Finding Your Primary Muscle Fiber Type!

What predominant muscle fiber type are you? Knowing your predominant muscle fiber type really matters. This article will explain why is that so and will also show you the easiest and fastest ways to determine your predominant muscle fiber type. By knowing what type of muscle fibers you have, you can tailor your training towards developing them to their maximum potential. The only way to get a fully reliable answer is to biopsy your muscles. But don’t worry! Fitness professionals have proposed few methods that can help you estimate your fast-twitch/slow-twitch ratio. These methods are the main subject of this article.

Brief introduction

There are two distinct types of muscle fibers that are present in skeletal muscle – fast twitch and slow twitch; the ratio is dependent on genetic make-up.

Fast twitch fibers are white in colour and contract rapidly but tire easily. They are like the engine of a racing car, used for high-speed movements, but for short periods of time. They predominantly use carbohydrate as fuel and produce lactic acid, which builds up in the muscle and inhibits muscle contractions.

Slow twitch fibres are red in colour and contract slowly but are able to keep going for longer as they have a better oxygen supply. They are like the engine of a touring car, as they produce less power but can continue for longer periods as they work at a lower level of intensity which can be sustained for longer.  They use a combination of carbohydrate and fat which is burned in the presence of oxygen.

Each body has a different proportion of fast-twitch and slow-twitch fibers. You could have a higher percentage of either fast-twitch or slow-twitch muscle, or even an equal amount of both. These percentages play an important role in how successful you can be at achieving your training goals.

Why knowing your predominant muscle fiber type matters?

Every individual naturally possesses either more slow twitch muscle or more fast twitch muscle that helps determine what activities they will favor.

Those with more natural slow twitch muscle tend to excel in long distance events and seem to prefer them, while those with more natural fast twitch muscle tend to excel in the sprint events and seem to like them more.

For example, long-distance runners (marathoners) have a higher percentage of slow-twitch fibers, while sprinters and power lifters typically have more fast-twitch fibers. In fact, some athletes may have as much as 80 percent of one muscle fiber type.

This is not because the athlete chose a sport and then developed a greater percentage of appropriate fibers to suit the demands of the sport. As earlier mentioned in this article, the percentage of fast-twitch and slow-twitch fibers is fixed at birth. Thus, these people dis­covered the sport in which they excelled and they excelled at these sports because their bodies were designed for these specific endeavors, largely based on their individual composition of muscle fibers.

This was a twofold process: the person realized that they were good at a sport, and then found enjoyment or fun in being able to succeed. This sense of sat­isfaction was due in large part to muscle composition.

The easiest and fastest ways to determine your muscle fiber type

Much of our knowledge concerning the fiber types and their characteristics in human muscle is based on the analysis of tissue samples obtained by muscle biopsy. Therefore the only way to get a fully reliable answer is to biopsy your muscles. This procedure involves having a lab technician take core samples of every major muscle in your body with a giant needle. After that they will simply analyze the relative proportion of different fiber types under a microscope. Not a fun — or cost-effective — proposition.

We have come across a variety of other tests that can determine your fiber com­position. Some techniques are accurate but involve expensive, hard-to-find pieces of equipment, or are exhausting and difficult to do. Others are easy but inaccurate. Here is a brief description of some tests. All of the recommended tests have a blend of ease, accessibility, and accuracy.

Tests we do highly recommend

I. Vertical Jump Test/Power test

Your performance in this test will indicate if you are more fast-twitch or slow-twitch muscle. The higher you jump, the more you are a fast-twitch person; the lower you jump, the more your muscles are slow-twitch. The only downside to the test is that you will not get an exact percentage of muscle fiber. It only gives you a range compared to your peers—a good indication of your fiber type but not an exact percentage. Nevertheless, it is accurate and gives you a good idea of how you should be exercising. Step-by-step instructions on how to perform the test and calculate/interpret your results can be found in our previous post: Vertical Jump Test/Power test: What Does It Show Us?

2. Thorstensson Fatigue Test

Try to locate the Thorstensson Isokinetic Dynamometer first: it is an excellent tool. If you can find it, the Thorstensson Test is the only thing you’ll need to determine your muscle fiber composition and select an appropriate exercise plan. If the Thorstensson Test proves dif­ficult to locate, we recommend doing the Vertical Jump/Power Test.

The Thorstens­son Isokinetic Dynamometer is a leg extension machine attached to a computer that measures the power output of muscles. Please take a look at this article (Thorstensson Fatigue Test: Determining Muscle Fiber Composition) in order to find out how exactly you should perform the Thorstensson fatigue test and how to interpret obtained results.

3. Magnetic Resonance Imaging (MRI)

The MRI is an accurate and easy test, but it can be very expensive. It is also a relatively new method, so finding a technician or radiologist who knows what to look for regarding muscle com­position might be a challenge.

Tests we don’t recommend

Here is a brief description of some tests we don’t recommend but you might hear about as you go about testing your own fiber type.

1. The Wingate Test

A bike connected to a computer calculates your power as you pedal as hard as you can for 30 seconds. You exert so much ener­gy during the test, your legs will not work for a while afterward. You could hardly even breathe after the test. It is very accurate in determining the power you produce and indicating your explosive abilities, but it leads to total muscle failure.

2. The Margaria Stair Climb Test

A good quick test, but it involves a special timing device that is difficult to find or purchase.

3. The Anaerobic Step Test

The test involves stepping up and down for a minute. It is like a sprint up a staircase—exhausting and difficult to do for someone out of shape.

4. Bench Press Test

We came across a bench press test, but we doubt that it provides accurate fiber percentages. It is more likely an indicator of strength, not fiber composition.

Final Thoughts on Determining Your Fiber Type

As this topic becomes more popular and better studied, there may be new and more effective ways to find out how you are built. We came across some new theories during our research, but they had yet to be fully explored. The three tests we recommend—the Thorstensson Test, the Vertical Jump/Power Test, and the Magnetic Resonance Imaging (MRI) —are the best tests we have found and are proven methods to determine your fiber type and explosive abilities.

Once you determine what dominant muscle fiber type you are, you’ll be able to train based on how your body responds. It is interesting for athletes to know the composition of their muscle fibers. If they are primarily a strength or speed athlete, they want fast twitch fibers. For endurance athletes, more slow twitch fibers is optimal.

Related articles:

1. Types of muscle fibers: Slow-twitch Vs. Fast-twitch
2. Thorstensson Fatigue Test: Determining Muscle Fiber Composition
3. Vertical Jump Test/Power test: What Does It Show Us?

References

(1) Foster, C., L.L. Hector, K.S. McDonald, and A.C. Snyder (1995). Measurement of Anaerobic Power and Capacity. In: Physiological Assessment of Human Fitness. Champaign, Illinois: Human Kinetics, pp. 73-76.

(2) McArdle, W.D., F.I. Katch, and V.L. Katch (2001). Individual Differences and Measurement of Energy Capacities. In: Exercise Physiology- Energy, Nutrition, and Human Performance. Baltimore, Maryland: Lippincott Williams & Wilkins, pp. 222-231.

(3) Kearney, J.T., K.W. Rundell, and R.L. Wilber (2000). Measurement of Work and Power in Sport. In: Exercise and Sport Science. Philadelphia, Pennsylvania: Lippincott Williams & Wilkins, pp. 31-52.

(4) Logan, P., D. Fornasiero, P. Abernethy, and K. Lynch (2000). Protocols for the Assessment of Isoinertial Strength. In: Physiological Tests for Elite Athletes. Champaign, Illinois: Human Kinetics, pp. 219.