Red fibers VS white fibers
Subsequently, more accurate classifications have been proposed which consider specific parameters such as the contraction velocity MEASUREMENT and the METABOLIC prevalence of muscle fibrocells.
Today, all known parameters are UNIFIED in the specific and detailed description of:
- slow fibers (red - type I - βr - Slow Oxidative [SO])
- intermediate fibers (clear - type IIA - αr - Fast Oxidative Glycolytic [FOG])
- fast fibers (white - type IIB - αw - Fast Glycolytic [FG]).
In adult skeletal muscles there is a third type of fiber, called IIx, with intermediate characteristics between IIa and IIb.
Obviously every muscle contains a certain percentage of ALL the fibers and its composition is never 100% of one type or the other; furthermore, we remind you that:
- Among them, the various skeletal muscles have a composition of different fibers.
- Muscular predisposition is ALSO genetically determined.
- Muscle fibers can be partly specialized with training.
Characteristics of red fibers
Red fibers are functional units of skeletal muscle; they, like white fibers and those defined as "intermediate" are responsible for the transformation of chemical energy (adenosine tri phosphate - ATP) into mechanical or kinetic energy.
Red fibers have a color very similar to that of blood due to some biochemical and structural characteristics; in particular:
- Dense capillary ramifications.
- High concentration of myoglobin, a storage protein (similar to the hemoglobin contained in red blood cells) that acts as a muscle oxygen RESERVE.
- High concentration of mitochondria.
Compared to IIA and IIB, red fibers have a rather reduced contraction speed; in ALL humans (and in all mammals), the greatest muscular concentration of red fibers is:
- In the muscles responsible for maintaining the posture (eg back supporters)
- In the muscles responsible for performing "slow and repeated" movements (such as some thigh and leg muscles useful for walking, eg psoas-iliac and soleus).
Furthermore, the red fibers contain a large amount of mitochondria that work effectively in the oxidative energy production (aerobic), supported by the large blood supply of the dense capillary bed.
NB . Often in the body-building the muscular training table is varied - increasing: 1. repetitions 2. the series and 3. the volume of training - with the aim of partially promoting the increase of the muscular mass managing ALSO the proliferation of the mitochondria and of capillaries. In reality, although it constitutes a valid alternative in the cyclization of training, it is appropriate to specify that, through this variant, the increase in mitochondria and capillaries is quite limited and does NOT significantly affect the increase in volume and overall muscle mass.
Ultimately, red fibers are suitable for mild, slow and repeated efforts; they brilliantly resist fatigue even if they do not contain large volumes of glycogen (higher in fibers IIa and IIB).
To summarize the concepts expressed above, we refer to the critical reading of the following tables
Slow or red fibers or II | Fast or white fibers or IIb | Intermediate fibers or IIa | |
Atp production | Oxidative phosphorylation (aerobic) | Glycolysis (anaerobic lactate) phosphocreatine (anaerobic alactacid) | Oxidative phosphorylation (aerobic) Glycolysis (anaerobic lactate) |
| Oxidative enzymes | Abundant | poor | Intermediate characteristics |
| Glycolytic enzymes | meager | Abundant | |
Color (myoglobin) | Intense red | Clear | |
Mitochondria | Numerous | meager | |
| Energy substrates | Mainly lipids | Mostly carbohydrates | |
Fiber diameter | Small with many capillaries | Great with a few capillaries | |
Features motor neurone | Small axon and body mobile phone, low speed of conduction e discharge frequency | Great axon and body mobile phone, high speed of management and frequency of download | |
Speed of fatigue | slow | rapid | |
Feature | Maintain activities tonic for long periods | They maintain an activity explosive and powerful for few moments |
Percentage of slow and fast fibers present in human skeletal muscles (*)
| MUSCLE | % Red fibers | % Intermediate fibers | % White fibers |
Short lead Great adductor Great buttock Ileo psoas Pettineo Psoas gracile semimembranosus Lata fascia tensor Large Quadric intermediate. Femor. Large Quadric medial. Femor. Soleo Great backbone Brachial biceps Deltoid Rhomboid Keystone Long connector Gemini Medium / small buttock External / internal shutter piriformis Hamstring Sartorio Semitendinosus popliteal Wide side Quadric rectus femoris. Femor. Anterior Tibial Right abdomen Brachioradials Great Pectoral Brachial triceps supraspinatus | 45 55 50 50 45 50 55 50 70 50 50 75 50 50 60 45 54 45 50 50 50 50 65 50 50 50 45 45 70 46 40 42 33 60 | 15 15 20 - 15 20 15 15 10 15 15 15 - - - - - 15 20 20 20 20 10 20 15 15 20 15 10 - - - - - | 40 30 30 50 40 30 30 35 20 35 35 10 50 50 40 55 46 40 30 30 30 30 25 30 35 35 35 40 20 54 60 58 67 40 |
Training: optimization of red fibers and specialization of intermediate fibers
Personally I have always been of the idea that every athlete should make the "predisposition" his strong point. Although apparently paradoxical, at times, favoring the development of a "natural" tendency can determine an absolutely unparalleled performance increase. Obviously, it is not possible to oppose the will of the student or client ... if a potential marathon runner wants to become a weightlifter ... there is little left to do!
However, a method frequently underestimated by most personal trainers - and which (unexpectedly) is fairly successful - is to PROMOTE athletic and motor development while respecting the physiological tendency of the sportsman.
Practical example:
- Objective: development of the general resistant force
- Subject: tank tops (middle-distance runner) characterized by a genetic prevalence of red fibers
- Method: CIRCUIT TRAINIG (see article Resistant force)
According to this principle, the choice of the number of repetitions and the intensity of exercise could be oriented more on the aerobic component (series of 7 'for each station) rather than mixed aerobic / anaerobic (series of 3' for each station). In this way, the naturally present red fibers have the possibility of manifesting their development to the maximum, both in structural terms (capillaries, mitochondria) and biochemical and enzymatic (myoglobin, enzymes of the oxidative chain, etc.); in parallel, the intermediate fibers (always present even if in variable quantities) evolve on the basis of the predominant stimulus (in this case AEROBIC).
The limit of this technique is obvious; using ONLY such a workout there is the possibility of considerably LIMITING the development of the athlete and insufficiently stimulating all the white-anaerobic muscle fibers ... but on the other hand, persisting in training a genetically poor "lactic power" could mean:
- Getting poor results on anaerobiosis
- Limit the development of the genetically stronger component.
The speech changes significantly in the event that the percentage of red and white fibers depends almost exclusively on the specialization of intermediate fibers (IIA); if the quantity of the latter prevails over the others, the athlete will have a greater ability to adapt to the stimulus, therefore, the training can be managed with greater freedom and also with more room for improvement.
Unfortunately, in addition to muscle biopsy, there are no PRECISE techniques that can evaluate the prevalence of one or the other fiber; on the other hand, aptitude tests are able to provide us with "good" information of a "metabolic" type, but in this case, to understand if the red fibers are genetically determined or if they are already specialized IIA fibers, it is very difficult.
Bibliography:
- Neurophysiology of movement. Anatomy, biomechanics, kinesiology, clinic - M. Marchetti, P. Pillastrini - Piccin - pag 29-30.
