Three Part Question on Fast Twitch vs Slow Twitch Muscles February 6, 2007
Posted by askatricoach in Running, Speedwork, Triathlon, coaching.trackback
Q: “What’s the difference between fast- and slow-twitch muscle fibres? I understand that we all have different fast / slow ratios in our muscles. How can you tell what you have; how do you train them and will your composition affect how you race triathlons?“
A: Coach Patrick: Excellent question…to back up a bit, there are two specific muscle types: Type I (slow twitch) and Type II (fast twitch). In general, the breakdown in any given muscle between fast and slow- twitch fibers for most folks is 50%. As their name explains, slow-twitch fibers are excellent at fueling repeated and extended muscle contractions (as in an endurance event) because they make much greater use of oxygen. Fast-twitch fibers produce the same amount of force as their slow-twitch bretheren…only much faster.
In general, speeds above 8.5 mph are produced only by anaerobic fast-twitch fibers, which can contract three times faster than slow-twitch fibers (25 milliseconds vs. 75 milliseconds). The fast-twitch fibers can produce a speed in excess of 25 miles per hour, i.e., in the 100 and 200-meter dashes.
In terms of how to tell what dominates your muscle make-up, aside from a muscle biopsy (ouch!) I’d have to say take a look at what you are naturally good at. If you excel at sports that require short bursts of movement or, conversely, activities that require more aerobic participation such as long-distance running, you might already have your answer.
As for your training, I don’t think your muscle composition really determines how you train…it’s more of what your goals are and what the race course looks like that’s important. If you do have a natural tendency towards a good sprint, for example, that might change your race day finish line strategy…but otherwise, it’s good hard work…and not genetics…that will get you to the finish line first on race day!
Hi Coach Patrick -
Thanks for this. When I asked, I guess I was hoping for some magical-words-of-wisdom that would give the ultimate training & race day strategies. Your answer is probably more reassuring though – like it said on most of my school reports, “Could try harder” seems to be THE winning strategy!
Thanks,
Karl.
Hi Coach Patrick -
This was very good information for me about fast and slow twitch fibers but how do you train fast twitch fibers.
-Thanks, Jameson
Jameson -
From a tri perspective, you have to really think about WHY you want to train fast twitch fibers. Since even our shortest races take elite folks an hour (sprint tris), the effectiveness of fast twitch fibers is reduced over that timeframe. I think fast twitch work plays a very strong role in tri technique / execution, however, regardless of the overall race distance. I recommend folks include spin ups (to max cadence and hold for 1 min) on the bike in the base training phase and 1- to 3-min bursts / accelerations in the tapering phase. From a running perspective, high turnover efforts are good, as is including strides (30-seconds fast, jog back recovery) at the end of long slow runs is also effective.
Explosive weight training is another way to target FT muscles…but most folks don’t have the proper technique to execute these…so I won’t really get into that here.
Good luck!
If my 14 year old daughter trains for 800 and 1600m instead of 100 and200 will she lose FT muscle effectiveness?
Shelly –
While the 800/1600 won’t be as specific as the 100/200, she won’t lose that much. It will be more of an execution thing…any “trouble” she has going back to racing the 100/200 will only be getting used to that distance. And, at the end of the day, she’s 14! Diversity of training is critical for fun and to identify where, in fact, she naturally excels. Good luck to her!