Confuse with muscle fibre

[derp2121]

Just want to clear things up. For example if a beginner started going to the gym and started doing free weights he would feel fatigue due to his poor endurance if he had never really exercise. Over time if he continue his work out he will improve. is it the effect of type 1 muscle fiber help overcoming the muscle fatigue and improved his endurance or is it because of muscle repair

[Matthew Blackhand]

Hi,

 

all of the muscles in human body contain all of the muscle fiber types(I,IIA and IIB) in a ratio, which is relatively stable thrughout your whole life and is dependent on genetics as well as on the function of the muscle (e.g. the postural muscles contain much much more fibers of slow type I, because they have to endure very long time w/o exhaustion, but they don't have to be that fast). These fibers are distinguished by different type of myosine ATPase. (There are also another methods of distinguishing fibers, such as according to their myosine heavy chain structure).

 

When a beginner starts pulling weight, his muscle fibers (syncytia = collection of many cells) contain some myofibrils and mitochondria. He has few myofibrils, so he isn't able to pull much weight. Also, the number of mitochondria isn't that big, so he can run out of energy very fast. However, as he exercises, syncytia produce more myofibrils and also number of mitochondria raises, so he has more strength and also more energy, which leads to higher endurance. It's controversial, whether the number of muscle fibers itself raises.

 

This "training" happens in the fibers, which are exercised, so doing endurance excercise will "train" primarily muscle fibers type I.

 

As for muscle repair, if you excercise too much/hard, so that you will damage the fibers (it happens often, but this is above some level), it actually lowers the ability of muscles to become more effective in a way mentioned above, because the fiber has to spend more energy on the repair itself than on becoming more efficient.

 

So to sum an answer to your question: It's about the current fibers becoming more effective.