Muscle fibres. We’ve all heard of them and most, if not all of us, will know they are important for physical performance. But how many of you know the details? Perhaps not too many.

So I’ve been reading up on muscle fibre and have discovered that there are different types.

Do they affect training adaptation?

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Although the answer is ‘Yes’, this is an extremely difficult question to answer in a short space.

Our muscles are made up of two basic types of muscle fibre, slow twitch (also called ‘red’, type I) fibres and fast twitch (also called ‘white’, type II) fibres.

All these fibres are involved in generating muscular activity. However, depending on the activity, either more or less of one type will be used to suit what is being demanded of the body.

Lift a chest of drawers and it’ll be your fast twitch fibres that supply the power, go for a walk in the park and it’ll be the slow ones that produce most of the energy.

Training your muscle fibres

You can specifically train muscle fibres to develop either more power and speed or greater endurance, or a combination of the two.

A sprinter would perform lots of weight training, plyometric (jumping type) exercises and sprints of course. All with long recovery periods to maintain quality, to develop their fast twitch fibres and improve their speed.

Fast twitch fibres will specifically respond to this training normally by increasing in their size (leading to bigger muscles) and rate of force production. All leading to greater explosive energy and power.

On the other side of the muscle fibre coin you’d have the endurance athlete who will be performing long efforts (30 minutes plus at a steady pace) and this will target their slow twitch fibres.

These fibres will adapt by improving their ability to process oxygen and sustain muscular contraction.

Now the key issue:

muscle fibre_2For aa long time it was thought that these two muscle fibres were entirely separate and unlikley to share of evolve common characteristics. However more recent research indicates that muscle fibre can ‘convert’ between types i.e. fast twitch muscle fibre, when subject to the ‘right’ training can take on more of an oxygen processing function to boost endurance.

The right training in this case would include high intensity interval training, where to generate the increased speed more fast twitch fibre is recruited.

Whether these training induced changes are permanent or not is, as yet, unclear. Interestingly research has actually indicated that human muscle fibre has a ‘fast twitch default setting’ – and that muscle that is inactive over a long period through injury for example, tends to increase its fast twitch fibre content. There will be keyt evolutionary reasons for this as there are for practically everything. Perhaps the body worked out that, in order to survive, our earliest ancestors would benefit  more from power and speed and reaction time rather than sustained feats of endurance.

The key is sustained training that targets a particular muscle type specifically.

Connect with Expert John Shepherd.

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