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To break this down to basics, bodybuilding-style training and strength-training appear to elicit different changes within a muscle, changes which, over time, can manifest themselves into two types of trainees:

– the ‘pumped-up’ lifter who is strong, but much weaker than he looks

– the smaller trainee who lifts houses, though you may not have guessed that based on their outward appearance.

In general, hypertrophy is caused by a period of protein accretion that results in the growth of muscle, and, as many of you know, this is often elicited by resistance exercise and subsequent recovery — but, what many of you may not know, is that different methods of training may very well alter the type of growth that occurs within the muscle.

The fundamental difference between the training approaches of the two trainees above, is that one is likely to have trained more frequently in a manner that encourages greater ‘sarcoplasmic’ growth, the other, in greater ‘myofibrillar’ growth.

So while hypertrophy is often thought of as the enlargement of a muscle fiber, in reality there are actually two forms. Failure to note the difference and adapt your training accordingly is likely to be a significant error leading to an inability to make maximal gains.

The Structure of Skeletal Muscle

In the figure below, you can see a muscle divided into its component parts. You can see there is a sarcolemma, which is the surrounding tissue of a muscle fiber, and inside the sarcolemma, there are the myofibrils – the contractile portions of the muscle fiber. As you may have already guessed, sarcoplasmic hypertrophy is the growth of components within the sarcolemma, while myofibrillar hypertrophy is the growth of the myofibrillar components.

Sarcoplasmic Hypertrophy

Sarcoplasmic hypertrophy can be thought of as a more long lasting form of hyperemia (a.k.a. cell swelling). Increases in non-contractile substances such as intracellular fluid or muscle glycogen increase the size of a muscle.

An often used analogy is to compare this to filling a balloon with fluid to increase its size.

Sarcoplasmic hypertrophy can often be caused by hyperemia, or the pump. When a pump is large enough, it makes the sarcolemma expand, literally blowing up the muscle fiber to the point where it must grow, or risk bursting. This process is often the goal of bodybuilding-style exercise programs.

Myofibrillar Hypertrophy

Myofibrils are the contractile portions of a muscle fiber, and myofibrillar hypertrophy is defined as the increase in the myofibrillar content of a muscle. The increase in myofibrils can be thought of as increasing the density of a muscle fiber (think, the thickening of the ‘skin’ of a balloon) — not the volume like sarcoplasmic hypertrophy — a process which leads to greater gains in strength. This is where people will commonly relate olympic lifters, who tend to be immensely strong without being very big — a result of their training methods, which aim to maximize myofibrillar hypertrophy.

Training

Training for sarcoplasmic hypertrophy (the more traditional ‘bodybuilder-style’) is commonly done in the lower intensity ranges (intensity in terms of a 1 Rep Max) — with loads falling between 65% to 80% of 1RM. Training is also taken to muscular fatigue — and the combination of these tactics is what stimulates the maximum number of muscle fibers while eliciting the hormonal response and blood flow that will eventually lead to sarcoplasmic hypertrophy.

On the other-hand, myofibrillar hypertrophy (traditional ‘power-lifter’ style) is commonly linked to a higher training intensity (using at least 85% of 1RM, even up to a full 100% 1RM). In other words, typically using very heavy weights. Along with stimulation of the CNS, this type of training will trigger the proliferation and differentiation of satellite cells, muscle stem cells that are used to repair myofibrils. This heavy training causes physical damage to the myofibrils, and it is this damage that activates satellite cells and elicits myofibrillar hypertrophy.

Putting this Knowledge to Use

If you predominantly want to get “bigger”, then reason perhaps suggests you should gear all of your training towards eliciting sarcoplasmic hypertrophy, or, if trying to get stronger, to solely to maximize myofibrillar hypertrophy.

Firstly though, it should be noted for completeness that you can’t get all of one without the other, a bigger muscle is often a stronger muscle, and a stronger muscle is often a bigger one.

Secondly, and importantly, one of the keys for achieving MAXIMAL growth (which is why I presume you’re here) is actually to strategically incorporate BOTH styles of training into a periodized program…

Proportionately short periods of time spent focussing on increasing maximal strength, via the use of heavier weights and lower reps, is likely to result in a greater capacity to handle heavier weights when returning to a traditional bodybuilder-style workout (a result of neural adaptations) — more weight lifted means an increase in tension placed on a muscle, more tension equals more growth.

As a practical example, one approach could be to spend 12-16 weeks training for “size”, followed by 3-4 weeks training for strength.

Ultimately, spending more of your training time trying to elicit one type of hypertrophy over the other will likely determine the degree to which training effect you achieve more of, though, importantly, the two can work synergistically to help you maximize your growth in the long term. In other words, plan them both into your routine over time for best results.

References

• Exercise Metabolism Research Group, Department of Kinesiology, McMaster University, 1280 Main St. West, Hamilton, ON L8S 4K1, Canada, N.A. Burd,* C.J. Mitchell, T.A. Churchward-Venne, and S.M. Phillips. “Bigger Weights May Not Beget Bigger Muscles: Evidence from Acute Muscle Protein Synthetic Responses After Resistance Exercise.”Http://www.nrcresearchpress.com/doi/pdf/10.1139/h2012-022. Department of Human Movement Sciences, Maastricht University Medical Centre, n.d. Web. 22 Jan. 2014.
• Stoppani, Jim. “Damage, Inc.” Damage, Inc. Jim Stoppani, 19 Apr. 2012. Web. 26 Jan. 2014.
• Esgro, Ben, B.S CISSN. “Skeletal Muscle Hypertrophy.” ABCbodybuilding. ABCbodybuilding, Dec. 2009. Web. 23 Jan. 2014.
• Foss, M.L. and Keteyian, S.J. (1998). Fox’s Physiological Basis for Exercise and Sport. WCB McGraw-Hill.
• Rasmussen, R.B., and Phillips, S.M. (2003). Contractile and Nutritional Regulation of Human Muscle Growth. Exercise and Sport Science Reviews. 31(3):127-131
• Young Sub Kwon, M.S. and Len Kravitz, Ph.D. “How Do Muscles Grow?” How Do Muscles Grow? Charge, S. B. P., and Rudnicki, M.A. (2004). Cellular and Molecular Regulation of Muscle Regeneration. Physiological Reviews, Volume 84, 209-238, n.d. Web. 24 Jan. 2014.