Muscle fibres

My guess is that most of you have heard, read or know something about muscle fibres because they are just so frequently mentioned in and around the gym now. What tends to happen with these hot topics is that a lot of us get carried away with discussing them and then forget to actually make sure that we understand them fully. And even when we think we have got to grips with what it is all about, new research comes out to challenge everything we thought we knew. 

I’m sure you know that there are two main categories of muscle fibres: fast twitch and slow twitch. Basically they contribute to generating all of our muscular activity. In simplified terms, whenever we do physical exercise our bodies use more or less of the fibres, depending on the activity that we are doing. So, for example, if we are using explosive, powerful movements our bodies will depend more on fast twitch fibres. Whereas if we are going for a long distance run then we are more reliant on the slow twitch fibres.

Unfortunately for us it isn’t as simple as just having both types in unlimited quantities to call upon whenever we need them. If it was, we could then you might see Usain Bolt competing in as many marathons as he does sprint races. What this all means is that to improve at certain activities, we have to specifically train the fibres. So a sprinter has to train with explosive weight exercises to develop fast twitch fibres, while an endurance athlete will have to train for longer at a steadier pace.

You might think that this all seems quite simple and in theory it should be, but the reality is never quite the same, is it? This is where it can get a little bit complicated. For a long time it was generally accepted that each muscle fibre type existed independently of the other and therefore conversion between the two was impossible. What that means is that you couldn’t train fast twitch fibres to become slow twitch fibres and vice versa. Recently though people have started to notice that by utilising HIIT fast twitch fibres they have appeared to adopt a greater ability to process oxygen, which is a primary feature of slow twitch fibres.

A lot of this study is in its infancy and we might not know for some time whether or not we can convert the different types of fibre. What we do know is that someone who trains slow twitch fibres isn’t bound to a life where he/she is unable to perform any explosive movements. Similarly, if you focus on training for fast paced exercise, it doesn’t mean that you have an inability to endure exercise for an extended period of time. I mean, just look at Mo Farah. He demonstrates world class levels of both endurance and power almost every time that he takes to the track!

Muscular composition plays a major role in all of this. So marathon runners might have 90% slow twitch fibres, whereas a sprinter could have as little as 20, or 25%. None of this is permanent though. As with any form of training you have to maintain it over your life if you want to improve. So we don’t know absolutely everything about muscle fibres but there is no doubt that we know more than enough to excel at a wide range of different physical activities.

Ollie Lawrence
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