FT fibres of muscle which are suitable for sprint type activity are characterized by A. High glycolytic capacity B. Low capillary density C. A small force of contraction D. Low fatigability E. Low aerobic capacity Choose the correct answer from the options given below:
A, B and E only
Understanding Muscle Fibres and Sprint Activity
Sprinting is a high-intensity, short-duration activity that requires explosive power and speed. The type of muscle fibres predominantly used in sprinting are Fast-Twitch (FT) fibres, specifically Type IIx (Fast Glycolytic) and to some extent Type IIa (Fast Oxidative-Glycolytic). These fibres have characteristics that enable rapid and forceful contractions, primarily relying on anaerobic energy systems.
Analyzing Muscle Fibre Characteristics for Sprinting
Let's examine the characteristics provided and see which ones are typical of muscle fibres suitable for sprint-type activity:
- A. High glycolytic capacity: Sprinting relies heavily on the breakdown of glucose (glycolysis) for energy, as it's an anaerobic process that produces ATP quickly. Fast-Twitch glycolytic fibres have a high capacity for glycolysis. This characteristic is suitable for sprinting.
- B. Low capillary density: Fast-Twitch glycolytic fibres are less reliant on a constant supply of oxygen from blood (delivered by capillaries) compared to slow-twitch fibres. They have fewer capillaries surrounding them. This characteristic is suitable for sprinting as it relies on anaerobic pathways.
- C. A small force of contraction: Fast-Twitch fibres, especially Type IIx, are designed for powerful and rapid contractions. They generate a large force. A small force of contraction is characteristic of slow-twitch fibres. This characteristic is not suitable for sprinting.
- D. Low fatigability: Fast-Twitch glycolytic fibres produce energy rapidly but fatigue relatively quickly because of the accumulation of metabolic byproducts from anaerobic metabolism. Low fatigability is a characteristic of slow-twitch fibres, which are built for endurance. This characteristic is not suitable for sprinting.
- E. Low aerobic capacity: Sprinting primarily uses anaerobic energy systems (like glycolysis and the phosphagen system). Fast-Twitch glycolytic fibres have a limited capacity for aerobic respiration (using oxygen), unlike slow-twitch fibres which have high aerobic capacity. This characteristic is suitable for sprinting.
Based on this analysis, the characteristics that describe FT fibres suitable for sprint type activity are High glycolytic capacity (A), Low capillary density (B), and Low aerobic capacity (E).
Summary of Sprint Muscle Fibre Characteristics
The muscle fibres best suited for sprinting are those that can generate significant force quickly and are optimized for anaerobic energy production. These are the Fast-Twitch (FT) fibres, exhibiting the following:
- Strong reliance on glycolysis (High glycolytic capacity).
- Less reliance on oxygen transport via blood supply (Low capillary density).
- Limited ability to produce energy using oxygen (Low aerobic capacity).
Therefore, characteristics A, B, and E align with the properties of muscle fibres used in sprint activities.
Revision Table: Muscle Fibre Type Comparison
| Characteristic | Slow-Twitch (Type I) | Fast-Twitch Oxidative-Glycolytic (Type IIa) | Fast-Twitch Glycolytic (Type IIx) |
|---|---|---|---|
| Speed of Contraction | Slow | Fast | Very Fast |
| Force Production | Low | Medium | High |
| Primary Energy System | Aerobic | Aerobic & Glycolytic | Glycolytic |
| Fatigability | Low (High Endurance) | Medium | High (Low Endurance) |
| Mitochondria Density | High | High/Medium | Low |
| Capillary Density | High | High/Medium | Low |
| Glycolytic Enzyme Activity | Low | High | Very High |
Additional Information on Sprint Energy Systems
Sprint activities (up to ~10-15 seconds) primarily use the phosphagen system (ATP-PC system) and the initial phase of anaerobic glycolysis. The phosphagen system provides immediate energy but is quickly depleted. Anaerobic glycolysis then becomes the main source, producing ATP and lactic acid. Muscle fibres adapted for sprinting must be able to utilize these pathways efficiently. The characteristics of Fast-Twitch fibres, particularly Type IIx, are perfectly suited for the high power output and rapid energy demands of these anaerobic systems.
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