Muscle Properties - Speed and Force
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Questions and Answers

What happens to the number of bound cross-bridges as sarcomere length increases?

  • The number of bound cross-bridges increases.
  • The number of bound cross-bridges remains constant.
  • The number of bound cross-bridges is unaffected by sarcomere length.
  • The number of bound cross-bridges decreases. (correct)

    • What is the relationship between force and velocity in muscle contraction?

  • As velocity increases, force also increases.
  • As velocity increases, force decreases. (correct)
  • Force remains constant regardless of velocity.
  • Force and velocity are unrelated.

    • What is the relationship between force and length in a muscle?

  • Force remains constant regardless of length.
  • Force decreases as length increases. (correct)
  • Force increases as length increases.
  • Force and length are unrelated.

    • What is the optimal length for maximum force production in a sarcomere?

    <p>Optimum length (~2.7 µm)</p> Signup and view all the answers

    What is the term for the relationship between the speed of muscle shortening and maximum force production?

    <p>Force-velocity relation</p> Signup and view all the answers

    What can be said about the length of sarcomeres within a muscle?

    <p>Sarcomeres can be at different lengths within a muscle.</p> Signup and view all the answers

    What is the approximate length of a sarcomere at optimal force production?

    <p>2.7 µm</p> Signup and view all the answers

    What is the unit of measurement for sarcomere length?

    <p>Micrometers (µm)</p> Signup and view all the answers

    What is the main purpose of studying human functional anatomy?

    <p>To better understand factors that influence both injury risk and human physical performance</p> Signup and view all the answers

    What is Prof. Anthony Blazevich's role in the School of Medical and Health Sciences?

    <p>All of the above</p> Signup and view all the answers

    What is the focus of the end-semester exam in ECU Exam Week?

    <p>Lectures 1-11, with a focus on 6-11</p> Signup and view all the answers

    What is the due date for Assignment 1?

    <p>Week 9</p> Signup and view all the answers

    What is the topic of Research Process, as mentioned in the Semester Overview?

    <p>Research process</p> Signup and view all the answers

    How does functional anatomy interact with other areas of study?

    <p>It interacts closely with anatomy, biomechanics, physiology, and motor control</p> Signup and view all the answers

    What is the area of science that functional anatomy belongs to?

    <p>Human functional anatomy</p> Signup and view all the answers

    What is studied in functional anatomy?

    <p>The functional role of musculoskeletal and neurological structures</p> Signup and view all the answers

    What is the main difference in the in vivo operating length relative to optimum between muscles?

    <p>The optimum length is shorter in the Biceps Brachii than in the Gastrocnemius</p> Signup and view all the answers

    What is the effect of increasing frequency on electrically-stimulated forces?

    <p>Forces increase at low frequencies and decrease at high frequencies</p> Signup and view all the answers

    What is the effect of lengthening the muscle on force at high frequencies?

    <p>Force decreases with lengthening</p> Signup and view all the answers

    At which length are actin and myosin more likely to interact for a given activation level?

    <p>At long lengths</p> Signup and view all the answers

    What is the relationship between muscle length and force?

    <p>Force decreases with increasing length</p> Signup and view all the answers

    What is the reason for the shift in optimum length with frequency?

    <p>The change in actin and myosin interaction</p> Signup and view all the answers

    What is the main difference between the Biceps Brachii and Gastrocnemius muscles?

    <p>The Biceps Brachii has a shorter optimum length</p> Signup and view all the answers

    What is the effect of activation level on the force-length relation?

    <p>The force-length relation shifts with increasing activation</p> Signup and view all the answers

    What is the primary function of muscles in the context of movement?

    <p>To move about joints, through planes of motion, about axes</p> Signup and view all the answers

    What is the function of the light chains in myosin?

    <p>To influence the function of myosin</p> Signup and view all the answers

    What is the significance of the motor domain being very short in myosin?

    <p>It requires myosin to work in low gear, needing many strokes to pull actin</p> Signup and view all the answers

    How do myosin molecules arrange themselves in a unique way?

    <p>Tails together and heads at the ends</p> Signup and view all the answers

    What is the name of the model that describes the mechanism of muscle contraction?

    <p>The cross-bridge model</p> Signup and view all the answers

    What are the major constituents of the sarcomere?

    <p>Actin and myosin</p> Signup and view all the answers

    What is the consequence of increasing the cross-bridge cycling rate?

    <p>The force produced by myosin decreases</p> Signup and view all the answers

    What is the term for the attachment of myosin to actin during muscle contraction?

    <p>Cross-bridge formation</p> Signup and view all the answers

    What is the advantage of having longer fibres/fascicles in muscles?

    <p>More work can be performed</p> Signup and view all the answers

    What is the characteristic of muscles that have shorter fibres?

    <p>Lower metabolic cost</p> Signup and view all the answers

    What happens to the shortening velocity of a muscle as the fibre length increases?

    <p>It decreases</p> Signup and view all the answers

    Which type of muscle is best suited for dynamic movements?

    <p>Long-fibred muscles</p> Signup and view all the answers

    What is the relationship between fibre length and isometric force?

    <p>Fibre length has no effect on isometric force</p> Signup and view all the answers

    Why are shorter-fibred muscles more efficient for low-metabolic cost activities?

    <p>They use less ATP to generate tension</p> Signup and view all the answers

    What is the advantage of having highly pennate fibred muscles?

    <p>Increased isometric force</p> Signup and view all the answers

    What is the relationship between fibre length and sarcomere shortening?

    <p>Longer fibres have a longer range of shortening</p> Signup and view all the answers

    What is the function of the light chains in myosin?

    <p>To influence myosin function</p> Signup and view all the answers

    Why is the motor domain of myosin very short?

    <p>To allow myosin to work in low gear</p> Signup and view all the answers

    What is the primary factor affecting the number of bound cross-bridges in a sarcomere?

    <p>Sarcomere length</p> Signup and view all the answers

    How do myosin molecules arrange themselves?

    <p>Tails together and heads at the ends</p> Signup and view all the answers

    Which of the following statements is true about the force-velocity relation?

    <p>As muscle shortening velocity increases, maximum force production decreases</p> Signup and view all the answers

    What is the name of the model that describes the mechanism of muscle contraction?

    <p>Cross-bridge model</p> Signup and view all the answers

    What is the consequence of sarcomere lengthening on muscle force production?

    <p>Muscle force production decreases</p> Signup and view all the answers

    What is the consequence of increasing the cross-bridge cycling rate?

    <p>Less force can be produced</p> Signup and view all the answers

    What is the relationship between muscle velocity and force production?

    <p>As muscle velocity increases, force production decreases</p> Signup and view all the answers

    What is the term for the attachment of myosin to actin during muscle contraction?

    <p>Cross-bridge</p> Signup and view all the answers

    What is the optimal length for maximum force production in a sarcomere?

    <p>When the sarcomere length is approximately 2.7 µm</p> Signup and view all the answers

    What are the major constituents of the sarcomere?

    <p>Actin and myosin</p> Signup and view all the answers

    What is the reason for the varying force production within a muscle?

    <p>Due to differences in sarcomere length</p> Signup and view all the answers

    What enables muscles to move about joints, through planes of motion, about axes?

    <p>Muscles acting as motors</p> Signup and view all the answers

    What is the consequence of shortening velocity on maximum force production?

    <p>As shortening velocity increases, maximum force production decreases</p> Signup and view all the answers

    What is the relationship between muscle length and force production?

    <p>As muscle length increases, force production decreases</p> Signup and view all the answers

    What is the primary reason for the difference in in vivo operating length relative to optimum between muscles?

    <p>Varied muscle functions</p> Signup and view all the answers

    What happens to the force-length relation as activation level changes?

    <p>It shifts to the right</p> Signup and view all the answers

    At what length are actin and myosin more likely to interact for a given activation level?

    <p>Long lengths</p> Signup and view all the answers

    What is the effect of increasing frequency on electrically-stimulated forces at low frequencies?

    <p>Forces increase</p> Signup and view all the answers

    What is the difference between the force-length relation at low and high frequencies?

    <p>The relation is more non-linear at high frequencies</p> Signup and view all the answers

    What is the reason for the shift in optimum length with frequency?

    <p>Changes in actin and myosin interaction</p> Signup and view all the answers

    What is the effect of lengthening the muscle on force at low frequencies?

    <p>Force increases</p> Signup and view all the answers

    What is the reason for the difference in the in vivo operating length relative to optimum between the Biceps Brachii and Gastrocnemius muscles?

    <p>Different muscle functions</p> Signup and view all the answers

    What is the effect of pennation on the physiological cross-sectional area (PCSA) of a muscle?

    <p>Increases PCSA for a given anatomical cross-sectional area (ACSA)</p> Signup and view all the answers

    What is the benefit of fibre rotation during muscle contraction?

    <p>Allows fibres to shorten less and maintain optimal length</p> Signup and view all the answers

    What happens to the force production of sarcomeres as they shorten slower?

    <p>Increases due to optimal length maintenance</p> Signup and view all the answers

    What is the advantage of muscles with high pennation angles?

    <p>Increased force production due to more contractile tissue</p> Signup and view all the answers

    What is the effect of fibre rotation on muscle force production?

    <p>Increases force production due to optimal length maintenance</p> Signup and view all the answers

    What is the relationship between fibre length and muscle force production?

    <p>Fibre length affects force production, but the relationship is complex</p> Signup and view all the answers

    What is the benefit of pennate muscles in dynamic contractions?

    <p>Improved force production due to optimal length maintenance</p> Signup and view all the answers

    What is the effect of fibre rotation on sarcomere shortening?

    <p>Allows sarcomeres to maintain optimal length</p> Signup and view all the answers

    What type of behaviours do tendons exhibit?

    <p>Both viscous and elastic behaviours</p> Signup and view all the answers

    What happens to the stress in a tendon when it is held at a constant length?

    <p>The stress falls slowly</p> Signup and view all the answers

    What is the effect of rapid loading on tendons?

    <p>Decreased injury risk</p> Signup and view all the answers

    What is the result of fibril sliding in tendons?

    <p>Increased viscoelasticity</p> Signup and view all the answers

    What happens to the strain in a tendon when it is pulled with a constant force?

    <p>The strain continues</p> Signup and view all the answers

    What is the role of tendons in movement?

    <p>To transfer muscular forces</p> Signup and view all the answers

    What is the relationship between tendon stiffness and injury risk?

    <p>Increased stiffness reduces injury risk</p> Signup and view all the answers

    What is the key concept in understanding tendon function during movement?

    <p>Viscoelasticity</p> Signup and view all the answers

    What is the effect of increasing sarcomere length on the number of bound cross-bridges?

    <p>The number of bound cross-bridges decreases</p> Signup and view all the answers

    What happens to muscle force production when sarcomeres are at optimal length?

    <p>Force production increases</p> Signup and view all the answers

    What is the relationship between muscle power and velocity?

    <p>Power increases as velocity increases</p> Signup and view all the answers

    What can be said about the length of sarcomeres within a muscle?

    <p>Sarcomeres can be at different lengths</p> Signup and view all the answers

    What is the effect of shortening velocity on maximum force production?

    <p>Maximum force production decreases with shortening velocity</p> Signup and view all the answers

    What happens to the number of bound cross-bridges at optimal sarcomere length?

    <p>The number of bound cross-bridges is at its maximum</p> Signup and view all the answers

    What is the relationship between muscle force production and velocity?

    <p>Force production decreases with velocity</p> Signup and view all the answers

    What happens to muscle power production when force and velocity are high?

    <p>Power production increases</p> Signup and view all the answers

    What is the hierarchical structure of tendon?

    <p>molecule, fibril, fascicle, tendon</p> Signup and view all the answers

    What is the fundamental component of tendon?

    <p>Collagen</p> Signup and view all the answers

    What is the relationship between fibre length and work performed by a muscle?

    <p>Longer fibres perform more work due to greater range of shortening.</p> Signup and view all the answers

    What is the advantage of having shorter fibres in muscles?

    <p>They are more efficient in low-metabolic cost activities.</p> Signup and view all the answers

    What is the effect of cross-linking of collagen fibrils?

    <p>Increases stiffness and reduces breaking of fibrils</p> Signup and view all the answers

    What happens to tendons when loaded?

    <p>They stretch</p> Signup and view all the answers

    How does fibre length affect shortening velocity?

    <p>Longer fibres have slower shortening velocity.</p> Signup and view all the answers

    What is the purpose of normalizing force and length in tendon stress-strain relation?

    <p>To compare tendons of different sizes and types</p> Signup and view all the answers

    What is the characteristic of muscles that have longer fibres?

    <p>They perform more work.</p> Signup and view all the answers

    What is the relationship between fibre length and sarcomere shortening?

    <p>Longer fibres have more sarcomeres in series.</p> Signup and view all the answers

    What is the term for the energy lost or dissipated during relaxation of tendon?

    <p>Hysteresis</p> Signup and view all the answers

    What is the advantage of having highly pennate fibred muscles?

    <p>They can have varying architecture.</p> Signup and view all the answers

    What is the characteristic of biological tissues, including tendon?

    <p>Viscoelasticity</p> Signup and view all the answers

    What is the effect of fibre length on isometric force?

    <p>Fibre length has no effect on isometric force.</p> Signup and view all the answers

    What is the benefit of tendon's ability to dissipate energy?

    <p>It helps in injury prevention and braking</p> Signup and view all the answers

    Which type of muscle is best suited for dynamic movements?

    <p>Muscles with longer fibres.</p> Signup and view all the answers

    What is the main reason why the optimum muscle-tendon unit length, and therefore the optimum joint angle, changes little with changes in force?

    <p>The muscle works at shorter length due to higher force stretching the tendon</p> Signup and view all the answers

    What is the primary function of the parallel elastic component (PEC) in muscle contraction?

    <p>To keep the muscle from overstretching during contraction</p> Signup and view all the answers

    What happens to the passive force contribution from the parallel elastic component (PEC) during muscle contraction?

    <p>It decreases, often to zero</p> Signup and view all the answers

    What is the significance of the series elastic component (SEC) in muscle contraction?

    <p>It is stretched during muscle contraction, allowing the muscle to work at shorter lengths</p> Signup and view all the answers

    What is the relationship between the muscle-tendon unit length and joint angle during muscle contraction?

    <p>The muscle-tendon unit length determines the joint angle</p> Signup and view all the answers

    Why is the concept of optimum muscle length important in muscle contraction?

    <p>It determines the maximum force production</p> Signup and view all the answers

    What is the effect of a muscle connecting to a long tendon on the muscle-tendon unit length?

    <p>It allows the muscle to work at shorter lengths</p> Signup and view all the answers

    What is the primary function of the muscle-tendon unit in muscle contraction?

    <p>To transmit force from the muscle to the bone</p> Signup and view all the answers

    What is the characteristic of tendons that allows them to exhibit both viscous and elastic behaviours?

    <p>Fibril sliding</p> Signup and view all the answers

    What happens to the stress on a tendon when it is held at a constant length?

    <p>It falls slowly</p> Signup and view all the answers

    What is the result of strain continuing when a tendon is pulled with a constant force to a new length?

    <p>Creep</p> Signup and view all the answers

    What is the main function of tendons in movement?

    <p>To transfer muscular forces</p> Signup and view all the answers

    What is the consequence of rapid loading on tendons?

    <p>Greater protection from injury and over-elongation</p> Signup and view all the answers

    What is the result of increased stiffness in tendons?

    <p>Decreased injury risk</p> Signup and view all the answers

    What is the relationship between strain velocity and stress in tendons?

    <p>Directly proportional</p> Signup and view all the answers

    What is the characteristic of tendons that allows them to exhibit 'intelligent function'?

    <p>Viscoelasticity</p> Signup and view all the answers

    Study Notes

    Muscle Properties - Speed

    • As muscles shorten faster, maximum force decreases, following the force-velocity relation.
    • Power is calculated as F x v, leading to a power-velocity relation.
    • There is a trade-off between speed and force, meaning we can either move slowly and lift heavy or move quickly and lift light, but not both.

    Muscle Properties - Length

    • Shortening and lengthening of sarcomeres changes the overlap of myosin and actin, affecting the number of bound cross-bridges and ultimately sarcomere and muscle force.
    • Optimum length is approximately 2.7 µm, which is about 1/10 the width of a fine hair.
    • Changes in actin-myosin overlap largely underpin the force-length relation.
    • Within a muscle, sarcomeres can be at different lengths.
    • The force-length relation shifts as activation changes, with a shift in optimum length with frequency (force).

    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, working in low gear.
    • Myosin molecules arrange themselves with tails together and heads at the ends.

    Muscle Structure - Sarcomere

    • Actin and myosin are the major constituents of the fundamental unit of muscle: the sarcomere.
    • The sarcomere has a lattice structure.

    Muscle Properties

    • Myosin heads rotate, detach, recover, and reattach to actin in a process called cross-bridge cycling.
    • The recover-reattach time is constant, so faster cycle rates result in less time for myosins to be in contact with actin, reducing force production.

    Muscle Architecture

    • Different muscle architectures include pennate and parallel-fibred muscles.
    • Long fibres/fascicles allow for large range of motion and more work, but have higher metabolic costs.
    • Short fibres have lower metabolic costs.
    • Longer fibres have more sarcomeres in series, which don't increase isometric force but use more ATP.

    Fibre Length and O2/ATP

    • Longer fibres have more sarcomeres in series, using more ATP to generate tension.
    • Shorter fibres have lower metabolic costs.

    Fibre Length and Speed

    • Longer fibres have more sarcomeres in series, resulting in slower shortening velocity.
    • Shorter fibres are better suited for high-speed movements.

    Fibre Length and Work

    • Longer fibres have a greater range of shortening, performing more work.
    • Longer fibres require less sarcomere shortening, leading to slower velocity.

    Muscle Properties - Speed

    • As muscles shorten faster, maximum force decreases, known as the force-velocity relation
    • Power is the product of force and velocity, resulting in a power-velocity relation
    • There is a trade-off between moving slowly and lifting heavy, or moving quickly and lifting light, but not both

    Muscle Properties - Length

    • Shortening and lengthening of sarcomeres changes the overlap of myosin and actin, affecting sarcomere and muscle force
    • Optimum length for muscle force generation is around 2.7 µm, similar to 1/10 the width of a fine hair
    • Changes in actin-myosin overlap underpin the force-length relation
    • Within a muscle, sarcomeres can be at different lengths
    • In vivo operating length relative to optimum differs between muscles

    Muscle Properties - Length (continued)

    • Force-length relation shifts as activation changes, with electrically-stimulated forces at low frequencies being good for lengthening the muscle, but not at high frequencies
    • Actin and myosin are closer together at long lengths, making interaction more likely for a given activation level

    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, working in low gear like a bike or car going up a hill
    • Myosin molecules arrange themselves with tails together and heads at the ends, allowing them to 'walk' along actin to cause muscle contraction

    Muscle Structure - Sarcomere

    • Actin and myosin are the major constituents of the sarcomere, the fundamental unit of muscle
    • The lattice structure of sarcomeres is important for muscle function

    Muscle Contraction

    • Myosin heads rotate, detach, recover, and reattach to actin in a process called cross-bridge cycling
    • The faster the cycle rate, the less time myosins are in contact with actin, resulting in less force being produced

    Pennation

    • Some muscles have high angles of pennation, allowing more contractile tissue to attach to the tendon/aponeurosis
    • This increases the physiological cross-sectional area (PCSA) of the muscle, allowing for more force production
    • Fibres also rotate as they shorten, reducing the amount of shortening required and increasing force production

    Pennation and Rotation

    • Sarcomeres shorten slower and generate more force due to the force-velocity relationship
    • Fibres can remain closer to optimum length, examples include gastrocnemius, vastus lateralis and medialis, and triceps brachii

    Viscoelasticity

    • Muscles exhibit viscoelastic properties, with creep (increased strain under constant stress) and stress relaxation (decreased stress at constant strain)
    • Viscoelasticity provides protection from injury and over-elongation when loaded rapidly
    • Tendon stiffness and hysteresis influence movement capacity

    Muscle Properties - Speed

    • As muscles shorten faster, maximum force decreases, known as the force-velocity relation
    • Power is the product of force and velocity (P = F x v), so there is also a power-velocity relation
    • We can either move slowly and lift heavy, or move quickly and lift light, but we can't do both (heavy and fast)

    Muscle Properties - Length

    • Shortening and lengthening of sarcomeres change the overlap of myosin and actin, affecting sarcomere and muscle force
    • At short lengths, there are fewer bound cross-bridges and actin-myosin collisions, resulting in decreased force
    • At optimum length (~2.7 µm), there are most bound cross-bridges, resulting in maximum force
    • At long lengths, there are again fewer bound cross-bridges and actin-myosin collisions, resulting in decreased force
    • The force-length relation is largely, but not completely, underpinned by changes in actin-myosin overlap
    • Within a muscle, sarcomeres can all be at different lengths
    • The "best" length is not always the "optimum" length determined during a maximal contraction

    Muscle Properties - Length (continued)

    • When a muscle connects to a long tendon, higher force stretches the tendon, causing the muscle to work at a shorter length
    • Alternatively, reducing force allows the tendon to shorten, stretching the muscle anyway
    • The optimum "muscle-tendon unit" length, and therefore the optimum joint angle, probably changes little with changes in force
    • Passive forces also contribute when a muscle is stretched, including the parallel elastic component (PEC)
    • The PEC includes membranes surrounding fibers, fascicles, and whole muscles, keeping the muscle from overstretching
    • However, the PEC passive force decreases or becomes zero during contraction as the fibers shorten and stretch the series elastic component (SEC)

    Muscle Architecture

    • Muscles can have varying architectures, including pennate and parallel fibers
    • Long fibers/fascicles allow for a large range of motion (ROM) and perform more work (F x d)
    • Long fibers/fascicles have high shortening speeds
    • Short fibers have lower metabolic cost (less ATP use)
    • Longer fibers have more sarcomeres in series, generating good force at higher shortening speeds
    • Examples of muscles with different architectures include the vastus lateralis, hamstrings, and gluteus maximus

    The Tendon

    • Muscles transfer their forces through tendons to the bones
    • Understanding the tendon is key to understanding functional movement
    • Tendons have a hierarchical structure, including molecules, fibrils, fascicles, and tendons
    • The fundamental component is collagen, which is elastic due to covalent bonds between amino acids
    • Cross-linking of collagen fibrils increases stiffness and reduces breaking of fibrils
    • Load sharing occurs between fibrils and fascicles, and shear between these constituents allows for tendon elongation

    Tendon Force-Length Relation

    • Tendons stretch when loaded, but properties vary
    • The force-length relation has a toe region, linear region, and failure region
    • When loaded, collagen stretches, and some collagen stretches, resulting in damage to collagen and filamentous/fascicular shear

    Tendon Stress-Strain Relation

    • To compare tendons of different sizes and types, we normalize force and length
    • Stress is the force change per cross-sectional area (N/mm²)
    • Strain is the length change per initial length (%)
    • The stress-strain relation shows that tendons dissipate energy partly through shear between fibrils and fascicles during relaxation

    Viscoelasticity

    • Biological tissues, including tendons, exhibit viscoelastic behavior, combining viscous and elastic properties
    • Viscoelasticity is important for injury prevention and braking, but not for propulsion/locomotion
    • Creep occurs when there is increased strain under constant stress, and stress relaxation occurs when there is decreased stress at constant strain
    • Fibril sliding causes viscoelasticity, providing greater protection from injury and over-elongation when loaded rapidly

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