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KNES 361 Final > Biomechanics of Skeletal Muscle > Flashcards

Biomechanics of Skeletal Muscle Flashcards

(62 cards)

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1
Q

Muscle Action

A

Muscles have active contractile component that develops force-

Active force dependent on:
Neural factors
Mechanical factors
Fiber type
Muscle architecture

Muscle force transmitted through tendon to bone-

Muscle force creates joint torque or moment → motion

Joint torque/moment dependent on:
Muscle force
Moment arm / Lever arm
Joint position (angle of pull)

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2
Q

Breakdown of Skeletal Muscle

A

Epimysium
Perimysium
Endomysium
Sarcolemma

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3
Q

Sarcomere

A

Basic contractile unit of muscle that develops force

Actin and Myosin (myofilaments) cycling

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4
Q

Sliding Filament Theory

A

↑ cross-bridge formation = ↑ force

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5
Q

Muscles “do work”

A

Work refers to the product of force and displacement (Work = Force x distance)
Displacement = the parallel displacement component relative to the force applied

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6
Q

Motor Unit

A

Single motor neuron and all the muscle fibers it innervates
3 to 2,000 fibers innervated (innervation ratio)
Functional unit of muscle
Smallest unit of muscle contraction
All muscle fibers respond as one
“All or None”

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7
Q

Synergist

A

Two or more muscles working together to produce a movement

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8
Q

Agonist

A

Cause or assist movement

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9
Q

Stabilizer

A

Active in one segment so that a movement in an adjacent segment can occur

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10
Q

Antagonist

A

Perform movement opposite of agonist

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11
Q

Neutralizer

A

Active to eliminate an undesired joint action of another muscle

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12
Q

Concentric action

A

Shortening of fibers to cause joint movement

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13
Q

Eccentric action

A

Lengthening of fibers to control or resist joint movement

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14
Q

Isometric action

A

Minimal change in fiber length

No joint movement

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15
Q

Factors Influencing Active Muscle Force Production

A

Neural Factors

Fiber type

Mechanical Factors

Muscle Architecture

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16
Q

Neural Factors Affecting Active Muscle Force

A

Activation & Discharge Rate

Motor unit recruitment

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17
Q

Muscle Fiber Activation & Discharge Rate

A

Twitch
Summation
Tetanus

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18
Q

Twitch

A

response of muscle to single stimulus

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19
Q

Summation

A

the overall effect of added stimuli

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20
Q

Tetanus

A

sustained maximal tension due to high frequency stimulation

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21
Q

Motor Unit (m.u.) Recruitment

A 
Muscle force is proportional to number of m.u.’s recruited
# crossbridge formations

Muscle force is proportional to rate of stimulation (or firing)
Rate of crossbridge cycling

Synchronization of firing impulses may increase muscle force
Important in fatiguing exertions

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22
Q

Fiber Type Comparison

A

Fiber type affects muscle force, rate of force production,
& recruitment order

*look at chart

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23
Q

Fast Twitch vs Slow Twitch

A

FT peak force > ST peak force

FT rate of force production > ST rate of force production

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24
Q

Fiber Type (cont.)

A

All fibers within a m.u. are the same type
Within a muscle, however, there are a mixture of fiber types

Ordered recruitment (Henneman’s size principal)
Type I recruited 1st (lowest threshold)
Type IIa recruited second
Type IIb recruited last (highest threshold)

Reduction in tension accomplished in reverse order
Allows for controlled, smooth gradation of force
Largely genetic, but may change with training

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25
Mechanical Factors Affecting Muscle Force
Length | Velocity
26
Force-Length Relationship
``` Optimal (~resting length) (max crossbridges → ↑ force) Shortened = Crossbridge overlap (↓ crossbridges → ↓ force) Lengthened = Crossbridges are pulled apart (↓ crossbridges → ↓ force) ```
27
Force-Length Relationship:
Concentric vs. Eccentric
Same muscle length: ForceECC > ForceCON More crossbridges in ECC ECC uses less energy No ATP used to break crossbridge like in CON Stretched – therefore more elastic energy stored  More force Less Friction F-L relationship occurs during concentric & eccentric muscle action
28
Force-Length Relationship:
Active & Passive
Stretch beyond resting length causes: ↓ Active tension ↑ Passive tension Total tension may be greater at extremes of motion Due to passive tension
29
Force-Velocity Relationship | Why Concentric F-V?
More crossbridges in release stage at a given time Concentric - some CBs stay bound to too long (braking effect) In eccentric – pulling apart makes it easier for crossbridges to cycle
30
Concentric
Shortening | CB Resists = “Negative Braking effect”
31
Eccentric
Resisting Lengthening | CB Assists: "Positive braking effect"
32
F-V Impact
At a given level of activation, muscles contracting more slowly produce greater force than muscles contracting more quickly To achieve a given force, muscles contracting slowly need less activation as muscles contracting quickly
33
Muscle Power
Power refers to the rate at which work is performed Power = Work / Time OR Power = Force x Velocity Muscle power is especially important to functional and athletic tasks in comparison to strength – examples?
34
Activation History | Stretch-Shorten Cycle
↑ muscle work when shortening immediately follows stretching Squat jump vs. Counter-movement jump If stretch is held too long before shortening the effects are lost Basis is not well understood Stored elastic energy Reflex activation
35
Muscle Architecture
Arrangement of contractile components (sarcomere) affects force production, excursion, & velocity Muscle fiber arrangement: Parallel: side to side arrangement Series: end to end arrangement
36
Longitudinal
Esophagus
37
Unipennate
Lumbricals
38
Bipennate
Gastrocnemius m.
39
Fusiform
Wider in middle than ends (biceps brachii m.)
40
Muscle Architecture & Force
Arrangement of contractile components (sarcomere) affects force production Muscle force is proportional to number of fibers / crossbridges active in parallel Parallel = greater force production Series = greater shortening velocity
41
Parallel Muscle Fiber Arrangement
side to side arrangement
42
Series Muscle Fiber Arrangement
end to end arrangement
43
Muscle Displacement and Velocity
Muscle displacement & velocity are proportional to number of fibers / crossbridges in series Each fiber undergoes a change in length Δ LengthTOTAL= ∑ ΔLengthSERIES FIBERS ↑ Δ LengthTOTAL in same time → ↑ Velocity
44
Muscle Force
Muscle force is proportional to number of fibers / crossbridges active in parallel Muscle Force = ∑ForcePARALLEL FIBERS Muscle Force = Avg ForceSERIES FIBERS
45
Angle of Pennation
Alignment of muscle fibers relative to line of pull Pennation θ = 0° → Fibers aligned with line of pull ↑ resultant force directed along line of pull in less pennated fiber arrangements ↑ overall force in less pennated (longitudinal) arrangements???
46
Muscle Architecture
For the same muscle volume, longitudinal arrangements produce less force than pennate arrangements
47
Energy
``` The capacity to do work Scalar quantity We are most interested in mechanical energy (associated with motion and position) Kinetic: energy of motion Potential: energy of position ```
48
Types of energy
Mechanical, chemical, heat, sound, light, etc
49
Mechanical Energy
Strain or Elastic Energy Special form of potential energy Energy due to deformation This type of energy arises in compressed springs, squashed balls ready to rebound, stretched tendons inside the body, and other deformable structures (like muscles!!) Tennis Ball Bounce
50
Stiffness
Force response to a mechanical stretch Muscle fibers possess stiffness Stiffness (K) = ΔF/ΔL
51
Stiffness Recruitment
Stiffness can be controlled Preparatory muscle activation (intrinsic stiffness) Reflex activation (reflex mediated stiffness) Co-activation (joint stiffness)
52
How do reflexes maintain muscle stiffness?
Muscle spindle excitation facilitates increased motor unit recruitment Change in muscle length Change in rate of muscle lengthening Increased number of fibers aligned in parallel Increased muscle stiffness
53
Co-Activation and Joint Stiffness
↑ number of fibers aligned in parallel Agonist & antagonist muscles Antagonist muscle activity → ↑ agonist muscle activity Offset antagonist muscles → ↑ number of fibers aligned in parallel ↑ joint compression → ↑ friction
54
Role of Stiffness
Stiffness creates stability Musculoskeletal injury (joint stability) Balance (postural stability)
55
Preventing Joint Injury
Biomechanical stability is required to prevent joint injury Ability of a loaded structure to maintain static equilibrium after perturbation around the equilibrium position (Bergmark, 1989)
56
Joint Biomechanical Stability
Perturbation to Joint (e.g. anterior tibial shear force) > Limited Athrokinematic Motion > Return to Resting Position > Maintenance of Joint Biomechanical Stability
57
Biomechanical Stability Factors
Sufficient potential energy (PE) is needed to maintain biomechanical stability after perturbation (Bergmark, 1989) System able to return to equilibrium position Quantifying Biomechanical Stability Work (J) performed during perturbation ≤ PE (J) inherent to the system → Stable system
58
Forms of Potential Energy (PE)
PE due to object height above reference PE = mgh (m = mass, g = gravitational acceleration, h = height) PE due to elastic deformation PE = ½kx2 (k=stiffness, x = distance stretched)
59
Elastic Energy, Stiffness & Stability
PE in form of elastic energy is most important for musculoskeletal applications PE = ½kx2 ↑ stiffness → ↑ PE → ↑ stability Thus, stiffness creates biomechanical stability
60
Ankle Stiffness
``` Stiffness of the evertor muscles can limit excessive inversion Peroneus longus Peroneus brevis ↑ stability ↓ injuries ```
61
Summary
Stiffness creates joint stability Active muscle stiffness most important Insufficient stiffness → inability to maintain stability Joint injury
62
Too much of a good thing?
could increase injury risk of bone and muscle injury

KNES 361 Final (4 decks)

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