Muscle Fibres/ Genetics - UK-Muscle Body Building Community

SportDr · 27-01-2005, 05:37 PM

First the science:

Anatomy of Muscle Fibres.

It is generally accepted that there are three basic types of muscle fibres. Slow twitch (Type I) muscle, fast twitch (Type IIa) and fast twitch (Type IIb) muscle fibre.
Human muscles contain a genetically determined mixture of both slow and fast fibres type. On average, we have about 50% slow and 50% fast fibres in most of the muscles used for movement. The slow muscles contain more mitochondria and myoglobin which make them more efficient at using oxygen to generate ATP without lactate acid build up. In this way, the slow twitch fibres can fuel repeated and extended muscle contractions such as those required for endurance events like a marathon.

The two fibres types generally produce the same amount of force per contraction, but fast twitch fibres produce that force at a higher rate (they fire more rapidly). So a lot of fast twitch fibres can be an asset to a sprinter when there is a limited amount of time to generate maximal force. The slow twitch fibres, on the other hand, fire less rapidly, but can go for a long time before they fatigue.

Fibre Type and Performance

The genetic component of muscle fibres type can not be overlooked when it comes to performance. Olympic athletes tend to be genetically blessed with large variations in fast and slow twitch fibres that perfectly suit their sport. Olympic sprinters have been shown to possess about 80% fast twitch fibres while those who excel in the marathon may have 80% slow twitch fibres.

Can you change your muscle fibre type by training?

Virtually all the available evidence suggests that the answer to the last question is no. In fact, it has been suggested that type IIb MHC and therefore IIb fibres constitute a 'default' fibre type setting in humans when activity is absent, and evidence of high proportions of this fibre type in paralysed muscle support this theory. It has also been known for some time that increases in activities like strength or power training can lead to conversion of muscle fibres. But, unfortunately, this conversion operates in one direction only, changing fast type IIb fibres into slower type IIa fibres. Moreover, if heavy loading of muscles continues for a month or more, virtually all type IIb fibres will transform to type IIa, with obvious consequences for sprinting potential.

What happens when heavy strength training stops? Do the newly formed type IIa fibres revert back to type IIb? The answer is yes, but recent research has revealed some extraordinary results to which a simple yes does not do justice. Scientists from the Copenhagen Muscle Research Centre examined training and detraining effects on muscle fibre type distribution. Biopsies (muscle samples) were taken from the vastus lateralis muscle of nine young sedentary males. All the subjects then undertook three months of heavy resistance training, aimed predominantly at the quadriceps muscle group, which ended with a second muscle biopsy. The subjects then abruptly ceased training and returned to their normal sedentary lifestyles before providing a third biopsy three months later.

So we see from the data above that, to have a greater percentage of fast twitch fibres is beneficial to sports that require explosive power, a typical sprinter has 76% FT and 24% ST fibre distribution and weight lifters 56% FT 44% ST. Therefore the genetically gifted amongst you may be carrying the perfect combination of fibres for powerlifting! But what about body building? To grow you have to hit all the muscle fibres effectively so short sets of 1-6 reps are not the optimal way to do this as they will only hit the FT fibres fully, no to train the entire range of fibres takes a different strategy which I will talk about in my next article.

SD

**hackskii** · 27-01-2005, 05:57 PM

Cool.
Ive read that 70% of your max will hit 90% of the muscle fibers.

winger · 27-01-2005, 06:22 PM

Quote:

Originally Posted by SportDr

To grow you have to hit all the muscle fibres effectively so short sets of 1-6 reps are not the optimal way to do this as they will only hit the FT fibres fully, no to train the entire range of fibres takes a different strategy which I will talk about in my next article.

SD

That is why I train heavy and light and I do cardio. Lets see what that guy has to say?

SportDr · 27-01-2005, 06:50 PM

Quote:

Originally Posted by hackskii

Cool.
Ive read that 70% of your max will hit 90% of the muscle fibers.

The more of your 1 RM you use, the more recruitment of muscle fibres, this will include the ST fibres also.

SD

winger · 27-01-2005, 06:59 PM

Quote:

Originally Posted by SportDr

The more of your 1 RM you use, the more recruitment of muscle fibres, this will include the ST fibres also.

SD

Gota disagree here mate. Taken from your own article.

Quote:

Originally Posted by SportDr

1-6 reps are not the optimal way to do this as they will only hit the FT fibres fully,

27-01-2005, 05:37 PM	#1 (permalink)
SportDr Getting HUGE! Join Date: Sep 2004 Location: E-Sussex UK Posts: 2,623	Muscle Fibres/ Genetics First the science: Anatomy of Muscle Fibres. It is generally accepted that there are three basic types of muscle fibres. Slow twitch (Type I) muscle, fast twitch (Type IIa) and fast twitch (Type IIb) muscle fibre. Human muscles contain a genetically determined mixture of both slow and fast fibres type. On average, we have about 50% slow and 50% fast fibres in most of the muscles used for movement. The slow muscles contain more mitochondria and myoglobin which make them more efficient at using oxygen to generate ATP without lactate acid build up. In this way, the slow twitch fibres can fuel repeated and extended muscle contractions such as those required for endurance events like a marathon. The two fibres types generally produce the same amount of force per contraction, but fast twitch fibres produce that force at a higher rate (they fire more rapidly). So a lot of fast twitch fibres can be an asset to a sprinter when there is a limited amount of time to generate maximal force. The slow twitch fibres, on the other hand, fire less rapidly, but can go for a long time before they fatigue. Fibre Type and Performance The genetic component of muscle fibres type can not be overlooked when it comes to performance. Olympic athletes tend to be genetically blessed with large variations in fast and slow twitch fibres that perfectly suit their sport. Olympic sprinters have been shown to possess about 80% fast twitch fibres while those who excel in the marathon may have 80% slow twitch fibres. Can you change your muscle fibre type by training? Virtually all the available evidence suggests that the answer to the last question is no. In fact, it has been suggested that type IIb MHC and therefore IIb fibres constitute a 'default' fibre type setting in humans when activity is absent, and evidence of high proportions of this fibre type in paralysed muscle support this theory. It has also been known for some time that increases in activities like strength or power training can lead to conversion of muscle fibres. But, unfortunately, this conversion operates in one direction only, changing fast type IIb fibres into slower type IIa fibres. Moreover, if heavy loading of muscles continues for a month or more, virtually all type IIb fibres will transform to type IIa, with obvious consequences for sprinting potential. What happens when heavy strength training stops? Do the newly formed type IIa fibres revert back to type IIb? The answer is yes, but recent research has revealed some extraordinary results to which a simple yes does not do justice. Scientists from the Copenhagen Muscle Research Centre examined training and detraining effects on muscle fibre type distribution. Biopsies (muscle samples) were taken from the vastus lateralis muscle of nine young sedentary males. All the subjects then undertook three months of heavy resistance training, aimed predominantly at the quadriceps muscle group, which ended with a second muscle biopsy. The subjects then abruptly ceased training and returned to their normal sedentary lifestyles before providing a third biopsy three months later. So we see from the data above that, to have a greater percentage of fast twitch fibres is beneficial to sports that require explosive power, a typical sprinter has 76% FT and 24% ST fibre distribution and weight lifters 56% FT 44% ST. Therefore the genetically gifted amongst you may be carrying the perfect combination of fibres for powerlifting! But what about body building? To grow you have to hit all the muscle fibres effectively so short sets of 1-6 reps are not the optimal way to do this as they will only hit the FT fibres fully, no to train the entire range of fibres takes a different strategy which I will talk about in my next article. SD __________________ I don't like Sports and I am not a Doctor! You expressed and challenged yourself, startled the dozing muscles and welcomed the sweet pain of gain. Boredom begets mediocrity. Enemies both, they deserve swift eradication. Let's hit the weights and build some muscle. Race ya to the bench press. Dave Draper A goal casually set and lightly taken will be freely abandoned at the first obstacle. Zig Ziglar Any advice given is for information only, always seek the advice of your medical practitioner. Use this My Protein refferer code and get a 5% DISCOUNT on your first order! MP2819

27-01-2005, 05:57 PM	#2 (permalink)
hackskii Super Moderator Join Date: Jul 2003 Location: Sunny Southern California U.S.A. Posts: 22,671	Cool. Ive read that 70% of your max will hit 90% of the muscle fibers. __________________ "Life is not measured by the number of breaths we take, but by the moments that take our breath away." - George Carlin Scott To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.