Sarcoplasmic vs. Myofibrillar hypertrophy… (Stuart Phillips, PhD )

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 examplehttp://www.ncbi.nlm.nih.gov/pubmed/22518835) 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!

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