Muscle Properties

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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?

Optimum length (~2.7 µm) Signup and view all the answers

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

Force-velocity relation Signup and view all the answers

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

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

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

2.7 µm Signup and view all the answers

What is the unit of measurement for sarcomere length?

Micrometers (µm) Signup and view all the answers

What is the main purpose of studying human functional anatomy?

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

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

All of the above Signup and view all the answers

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

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

What is the due date for Assignment 1?

Week 9 Signup and view all the answers

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

Research process Signup and view all the answers

How does functional anatomy interact with other areas of study?

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

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

Human functional anatomy Signup and view all the answers

What is studied in functional anatomy?

The functional role of musculoskeletal and neurological structures Signup and view all the answers

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

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

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

Forces increase at low frequencies and decrease at high frequencies Signup and view all the answers

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

Force decreases with lengthening Signup and view all the answers

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

At long lengths Signup and view all the answers

What is the relationship between muscle length and force?

Force decreases with increasing length Signup and view all the answers

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

The change in actin and myosin interaction Signup and view all the answers

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

The Biceps Brachii has a shorter optimum length Signup and view all the answers

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

The force-length relation shifts with increasing activation Signup and view all the answers

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

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

What is the function of the light chains in myosin?

To influence the function of myosin Signup and view all the answers

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

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

How do myosin molecules arrange themselves in a unique way?

Tails together and heads at the ends Signup and view all the answers

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

The cross-bridge model Signup and view all the answers

What are the major constituents of the sarcomere?

Actin and myosin Signup and view all the answers

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

The force produced by myosin decreases Signup and view all the answers

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

Cross-bridge formation Signup and view all the answers

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

More work can be performed Signup and view all the answers

What is the characteristic of muscles that have shorter fibres?

Lower metabolic cost Signup and view all the answers

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

It decreases Signup and view all the answers

Which type of muscle is best suited for dynamic movements?

Long-fibred muscles Signup and view all the answers

What is the relationship between fibre length and isometric force?

Fibre length has no effect on isometric force Signup and view all the answers

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

They use less ATP to generate tension Signup and view all the answers

What is the advantage of having highly pennate fibred muscles?

Increased isometric force Signup and view all the answers

What is the relationship between fibre length and sarcomere shortening?

Longer fibres have a longer range of shortening Signup and view all the answers

What is the function of the light chains in myosin?

To influence myosin function Signup and view all the answers

Why is the motor domain of myosin very short?

To allow myosin to work in low gear Signup and view all the answers

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

Sarcomere length Signup and view all the answers

How do myosin molecules arrange themselves?

Tails together and heads at the ends Signup and view all the answers

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

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

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

Cross-bridge model Signup and view all the answers

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

Muscle force production decreases Signup and view all the answers

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

Less force can be produced Signup and view all the answers

What is the relationship between muscle velocity and force production?

As muscle velocity increases, force production decreases Signup and view all the answers

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

Cross-bridge Signup and view all the answers

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

When the sarcomere length is approximately 2.7 µm Signup and view all the answers

What are the major constituents of the sarcomere?

Actin and myosin Signup and view all the answers

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

Due to differences in sarcomere length Signup and view all the answers

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

Muscles acting as motors Signup and view all the answers

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

As shortening velocity increases, maximum force production decreases Signup and view all the answers

What is the relationship between muscle length and force production?

As muscle length increases, force production decreases Signup and view all the answers

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

Varied muscle functions Signup and view all the answers

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

It shifts to the right Signup and view all the answers

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

Long lengths Signup and view all the answers

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

Forces increase Signup and view all the answers

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

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

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

Changes in actin and myosin interaction Signup and view all the answers

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

Force increases 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?

Different muscle functions Signup and view all the answers

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

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

What is the benefit of fibre rotation during muscle contraction?

Allows fibres to shorten less and maintain optimal length Signup and view all the answers

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

Increases due to optimal length maintenance Signup and view all the answers

What is the advantage of muscles with high pennation angles?

Increased force production due to more contractile tissue Signup and view all the answers

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

Increases force production due to optimal length maintenance Signup and view all the answers

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

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

What is the benefit of pennate muscles in dynamic contractions?

Improved force production due to optimal length maintenance Signup and view all the answers

What is the effect of fibre rotation on sarcomere shortening?

Allows sarcomeres to maintain optimal length Signup and view all the answers

What type of behaviours do tendons exhibit?

Both viscous and elastic behaviours Signup and view all the answers

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

The stress falls slowly Signup and view all the answers

What is the effect of rapid loading on tendons?

Decreased injury risk Signup and view all the answers

What is the result of fibril sliding in tendons?

Increased viscoelasticity Signup and view all the answers

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

The strain continues Signup and view all the answers

What is the role of tendons in movement?

To transfer muscular forces Signup and view all the answers

What is the relationship between tendon stiffness and injury risk?

Increased stiffness reduces injury risk Signup and view all the answers

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

Viscoelasticity Signup and view all the answers

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

The number of bound cross-bridges decreases Signup and view all the answers

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

Force production increases Signup and view all the answers

What is the relationship between muscle power and velocity?

Power increases as velocity increases Signup and view all the answers

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

Sarcomeres can be at different lengths Signup and view all the answers

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

Maximum force production decreases with shortening velocity Signup and view all the answers

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

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

What is the relationship between muscle force production and velocity?

Force production decreases with velocity Signup and view all the answers

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

Power production increases Signup and view all the answers

What is the hierarchical structure of tendon?

molecule, fibril, fascicle, tendon Signup and view all the answers

What is the fundamental component of tendon?

Collagen Signup and view all the answers

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

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

What is the advantage of having shorter fibres in muscles?

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

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

Increases stiffness and reduces breaking of fibrils Signup and view all the answers

What happens to tendons when loaded?

They stretch Signup and view all the answers

How does fibre length affect shortening velocity?

Longer fibres have slower shortening velocity. Signup and view all the answers

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

To compare tendons of different sizes and types Signup and view all the answers

What is the characteristic of muscles that have longer fibres?

They perform more work. Signup and view all the answers

What is the relationship between fibre length and sarcomere shortening?

Longer fibres have more sarcomeres in series. Signup and view all the answers

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

Hysteresis Signup and view all the answers

What is the advantage of having highly pennate fibred muscles?

They can have varying architecture. Signup and view all the answers

What is the characteristic of biological tissues, including tendon?

Viscoelasticity Signup and view all the answers

What is the effect of fibre length on isometric force?

Fibre length has no effect on isometric force. Signup and view all the answers

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

It helps in injury prevention and braking Signup and view all the answers

Which type of muscle is best suited for dynamic movements?

Muscles with longer fibres. 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?

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

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

To keep the muscle from overstretching during contraction Signup and view all the answers

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

It decreases, often to zero Signup and view all the answers

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

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

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

The muscle-tendon unit length determines the joint angle Signup and view all the answers

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

It determines the maximum force production Signup and view all the answers

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

It allows the muscle to work at shorter lengths Signup and view all the answers

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

To transmit force from the muscle to the bone Signup and view all the answers

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

Fibril sliding Signup and view all the answers

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

It falls slowly 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?

Creep Signup and view all the answers

What is the main function of tendons in movement?

To transfer muscular forces Signup and view all the answers

What is the consequence of rapid loading on tendons?

Greater protection from injury and over-elongation Signup and view all the answers

What is the result of increased stiffness in tendons?

Decreased injury risk Signup and view all the answers

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

Directly proportional Signup and view all the answers

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

Viscoelasticity 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.

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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Description

This quiz explores the relationship between muscle speed and force, including the force-velocity relation and power-velocity relation.