You may have heard about two different types of hypertrophy - myofibrillar vs. sarcoplasmic. As the story goes, you can enlarge your muscles either one way or the other. Myofibrillar hypertrophy refers to the enlarging of the structural framework of the muscle fibers whereas sarcoplasmic hypertrophy refers to the increased fluid of the muscle cell sarcomeres.
Anywhere from 70-80% of a muscle cell is made up of structural proteins. If you were to increase the volume of the sarcoplasm and therefore the sarcomere, you would have to increase the overall structural framework of the muscles too. It would be like trying to make the inside your house bigger without actually building any additional walls. In order to increase the size of the sarcoplasm/sarcomere, you have to increase the amount of contractile proteins too. Don't believe me? Check out this study:
The linear distance between myosin filaments (38.7 +/- 0.3 nm before, 38.7 +/- 0.4 nm after training; mean +/- S.E.M.) as well as the ratio of actin to myosin filaments (3.94 +/- 0.03 before, 3.86 +/- 0.06 after training) did not change with training. 3. These results refute the concept that the increases in muscle strength or radiological density during short-term heavy-resistance training are caused by changes in myofilament spacing.
In other words, although the muscles got bigger, the framework didn't simply increase in distance, it had to increase in overall quantity. Both sarcoplasmic and myofibrillar hypertrophy happen at the same time making any discussion about differentiating them total b.s. There is zero evidence to back up sarcoplasmic hypertrophy. Period.
Ok, so for the purposes of hypertrophy training, here is what we can summarize:
Lifting heavy things makes you better at lifting heavy things. The heavier you lift (fewer reps), the stronger you will get.
Lifting lighter things many times makes you better at, well, lifting lighter things multiple times. In other words, your muscles become more fatigue resistant, also known as endurance or capacity training.
Volume is the key. You must push your muscles to at least close to failure multiple times to promote growth.
Oxygen depletion seems to also promote hypertrophy signalling, so by training at a high rate of metabolism, such as during high-intensity interval training (HIIT), you can still promote muscular growth.
Forget the term "toned." Nobody should train at higher repetitions to "tone."
Stimulating muscle cells to increase in size through resistance training can only take you so far, a proper diet rich in protein and sufficient calories is what makes or breaks most cases of hypertrophy. Oh yeah, hormones and genetics count too.
There is no such thing as sarcoplasmic hypertrophy so don't let anyone tell you otherwise.
Tyler Robbins B.Sc. CSCS
Director of Fitness
Head of CrossFit