Difference Between Red and White Muscle: Composition, Function

What are Red and White Muscles?

Red and white muscles are the two major types of skeletal muscle fibres identified according to their looks and operation. Muscles facilitate motion, posture, and other physiological functions of the body. Three major kinds of muscles are there in the body: skeletal (voluntary m striated), smooth (involuntary, non-striated), and cardiac (involuntary, striated).

Overview of Skeletal Muscles

Skeletal muscles are those used for voluntary body movements and posture. Characterised by a striated appearance, these muscles anchor into bones via tendons they are known to fatigue more easily. Slow twitch fibres, on the other hand, especially red muscles, hold many mitochondria and much myoglobin and are reserved for endurance. Fast twitch fibres, white muscles, contain fewer mitochondria and are meant for short, powerful movements.

Red Muscle Fibres (Slow Twitch – Type I)

The properties of Red Muscle Fibers are discussed below-

Characteristics of Red Muscle Fibres

They have lots of myoglobin, so these fibres are red and well adapted for oxygen storage intensive vascularisation guarantees constant oxygen delivery with blood and the necessary nutrients, much mitochondria for aerobic energy production.

Functionality of Red Muscle Fibres

Red muscle fibres have a slow contraction and are supposed to perform activities for long-lasting durations. It is highly enduring as it maximally uses oxygen optimally thereby resisting fatigue. From this, its source of energy is aerobic respiration, hence maintaining activity for a long while.

Examples of Red Muscle Fibres

It is these fibres that are dominant in the muscles of posture, for example, the spinal erectors of the back. They are also dominant in endurance-type activities such as marathon running and swimming, where contractions of moderate intensity must be maintained for extended durations.

White Muscle Fibres (Fast Twitch – Type II)

The properties of White Muscle Fibers are discussed below-

Characteristics of White Muscle Fibres

White muscle fibres, or fast-twitch fibres, have low myoglobin content, which gives them a pale appearance. They receive less blood supply compared to red muscle fibres and contain fewer mitochondria. This begets less-suited characteristics for prolonged activities but adequate efficiency for short, intense exertions.

Functionality of White Muscle Fibres

Such fibres are formed in a way to contract quickly and exert much force and, thus, are capable of making rapid and strong movements. But, on the contrary, they have a very low duration of fatigue and, therefore, get tired very easily. They mainly rely on the process of anaerobic respiration by cells in the generation of energy and can thus support periods of activity that last very short durations of time without oxygen.

Examples of White Muscle Fibres

White muscle fibres are used in muscles for fast, explosive activities, such as sprinting and weight lifting. They are important in activities that require instantaneous, high-intensity exertion rather than endurance over a length of time.

Comparison of Red and White Muscle Fibres

The difference between red and white muscle fibres is discussed in the table below:

Importance of Red vs White Muscle Fibres

Red and white muscle fibres have different functions, allowing muscles to adapt to specific activities and physiological needs.

Muscle adaptation: Red fibres support endurance activities through sustained contractions, while white fibres enable quick, powerful movements.

Sports physiology relevance: Athletes develop fibre based on training, endurance sports favouring red fibres and sprint or power sports favouring white fibres.

Energy metabolism differences: Red fibres rely on aerobic metabolism, whereas white fibres depend on anaerobic pathways for rapid energy release.

Clinical relevance: Certain muscle diseases affect specific fibre types, making their distinction important in diagnosis and treatment planning.

Red vs WHite Muscles Fibres NEET MCQs (With Answers & Explanations)

Important questions asked in NEET from this topic are:

• Functionality of red and white muscle fibres

• White vs red muscle fibres

Practice Questions for NEET

Q1. Which is not true for red fibres?

1. Muscles contain a red coloured oxygen storing pigment

2. Muscles contain plenty of mitochondria

3. They are also called aerobic muscles

4. Amount of sarcoplasmic reticulum is high

Correct answer: 4) Amount of sarcoplasmic reticulum is high

Explanation:

Red and White Fibres are two types of muscle fibres with distinct characteristics related to their function and energy use. Red fibres contain a high amount of myoglobin, an oxygen-storing pigment that gives them a reddish appearance. These fibres also have abundant mitochondria, which enable them to perform aerobic respiration and produce ATP efficiently using oxygen. As a result, red fibres contract slowly but can sustain contraction for a longer duration, making them suitable for endurance activities. In contrast, white fibres have lower myoglobin content and appear pale or whitish. They have fewer mitochondria but a higher quantity of sarcoplasmic reticulum. White fibres rely on anaerobic metabolism for energy, allowing them to contract rapidly but for shorter durations, making them suited for quick, explosive movements. Repeated activation of muscles can lead to the accumulation of lactic acid due to anaerobic glycolysis, contributing to fatigue, especially in white fibres.

Hence the correct answer is option 4) The Amount of sarcoplasmic reticulum is high

Q2. The number of mitochondria is few in them, but the amount of sarcoplasmic reticulum is high. What kind of muscle fibres are these?

1. Red muscle fibres

2. White muscle fibres

3. Both a and b

4. None of these

Correct answer: 2) White muscle fibres

Explanation:

Red and White Fibres -

• Repeated activation of the muscles can lead to the accumulation of lactic acid due to the anaerobic breakdown of glycogen in them, causing fatigue.

• Muscle contains a red-coloured oxygen-storing pigment called myoglobin.

• Myoglobin content is high in some of the muscles which gives a reddish appearance.

• Such muscles are called the Red fibres.

• These muscles also contain plenty of mitochondria which can utilise a large amount of oxygen stored in them for ATP production.

• These muscles, therefore, can also be called aerobic muscles.

• On the other hand, some of the muscles possess a very small quantity of myoglobin and therefore, appear pale or whitish.

• These are the White fibres.

• The number of mitochondria is also few in them, but the amount of sarcoplasmic reticulum is high.

• They depend on the anaerobic process for energy.

• Red muscle fibres contract slowly but stay contracted for a longer duration

• White muscle fibres contract rapidly but for a shorter duration.

• Some of the muscles possess a very small quantity of myoglobin and therefore, appear pale or whitish. These are the White fibres. The number of mitochondria is also few in them, but the amount of sarcoplasmic reticulum is high.

Hence, the correct answer is option 2) white muscle fibres.

Q3. he slow twitch muscle fibres which are rich in myoglobin and have abundant mitochondria are

1. WHite skeletal muscle

2. Cardiac muscle

3. Red skeletal muscle

4. Involuntary muscle

Correct answer: 3) Red skeletal muscle

Explanation:

Red fibres -

Muscle contains a red coloured oxygen storing pigment called myoglobin.

- wherein

Myoglobin content is high in some of the muscles which gives a reddish appearance. Such muscles are called the Red fibres.

Hence, the correct answer is option 3) Red skeletal muscle.

Also Read:

• MCQs on Difference between Red and White Fibres

• Cori Cycle

• Human Skeletal System

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