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Questions and Answers
Which characteristic is NOT typically associated with slow-oxidative (SO) muscle fibers?
Which characteristic is NOT typically associated with slow-oxidative (SO) muscle fibers?
- High capillary density
- High myoglobin content
- Well-developed glycolytic capacity (correct)
- Low myosin ATPase activity
A powerlifter is performing a set of heavy squats. Which type of muscle fiber is MOST likely to be primarily recruited during this activity?
A powerlifter is performing a set of heavy squats. Which type of muscle fiber is MOST likely to be primarily recruited during this activity?
- Type IIa (FOG)
- Type IIx (FG) (correct)
- Type I (SO)
- A mix of Type I and Type IIa in equal proportion
Which of the following mechanisms contributes to the rapid energy generation in fast-twitch muscle fibers?
Which of the following mechanisms contributes to the rapid energy generation in fast-twitch muscle fibers?
- Efficient sarcoplasmic reticulum for rapid Ca2+ release and uptake (correct)
- Low rate of crossbridge turnover
- Low glycolytic enzyme level
- Slow calcium handling ability
An athlete is participating in a stop-and-go sport that requires frequent changes of pace. Which muscle fiber type would be MOST beneficial for this athlete?
An athlete is participating in a stop-and-go sport that requires frequent changes of pace. Which muscle fiber type would be MOST beneficial for this athlete?
How does the speed of shortening and tension development in fast-twitch fibers compare to that of slow-twitch fibers?
How does the speed of shortening and tension development in fast-twitch fibers compare to that of slow-twitch fibers?
Which characteristic is NOT a primary factor in classifying motor units?
Which characteristic is NOT a primary factor in classifying motor units?
What is a key characteristic of Type IIx muscle fibers?
What is a key characteristic of Type IIx muscle fibers?
How do motor neurons influence the properties of the muscle fibers they innervate?
How do motor neurons influence the properties of the muscle fibers they innervate?
If a muscle is composed of approximately 80% Type I fibers, which muscle is it MOST likely to be?
If a muscle is composed of approximately 80% Type I fibers, which muscle is it MOST likely to be?
Which biochemical property of skeletal muscle fibers is MOST directly related to its oxidative capacity?
Which biochemical property of skeletal muscle fibers is MOST directly related to its oxidative capacity?
What aspect of a muscle fiber MOST directly determines its speed of contraction (Vmax)?
What aspect of a muscle fiber MOST directly determines its speed of contraction (Vmax)?
How does Sarcoplasmic Reticulum (SR) development affect muscle fiber contractile properties?
How does Sarcoplasmic Reticulum (SR) development affect muscle fiber contractile properties?
During near-maximum voluntary muscle contractions, what is the contribution of slow and fast muscle fiber types?
During near-maximum voluntary muscle contractions, what is the contribution of slow and fast muscle fiber types?
Which factor plays the MOST significant role in initially determining an individual's muscle fiber type composition?
Which factor plays the MOST significant role in initially determining an individual's muscle fiber type composition?
An aging individual experiences a reduction in type II motor units. What is a likely consequence of this change?
An aging individual experiences a reduction in type II motor units. What is a likely consequence of this change?
According to the size principle, which motor units are typically recruited FIRST during a low-intensity activity?
According to the size principle, which motor units are typically recruited FIRST during a low-intensity activity?
During a maximal effort sprint, an athlete selectively recruits high-threshold motor units early in the movement. How does this recruitment strategy affect force production?
During a maximal effort sprint, an athlete selectively recruits high-threshold motor units early in the movement. How does this recruitment strategy affect force production?
The central nervous system (CNS) utilizes orderly motor unit recruitment to fine-tune skeletal muscle activity. What is the primary benefit of this process?
The central nervous system (CNS) utilizes orderly motor unit recruitment to fine-tune skeletal muscle activity. What is the primary benefit of this process?
How might the size principle be overridden during a ballistic movement, such as throwing a baseball, and what is the likely outcome?
How might the size principle be overridden during a ballistic movement, such as throwing a baseball, and what is the likely outcome?
A powerlifter is training to increase the amount of weight they can lift in a single repetition. How does the size principle relate to their training?
A powerlifter is training to increase the amount of weight they can lift in a single repetition. How does the size principle relate to their training?
An athlete performs a plyometric exercise involving a rapid stretch-shortening cycle. How would selective recruitment benefit their performance in this exercise?
An athlete performs a plyometric exercise involving a rapid stretch-shortening cycle. How would selective recruitment benefit their performance in this exercise?
Flashcards
Slow-Twitch Fibers (SO)
Slow-Twitch Fibers (SO)
Muscle fibers that generate energy primarily through the aerobic system; also known as slow-oxidative fibers.
SO Fiber Characteristics
SO Fiber Characteristics
Lower myosin ATPase activity allows for slower calcium handling and shortening speed. Good for long distance!
Fast-Twitch Fibers
Fast-Twitch Fibers
Muscle fibers with a high capacity for electrochemical transmission of action potentials, rapid crossbridge turnover, and generate quick, powerful actions.
Fast twitch energy
Fast twitch energy
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Type II Fiber Subtypes
Type II Fiber Subtypes
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Motor Unit Composition
Motor Unit Composition
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Motor Unit Classification
Motor Unit Classification
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Type I Motor Unit
Type I Motor Unit
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Type IIx Motor Unit
Type IIx Motor Unit
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Type IIa Motor Unit
Type IIa Motor Unit
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Motor Neuron Effect
Motor Neuron Effect
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Oxidative Capacity
Oxidative Capacity
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Glycolytic Capacity
Glycolytic Capacity
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Fiber type determinant
Fiber type determinant
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Training and aging effects on fiber type
Training and aging effects on fiber type
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Factors beyond fiber type for predicting success
Factors beyond fiber type for predicting success
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Motor unit recruitment order
Motor unit recruitment order
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Typical motor unit recruitment
Typical motor unit recruitment
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Orderly recruitment benefit
Orderly recruitment benefit
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Selective Recruitment
Selective Recruitment
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Size Principle
Size Principle
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Study Notes
- Muscle fiber types include slow-twitch (Type I) and fast-twitch (Type II) fibers
- Motor units contain one specific muscle fiber type (Type I or Type II), or a subdivision of Type II with the same metabolic profile.
- Motor units are classified based on twitch, tension, and fatigability characteristics of the muscle fibers they innervate.
Twitch Characteristics
- Type I fibers are slow twitch, generate low force, and are fatigue resistant
- Type IIx fibers are fast twitch, generate high force, and fatigue quickly.
- Type IIa fibers are fast twitch, generate moderate force, and are fatigue resistant
- Motor neurons modulate the properties and adaptive response of muscle fibers to stimuli
Muscle Fiber Types
- The proportions of each muscle fiber type varies from muscle to muscle and from person to person
- Skeletal muscle fibers differ in biochemical and contractile properties.
Slow-Twitch Fibers (Type I)
- Primarily generate energy for ATP resynthesis through the aerobic system
- They are slow-oxidative fibers (SO) that rely on oxidative metabolism
- Six distinguishing characteristics include:
- Low myosin ATPase activity
- Slow calcium handling ability and shortening speed
- Less well-developed glycolytic capacity
- Large and numerous mitochondria
- High capillary density and myoglobin
- Red in color
Fast-Twitch Fibers (Type II)
- Have a high capability for electrochemical transmission of action potentials
- High rate of crossbridge turnover, including high myosin ATPase activity and rapid Ca2+ release and uptake by an efficient sarcoplasmic reticulum
- High glycolytic enzyme level and are very fatigable
- White in color
- Contribute to rapid energy generation for quick, powerful muscle actions
- Speed of shortening and tension development is 3-5x faster than slow-twitch fibers
- Rely on a well-developed, short-term glycolytic system for energy transfer
- Predominate in anaerobic-type sprint activities and other forceful muscle actions, relying almost entirely on anaerobic energy metabolism
- Important role in stop-and-go, or change-of-pace sports
- Type II fibers are broken down into subtypes:
- Type IIx fibers possess the greatest anaerobic potential and most rapid shortening velocity; "True" fast-glycolytic fiber (FG)
- Type IIa fibers represent the fast-oxidative-glycolytic fibers (FOG)
Muscle Fiber Types Characteristics
- Type I fibers have small motor neuron size, low recruitment threshold, slow nerve conduction velocity, slow contraction and relaxation speed, high fatigue resistance and endurance, low force production and power output, high aerobic enzyme content, low anaerobic enzyme content, low sarcoplasmic reticulum complexity, high capillary density, myoglobin content, and mitochondrial size/density, small fiber diameter, and red color.
- Type IIa fibers have large motor neuron size, intermediate/high recruitment threshold, fast nerve conduction velocity, fast contraction and relaxation speed, intermediate/low fatigue resistance and endurance, intermediate force production and power output, intermediate/low aerobic enzyme content, high anaerobic enzyme content, intermediate/high sarcoplasmic reticulum complexity, intermediate capillary density, low myoglobin content, intermediate mitochondrial size/density, intermediate fiber diameter, and white/red color
- Type IIx fibers have large motor neuron size, high recruitment threshold, fast nerve conduction velocity, fast contraction and relaxation speed, low fatigue resistance and endurance, high force production and power output, low aerobic enzyme content, high anaerobic enzyme content, high sarcoplasmic reticulum complexity, low capillary density, myoglobin content, and mitochondrial size/density, large fiber diameter, and white color
Determinants of Fiber Type
- Fiber type is determined by genetic factors (which α-motor neurons innervate fibers and fiber differentiation based on α-motor neuron) and training factors
- Training factors can induce small (10%) changes in fiber type
- Aging causes muscles to lose Type II motor units
- Fiber type is not the sole predictor of success; cardiovascular function, motivation, training habits, and muscle size also play a role.
Size Principle
- Low-threshold motor units are recruited first and have lower force capabilities than higher-threshold motor units
- To get to the high-threshold motor units, the body must first recruit the lower-threshold motor units
- Orderly recruitment of specific motor units to produce a smooth muscle action allows the CNS to fine-tune skeletal muscle activity to meet demands of the motor task
- Exceptions exist, especially with respect to explosive, ballistic contractions that can selectively recruit high-threshold units to rapidly achieve more force and power (Selective recruitment)
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Description
Explore muscle fiber types including slow-twitch (Type I) and fast-twitch (Type II) fibers. Understand motor unit classification based on twitch, tension, and fatigability characteristics. Learn how motor neurons modulate muscle fiber properties and their adaptive response to stimuli.
