Podcast, Science and Physiology, Uncategorized

Muscle fiber types, recovery and training adaptations, and overreaching with Phil Bellinger, PhD | EP#297

 August 2, 2021

By  Mikael Eriksson


Phil Bellinger, PhD, is a researcher and lecturer at Griffith University, Australia. His work includes training interventions, nutritional interventions, and more recently using magnetic resonance spectroscopy to non-invasively assess muscle fibre typology and investigate how it relates to performance and training adaptations. He has also recently published a literature review on functional overreaching in endurance sports. 

In this Episode you'll learn about:

  • Fundamentals of different muscle fibre types, and muscle fibre type distribution
  • How an athlete's muscle fibre typology impacts recovery within and from high-intensity exercise
  • How an athlete's muscle fibre typology impacts adaptations to training resulting from periods of "overload training" (increased volume)
  • The differences between acute fatigue, functional overreaching, and non-functional overreaching
  • Is functional overreaching necessary to induce training adaptations? 

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04:00 -

  • I am an Australian University lecturer and researcher, mainly focusing on applied sports physiology.

    Recently I have done a lot of research on muscle fibre phenotype and its training applications.

Muscle fiber types composition

05:30 -

  • There are basically two major type of muscle fiber types, the type 1 and type 2 fibers.

    The type 1 fibers are highly dominant in endurance athletes, some endurance runners do have up to 90-95 % type 1 fibers in their body.

    They are fatigue resistent, highly oxidative (high fat metabolism) and not especially glycolytic and hence they cannot contract so rapidly or produce as much power.

    The type 2 fibers are more fatigue prone and glycolytic but can contract more rapidly and produce more power.

    These muscle fibers are prominent in athletes involved in more explosive sports.
  • Recent research has shown that the composition of muscle fibers plays a role in regards to how an athlete respons to training.
  • For quite a long time, it was believed that muscle fiber types could alter due to response to training, like type 1 fibers turning into a type 2 fibers, however, more recently we have seen that this is not really the case.

    It appears that subgroups within the main muscle fiber types can alter between each other but type 1 fibers can not really turn into type 2 fibers and vice versa.

    However, the function of the muscle fibers are highly adaptable to training.
  • The average person (who casually trains 2-3 times per week) has a mixed composition of muscle fiber types.

Study 1

17:30 -

  • In the first study, a group of athletes expressing a high fast twitch muscle fiber distribution was compared agaoimant a group that expressed a high slow twitch muscle fiber distribution.

    The recovery time following a bike session including three 30s maximal efforts (Wingate tests) was then compared between the groups.

    The group that expressed a high slow twitch muscle fiber distribution did recover significantly faster than the group who expressed a high fast twitch muscle fiber distribution.

    Even after five hours of rest, the fast twitch muscle fiber group wasn’t even fully recovered (using maximal knee extension torque as a proxy for recovery).
  • Also, there was a big difference between the groups in terms of the power production on the Wingate tests, the fast twitch muscle fiber group had by far the greatest power production in the first sprint of the session and had very prominent decline in power over the course of the sprints.

    The slow twitch muscle fiber group didn’t show an equally big decline in power over the three sprints and also kept a more even power during the 30s all out efforts.

Study 2

26:00 -

  • In the second study we investigated more long term reactions to training and its relation to muscle fiber fenotypes.
  • In the study we let two groups, one fast and one slow twitch dominant undergo a period of overreaching and a consequent taper period, after which several performance assessments were made.

    The main findings were that the slow twitch dominant muscle fiber group appeared to get more benefit from a period of overload training compared to the slow twitch muscle fiber group.
  • The practical applications from this would be that training load and consequent de-load periods should be adjusted accordingly to the kind of muscle fiber type that an athlete express the most of.

Functional and non-functional over reaching

41:05 -

  • The definition of functional overreaching is that you start to see a performance decline based on overloading but as training is dialed down you get back to a baseline level or even slightly higher than baseline.

    Non-functional overreaching is when you don’t see that performance gets back to normal after dialing back the training load.
  • In a review study, we did find that physiological adaptations were equally high in a group who reported fatigue but did not actually show any performance decline as in a fatigued group that did actually display a performance decline.

    This would indicate that any kind of overreaching might not be needed at all in order to achieve maximum performance gains, as was previously believed.

    Large declines in performance are also related to increased injury and infection risk, poor sleep quality and malnutrition, which are all obvious things that you would like to avoid.

Rapid fire questions

01:01:40 -

  • What is your favorite book, blog or resource related to endurance sports? I love podcasts and my current favorite is ”From Paper to Podium”.
  • What is a personal habit that has helped you achieve success? My building good relations with coaches and athletes.
  • Who is somebody you look up to and has inspired you? My mentor here at the University, Professor Alan Han.


Mikael Eriksson

I am a full-time triathlon coach, founder of Scientific Triathlon, and host of the top-rated podcast That Triathlon Show. I am from Finland but live in Lisbon, Portugal.

Please contact me if you have feedback on the podcast or want to make suggestions for improvement or send in a question for a Q&A episode.

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