What is Sarcoplasmic & Myofibrillar Muscle Hypertrophy?

In a medical sense, hypertrophy is defined as the increase of bulk in an organ without the multiplication of that organ or elements.

In strength training, we use hypertrophy to refer to skeletal muscle hypertrophy or the growth of muscles like the biceps.

To truly understand muscle hypertrophy and how it occurs, we need to understand muscle anatomy.

What is a muscle fiber?

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

Within a single muscle fiber, hundreds of myofibrils 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 has everything else.

The myofibrils are responsible for the actual contraction of a muscle fiber that causes the muscle to shorten.

When we refer to skeletal muscle hypertrophy, it is the muscle fiber increasing in size. So when we grow our muscles, it is because we are making the muscle fibers larger, and we do this by increasing the number of myofibrils and the volume of sarcoplasm. I will explain how that happens next.

There are two types of hypertrophy

Sarcoplasmic hypertrophy and myofibrillar hypertrophy are related but distinct ways that your muscle fibers grow.

Sarcoplasmic hypertrophy is the increase in the volume of the sarcoplasm within the muscle fiber, which increases its size. Remember that the sarcoplasm is everything in a muscle fiber that is not myofibrils.

Myofibrillar hypertrophy increases the number of myofibrils within the muscle fiber which increases its size. Increasing the number of myofibrils in the muscle fiber creates a stronger muscle by providing more contractile units.

Let me explain with balloons, Water, and sticks

To help you further understand the differences between sarcoplasmic and myofibrillar hypertrophy, I want you to picture one of those long balloons clowns use to make animals.

This balloon represents a single muscle fiber.

Next, I want you to imagine this tubelike balloon is filled with long sticks that run the length of the entire balloon.

Those sticks represent the myofibrils.

Last, imagine the balloon is filled with water instead of air.

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

Sarcoplasmic hypertrophy is like adding more water to the balloon to increase its size.

Myofibrillar hypertrophy is like adding more sticks to the balloon while keeping the same water volume. This will also increase the volume of the balloon.

Whether you increase the volume of water (sarcoplasm), or the number of sticks (myofibrils), both will increase the size of the balloon (muscle fiber size).

The critical difference is that adding myofibrils increases the contractile components of the muscle, which increases strength. In addition, adding more sarcoplasm increases the workload the myofibrils can perform.

Is sarcoplasmic or myofibril hypertrophy better?

This is a bit of a trick question.

Sarcoplasmic hypertrophy (an increase in the volume of sarcoplasm in a muscle fiber) will increase the muscle’s work capacity. This means more sets and reps can be performed because, in the most basic sense, the myofibrils have more supplies to do their work.

Myofibrillar hypertrophy, the multiplication of myofibrils, increases muscle fiber strength because more contractile units are pulling on your bones. This will lead to higher one-rep maxes and bigger lifts.

The tricky part is that these two types of muscle growth are impossible to separate.

Depending on the strength training you are doing, and the rep ranges you lift in, you can influence one more than the other, but they will always coincide.

Your muscles will grow strongest and largest when you take turns focusing on both types of hypertrophy.

The best way you grow your muscles

Inducing overall muscle hypertrophy starts with a great training program.

This means following a program that will target both types of hypertrophy.

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

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

There are many different ways to accomplish muscle growth, but what’s essential for growing your muscles the quickest and largest is working in various rep ranges.

Good strength training programs will ensure you have a mix of high rep, moderate rep, and low rep workouts. We have a variety of free programs you can download.

The Seriously Strong Beginner Program

The Seriously Strong Intermediate Program

The Seriously Strong Advanced Program

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

You should check out How to Get Started With Strength Training if you’re new to strength training.