibrillar hypertrophy by working in different repetition ranges. While training with lower or higher repetition ranges can result in differences in improvements in strength relative to local muscular endurance, you can’t separate strength from hypertrophy. After the first couple months of training when neural adaptations contribute more to strength increases than hypertrophy, if you get stronger your muscles will be bigger, and if your muscles get bigger you will be stronger.The relationship between muscular strength and size varies between individuals due to numerous genetic factors, however, so regardless of how you train some people will gain a lot of strength without much size, some will gain a lot of size without getting very strong, and most of us will be somewhere in between:

…chronic resistance exercise training induces skeletal muscle hypertrophy as well as increases in strength. However, not every individual can expect the same magnitude of muscle responses to a standard program because of genetic and environmental factors yet to be thoroughly characterized.

One study with five hundred and eighty five men and women performing the same program of unilateral arm flexor training for twelve weeks showed a huge difference in muscular size and strength gains. The worst responders lost about two percent muscle size while the best responders gained an impressive fifty nine percent. Strength gains varied from zero to as much as two hundred and fifty percent (2):

Men and women exhibit wide ranges of response to resistance training, with some subjects showing little to no gain, and others showing profound changes, increasing size by over 10 cm and doubling their strength. Men had only a slight advantage in relative size gains compared with women, whereas women outpaced men considerably in relative gains in strength.

I suspect the belief you can selectively train for either sarcoplasmic or myofibrillar hypertrophy is based on observation of the difference in training between bodybuilders and strength athletes like powerlifters, and failure to consider selection bias as a significant factor in the differences in the relative muscular strength and size between the two. Any program done hard, progressively, and consistently with a volume and frequency appropriate for the individual will eventually get them as big and strong as their genetics will allow, but the ratio of strength to size gains will vary considerably between individuals. People who can get very strong without much hypertrophy will tend to gravitate towards strength sports where a high ratio of strength to body weight is advantageous. People who are able to gain a lot of muscular size relative to strength will tend to gravitate towards bodybuilding where muscularity is the goal but strength has no bearing on competition.

Someone who fails to consider this selection bias might assume the bodybuilders had a higher ratio of hypertrophy to strength due to their training and the powerlifters have a higher ratio of strength to hypertrophy due to their training, when the differences are mostly genetic.

If you remove this selection bias and randomly assign people to either a “bodybuilding” or “strength” program with equal volume as Brad Schoenfeld did in a recent study (4), you’ll find no significant difference in the average hypertrophy between the two. The strength group in this study increased their one-repetition-maximum more than the hypertrophy group, but this is most likely due to specific neural adaptations to the lower rep ranges used and if a ten-repetition-maximum test was done instead the hypertrophy group probably would have improved their performance more than the strength group.

If your goal is to improve your performance in a specific range of repetitions you should train in that range, but if your goal is general improvements in strength and hypertrophy the optimal repetition range is whatever you respond best to based on your genetics, and not some arbitrary range of repetitions claimed to be specific for hypertrophy.

Stuart Phillips, PhD from the kinesiology department at McMaster University recently had this to say about the subject:

Sarcoplasmic vs. Myofibrillar hypertrophy… perhaps you’ve heard those terms and even read information from some guru who says there are different types of ‘hypertrophy’. This is unadulterated garbage and basically anyone who has ever taken a course in muscle physiology, exercise physiology, and knows a little biochemistry would tell you so. The amount of myofibrillar protein in skeletal muscle fibre remains remarkably constant! There are no examples of where a muscle fibre hypertrophies with resistance training and the myofibrillar pool doesn’t grow but the sarcoplasm does! The occasional example of a discordance between hypertrophy and strength gain (for example http://www.ncbi.nlm.nih.gov/ pubmed/22518835 (5)) is not, no matter what the pundits think, due to a ‘sarcoplasmic’ hypertrophy in the low-load condition. The obvious explanation is a neuromuscular training-zone specific strength response in the low vs. the high load groups – muscle/exercise physiology 101. Similarly, I’ve heard some say that blood flow restriction (BFR) training leads only to ‘sarcoplasmic’ hypertrophy… it’s a myth! Hypertrophy, when it happens is due to expansion of the myofibrillar protein pool. For people who think that your fibres can grow (not transiently due to fibre swelling – a short-lived phenomenon) by expanding their sarcoplasm are incorrect. If this happened the energetics of the fibre would be a complete mess due to greatly, on a relative scale, increases in intracellular distances for chemical reactions… like propagation of the electrical impulse from a t-tubule to the SR to cause contraction!So the next time you hear someone spouting off about sarcoplasmic hypertrophy you can tell them, with confidence, that no such thing exists! It’s a construct of bodybuilding forums… hypertrophy is hypertrophy and strength is strength. There’s no difference between the hypertrophy you get with one routine versus the next!

I also recently discussed this with Ryan Hall and he also shared the following:

I reviewed a few studies concerning sarcoplasmic vs. myofibrilar hypertrophy several years ago: This is in line with other research I’ve seen suggesting that all structural components of muscle fibers hypertrophy simultaneously with training. “This implies that with exercise-induced hypertrophy, the sarcoplasmic reticulum, cytoplasm, and lipid components increase proportionately with contractile protein…” Functional and structural adaptations in skeletal muscle of trained athletes. S. E. Alway , J. D. MacDougall , D. G. Sale , J. R. Sutton , A. J. McComas. Journal of Applied PhysiologyMar 1988,64(3)1114-1120; Other studies show similar results. “This hypertrophy of muscle fibers by 30% with training resulted in no change in the cytoplasm-to-myonucleus ratio.” Effects of high-intensity resistance training on untrained older men. II. Muscle fiber characteristics and nucleo-cytoplasmic relationships. Hikida, RS, Staron, RS, Hagerman, FC, Walsh, S, Kaiser, E, Shell, S and Hervey, S. J Gerontol A Biol Sci Med Sci 55:7, B347-54 (2000) Given the above data, it seems unlikely that selective hypertrophy occurs, at least in the confines of most strength training protocols.

In a nutshell, you don’t need to train with different repetition ranges for general strength increases or hypertrophy. A variety of repetition ranges can be effective for both. However, depending on your genetics you may respond better to either a lower or higher repetition range. I cover this in detail in the chapter How To Find Your Optimal Repetition Range in the updated and expanded High Intensity Workouts.

References:

1. Association of interleukin-15 protein and interleukin-15 receptor genetic variation with resistance exercise training responses. Steven E. Riechman, G. Balasekaran, Stephen M. Roth, Robert E. Ferrell. Journal of Applied PhysiologyDec 2004,97(6)2214-2219;DOI:10.1152/japplphysiol.00491.2004

2. Hubal MJ, Gordish-Dressman H, Thompson PD, Price TB, Hoffman EP, Angelopoulos TJ, Gordon PM, Moyna NM, Pescatello LS, Visich PS, Zoeller RF, Seip RL, Clarkson PM. Variability in muscle size and strength gain after unilateral resistance training. Med Sci Sports Exerc 37: 964–972, 2005.

3. Timmons JA. Variability in training-induced skeletal muscle adaptation. J Appl Physiol (1985)2011;12:846–853. doi: 10.1152/japplphysiol.00934.2010.

4. Effects of different volume-equated resistance training loading strategies on muscular adaptations in well-trained men. Schoenfeld BJ, Ratamess NA, Peterson MD, Contreras B, Tiryaki-Sonmez G, Alvar BA. J Strength Cond Res. 2014 Apr 7. [Epub ahead of print]

5. Resistance exercise load does not determine training-mediated hypertrophic gains in young men. Cameron J. Mitchell, Tyler A. Churchward-Venne, Daniel W. D. West, Nicholas A. Burd, Leigh Breen, Steven K. Baker, Stuart M. Phillips. Journal of Applied PhysiologyJul 2012,113(1)71-77;DOI: 10.1152/japplphysiol.00307.2012