Neuromechanics of Human Movement Flashcards
1
Q
Introduction to Neuromechanics of Muscle
A
- excitable tissue serves as basis for movement
- possesses “plasticity”
- PTs must have solid biomechanical understanding of tissue and organ system
2
Q
Introduction to Neuromechanics of Skeletal Muscle
A
- most abundant tissue in human body
- represents 40-45% of total body weight
- transforms chemical energy into mechanical energy
- mechanical energy results in the generation of internal forces
- muscle is very resilient
- can be stretched or shortened at fairly high speeds
- can withstand considerable activity without damage
- skeletal muscle performance dictated by four properties: irritability, contractility, extensibility, elasticity
3
Q
Irritability
A
- ability to respond to stimulation
- skeletal muscle is one of the most sensitive and responsive tissues in the body
- only nerve tissue is more sensitive
4
Q
Contractability
A
- ability to shorten
- occurs when muscle tissue receives sufficient stimulation
- some muscles can shorten as much as 50-70% of their resting length
- shortening distance limited by its confinement in the body
5
Q
Extensibility
A
- ability to stretch or lengthen
- muscle itself cannot produce the elongation
- another muscle or force is needed
- determined by connective tissue found in: perimysium, epimysium, fascia surrounding and within
6
Q
Elasticity
A
- ability to return to resting length after stretching or lengthening
- determined by connective tissue in muscle
- a critical component in facilitating output in a shortening muscle action preceded by a stretch: aka stretch-shortening cycle
7
Q
Biomechanical Roles of Skeletal Muscle
A
- perform a variety of different functions
- all are important to performance of human body
- functions: production of movement, maintain postures and positions, stabilize joints, other functions
8
Q
Production of Movement
A
- motion is created secondary to generation of muscle tension
- tension or force transferring to bones
- resulting motion necessary for locomotion, other segmental manipulations
9
Q
Maintenance of Postures and Positions
A
- typically involves mm actions of lesser magnitude
- mm activity is often continuous
- results in small adjustments
- functional goal is to maintain head position, balance body weight over feet
10
Q
Stabilization of Joints
A
- mm action contributes significantly to joint stability
- mm tensions generated and applied across joints via tendons
- thus provide stability where they cross joints
- among primary joint stabilizers via tendons: shoulder, knee
11
Q
Other Functions of Skeletal Muscle
A
- not related directly to human movement
- support and protect visceral organs
- alter and control pressure within cavities
- maintenance of body temperature-secondary in producing heat
- control entrances and exits to body through voluntary control: swallowing, urination, defecation
12
Q
Architecture of Skeletal Muscle
A
- muscle as tissue: fascicle, muscle fiber, myofibril, sarcomere,myofilaments, SR
- review exercise phys notes
13
Q
Excitation-Contraction Coupling How Movement Starts
A
- transfer of chemical energy to mechanic energy: ATP –> Force Production
- good idea to review content from exercise phys
14
Q
Types of Muscle FIber
A
- 3 basic types of muscle fibers
- differentiate based on: predominant energy source, speed of contraction, intensity of neural stimulation
- review charts on page 6
15
Q
Fiber Typing: Clinical Example
A
- transverse abdominus and multifidi: slow oxidative, postural muscles, low recruitment threshold, low force production
- often poorly recruited in those with LBP: if so patients rely on prime movers for postural support
- PT can retrain TA and multifidi to fire correctly
16
Q
Type of Muscular Action: Static
A
- no resultant joint motion
- exerted against an immovable object
- used interchangeably with isometric action
17
Q
Type of Muscular Action: Dynamic
A
- muscular action involving joint motion
- muscle belly shortens or lengthens
- concentric action: two ends of muscle move closer together, shortening muscular action, positive work
- eccentric action: two ends of muscle move farther apart, lengthening muscular action, negative work
18
Q
Eccentric Muscular Action
A
- linked to DOMS, as a stimulus for muscular hypertrophy-microtears in muscle’s connective tissues
- exposure to extreme bouts of eccentric loading linked to rhabdomyolysis: often results in myoglobinuria, can prompt kidney failure
19
Q
Isotonic Muscular Action
A
- dynamic form of muscular activity
- external resistance remains constant through available ROM
- ex: free weights, wt cuffs, theraband
- commonly used in clinical practice
20
Q
Isokinetic Muscular Action
A
- dynamic form of muscular activity
- speed of muscular action remains constant
- aka accommodating resistance
- less commonly used
21
Q
Stretch-Shortening Cycle
A
- SSC
- plyometric muscular action
- describes concentric action immediately preceded by eccentric muscular action
- resulting concentric action produces greater force
- crucial component of human movement
22
Q
Elastic Component Contributions to the SSC
A
- stretch on muscle changes the muscle’s properties
- occurs secondary to storing of PE in SEC of muscle
- stretch on muscle produces small changes in muscle and tendon length
- maximizes accumulation of stored energy
- thus eccentric muscular action enhances recoil leads to increased force output of muscle tendon complex
- concentric muscle action also enhanced by stored elastic energy in PEC
- this contribution drops off quickly as muscle continues to shorten
- if shortening contraction occurs within reasonable time after stretch: stored energy is recovered and used 0-.9 seconds
- if stretch held too long, stored elastic energy is lost through conversion to heat
23
Q
Neural Contributions to SSC
A
- prestretch also stimulates muscle group thru reflex potentiation
- accounts for ~30% of increased subsequent concentric muscle action
24
Q
SSC and Muscular Performance
A
- SSC particularly evident in gait
- NM system may be trained to tap into this phenomenon
- net result increased muscular tension
- accounts for ~50% of total energy requirement in running
25
Neural Control of Muscular Action
- regulated through the somatosensory nervous system
- sensation allows us to interpret the world
- motor function allows us to investigate it
- muscle action merely one component: motor unit is basic functional component of muscular action
26
Somatosensory System
- all information from somatosensory system proceeds from receptor thru series of neurons to brain
- processing signals into meaningful information occurs in cerebrum
- interpretation known as perception may be conscious or unconscious
- motor neurons supply skeletal muscle
- cell bodies of these motor neurons are located in ventral horn
- axon is continuous: from origin in spinal cord to termination on muscle fiber
- motor axon terminates: release of ACh --> excitation and muscular action
27
Forms of Sensory Information
- superficial or cutaneous sensory information comes from skin: including touch (superficial pressure or vibration), pain, temperature
- information from MS system includes proprioception and pain
- proprioception provides information on stretch on muscles, tension on tendons, position of joints, deep vibration
- proprioception includes both static and dynamic sense of position
28
Somatic Nervous System
- considered to be under voluntary control but much is subconscious
- posture, balance, stereotypic movements
- motor neurons may be destroyed by disease: polio selectively affects cell bodies; ALS is characterized by progressive degeneration and death of motor neurons
29
Motor Unit and Musculoskeletal Innervation
- motor unit is basic functional component of muscle function
- defined as alpha motor neuron and all fibers it innervates: motor neuron + all fibers it innervates, fibers range from a few to thousands, 300k in entire body
- alpha motor neuron has cell body in anterior horn of SC
- axon extends to muscle where it has few or many ranches
- terminates on the muscle fiber at the motor end plate
30
Variations in Motor Units
- type of muscle fiber: all fibers within MU are same type; can change some characteristics with training FOG --> endurance vs. intensity
- size of cell body and axon diameter: smaller the diameter --> slower the conduction; smaller innervate SO fibers
- fibers within MU do not necessarily lie next to each other
- need for precision influences ratio of fibers innervated within MU
31
All or None Law of Muscle Action
- all myofibrils within motor unit respond provided impulse is of sufficient duration, frequency, intensity
- results in sliding and forming of cross-bridges
- does not apply to entire muscle belly: allows us to produce graded force production
32
Other Important Organs in the Somatic Nervous System
- alpha motor unit connected to efferent neuron: innervates extrafusal fibers, stimulates muscle action
- gamma efferent neuron: innervates intrafusal fibers: MSFs and GTOs, stimulates increased sensitivity of intrafusal fibers
33
Intrafusal Fibers as Sensory Neurons
- MSF apparatus: attached to intrafusal fibers, run parallel to extrafusal fibers, chain fibers detect change in length, bag fibers detect changes in speed
- GTOs detects change in tension on tendons
34
Muscle Spindle Fibers
- contribute to proprioception
- sensory ending respond to changes in muscle length, velocity of change in length
- afferent sensory arise from intrafusal fibers: type Ia respond to quick and tonic tension, type II respond to tonic tension
- type Ia and II sensory fibers are activated with stretch
- small efferent fibers adjust spindle fiber so its responsive throughout muscles' physiologic range
35
GTO's
- also contribute to proprioception
- encapsulated at junction of extrafusal fibers and tendons: woven among collagen strands in tendon, located near musculotendinous junction
- attached in series
- sensitive to changes in tension: passive stretch, active muscular stretch
- sensitive to very slight change in tension
- serves to prevent overactivity of alpha motor neurons
- GTO fires with stimulation > threshold: prolonged stretch, prolonged isometric action
- can override input from MSF
- thus allows relaxation --> elongation
36
Clinical Applications: Stretching
- static stretching: sustained, load is constant, most common clinical form
- ballistic stretching: high impulse, integral to plyometric training, important in return to most sport/fitness
- PNF: originally used in neuro rehab, autogenic or reciprocal inhibition used to reset sensors in muscle and increase AROM and PROM, has both stretching and strengthening components
37
Static Stretching
- muscle is slowly elongated
- positioned to tolerance and maintained
- individual feels in this position: mild tension, mild discomfort
- extreme pain or discomfort should be avoided
- slow, prolonged stretch helps to: circumvent muscle spindle reflex, facilitates muscle inhibition via GTOs
- thus combined neuro effect is to minimize influence of muscle spindle fibers, maximize influence of GTOs
38
Autogenic Inhibition
- stimulation of muscle causing its neurologic relaxation
- occurs with activation of GTO
- serves as basis for static stretching and some PNF stretching techniques
39
Reciprocal Inhibition
- stimulation of muscle causing neurologic relaxation of its antagonist
- helps ensure ability to move through available ROM
- serves as basis for some PNF stretching techniques
40
Factors Affecting Force of Muscular Action
- fiber stimulation
- diameter of muscle
- fibers/motor unit
- number of motor units fired
- length of muscle when it's recruited
- length of muscle when it's recruited
- force-velocity curve
- angle of muscular attachement
41
Frequency of Stimulation
- AP --> series of events
- series of events: last ~100 msec; results in a single twitch
- if AP's are far enough apart --> twitch, relax, return to resting state
- if APs are close together --> does not return to resting point
- this 2nd phenomenon is known as temporal summation aka graded response
- no resting period --> temporal summation
- if stimulus is fast enough --> tetany (sustained contraction)
42
Diameter of the Muscle
- force is directly proportional to cross-sectional area
| - bigger muscle, bigger force
43
Number of Fibers/Motor Unit
- motor unit: alpha motor neuron; all fibers it innervates
| - number varies from a few fibers to thousands: 5-10 in eyelids but over 1000 in gluteus maximus
44
Number of Motor Units Fired
- aka recruitment principle
- each motor unit has summation threshold
- larger the motor unit, higher the threshold
- smaller units are fired first at low tensions
- allows gradation of tension and more fine control
45
Length of Muscle When Stimulated
- CE=contractile element: actin and myosin
- PEC=parallel elastic component: connective tissue
- SEC=series elastic component: tendon
- force depends on length
- optimal length exists for force/tension
- above or below, tension decreases
46
Force-Velocity Curve
- lightest load at max velocity
- max load at slowest velocity
- at highest velocity: concentric results in smallest tension and eccentric results in highest tension
47
Practical Applications
- muscle position when stimulated
- muscle length pathology
- look at slides in notes on page 19
48
Angle of Muscular Attachment
- not all force produced is put to use in generating segmental rotation
- depending on angle of insertion: some force directed to joint stabilization or destabilization
- thus pulls bone into, or away from, the joint
- even while muscle tension may be maintained during joint movement
- the rotary component and torque will vary depending on angle of insertion
- many of neutral starting positions are "weak" positions mechanically: secondary to most mm force is directed along length of bone
- thus less weight can typically be lifted as compared to starting with some flexion/extension in the joint
49
Angle of Muscular Attachment in Action
- at acute angles the parallel component of the force is highest and stabilizes the joint while the rotary force is low
- as angle increases to 90* rotary component increases to its maximum, there it hits functional "sticking point"
- as angle increases beyond 90*, rotary component diminishes, parallel component increases to produce a dislocating force
50
Classification of Skeletal Muscles
- spurt vs. shunt
- type of movement
- fiber arrangement
51
Spurt vs. Shunt Muscle
- spurt...
- proximal point of attachment is far from join axis
- allows more rotary than stabilizing movement
- length of mm along fixed body segment greater than mm length along moving segment
- ex: biceps brachii, rectus femoris
- shunt...
- proximal attachment close to joint axis
- distal attachment far from joint axis
- allows more stabilizing than rotary movement
- ex: brachioradialis
52
Fiber Arrangement
- fusiform (spindle): fibers arranged in spindle shape; brachialis and tibialis anterior
- parallel: fibers are parallel to each other; sartorius and rectus abdominis
- pennate: fibers are arranged in feather-like pattern; unipennate (FPL), bipennate (RF, TP), multipennate (deltoid)
- triangular: like fusiform, with more flat orientation; pectoralis, trapezius, latissimus dorsi, gluteus medius
- sphincter: fibers arranged in circular direction; orbicularis oris
53
Functional Roles of Skeletal Muscles
- prime mover vs. assistant mover
- agonist vs. antagonist
- stabilizers and neutralizers
- one joint vs. two joint muscles
54
Skeletal Muscle as Prime Mover
- describes muscles primarily responsible for a given movement
- ex: lats, p major shorten to produce extension
55
Skeletal Muscle as Assistant Mover
- describes muscles recruited to help prime movers
- typically recruited when increased force is needed
- ex: triceps, teres major may help with extension
56
Skeletal Muscle as Agonist
- describes muscles creating same joint movement
| - typically describes muscles directly producing a given motion
57
Skeletal Muscle as Antagonist
- describes muscles opposing or producing the opposite joint motion
- must relax to allow a movement to occur
- or contract concurrently with agonists to control or slow a joint motion; aka co-contraction
58
Agonists vs. Antagonists
- look at slides on p 25
- muscle may be more susceptible to injury when playing role of antagonist
- either at attachment or in muscle fiber itself
- secondary to muscle at times being simultaneous contracted and stretched
59
Skeletal Muscle as Stabilizer
- acting in one segment so specific motion in adjacent joint can occur
- very important in many regions: shoulder girdle during UE motion, hip region and pelvic girdle during gait, lumbar spine during many tasks
- scapular, hip, spinal/cervical are the main ones
60
Skeletal Muscle as Neutralizer
- also described as synergizer
- muscle acts to eliminate unwanted joint action of another muscel
- g. max contributes to hip extension but also IR femur
- if ER undesired: glute min and TFL contract-produce neutralizing IR action so cancel out ER action of G max
61
One- and Two-Joint Muscles
- most cross one joint so dominating action is at joint it crosses
- muscles crossing two joints create a multitude of different joint motions
- actions depends upon position of the body, interaction with external objects such as the ground
- two joint muscles act primarily on joint where it has largest moment arm
- look at examples on page 27
- two joint muscles decrease work required from single-joint muscles
- contribute to mechanical coupling of joints allowing for rapid release of stored energy
- may allow positive work at one joint and negative work at anotehr
62
Indirect Action
- a muscle can even create motion in joints it does not span
| - ex: soleus PF ankle actively and extends knee indirectly in standing in closed chain position
63
Active Insufficiency
- decreased ability of mm to produce or maintain active tension: no cross bridges left when muscle activated in shortened position
- typically occurs as 2 joint muscle contracts across 2 joints simultaneously
- results in severely compromised tension
64
Passive Insufficiency
- limitation of motion caused by elongation of muscle
- typically occurs as a 2 joint muscle is lengthened across 2 joints simultaneously: hip flexion with knee extended
- this passive tension or insufficiency may cause secondary joint motion: finger extension with active wrist flexion
65
Tendoesis
- Movement caused by passive tension
- ex: hand movement in quadriplegics: often have wrist extension but no finger flexion; wrist flexion opens fingers, then placed hand over object; wrist extension closes fingers, exerting force on object
- functionally beneficial for these people to use joystick controller
