General anatomy and histology: muscle fibre types: practice question

A Anatomy question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Anatomy · General anatomy and histology: muscle fibre types

Sample item

A marathon runner's muscle biopsy is stained for myoglobin and oxidative enzymes. Most fibres are dark, rich in mitochondria and capillaries, slow to contract and highly resistant to fatigue. What are these fibres?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

C. Type I (slow oxidative)

Type I fibres are red, slow-twitch and oxidative, suited to sustained postural and endurance work. Type IIb fibres are pale, fast and fatigable, while type IIa are intermediate. Intrafusal fibres belong to the muscle spindle and are not force-generating fibres.

Option by option

  • A. Intrafusal nuclear bag fibres

    Intrafusal fibres are sensory-regulating spindle fibres, not the bulk of the muscle.

  • B. Type IIb (fast glycolytic)

    Type IIb fibres are pale, glycolytic and fatigue quickly.

  • C. Type I (slow oxidative) (correct)

    Correct. High myoglobin, mitochondria and fatigue resistance define slow oxidative fibres.

  • D. Type IIa (fast oxidative-glycolytic)

    Type IIa fibres are fast and only moderately fatigue resistant.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is C, Type I (slow oxidative). Type I fibres are red, slow-twitch and oxidative, suited to sustained postural and endurance work.

Why is "Intrafusal nuclear bag fibres" not the answer?

Intrafusal fibres are sensory-regulating spindle fibres, not the bulk of the muscle.

Why is "Type IIb (fast glycolytic)" not the answer?

Type IIb fibres are pale, glycolytic and fatigue quickly.

Why is "Type IIa (fast oxidative-glycolytic)" not the answer?

Type IIa fibres are fast and only moderately fatigue resistant.

What concept does this question test?

It tests General anatomy and histology: muscle fibre types in Anatomy. Type IIb fibres are pale, fast and fatigable, while type IIa are intermediate. Intrafusal fibres belong to the muscle spindle and are not force-generating fibres.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study General anatomy and histology: muscle fibre types?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.