The Real & Basic Muscle Growth Science Broken Down for Bros

Learn everything you need to know about the basic science behind building muscle! Then, apply it to your own training and begin building bigger muscles.
You want to build muscle, and you’ve seen some workouts and exercises that might get you there. And that’s okay if you just want to hop around until something works for you.

But if you truly want to excel at building muscle, then you should know some of the science behind what goes on.

If you can understand the basic science of hypertrophy, you’ll never look at another workout program or exercise the same way again.

Become a muscle building pro!

The Two Types of Hypertrophy
Muscle hypertrophy can be broken down in to two different types, sarcoplasmic and myofibrillar.

Sarcoplasmic hypertrophy can be considered an increase in size of the non-contractile elements and fluid within the muscle. It’s sometimes called “non-functional” hypertrophy as increases in muscle size can be seen without similar increases in strength. Ever wonder why some bodybuilders aren’t as strong as they look? Non-functional hypertrophy is your answer.

The more sarcoplasmic hypertrophy the more muscle glycogen you can store however, and a greater muscle pump can be achieved. The fact that the muscle can store more energy though is a benefit, and therefore shouldn’t really be considered “non-functional”.

Myofibrillar hypertrophy on the other hand is an increase in size and amounts of the contractile protein’s actin and myosin, and number of sarcomeres in parallel. When we talk about the amount of muscle that makes up the human body, only 20% of that muscle is made of muscle proteins. These muscle proteins are the “functional” myofibrillar stuff we’re talking about.

Related: Work Out Smarter - 3 Keys to Maximizing Muscle Growth

So, in theory the other around 80% being non-functional hypertrophy has a larger capacity to build muscle. It’s important to mention here that functional hypertrophy is generally built using lower repetition ranges (e.g., 4-6 reps), whilst non-functional using higher reps (e.g., 8-15 reps or even more).

3 Factors Responsible for Muscle Growth
It’s suggested that there are three primary factors that are responsible for initiating the muscle building response1.

Understanding these is of importance if you’re looking to understand how an exercise may benefit you, or how a training program can be manipulated to build maximum muscle.

  1. Mechanical Tension
    When a muscle passively stretches (stretching the muscle without actively contracting it), it is what’s referred to as passive elastic tension2. On the other hand, if you place tension on a muscle by isometrically flexing it as hard as possible, this is referred to as active tension.

During both cases high amounts of mechanical tension are formed. High mechanical tension appears to be great at building muscle, as well as preventing muscle atrophy.

Performing some high-tension isometrics as part of your training could be a great way to grow muscle and prevent muscle breakdown. Isometric training could therefore be something to consider as we pass through our 40’s, 50’s and beyond and are fighting the effects of muscle breakdown.

In addition, stretching can play an important role in building and maintaining muscle, and should form part of any good weight training program. Taking a slightly holistic approach to training by stretching the targeted muscle between sets of exercise, may also be of some use when trying to maximize growth.

Taking a muscle through its full range of motion and lengthening, or “stretching” it under load will also produce a significant muscle building response. For example, stretching the latissimus muscles fully at the bottom range of a pull-up, flaring the elbows outward, and performing what has sometimes been referred to as a “loaded stretch”, can trigger muscle growth.

This isn’t surprising because high amounts of mechanical tension are happening during these loaded stretches, as high eccentric force is being produced by the muscle in a lengthened state.

  1. Metabolic Stress
    Studies have shown metabolic stress to play an important role within the muscle building response3. Some have even suggested high metabolic stress and metabolite production to be even more important than high mechanical tension.

Metabolic stress is a result of exercise that relies on anaerobic glycolysis for energy production and is typically achieved with the type of training associated with high lactate production, change in blood PH, and subsequent muscle burning sensation. This build-up of metabolic by-products can trigger an anabolic hormonal surge, including growth hormone (hGH) and insulin-like growth factors (IGF-1), among other things4.

The occlusion of veins by repeated muscle contractions also prevent blood from escaping, and cell swelling to occur, as well as a lack of oxygen supply to the muscles. One of the reasons why Blood-Flow Restriction (BFR) training can be so effective is by exploiting this mechanism5.

Simply, any training focused on producing metabolic stress and achieving a pump will help you gain some size, but solely chasing the pump isn’t all it takes.

  1. Muscle Damage
    Most of us are aware that muscle damage occurs during a heavy workout. It’s theorized that localized damage to muscle tissue can activate a hypertrophic response. The response to localized damage, or myotrauma, is one that can be compared to muscle injury and the inflammatory response to infection. Yes, you’re injuring yourself on purpose!

This response is believed to release various growth factors that may ultimately lead to building muscle. It’s a careful balance here though, and it’s not just about trashing a muscle group for it to grow. If there’s too much tissue breakdown that your body can’t keep up with (protein degradation exceeds synthesis6) you’re in a catabolic state before you know it.

A greater rate of tissue breakdown is achieved at higher intensities (i.e., lower rep ranges), however time under tension can be very short at these intensities, as sets of exercise do not last very long.

For example, the rate of tissue breakdown at 1-3 reps is very high, but the duration may be too short to build significant muscle. It has therefore been suggested that an optimal balance between both intensity and time under tension is achieved around 6-10 repetitions per set.

Furthermore, accentuating the eccentric component of the exercise, performing a stretch of the muscle while it is being activated, or overloading the eccentric portion of the exercise can all form high amounts of mechanical tension and tissue breakdown.

How to Combine All These Muscle Growth Factors
It’s clear to see that there’s crossover between which mechanisms are active at any given time during an exercise or workout. The key however is to ensure you’re covering a variety of exercises and methods to hit all of them.

To help you better understand how certain techniques you may be using right now would fit in to a muscle building program, this table has got you covered.

How to Combine Muscle Growth Factors Table

Making Building Muscle Easier
As mentioned previously the way in which our muscles respond to training and increase in size is complex. We’ve just skimmed the surface here, but with this information you’ve got a better understanding of how a good muscle building program might look.

A complete hypertrophy workout should consist of the following, but it’s up to you to put in the work:

Perform full range of motion exercises.
Perform some isometric exercises.
Stretch before, during and after training.
Include some exercises that emphasize the “loaded stretch”.
Include some exercises that focus on the peak contraction or “squeeze”.
Perform some moderate-high load exercises (4-6 sets of 4-6 reps).
Perform some moderate load exercises (3-5 sets of 8-15 reps)
Perform some low-moderate load exercises on occasion where maximizing blood flow and muscle pump are the goal (2-4 sets of 15-25 reps)
Consider using a slower repetition speed when trying to achieve more time under tension, and metabolic stress.
Employ some special intensity techniques such as drop-sets, back-off sets, 21’s, mechanical drop sets, pre-fatigue supersets, post-fatigue supersets, and so on to hit a variety of mechanisms and increase volume.
You can structure your training cycles in a few ways. First off you could choose to hit all mechanisms and all rep ranges in one training cycle (a more conjugated approach). Or you could devote say 3-4 weeks emphasising mechanical tension and lower repetition ranges, followed by 3-4 weeks emphasising metabolic stress and higher repetition ranges.

Both can work equally as well, and you’ll have some fun experimenting with different methods of training.