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DPT 726: Orthopaedic Foundations > Neuromechanics of Human Movement > Flashcards

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Introduction to Neuromechanics of Muscle

-excitable tissue serves as basis for movement
-possesses "plasticity"
-PTs must have solid biomechanical understanding of tissue and organ system


Introduction to Neuromechanics of Skeletal Muscle

-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



-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



-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



-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



-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


Biomechanical Roles of Skeletal Muscle

-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


Production of Movement

-motion is created secondary to generation of muscle tension
-tension or force transferring to bones
-resulting motion necessary for locomotion, other segmental manipulations


Maintenance of Postures and Positions

-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


Stabilization of Joints

-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


Other Functions of Skeletal Muscle

-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


Architecture of Skeletal Muscle

-muscle as tissue: fascicle, muscle fiber, myofibril, sarcomere,myofilaments, SR
-review exercise phys notes


Excitation-Contraction Coupling How Movement Starts

-transfer of chemical energy to mechanic energy: ATP --> Force Production
-good idea to review content from exercise phys


Types of Muscle FIber

-3 basic types of muscle fibers
-differentiate based on: predominant energy source, speed of contraction, intensity of neural stimulation
-review charts on page 6


Fiber Typing: Clinical Example

-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


Type of Muscular Action: Static

-no resultant joint motion
-exerted against an immovable object
-used interchangeably with isometric action


Type of Muscular Action: Dynamic

-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


Eccentric Muscular Action

-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


Isotonic Muscular Action

-dynamic form of muscular activity
-external resistance remains constant through available ROM
-ex: free weights, wt cuffs, theraband
-commonly used in clinical practice


Isokinetic Muscular Action

-dynamic form of muscular activity
-speed of muscular action remains constant
-aka accommodating resistance
-less commonly used


Stretch-Shortening Cycle

-plyometric muscular action
-describes concentric action immediately preceded by eccentric muscular action
-resulting concentric action produces greater force
-crucial component of human movement


Elastic Component Contributions to the SSC

-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


Neural Contributions to SSC

-prestretch also stimulates muscle group thru reflex potentiation
-accounts for ~30% of increased subsequent concentric muscle action


SSC and Muscular Performance

-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


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


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


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


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


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


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