Slow-twitch muscle fibers are characterized by

Question

BlackTom AI · Accepted Answer

Slow-twitch (Type I) muscle fibers are specialized for endurance and sustained activity because they are highly oxidative and resist fatigue.

1) Relevant knowledge points and concepts
- Muscle fiber types: Type I (slow-twitch) vs Type II (fast-twitch).  
- Metabolic pathways: aerobic (oxidative phosphorylation) vs anaerobic (glycolysis/phosphocreatine).  
- Structural features: high mitochondrial density, abundant myoglobin, rich capillary supply, smaller fiber diameter in Type I fibers.  
- Functional consequences: slower contraction speed, lower peak force/power, but greater endurance and fatigue resistance.

2) Step-by-step reasoning
- Slow-twitch fibers contain many mitochondria and myoglobin, enabling efficient aerobic ATP production.  
- Aerobic metabolism yields far more ATP per glucose than anaerobic glycolysis, supporting prolonged contraction.  
- High capillary density supplies oxygen continuously, preventing rapid accumulation of metabolic byproducts that cause fatigue.  
- Because their contraction machinery is tuned for sustained activity, they contract more slowly and produce less peak power, but maintain tension for long periods.

3) Calculations/intermediate steps
- No numerical calculation is required; the conclusion follows from comparing metabolic yields and structural specializations (oxidative capacity → sustained ATP supply → fatigue resistance).

4) Why the correct answer is correct
- “Fatigue resistance” directly follows from Type I fibers’ oxidative metabolism, high mitochondria/myoglobin, and capillary network, all of which prevent early energy depletion and metabolite accumulation that cause fatigue.

5) Why the other options are incorrect
- “Reliance on anaerobic metabolism.” Incorrect: that describes fast-glycolytic (Type IIx) fibers, which fatigue quickly.  
- “Their use in power activities.” Incorrect: power activities recruit fast-twitch fibers that generate high force quickly.  
- “Rapid contraction.” Incorrect: slow-twitch fibers contract slowly; rapid contraction is a property of fast-twitch fibers.

6) Conclusion
- The best answer is “fatigue resistance.” This matches the provided correct answer.

Slow-twitch muscle fibers are characterized by单项选择题

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Question at position 69 Fast glycolytic muscle fibers rely on aerobic metabolism to generate ATP and have high myoglobin content.TrueFalse

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