Muscle Anatomy Basics PT 1 – Types Of Muscle Fibers

The human body has a complex muscular system built from two main types of muscle fibers – slow-twitch muscle fibers and fast-twitch muscle fibers. Each of these types is suitable for different activities, and in this article, we will dive into those details. So without further ado, let’s get to it!


Muscle Unit Activation

Before we get to the types of muscle fibers, let’s talk about muscle unit (muscle fiber) activation!

You have different types of fibers as the human body is capable of many kinds of activities. You can run for hours on end, but you can also do short-burst, quick sprints. Think of it this way – The more you increase your training intensity (strain), the more muscle units you activate.

At about 75-80% of your maximum strength capabilities, nearly all muscle fibers (muscle units) are recruited and activated. Going above that 75-80% mark is only possible via an increased frequency of the mind-muscle signals.

This implies a very intricate connection between your muscle fibers and the central nervous system responsible for delivering contraction signals.

Now let’s have a look at the two types of muscle fibers!


Slow-Twitch Muscle Fibers

Slow-twitch muscle fibers are the muscles you use when you’re running a marathon or biking for distance.

They provide endurance and stability, but they aren’t really capable of high power output.

These muscle units have low force production capabilities, so their primary function is to produce energy for long periods of time.

Slow-twitch muscle fibers are recruited when you are far from your maximum strength capabilities, or in other words, when the activity isn’t really strenuous but instead requires endurance.


Fast-Twitch Muscle Fibers

On the other hand, Fast-twitch muscle fibers are what you use when doing short, intense sprints, heavy lifting, climbing, and any other strenuous activity that demands a certain level of power and strength. These units can contract quickly and have a high strength output for quick, short power bursts.

Interestingly, fast-twitch muscles have a fast fatigue rate because their energy source, ATP, gets used up in seconds!

Furthermore, as opposed to slow-twitch fibers, this type of “muscle unit” has much greater growth potential.

This means that if you are looking for visual muscle development, you should stimulate fast-twitch fibers!


How To Stimulate Fast-Twitch Fibers

To stimulate Fast-twitch fibers, you should utilize a high-intensity method with resistance training, calisthenics, climbing, and sprinting.

Such activities allow you to get closer to your maximum strength capabilities, thus activating and stimulating the development of your fast-twitch muscle fibers.

Generally speaking, as a beginner/intermediate trainee, 5-10 challenging working sets per muscle group per week should be sufficient for the goal of increasing the size and strength of your muscles.


How To Stimulate Slow-Twitch Fibers

On the other hand, to stimulate slow-twitch muscle fibers and develop endurance capabilities, you should engage in activities that utilize these – such as running, swimming, and skipping for prolonged periods.

Nevertheless, be mindful when implementing this training style if you look to improve your appearance and strength. Exercising to enhance muscle conditioning will come with higher caloric expenditure. Unless you’re consuming these calories, your exercise could convert hard-earned lean body mass for energy. This topic is something I could devote an entire book to – perhaps another time, though.


Final Words

So, to recap: Fast-twitch fibers provide quick and powerful bursts of energy, while slow-twitch fibers provide endurance capabilities.

Plan your workouts to tip the scales in favor of your goals. If you want to look better and be stronger, focus on quick, powerful bursts and fewer long-duration cardiovascular activities – or the opposite if your main goal is endurance.

In part 2 of this article series, we’ll go through the two types of muscle growth. So stay tuned if you’ve liked this article!




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