Hy·per·tro·phy; the enlargement of the cross-sectional size of an organ or tissue from the increase in size of its cells. In Jacked Street terms: creating larger muscles.
We have all heard this term thrown around, associated it with gaining size and assumed that is all there is to it. However, you need to understand that not all hypertrophy is created equal. Did you know there are two different types of muscle hypertrophy? Which one you want to focus on needs to fall in line with “What Are You Training For?”
Let’s dive in and see which type of hypertrophy your training is driving.
Before we dive into the good stuff let's exam a muscle fibre real quick. For the purpose of this discussion there are two parts that we are concerned with. First is sarcoplasm which is made up of non-contractile proteins that surround the myofibrils. The second is myofibrils which are comprised of contractile filaments called sarcomeres composed of actin and myosin filaments (2).
Now that we have some vocabulary set, let's dive in. The first way that we are able to increase the cross-sectional size of muscles is through myofibrillar hypertrophy. The increase in cross-sectional size is attributed to an increase in the size and number of myofibrils within the muscle fiber. The force produced by a muscle is dependent on the activity of the muscle’s subunits; sarcomeres, myofibrils, and muscle fibers. From this we know that myofibrils = force production. This form of hypertrophy is linked to a greater ability to exert muscular strength.
There is also an increase in the density of Type IIB fast-twitch muscle fibers, which are good for very short-duration and high-intensity bursts of power. In summary: when cross-sectional size goes ⬆︎, muscle fiber density and Type IIB fast-twitch muscle fiber density go ⬆︎ (1).
With those points in mind, this specific adaptation should be the primary focus of those who have an answer to “What Are You Training For?” that falls in line with competing in weightlifting, powerlifting, rink, pool, court, and field sports. The way that we drive this specific adaptation is by using higher intensity and lower volume by operating within in the rep ranges of 4-7. This format is commonly seen in programs such as Bedrock and Field Strong.
The second way we are able to increase the cross-sectional size of muscles is through sarcoplasmic hypertrophy, a result of the increase in the volume of non-contractile sarcoplasmic fluid. There is not an increase in muscular strength associated with this hypertrophy because the increase in muscle size is a result of the increase of non-contractile fluid.
This type of hypertrophy also leads to an increase in the density of Type IIA fast-twitch muscle fibers which are used more during sustained power efforts and are more resistant to fatigue. In summary: when cross-sectional size goes ⬆︎, muscle fiber density goes ⬇︎ and Type IIA fast twitch muscle fiber density goes ⬆︎ (1).
Now that we know what adaptations are at work this style of training should be the primary focus for those who have an answer to “What Are You Training For?” that falls in line body building, purely aesthetics, or the need to cultivate mass. The way we drive this specific adaptation is by using moderate intensity and higher volume by operating within in the rep ranges of 8-12. This format is commonly seen in Jacked Street.
Dialing it In
This doesn’t mean in a program like Field Strong you will never see sarcoplasmic hypertrophy rep ranges, and in Jacked Street you will never see myofibrillar hypertrophy. Think of these adaptations as the knobs on this audio control board. Just as you would adjust up and down the bass and treble for a desired sound, the same is said for training. Those on Field Strong still need those rep ranges to build armor to survive the physicality of sports as well as create larger structures to be able to support heavier weights thereby allowing myofibrillar hypertrophy to develop even further.
If you have a 6’1” 145 lbs athlete who wants to play defensive line you better know a little about how to put weight on him. Those on a program like Jacked Street need myofibrillar hypertrophy to increase their strength so they can handle greater weights at the 8-12 rep ranges and further stress to progress.
One last thing that needs to be taken into consideration before going forth and empowering your performance is that load, not reps will determine which adaptation is being driven. You cannot walk up to and empty barbell, do 5 Back Squats and say, “I just trained myofibrillar hypertrophy.” It doesn’t work like that. The load needs to be heavy enough that your max effort attempt falls in line with the desired adaptation. Myofibrillar better fall between 4-7 reps, and sarcoplasmic better fall between 8-12.
Which knob you turn up more than the other all comes back to the S.A.I.D Principle, overload, and “What Are You Training For?”
- Verkhoshansky, Yuri, and Mel Cunningham Siff. Supertraining. Verkhoshansky, 2009.
- Zatsiorsky, V. M., & Kraemer, W. J. (2006). Science and Practice of Strength Training. Human Kinetics.
After an introduction to CrossFit in 2007, Carl became a certified coach in 2009 and co-owner of CrossFit South Bend in 2011. In addition to coaching CrossFit and CrossFit Football classes at the gym, Carl has been coaching high school rugby since 2009. He uses the CrossFit Football and Power Athlete concepts to help his young athletes identify their goals and provides pointed instruction to help achieve those goals.
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