The Science Behind Muscle Hypertrophy

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The science behind muscle hypertrophy is often not discussed since people usually just think protein consumption and intense exercise programs build muscle, and that’s the end of the story. However, muscle hypertrophy is something that you should be familiar with since you are training in hopes to increase skeletal muscles, strength, and endurance.

Believe it or not, but a lot of people actually train better when they know how their body actually functions. The reason probably has to do with how the mind perceives the thought and functions during a lift, but research cannot fully prove this yet.


What is Muscle Hypertrophy?

This is the term used for when the muscle cells grow and increase in size, and the common way to accomplish this task is through various forms of exercise, which could be weight training, cardio, or even bodyweight training.

Muscle cells are referred to as “muscle fibers” because they are long strands that have a thick sheathing around them holding multiple fibers in a bundle.

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The opposite of muscle hypertrophy is atrophy, which means you either have something medically wrong, you’re overtraining, or you’re just lazy and lose muscle from the lack of physical use.

The most common causes of muscle atrophy are basically human error.

Moving forward, there are different types of muscle fibers that react differently in response to the intensity of the training.

These muscle fibers are placed into three major classes:

  • Slow Twitch (Type I)
  • Fast Twitch (Type IIa)
  • Fast Twitch (Type IIx)


Slow Twitch (Type I) Muscle Fibers

Slow twitch muscle fibers are meant for muscular endurance. This is the muscle fiber that has the lowest potential for force output and growth. However, they make up for these negatives with having dense capillaries (small blood vessels) and an abundance of myoglobin (protein with oxygen attached) and mitochondria (energy producing cells), which basically means they take a long time to fatigue.

An example would be cross country runners having strong slow twitch muscle fibers to run the long distances that they do.


Fast Twitch (Type IIa, Type IIx) Muscle Fibers

Fast twitch muscle fibers fatigue very fast, but they are capable of exerting a lot of “explosive” force compared to slow twitch muscle fibers, and they have the higher potential for muscle hypertrophy.

An example would be a football lineman. He must exert a lot of power under a short period of time, but is not going to be using it without a pause between plays.

Genetically speaking, we all have every type of muscle fiber in our bodies, but the amount mainly depends on how we perform physically. Running often will increase slow twitch muscle fibers in the legs, and then same applies to heavy weight squat training, which increases fast twitch muscle fibers.

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Benefits of Heavy Weight Training

You can benefit from heavy weight training with lower reps because:

  • You increase the number count of myofibrils in each individual cell.
  • Increase the amount of connective tissue and glycogen (glucose) storages.
  • Sarcoplasm fluid volumes increase, which is the fluid filled with protein found around each cell.

What all this accounts for is muscle hypertrophy mainly with type IIx muscle fibers, and larger muscles have essentially proven to come from heavier lifts with lower rep amounts as a result.

That is why a lot of people perform the 5×5’s workouts with compound training, and sometimes even perform 10×1’s, which is a bit more advanced due to the large weight settings used for each rep you perform.

You generally see this type of training with deadlifts, bench press, squats, cleans, military presses, and the likes. Sitting and performing a lateral pull-down for one rep is just not going to work.

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The Benefits of Higher Reps

Muscle hypertrophy is also accomplished through performing higher reps with moderate weight, but don’t get too light on the weight chosen. Light weight settings are good for warming up, body maintenance, or you are able to use them for increasing slow twitch fibers.

However, if you want to stimulate muscle hypertrophy for mass, then you need to increase your weights to where you strain towards the end of the set.

You want to occasionally perform higher reps with exercises since it builds up your mitochondria, which are known as a cells “powerhouse” since it converts chemical energy over to cellular energy and 25% or more of your muscles sizes arheavy weight traininge accounted from an increase in your mitochondria.

So isolation exercises, such as the lateral pull-down, needs to be performed with a little bit more reps, or 8-12 reps to be more specific.

The best way to increase overall muscle mass is through focusing on fast twitch muscle fibers first, and then slow twitch muscle fibers secondly. Let’s have a better look at the cause and effect of muscle hypertrophy.


Stimulating Muscle Growth

The science behind muscle hypertrophy revolves around how you stimulate your muscles. You already learned the basics about muscle fibers, and how different training techniques benefit different types of muscle cells, so now we can get into the primary methods that stimulate muscle hypertrophy.

  • Muscle Damage
  • Muscle Cell Fatigue
  • Progressive Overload Training

Let’s review these stimulators a little more in-depth.

Muscle Damage

You may be questioning muscle damage at this point because it does have a negative sound to it, but there is reasoning behind why muscle damage is a part of muscle growth. The cycle of muscle growth begins with damage from high levels of tension.

Your muscle fibers have microscopic tears in them from this damage, and then your body sends signals for repair to take place, which in turn causes the muscle cells to grow larger from the repair.

This is the process that uses nutrients such as protein to support this repair, and that is one of the only reasons protein powder, bars, etc. are considered supplements for muscle growth. Muscle building needs protein regardless if you want to be lean or bulky, and regardless if you are male or female.

The idea revolves around protein synthesis, which is also why you have to take proper rest days to for damaged muscle fibers.

Protein synthesis for muscle hypertrophy essentially takes proteins that you consumed and send them through your bloodstream to the muscle cells. Proteins within the muscle cells are damaged and either get replaced strength-training-encourages-lean-muscle-growth-and-decreases-body-fator repaired during protein synthesis with stronger and denser proteins.

Thus the reason behind muscles getting larger since the proteins are growing. But not necessarily multiplying. Science is still in debate whether protein cells multiply or simply get larger though.

Rest is also an important factor to muscle repair, and this is what allows your body to not feel so sore the next couple of days.

Soreness will be there, don’t get me wrong, but you decrease it significantly with adequate amounts of nutrients and rest.

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Muscle Cell Fatigue

Muscle cell fatigue occurs when you push your muscles to their metabolic limits. This mainly applies to high repetition sets, burnouts, drop sets, supersets, etc where the load is pretty light.

The only issue with this type of focused training is slow twitch muscle fibers are being activated primarily, which you learned have low growth abilities. Thus the reason people who focus on higher repetitions usually don’t have muscle mass, but this is not stating they aren’t strong either.

~~~~Strength doesn’t always mean mass.~~~~


Progressive Overload Training

The fastest way to stimulate muscle hypertrophy is with progressive overload training, which is basically when you keep increasing the amount of weight being used, and the repetitions are below 10. You should focus on using compound lifts primarily because they enable the use of multiple muscle groups instead of just a few, and some of these lifts are deadlifts, squats, lunges, military press, pull-ups, etc.

Notice that compound exercises are basically whole body movements.
Research shows that fast twitch muscle fibers grow at a significant pace when placed under progressive overload training paired with compound lifts. Isolation lifts are a bit different since they focus on 1-2 muscles being placed under most of the contraction.

I would recommend placing more emphasis on isolation techniques AFTER you reached a plateau in muscle hypertrophy from compound training. This is when specialized training comes into effect, but let’s save that topic for another day. Feel free to leave any comments and give your input on the subject.

Brian Pankau

Brian Pankau

Experienced personal trainer and strength coach

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