Download Groups of Muscles

Characteristics of Muscle
 Irritability
 Ability to respond to stimulation
 Contractility
 Ability to shorten when it receives sufficient stimulation
 Unique to muscle tissue
 Extensibility
 Ability to stretch/lengthen beyond resting length
 Protective mechanism
 Elasticity
 Ability to return to resting length after being stretched
 Protective mechanism
Groups of Muscles
 Muscles typically act in unison – not individually
 Fascia
 Sheet of fibrous tissue
 Compartmentalizes groups of muscles
Individual Muscle
Organization
 Belly
 Thick central portion
 Epimysium
 Outside covering of a
muscle
 Fascicles
 Bundles of muscle fibers
 Perimysium
 Dense connective sheath
covering a fascicle
 Fibers
 Cells of a skeletal muscle
Individual Muscle Organization
(cont.)
 Endomysium
 Very fine sheath covering individual fibers
 Sarcolemma
 Thin plasma membrane branching into muscle
 Myofibrils
 Rod-like strands of contractile filaments
 Many sarcomeres in series
 Sarcoplasma
 Cytoplasm of muscle cell
 Sarcoplasmic reticulum
 Specialized endoplasmic reticulum of muscle cells
Individual Muscle Organization
(cont.)
 T-tubules
 Extension of sarcolemma that protrudes into muscle
cell
 Also called, transverse tubule
 Myosin
 Thick, dark filament
 Actin
 Thin, light filament
 Sarcomere
 Unit of myosin and actin
 Contractile unit of muscle
Fiber Organization
 Fusiform
 Parallel fibers and fascicles
 High speed of contract, force production
 ACS = PCS
 Anatomical Cross-Section (ACS)
 Physiological Cross-Section (PCS)
 Sartorius, biceps brachii, brachialis
Fiber Organization
 Penniform
 3 Types
 Unipennate
 Off one side of tendon
 Semimembranosus
 Bipennate
 Off both sides of tendon
 Gastrocnemius
 Multipennate
 Both varieties
 Deltoid
 PCS > ACS
Fiber Type
 Type I
 Slow twitch, oxidative
 Red (because of high myoglobin content)
 Endurance athletes
 Type IIa
 Intermediate fast-twitch, oxidative-glycolytic
 Type IIb
 Fast twitch, glycolytic
 White
 Sprinters, jumpers
Muscle Attachment
 3 ways muscle attaches to bone
 Directly
 Via a tendon
 Via an aponeurosis
 Tendon
 Inelastic bundle of collagen
fibers
 Aponeurosis
 Sheath of fibrous tissue
 Origin
 More proximal attachment
 Insertion
 More distal attachment
Characteristics of a Tendon
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Transmits muscle force to associated bone
Can withstand high tensile loads
Viscoelastic stress-strain response
Myotendinous junction
 Where tendon and muscle join
Functions of Muscle
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Produce movement
Maintain postures and positions
Stabilize joints
Other functions
 Support and protect visceral organs
 Alter and control cavity pressure
 Maintain body temperature
 Control entrances/exits to the body
Role of Muscle
 Prime mover

Muscle(s) primarily responsible for a given movement
 Assistant mover

Other muscles contributing to movement
 Agonist

Muscles creating same joint movement
 Antagonist

Muscles opposing joint movement
 Stabilizer

Holds one segment still so a specific movement in an
adjacent segment can occur
 Neutralizer

Muscle working to eliminate undesired joint movement of
another muscle
Muscle Actions
 Isometric
 Tension produced without visible change in joint
angle
 Holding arms out to sides
 Concentric
 Muscle visibly shortens while producing tension
 Up phase of a sit-up
 Eccentric
 Muscle visibly lengthens while producing tension
 Lowering phase of squat
Stretch-Shortening Cycle
 Pre-stretch
 Quick lengthening of a muscle before contraction
 Generates greater force than contraction alone
 Utilizes elastic component of muscle
 Prestretch & Fiber Type
 Type I
 Slower pre-stretch best because of slow crossbridging
 Type II
 Faster pre-stretch best because of fast crossbridging
Plyometrics
 Conditioning protocol that utilizes pre-stretching
 Single-leg bounds, depth jumps, stair hopping
One- and Two-Jointed
Muscles
 Muscles can cross one or two joints
 One-Jointed Muscles
 Brachialis, pectoralis major
 Two-Jointed Muscles (biarticulate)
 Save energy
 Gastrocnemius, hamstrings, biceps brachii
Two-Jointed Muscles
RF: Better leg extensor, H: better hip extensor
Motor Unit
 Group of muscles innervated by the same motor
neuron
 From 4 to 2000 muscle fibers per motor unit
 Action potential
 Signal to contract from motor neuron
 Neuromuscular junction
 Also called end plate
 Where action potential from neuron meets muscle
fiber
 Conduction velocity
 Velocity at which action potential is propagated
along membrane
Muscle Contraction
 Resting potential
 Voltage across the plasma membrane in a resting state
 Excitation-Contraction Coupling
 Transmission of action potential along sarcolemma
 Twitch
 Rise and fall reaction from a single action potential
 Tetanus
 Sustained muscle contraction from high-frequency
stimulation
Muscle Contraction
(cont.)
 Depolarization
 Loss of polarity
 Repolarization
 Movement to the initial resting (polarized) state
 Hyperpolarization
 State before repolarization
Sliding Filament Theory
 A.F. Huxley
 Seeks to explain production of
tension in muscle
 Myosin & actin
 Create cross-bridges
 Slide past one another
 Cause the sarcomere to
contract
Mechanical Model of
Muscle
 A.V. Hill
 3 Component Model
 Contractile (CC)
 Converts stimulation into
force
 Parallel elastic (PEC)
 Allows the muscle to be
stretched
 Associated with fascia
surrounding muscle
 Series elastic (SEC)
 Transfers muscle force to
bone
Factors Influencing Muscle Force
 Angle of attachment
 Force-time characteristics
 Force increases non-linearly due to elastic
components
 Length-tension relationship
 Force-velocity relationship
Electromyography
 Correct placement of electrodes is critical
 Electrodes oriented parallel to muscle fiber
 Prepare skin by…
 Shaving
 Abrading
 Cleaning with alcohol
 Signal must be amplified
 Sample rate ≥ 1000 Hz required
Electromyography
(cont.)
 Rectification
 Taking the absolute value of raw signal
 Linear envelope
 Time domain
 Frequency domain
 Electromechanical delay (EMD)
 Temporal delay between onset of EMG signal &
development of muscle tension
Muscle Fatigue
 Fatigue results from…
 Peripheral (muscular) mechanisms
 Central (nervous) mechanisms
 When motor unit fatigues…
 Change in frequency content
 Change in amplitude of EMG signal
 Sufficient rest restores initial signal content and
amplitude
Clinical Gait Analysis
 EMG used to investigate
which muscle group is used
in a certain phase of gait
 Determine activation order
 Raw or rectified EMG signal
is used
Ergonomics
 Ergonomics
 EMG used to investigate effects of…
 Sitting posture
 Carrying loads
Principles of Training
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Genetic predisposition
Training specificity
Intensity
Rest
Volume
Strength Training and the
Nonathlete
 ACSM
 2 days per week
 8–12 exercises per day
 Counteracts atrophy of muscle and bone
 Elderly
 Children
 High-intensity not recommended
 Epiphyseal plates susceptible to injury under
high loads
Training Modalities
 Isometric
 No visible movement
 Rehabilitation
 Isotonic
 Same weight throughout range of motion (ROM)
 Isokinetic
 Same velocity, varied resistance
 Close-linked
 Isotonic, in which one segment is fixed in place
 Variable resistive
 Supposedly overloads muscle throughout ROM
Injury to Skeletal
Muscle
 At risk
 Two-jointed muscles at greatest risk of strain
 Eccentrically contracted to slow limb movement
 Hamstrings, rotator cuffs
 Fatigued or weak muscles
 When performing unique task for first time
 Already injured
 Prevention
 Warm-up
 Build up when starting new program
 Recognize signs of fatigue
 Give body adequate rest
Summary
 Characteristics of muscle tissue
 Irritability, contractility, extensibility, elasticity
 Often act in compartmentalized groups
 Fiber organization
 Fusiform, penniform
 Fiber types
 Type I, IIa, IIb
 Functions of muscle
 Produce movement, maintain postures,
stabilize joints, and others