What is Sarcoplasmic & Myofibrillar Muscle Hypertrophy?

3 min Read

Written by

Nibin Varghese

Bicep Curl

Hypertrophy, in a medical sense, is defined as the increase of bulk in an organ or part without the multiplication of that organ or parts. In strength training we use hypertrophy to refer to skeletal muscle hypertrophy, or the growth of muscles like the biceps.

To truly understand what muscle hypertrophy is we need to understand muscle anatomy.

What is a muscle fiber?

Muscle Fiber AnatomyMuscle is the word commonly used to describe something like the biceps, but what we think of as a muscle is actually the muscle belly. The muscle belly is a grouping of muscle fibers that are arranged to all pull on a tendon, to pull a bone, and move your body.

Within a single muscle fiber there are hundreds of myofibrils that populate it. The area that fills and surrounds the myofibrils within the muscle fiber is called the sarcoplasm. Each myofibril contains the contractile units (myofilaments) responsible for creating force and movement. The sarcoplasm contains everything else.

When we refer to skeletal muscle hypertrophy, it is the muscle fiber that is increasing in size.

There are two types of hypertrophy 

Sarcoplasmic hypertrophy and myofibrillar hypertrophy.

Sarcoplasmic hypertrophy is the increase in volume of the sarcoplasm within the muscle fiber causing growth.

Myofibrillar hypertrophy is the increase in the amount of myofibrils within the muscle fiber causing growth.

Let me Explain with a Balloon and Sticks

Hypertrophy types

To better understand this think about a cylindrical balloon.

This balloon represents a single muscle fiber. This balloon contains sticks (the myofibrils) and water (the sarcoplasm). Let’s say you have four sticks in the balloon and the rest is filled with a cup of water. This will represent an untrained muscle fiber.

Sarcoplasmic hypertrophy is like adding another cup of water to the balloon to increase the size.

Myofibrillar hypertrophy is like adding another four sticks to the balloon while keeping the water volume the same.

Both will increase your muscle size. But adding sticks increases the contractile components of the muscle which increases strength.

How can we add more sticks? 

Inducing overall muscle hypertrophy starts with a great training program.

Increasing your muscle size will come from increasing your sticks (myofibrils) and water (sarcoplasm). 

Your style of training can influence which hypertrophy happens to a greater degree, but realize they are both happening if your muscles are growing. Think of it as a ratio of one happening more than the other.

Bodybuilding style strength training with high repetitions and low weights will create a greater degree of sarcoplasmic hypertrophy.

Heavier weight, low rep, strength training will create a greater degree of myofibrillar hypertrophy.

Ideally you want more sticks (myofibrils) to have muscles that are not only much bigger, but much stronger.

Lifting weights using compounds lifts in a variety of rep ranges will build the most muscle and strength.

To maximize hypertrophy you need to eat enough protein and be in a caloric surplus. 

If you’re ready to put on some muscle download our beginner program and get lifting!


Nibin Varghese

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