Jul 2014 12

Slow twitch, fast twitch

By: Dave Wheeler

So why is some chicken meat dark and some white?

It's all to do with muscle, and strangely we have dark and white muscle too...


pic courtesty of James Barker @ freedigitalphotos.net


Red muscle, white muscle (pink muscle)

Muscles are made up of fibres - strands of contractile soft tissue which run in parallel to one another.

But not all muscle fibres are born equal:

Red muscle fibres (slow twitch)

These slow twitch muscle fibres are:

  • thin
  • contain a lot of blood vessels, so have a good blood supply
  • red
  • powered by the aerobic system (see the previous blog post Who needs carbs anyway?)
  • also called type 1 fibres

White muscle fibres (fast twitch)

These fast twitch muscle fibres are:

  • thicker than slow twitch
  • don't have so many blood vessels, so have a relatively poor blood supply
  • white
  • powered by the anaerobic system (again, see the blog post Who needs carbs anyway?)
  • also called type 2a fibres

Pink muscle fibres (fast twitch)

These muscle fibres are also classed as fast twitch and are:

  • medium thickness
  • have an "in-between" number of blood vessels, so have a moderate blood supply
  • pink
  • powered partly by the aerobic system and partly by the anaerobic system
  • also called type 2b fibres

Each muscle in your body is actually made up of a mixture of these red, white and pink fibres to give muscle its characteristic stripey appearance, called striated.



It's all in the twitch

But the combination of fast twitch and slow twitch fibres is different in different muscles.

Fast twitch (type 2a) muscle fibres can contract quickly and provide lots of instant power. So the biceps and triceps in your arms contain quite a high concentration of fast twitch (type 2a, white) fibres. Whilst these fibres can provide intense powerful movements, they tire quickly. That's why, in the gym, you can do bicep curls to fatigue - the fact that the muscles fatigue within a relatively short space of time is because they're predominantly fast twitch fibres. Muscles with a high concentration of fast twitch fibres are called phasic muscles.


pic courtesy of David Castillo Dominici @ freedigitalphotos.net


Slow twitch (type 1) muscle fibres, on the other hand, are slow to contract but are great for endurance. Muscles that are in continuous use (the so-called postural muscles) contain a high proportion of slow twitch fibres. So neck muscle, which must support your head all day contain a lot of slow twitch fibres; so do the muscles in your lower back.

Unsurprisingly, pink muscle fibres (type 2b) are in-between both.


Is red meat born or made?

So white meat corresponds to phasic muscles (fast twitch fibres) and red meat coresponds to postural muscles (slow twitch fibres) - but what's interesting is that not everyone's muscles contain the same proportion of fast and slow twitch fibres.

A world-class sprinter like Usain Bolt has a massively high proportion of of fast-twitch fibres in his leg muscles, whereas a professional marathon runner will have an equally massive proportion of slow-twitch fibres in his or her leg muscles.

It seems that the type and number of fibres in a given muscle is pretty much set from birth: this means that each of us is more suited to one kind of sport than another. A world-class marathon runner will have been born that way (though obviously a lot of training will have been needed for the runner to reach his or her full potential).

So the runner who did a lot of sprinting at school, who's kept fairly fit since with strength training at the gym and who's now hit their 40's will probably consider himself fairly fit. If he decides to enter a marathon, he's going to have high expectations of himself - but the fact is that by birth and lifestyle his leg muscles are predominantly white meat (fast twitch) - he's built for power not endurance. It doesn't mean that he won't be able to do the marathon - he will. It's just that his training programme in the lead up to the event, his expectations, and how he recovers after will be different to the person built for endurance. 

Whether you're endurance or power, postural or phasic, type 1 or type 2, red or white, if you think I can help give me a call.