Thanks to advertising we know that not all yogurts are equal and thanks to 100 Days programme you will learn today that muscle fibres are not equal either.
Sure you can train using your own experience and empirical knowledge and in some cases it is worth doing but it is as well important to understand what is behind these empirical results. That is, certain theoretical aspects need to be explained and starting from today we begin a series of posts on scientific background, exercise physiology and biochemistry, applied to training and workout.
Energy production of the body
The major fuel for all cell structures is Adenosine Triphosphate (ATP). ATP is known as a universal energy source for all biochemical processes in living organisms. All other sources the human body cannot use directly but only through replenishing ATP stores. It is like burning all kinds of fuel, such as coal, oil, peat, gas, into electricity and then feeding all devices from it.
The first energy source to resynthesise ATP is creatine phosphate (CP). It is similar to a small spare tank, a sort of gerry can of petrol. Stores of CP are small but when energy is being spent free creatine and phosphate stimulate other energy sources.
Other energy sources
There are two groups of such sources:
Anaerobic, that is they do not use oxygen;
Aerobic, that is they use oxygen;
We will try to explain them as simple as possible.
After CP is spent, the body starts using glycogen or glucose to create more ATP, which is, in its turn, will be used to restore CP stores and this recombined CP, again, in its turn, is spent to recreate ATP burned by working muscle fibres.
During contractions muscles also produce pyruvate (pyruvic acid, a glucose metabolite), which is broken down to lactate and released into the bloodstream. Lactate in the blood is an indicator of active glycolysis.
At the same time free H+ ions accumulated in the cell are also being released from the cell into the blood. It is an indicator of anaerobic glycolysis as well.
How does it all affect muscle fibres? While lactate is not harmful at any rate, free H+ ions at high concentrations start destroying cellular structures and may ultimately destroy the whole cell. The rule is simple: the more H+ ions the more harm to the body.
Now let's look into the second process, which is depicted on the scheme below:
Our endurance depends on the number of mitochondria in cells. With more mitochondria we have more endurance and can do more repetitions.
When the cell contains enough mitochondria then pyruvate, a leftover from glycolysis, is not broken down to lactate and H+ ions but is completely oxydised in mitoxhondria to CO2, H2O and useful ATP.
Muscle fibre type: oxydative and glycolytic.
Muscle fibres that contain very few mitochondria and therefore have to rely on energy production without oxygen are called glycolytic fibres.
When the concentration of free H+ ions peaks (it takes about 60 seconds), then muscle fibres refuse to contract and you feel very heavy local fatigue.
Muscle fibre that have a lot of mitochondria and whose energy source is primarily aerobic, are called oxydative and because of use of oxygen are practically tireless.
There are two good points:
1. Unlike fast and slow fibres, ratio of oxydative and glycolytic fibres is not inherited.
2. The number of mitochondria in muscle fibres are subject to training. This is the goal if you want to increase the number of reps.
Types of muscle fibres: slow and fast.
We have already mentioned above that it is possible to change the way how muscle fibres provide themselve with energy. Now we will show you another classification of fibres which depends on the speed of their contraction:
Type I (red): slow muscle fibres
As you might have already guessed from their name, the speed of their conraction is slow but they can work for a long time thanks to relying in its energy production on oxydation.
These fibres are small in size and surrounded by a dense network of capillars, contain a lot of protein myoglobine, which is able to store small amounts of oxygen (actually myoglobine transports oxygen fron the blood into cells) and it can transfer stored oxygen to mitoxhondria if need arises. Multiple mitochondria provide high level of oxydative enzymes. Thus slow fibres derive their energy primarily from oxydation of fat and cards in their massive energy factories: mitochondria.
Type II: Fast muscle fibres (white)
It is clear from their name that they are able to contract fast, at 40-100% of possible speed of contraction but they cannot work for prolonged periods because of their energy production specifics. They obtain energy from glycolysis, oxygen free process of converting glucose and glycogen into ATP and lactic acid. Raise of lactix acid concentration changes pH in fibres and causes acidosis which leads to fatigue and inability to perform work.
Fast fibres are thick, they contain more glycogen (complex carbohydrate used by the body to store carbs in muscles and liver) and few mitochondria. Enzymes are primarily glycolitic, to support glycolysis.
There are two subtypes of fast fibres: subtype IIa and IIb.
Subtype IIa (intermediate fibres)
This kind of fibres can use two types of energy production, both aerobic and anaerobic. These fibres are moderately fast, they are able to contract at speed 25-40% of maximum contraction speed.
Subtype IIb
These are true fast fibres. They rely only on anaerobic energy production, they are the strongest and the fastest of all three types. These fibres are the major players in bodybuilding because all programmes target them for muscle growth.
Conclusion
Now it looks very simple. You have learned that there are two (actually three) types of muscle fibres, which are designed for opposite types of work. Some are used when there is a need for a lot of force for a small period of time and some are used when there is a need for little force for long periods. If you want to be versatile you need to train all types of fibres, shifting accents in training.
While you cannot change your genes you can change ways to power your muscles. It is possible to grow Type I muscle fibres as well but it will require a proper training programme which will be discussed in the following days.
