Podcast
Questions and Answers
What is the primary reason for the increased force in eccentric contractions?
What is the primary reason for the increased force in eccentric contractions?
Which of the following muscle architectures is most prone to injury at the muscle-tendon junction?
Which of the following muscle architectures is most prone to injury at the muscle-tendon junction?
What is the shape of the force and power curve during eccentric contractions?
What is the shape of the force and power curve during eccentric contractions?
What is the primary mechanism by which cross-bridges are detached during muscle contraction?
What is the primary mechanism by which cross-bridges are detached during muscle contraction?
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What is the current limitation of the cross-bridge model in predicting muscle contraction?
What is the current limitation of the cross-bridge model in predicting muscle contraction?
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Which of the following is a characteristic of muscle fibers during eccentric contractions?
Which of the following is a characteristic of muscle fibers during eccentric contractions?
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What is the primary factor contributing to the increased metabolic cost of muscle contraction?
What is the primary factor contributing to the increased metabolic cost of muscle contraction?
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Which of the following muscle architectures is characterized by a single row of fibers?
Which of the following muscle architectures is characterized by a single row of fibers?
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What is the primary mechanism by which muscle fibers generate force during contraction?
What is the primary mechanism by which muscle fibers generate force during contraction?
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What is the current understanding of muscle contraction mechanisms?
What is the current understanding of muscle contraction mechanisms?
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Study Notes
Muscle Architecture
- Muscle architecture can vary, with different types of muscles having different designs (e.g. strap, unipennate, multipennate, fusiform, bipennate)
- Pennate muscles have varying architectures, with long vs. short fascicles and highly pennate vs. parallel fibers
- Muscle injury is more likely to occur at the muscle-tendon junctions
Muscle Architecture Summary
- Long fibers/fascicles allow for large range of motion (ROM), resulting in more work (F x d)
- Long fibers/fascicles have high shortening speeds
- Short fibers have lower metabolic cost (less ATP use)
Fiber Length and O2/ATP
- Longer fibers have more sarcomeres in series, resulting in higher ATP use to generate tension
- Shorter fibers are optimum for low metabolic cost, examples: gastrocnemius and soleus for running
Fiber Length and Speed
- Longer fibers have more sarcomeres in series, resulting in slower shortening velocity
- Examples: hamstrings (biceps femoris, semimembranosus, semitendinosus), vastus lateralis
Fiber Length and Work
- Longer fibers have a greater range of shortening (d), resulting in more work performed
- Examples: gluteus maximus, hamstrings, quadriceps, pectorals, biceps brachii
Muscles
- Muscles are the motors that drive movement around joints, through planes of motion, about axes
- Muscles are incredible, producing huge forces with minimum mass
Muscle Structure - Myosin
- Myosin has a heavy chain (head, neck, and tail) and light chains that influence function
- The head/neck (motor) domain bends to pull on actin
- Motor domain is very short (20 nm), resulting in low gear movement (need many strokes to pull actin)
Muscle Structure - Myosin
- Myosin molecules arrange themselves in a unique way, with tails together and heads at the ends
- Myosin 'walks' along actin to cause muscle contraction (cross-bridge model)
Muscle Structure - Sarcomere
- Actin and myosin are the major constituents of the fundamental unit of muscle: the sarcomere
- Sarcomere has a lattice structure
Muscle Properties
- Myosin heads have to rotate, then detach, recover, and reattach to actin (cross-bridge cycling)
- Faster cycle rate results in less force produced
- Muscle properties will be discussed further in Lecture 6, where current understanding of muscle contraction will be challenged
Muscle Properties - Eccentric
- Eccentric portion of curve: Force and power increase (negatively), but have different shape
- Greater force in eccentric contractions due to:
- Extra force per cross-bridge as they're lengthened
- More cross-bridges attached because of higher energy required for detachment
- Cross-bridge model can't predict eccentric force accurately; it over-predicts both force and energy cost
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Description
This quiz assesses your understanding of muscle architecture, including pennate and parallel fibred muscles, and their characteristics.
