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Skeletal muscles are highly maintained tissues in animals, and contained in the entire body, to form a merged network with a central skeletal system through tendons to resist gravity and aid mobility. There are two main categories of muscle fibres in vertebrates:
1. Red muscle fibres
2. White muscle fibres
Red muscle and white muscle are skeletal muscles that execute different functions in the body. Red muscles are called so because they are solid with capillaries and abundant in myoglobin and mitochondria, which offers a featured red appearance.
Conversely, white muscles have moderately fewer mitochondria and myoglobin, providing the muscles with a “whitish” appearance. The major work of some muscles is to sustain a standing posture or to contract gradually during locomotion, chewing, or breathing. Such muscles are apt to contain a high amount of slow-contracting and fatigue-resistant fibres along with a high myoglobin concentration. The capillary bed of red muscles is more impenetrable than the white muscles.
Red and White Muscle: Difference
- Red fibres (slow-twitch, oxidative fibres) are minute in diameter and possess a red colour, due to their greater substance of myoglobin and affluent supply of capillaries. They have abundant large mitochondria underneath the sarcolemma and between the myofibrils. Lipid droplets are frequent in the sarcoplasm of these fibres. On the contrary, white fibres (fast-twitch fibres) are bigger in diameter. Their mitochondria and lipid drops are smaller and less plentiful than those of red fibres.
- The traits of red muscle fibres make them very efficient in postural protection, whereas white muscle fibres are suited for ruptures of extreme muscle activity.
- Red muscle fibres contract more gradually and are more defiant to fatigue than white muscle fibres because of their capacity to oxidatively stimulate ATP. On the contrary, ATP production in white muscle fibres relies on anaerobic glycolysis.
- Biochemical studies disclosed that the ATP activity of white muscle fibres is 3 times more than that of red muscle fibres. Nevertheless, in a resting state, whether ATP is accumulated for use in muscle fibres and whether the accumulated ATP content in red muscle fibres is more or less than that in white muscle fibres are still uncertain.
- Red muscle has a larger concentration of the pigment myoglobin, is usually lesser in soluble protein content, lesser in glycogen, and higher in lipid than white muscle.
- Red fibres are tinier in size than white fibres, are better furnished with capillaries, and possess more mitochondria. White fibres are endowed better for glycolytic metabolism than red fibres, which are devised for oxidative metabolism.
- Isolated sarcoplasmic reticulum parts from white muscle have a better vitro calcium-binding capacity than those from red muscle and the myosin from red muscle has a lesser ATP activity than that from white muscle.
Red and White Muscles: Comparison
| Parameters | Red Muscle Fibre | White Muscle Fibre |
| Definition | Red muscles are a kind of skeletal muscle that is thick with capillaries and is abundant in myoglobin and mitochondria | White muscles are also a kind of skeletal muscle, but hold lower amounts of myoglobin and mitochondria |
| Size | Red muscles are thin and smaller in size | White muscles are dense and bigger in size |
| Colour | Red muscles are red in colour as they have a large amount of myoglobin | White muscles are white in colour as they hold a small amount of myoglobin |
| Mitochondria | Red muscles contain an abundance of mitochondria | White muscles have fewer mitochondrion |
| Sarcoplasmic Reticulum | Red muscles have diminished quantities of SR. The Sarcoplasmic reticulum is somewhat developed | White muscles possess more SR. The Sarcoplasmic reticulum is well expanded |
| Vascularisation | The Red muscle fibres are supplied with plentiful blood capillaries | White muscles are somewhat vascularised |
| Lactic Acid | Lactic acid does not amass in red muscles | Lactic acid gathers in white muscles |
| Fatigue | Red muscles can execute aerobic oxidation without amassing much lactic acid – therefore, can contract for long periods | White muscles perform anaerobic oxidation and amass lactic acid much faster than red muscles – therefore, get exhausted after short ruptures of contraction |
| Rate of Contractions | Red muscles have a slow rate of contraction | White muscles have a fast rate of contraction |
| Work Pattern | Red muscles carry out deliberate and prolonged contractions for a long period | White muscles carry out quick work in a small duration |
| Respiratory pattern | Red muscles perform aerobic respiration | During strenuous exercise, white muscles transfer over to anaerobic respiration |
| Example | Extensor muscle | Muscles of the eyes |
Conclusion
The connection between fast and slow fibres in meat animals is relatively simple. It is a fact that fast fibres are generally white, whereas slow fibres are usually red. Red muscle fibre and white muscle fibre are skeletal muscles that accomplish different roles and functions in the body.
