Nerve and muscle: fast glycolytic fibre profile: practice question

A Physiology 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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Physiology · Nerve and muscle: fast glycolytic fibre profile

Sample item

A biopsy from an elite sprinter's lateral thigh muscle is examined. Which combination of features would be expected in the predominant fibre type?

ALow glycogen content with small fibre diameterBHigh capillary density with high oxidative enzyme activityCHigh myosin ATPase and glycolytic enzyme activity with few mitochondriaDAbundant mitochondria and myoglobin with slow myosin ATPase

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

The answer and the reasoning

C. High myosin ATPase and glycolytic enzyme activity with few mitochondria

Fast glycolytic (type IIx/IIb) fibres generate high force quickly, with fast myosin ATPase, abundant glycolytic enzymes and glycogen, few mitochondria and little myoglobin. They fatigue quickly. Slow oxidative fibres show the opposite profile.

Option by option

A. Low glycogen content with small fibre diameter
Fast glycolytic fibres are large and glycogen-rich.
B. High capillary density with high oxidative enzyme activity
High capillary density with oxidative enzymes is the profile of oxidative fibres.
C. High myosin ATPase and glycolytic enzyme activity with few mitochondria (correct)
Correct. Fast glycolytic fibres are rich in glycolytic enzymes and poor in mitochondria.
D. Abundant mitochondria and myoglobin with slow myosin ATPase
This describes slow oxidative type I fibres of the endurance athlete.

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.

Questions about this Physiology question

What is the answer to this Physiology question?

The best answer is C, High myosin ATPase and glycolytic enzyme activity with few mitochondria. Fast glycolytic (type IIx/IIb) fibres generate high force quickly, with fast myosin ATPase, abundant glycolytic enzymes and glycogen, few mitochondria and little myoglobin.

Why is "Low glycogen content with small fibre diameter" not the answer?

Fast glycolytic fibres are large and glycogen-rich.

Why is "High capillary density with high oxidative enzyme activity" not the answer?

High capillary density with oxidative enzymes is the profile of oxidative fibres.

Why is "Abundant mitochondria and myoglobin with slow myosin ATPase" not the answer?

This describes slow oxidative type I fibres of the endurance athlete.

What concept does this question test?

It tests Nerve and muscle: fast glycolytic fibre profile in Physiology. They fatigue quickly. Slow oxidative fibres show the opposite profile.

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 Nerve and muscle: fast glycolytic fibre profile?

For each system, sketch the key graph (pressure–volume loop, oxygen dissociation curve, nephron handling) and explain it aloud. Then use the flashcards and the other Physiology 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.