Biomechanics Ch3

Muscle characteristics

Irritability - respond to stimulation
Contractility - shorten when stimulation occurs
Extensibility - strength/lengthen beyond resting
Elasticity - return to resting length after stretch

Muscle function

Posture/position maintenance
Stabilize joints
Support/protect organs/cavity pressure/body temp/

Muscles act in ______, not _______

in unison (together), not individually

Muscle fiber organization (penniform)

penniform =
unipennate, - off side of tendon (semimembranosus)
bipennate, - off both sides of the tendon (gastro)
multipennate - both uni and bi combined (deltoid)

What do ACS and PCS stand for ?

anatomical cross section
physiological cross section

Muscle fiber organization (fusiform)

parallel fibers
high speed of contraction
(sartoruis, biceps brachii, brachialis)

Muscle architecture (2)

Parallel = flat, fusiform, strap, radiate, circular
Pennate = unipennate, bipennate, multipennate

Fiber type

Type 1 - slow, oxidative
Type IIa - intermediate fast, oxidative-glycolytic
Type IIb - fast, glycolytic

Parts of muscle

Belly - thick central portion
Epimysium - outside covering of muscle
Fascicles - bundles of muscle fibers
Perimysium - dense connective sheath covers a fascicle
Fibers - cells of a skeletal muscle

individual muscle organization

Parts of a muscle (cont)

Very fine sheath covering individual fibers
Thin plasma membrane branching into muscle
Rod-like strands of contractile filaments
Many sarcomeres in series
Cytoplasm of muscle cell
Sarcoplasmic reticulum

Parts of a muscle cont

Extension of sarcolemma that protrudes into muscle cell
Also called transverse tubule
Thick, dark filament
Thin, light filament
Unit of myosin and actin
Contractile unit of muscle

Motor unit

group of muscles innervated by the same motor neuron
action potential (signal from motor neuron)
neuromuscular junction (end plate) (where action pot from neuron meets muscle fiber)
conduction velocity (velocity at which action pot is propagated along mem

Muscle contraction

resting potential (voltage across plasma membrane in a resting state)
excitation-contraction coupling (transmission of action pot along sarcolemma)
twitch (rise and fall reaction from one single action pot)
tetanus (sustained muscle contraction from high

twitch and tetanus

sliding filament theory

AF Huxley
wants to explain production of tension in the muscle
myosin and actin (create cross bridges, slide past another, cause sarcomere to contract)

sliding filament theory

muscle attachment

3 ways;
via tendon
via aponeurosis
tendon; inelastic bundle of collagen fibers
aponeurosis; sheath of fibrous tissue
origin; more proximal attch
insertion; more distal attch

Tendon characteristics

transmits muscle force to bone
can withstand high tensile loads
viscoelastic stress strain response
myotendinous junction (where tendon and muscle join)

Model of Muscle (AV HILL)

3 component model
1. Contractile (CC)
- converts stimulation into force
2. Parallel elastics (PEC)
- allows muscle to be stretch
- associated with fascia surround muscle
3. Series elastic (SEC)
- transfers muscle force to bone

Hill muscle model

role of muscle

- closer to midline/ more proximal
- further towards midline/ distal

Roles of muscles

prime mover - primarily responsible for movement
assistant mover - contribute to movement
agonist - creating same joint movement
antagonist - opposing joint movement
stabilizer - holds one segment still so movement in adjacent segment can occur

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 s

isometric, concentric, eccentric

Factors that influence muscle force

angle of attachment
force-time characteristic
- force increases non-linearly due to elastic components
length-tension relationship
force-velocity relationship

force-velocity relationship

force-length relationship

stretch-shortening cycle

prestretch, counter movement of a plyo exercise

stretch-shortening cycle

prestretch - quick lengthening of a muscle before contraction, generates greater force than contraction alone, uses elastic component of muscle
type1- slower prestretch best because of slow cross bridging
type 2- fast prestretch best because of fast cross


conditioning protocol that uses prestretching
- single leg bounds, depth jumps, stair hopping

stretch-shortening cycle and exercise

muscle fatigue

fatigue results from =
- peripheral (muscular) mechanisms
- central (nervous) mechanisms
when motor units fatigue; change in frequency content, change in amplitude of EMG signal
sufficient rest restores initial signal content and amplitude

strengthening muscle

postraining = myofibril size increases and separates (becomes 2 or more)

principles of training

genetic predisposition, training specificity,

strength training and the non athlete

- 2 days a week
- 8-10 exercises per day
contracts atrophy of muscle and bone
(elderly, children)
high intensity not recommended

training modalities

isometric - no visible moment/ rehab
isotonic - same weight throughout ROM
isokinetic - same velocity, carried resistance
close linked - isotonic, one segment fixed in place
variable resistive - supposedly overloads muscle throughout ROM

injury to skeletal muscle

at risk:
- 2 joints muscles for strain
- eccentrically contracted to slow limb movement (hamstring, rotator cuff)
- fatigued/ weak muscles
- unique task
- pre injured
- warm up
- build up to strength
- recognize signs
- rest

characteristics of muscle tissue


fiber organization

fusiform and penniform