As we age our ratio of different muscle fiber types changes especially if we don’t continue to exercise. We lose not only muscle fiber size but actual muscle fibers. A lot of the research indicates these are mainly type 2 muscle fibers. The ones that grow the largest and the strongest.
One of the places that this is most noticeable is in our legs. As we age our legs shrink down until we have the dreaded, chicken legs.
This week I did some research to see whether or not we could get this lost muscle fiber back and if we can, how do we train, to get it back.
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One of the things I was surprised to learn is that there are actually 7 different muscle fiber types that get grouped down into the 3 main classifications, the ones we are used to hearing about. Those groups being type 1, 2a and type 2b.
It is important to have a basic understanding of these fiber types as one of the ways we can increase our type 2 fibers is through muscle fiber conversion. And we will be looking at a study where this happened, but first, let’s look at these 3 fiber types.
Type 1 fibers are our endurance fibers and mainly use oxygen for energy. We associate this type of muscle fiber with marathon runners.
Type 2a uses oxygen to convert glycogen to ATP which is an abbreviation for a-den-o-sine triphosphate which is then used for energy. Type 2b just uses stored ATP. These fibers are stronger and able to generate much more force than type one, but fatigue way quicker. We associate sprinters and weightlifters with these fiber types.
Most of us have a fairly even distribution of type 1 and type 2 muscle fibers
Now it has long been accepted 2a and 2b fibers can convert from one to the other, but there is growing evidence that at least some type 1 fibers can be converted into type 2.
They did a study on four groups of people two of the groups were younger between 20 and 30 and split into male and female the other two groups consisted of older ones again split into separate groups of men and women. Their age range was between 65 and 75.
They trained only one leg using leg extensions doing multiple sets of drop sets. So, each rep they did was close to failure with a total of 50 reps per workout. The other leg was not trained as they were using it as the control. After 9 weeks every group had slightly different results, but the older men’s trained leg was not only stronger than the untrained leg, but it also had increased muscle fiber size in all fiber types, but what is most interesting here is that while total fiber amount was the same there was an increase in type 2a fibers and a decrease in not only 2b fibers but also type 1 indicating that they changed into type 2 muscle fibers.
Another study done with physical education students had them sprinting and found that after 4 to 6 weeks of doing 30-second sprints a decrease in type one muscle fibres and an increase in type 2a fibres.
This establishes that to some extent we can increase our type 2 fibers by converting type 1 fibers, and because type 2 is able to grow larger than type 1.
There is another way to create muscle growth other than hypertrophy, it is called hyperplasia. This is where new skeletal muscle fibers are formed through one of two processes one being where a large muscle fiber splits becoming 2 fibers or it can happen through satellite cells undergoing mitosis fusing together ultimately creating new fibers.
Unfortunately, this is difficult to study in humans so the research is lacking. There are a lot of animal studies done on birds, cats and rodents. These kinds of studies don’t always translate well over to humans, but one technique used on these animals is muscle stretching and human exercise experiments have been done using muscle stretching in more than one way with good success. Resulting in increased muscle size.