In skeletal muscle histology, which histochemical staining technique is used to differentiate Type I (slow-twitch, oxidative) from Type II (fast-twitch, glycolytic) fibres?

• A Myosin ATPase (pH 9.4) — Type I fibres stain pale at alkaline pH; Type II fibres stain dark ✓
• B Haematoxylin and eosin (H&E) stain — Type II fibres stain darker
• C Myosin ATPase (pH 9.4) — Type I fibres stain dark/black at alkaline pH
• D Oil Red O stain — Type I fibres stain red due to high glycogen content

Explanation

The ATPase stain at alkaline pH (9.4) demonstrates Type I fibres (slow-twitch, high oxidative capacity, fatigue-resistant) as pale/light and Type II fibres (fast-twitch, high glycolytic capacity) as dark. This is the classical histochemical method for fibre typing. At acid preincubation pH (4.3), the staining reverses: Type I = dark, Type II = pale. Type I fibres have high mitochondria, myoglobin, and lipid content (hence oxidative); they are not differentiated by H&E. Oil Red O stains lipids; PAS stains glycogen.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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