If I work on speed first thing in the morning, then go out later and do a 3 mile run, do I ruin my fast twitch muscles or do the slow twitch muscles grow during a 3-mile run and the fast twitch ones stay the same?

Will my fast twitch muscles go away if I start running long distances consistently on top of working on speed?

To add some more context, this is for improving basketball speed, strength & endurance.

1 Answer 1


I do not know the exact answer but what I understand is that our muscle fibres has a threshold for it to be activated. They are recruited according to the demands on the activity. You can take a look at this article by Chris Beardsley https://medium.com/@SandCResearch/mechanical-loading-and-not-motor-unit-recruitment-is-the-key-to-muscle-growth-8d6f73ada6fc

If you’re fatigue, your body will start to recruit more motor units to do the work. So if you’re tired during your 3 mile round, there may be a chance your fast twitch fibres will be roped in.

Your body will adapt to the stress you place on it and chances are you may have a balance of both, with slightly more fast twitch as you might be fatigue and your body recruits more motor units. I am not sure about the research regarding changes in muscle fibre type due to training, so you gotta look that up.

What you eat before your workout may be important as well. But anecdotally, I am thinking about rugby and football players. They have both speed and endurance. So my take is, don’t worry too much about the muscle fibres

  • Thank you for the article. It was a great one.
    – Kamilski81
    Nov 18, 2020 at 4:47

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