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Adapting your workout to suit your muscle fibre type

Jamie Hale explains how your muscle fibre type determines your ideal strength training workout.

There is no single workout that can be labelled as the best workout. There are a couple of reasons for this, the first being the law of individuality which states each individual is different on a physical as well as the mental level and the second being the law of adaptability which states once the body adapts to a specific stimulus it no longer derives the same benefits as it did before adaptation occurred. These two factors make it impossible for there to be one magic workout.

Muscle Fibres

Each individual will react to a workout differently. A 6-foot 200-pound person has different physical attributes than a 5-foot 200-pound person. More than likely, these two individuals have a different muscle fibre make up as well as a difference in limb and muscle length. Muscle fibre makeup is one of the most important factors to consider when deciding which workout will produce better results. Each muscle contains three different types of muscle fibres. These include slow, intermediate and fast-twitch. Slow-twitch fibres, also known as red fibres due to their abundant supply of blood, are active during endurance activities such as running. They are highly oxidative and are not likely to hypertrophy very much. Fast-twitch fibres have little blood supply causing them to be white in appearance. They are power-oriented and fatigue quickly. These fibres tend to hypertrophy more than the slow-twitch. Intermediate fibres have properties of both of the previously mentioned fibres.

About 60% of people have intermediate muscle fibres. The remaining 40% is equally divided among the people between slow and fast-twitch. To ensure maximum growth, low, medium and high repetitions must be performed. Each muscle in the body has all three muscle properties, but the ratio of muscle fibre types can vary with each muscle.

Dr F. Hatfield's test for fibre type

Dr Hatfield has devised a test to determine the fibre composition of each muscle group. The first step is determining your 1repetition max (RM) on a particular exercise. Use 80% of the 1RM on each exercise to determine your fibre composition. Remember, one muscle can be fast-twitch while another is slow-twitch. For this reason, a variety of exercises should be performed using this test.

Hatfield has found a wide variety of repetition ranges with his 80% of 1RM test. While some athletes can perform 4 to 6 repetitions with 80%, others can perform 15 to 20 repetitions. The reason this occurs is that people performing the lower repetitions have mostly fast-twitch muscle fibres which have weak endurance capabilities. The people performing 15 to 20 repetitions have more slow-twitch fibres due to their greater endurance abilities. People performing 7 to 13 repetitions usually have mostly intermediate fibres.

Test protocol

  • Determine your one-repetition maximum (1RM) on an exercise
  • Perform as many repetitions as possible with 80% of your 1RM
  • Use your result to determine your fibre type:
    • Less than seven repetitions - fast-twitch (FT) dominant
    • 7 or 8 repetitions - mixed fibre type
    • more than eight repetitions - slow-twitch (ST) dominant

This test indicates whether you should perform high, medium, or low reps on a particular exercise. For instance, if you are FT dominant, then you should use heavier loads and lower repetitions in your training. ST dominant individuals, on the other hand, will respond better to lighter loads and higher repetitions.

The ratio of muscle fibre type

By determining muscle fibre ratios, we are better able to personalize our training style. A person with mostly fast-twitch fibres should spend the majority of time training with lower repetitions. In contrast, the person with mostly slow-twitch fibres should spend the majority of time in the higher repetition range. The athlete with mostly intermediate fibres should spend the majority of time training in the medium repetition range. To optimize the size of the muscle, the trainee must recruit as many muscle fibres as possible. Even if you have mostly fast-twitch fibres, you still must stress the intermediate and slow-twitch fibres because no muscle has 100% fast or slow-twitch. All muscles have a mixture of both; therefore, all fibres must be stressed through a variety of repetition ranges.

Grip width

The angle of exercise also plays an important role in recruiting specific muscle fibres. If you change the angle of an exercise, you create a different pattern of recruitment which stimulates different muscle fibres. If we perform a lat pull-down using a wide grip or a lat pull-down using a closer grip, we stimulate the same muscle, but by changing the width of the grip, we now have a different recruitment pattern of muscle fibres within the muscle. By altering the angle of exercise, we can expect other muscle fibres to be activated.

Speed of movement

Variations in the speed of exercise also result in different muscle fibre recruitment. Individual fibres are stimulated with high-velocity training that is not used when moving heavier weights slowly. It is also a good idea to use super slow training which could involve a tempo of 5-0-5. No matter what type of program you use, after a while, you will adapt to this specific stimulus and gains will come to a halt. By continuously varying your routines, your body does not have a chance to adjust. No routine is immune to the law of adaptation.


In conclusion, have an open mind about your workouts. Vary your training protocols and find out what works best for you. Also, do not forget the importance of nutrition, rest-recovery and a good supplement program. No matter how hard you train, if the factors mentioned above are not optimized, you will never reach your full potential.

Article Reference

This article first appeared in:

  • HALE, J. (2006) Adapting your workout to suit your muscle fibre type. Brian Mackenzie's Successful Coaching, (ISSN 1745-7513/ 37/ November), p. 6-7

Page Reference

If you quote information from this page in your work, then the reference for this page is:

  • HALE, J. (2006) Adapting your workout to suit your muscle fibre type [WWW] Available from: [Accessed

About the Author

Jamie Hale is a Sports Conditioning Coach in the USA, a member of the World Martial Arts Hall of Fame and contributor to numerous exercise and sports journals.