• internal motors of human body responsible for all movements of skeletal system

• only have the ability to pull

• must cross a joint to create motion

• can shorten up to 70% of resting length

Muscle

Muscle-Tendon Model

• 3 components

SECseries elastic component

CC contractile component

PECparallel elastic component

Muscle Model

WholeMuscle

•Contractile Component (CC)

–active shortening of muscle through actin-myosin structures

•Parallel Elastic Component (PEC)

–parallel to the contractile element of the muscle

–the connective tissue network residing in the perimysium, epimysium and other connective tissues which surround the muscle fibers

•Series Elastic Component (SEC)

–in series with the contractile component

–resides in the cross-bridges between the actin and myosin filaments and the tendons

PEC

CC

SEC

Tissue

SEC

CC

PEC

Both SEC & PEC behave like springs when acting quickly but they also have viscous nature

If muscle is statically stretched it will progressively stretch over time and will slowly return to resting length when the stretching force is removed.

Viscoelastic Structures

Stretch-Shortening Cycle

• a quick stretch followed by concentric action in the muscle

• Store energy in elastic structures

• Recover energy during concentric phase to produce more force than concentric muscle action alone

• examples

– vertical jump: counter-movement vs. no counter-movement

– plyometrics

WholeMuscle

SEC

CC

PEC

Tissue Properties of Muscle• irritability - responds to stimulation by a chemical

neurotransmitter (ACh)

• contractibility - ability to shorten (50-70%), usually limited by joint range of motion

• distensiblity - ability to stretch or lengthen, corresponds to stretching of the perimysium, epimysium and fascia

• elasticity - ability to return to normal state (after lengthening)

Tissue

Muscle Structure

“Bundle-within-a-Bundle”

Tissue

Sliding Filament Theory

1) Myosin filaments form a cross-bridge to actin

2) Myosin pulls actin

3) x-bridge releases 4) Myosin ready for another x-bridge formation

actin

myosin

Tissue

Sarcomere Organization

• the number of sarcomeres in series or in parallel will help determine the properties of a muscle

3 sarcomeres in series

(high velocity/ROM orientation)

3 sarcomeres in parallel

(high force orientation)

Tissue

1 sarcomere

3 sarcomeres in series

3 sarcomeres in parallel

Force 1 N 1 N 3 N

ROM 1 cm 3 cm 1 cm

Time 1 sec 1 sec 1 sec

Velocity 1 cm/sec 3 cm/sec 1 cm/sec

Sarcomere organization example:

Note that the values are not representative of actual sarcomeres.

• the longer the tendon-to-tendon length the greater number of sarcomeres in series

• the greater the physiological cross-sectional area (PCSA) the greater number of sarcomeres in parallel

Sarcomere Organization

sarcomeres in series sarcomeres in parallel

Muscle Structure Fusiform (parallel)

• fibers run longitudinally

• generally fibers do not extend the entire length of muscle

• tendon runs parallel to the long axis of the muscle, fibers run diagonally to axis (short fibers)

Muscle StructurePennate

Tissue

Fusiform vs. Pennate• fusiform

– advantage: sarcomeres are in series so maximal velocity and ROM are increased

– disadvantage: relatively low # of parallel sarcomeres so the force capability is low

• pennate– advantage: increase # of sarcomeres

in parallel, so increased PCSA and increased force capability

– disadvantage: decreased ROM and velocity of shortening

Tissue

Fiber Types

• all fibers within a motor unit are of the same type

• within a muscle there is a mixture of fiber types• fiber type may change with training• recruitment is ordered

– type I recruited 1st (lowest threshold)– type IIa recruited second– type IIb recruited last (highest threshold)

Tissue

Tissue

Fiber Type ComparisonType I Type IIa Type IIb

ShorteningSpeed

slow fast fast

Energy System oxidative oxidative,glycolytic

glycolytic

Size small large largeForceProduction

low high high

AerobicCapacity

high medium low

AnaerobicCapacity

low medium high

Fatigability low medium high

Tissue

Active Length-Tension

l0 - neither contracted nor stretched

Length

Tension

l0

Tissue

Length-Tension

L

T

l0

passive

l0 - neither contracted nor stretched

physiologicallimit

active

combined

Tissue

velocity of contraction

Force - VelocityRelationship

v < 0(eccentric)

v > 0(concentric)

v=0(isometric)

forc

e

Tissue

v

F

Power (F*v)

30% vmax

Power - VelocityRelationship

Tissue

Muscle Attachment - Tendons

Fusion b/w epimysium

and periosteum

Tendon fusedwith fascia

WholeMuscle

Muscle Termsattachment can be directly to the bone or indirectly via a tendon or aponeurosis

Origin -- generally proximal, fleshy attachment to the stationary boneInsertion -- generally distal, tendinous and attached to mobile bone

WholeMuscle

defining origin or insertion relative to action of bone is difficult

e.g. hip flexors in leg raise v. sit-up

Functions of Muscle• produce movement - when the muscle is

stimulated it shortens and results in movement of the bones

• maintain postures and positions - prevents motion when posture needs to be maintained

• stabilize joints - muscles crossing a joint can pull the bones toward each other and contribute to the stability of the joint

WholeMuscle

Functional Muscle Groups

• generally have more than 1 muscle causing same motion at a joint

• together these muscles are referred to as a functional group

• e.g. elbow flexors -- biceps brachii, brachialis, and brachioradialis - all flex elbow

WholeMuscle

Role of the Muscle• prime mover - the muscles primarily responsible for the

movement• assistant mover - muscles used only when more force is

required• agonist - muscles responsible for the movement• antagonist - performs movement opposite of agonist• stabilizer - active in one segment to stabilize a bone so that

a movement in an adjacent segment can occur• neutralizer - active to eliminate an undesired joint action of

another muscle

WholeMuscle

agonist: deltoidantagonist: latissimus dorsistabilizer: trapezius holds the shoulder girdle in place so the deltoid can pull the humerus up

neutralizer: teres minor if latissimus dorsi is active then the shoulder will tend to internally

rotate, so the teres minor can be used to counteract this via its ability to externally rotate the shoulder

SHOULDER ABDUCTIONWholeMuscle

Muscular Action• isometric action

– no change in fiber length

• concentric action– shortening of fibers to

cause movement at a jt

• eccentric action– lengthening of fibers to

control or resist a movement

WholeMuscle

WholeMuscle

eccentric

concentric

Eccentric action:• work with gravity to lower the body or objects• slow down body segments or objects

Concentric action:• work against gravity to raise the

body or objects• speed up body segments or objects

WholeMuscle

•push-up

up - concentric action of elbow extensors

down - eccentric action of elbow extensors

•catching a baseball

eccentric action of elbow extensors

•throwing a baseball

concentric action of elbow extensors

•pull-up

up - concentric action of elbow flexors

down - eccentric action of elbow flexors

Elbow Actions WholeMuscle

The countermovement elicitsan increase in force production

the increase in force productionis 30% neural and 70% elasticcontribution

Greatest return of energy is achieved using a “drop-stop-pop” action with only an 8”-12” drop

WholeMuscle

Number of Joints Crossed

• uniarticular or monoarticular - the muscle crosses 1 joint, so it affects motion at only 1 joint

• biarticular or multiarticular - the muscle crosses 2 (bi) or more (multi) joints, so it can produce motion across multiple joints

WholeMuscle

Multiarticular Muscles

• can reduce the contraction velocity

• can transfer energy between segments

• can reduce the work required of single-joint muscles

• more susceptible to injury

WholeMuscle

Insufficiency

• a disadvantage of 2-joint muscles– active insufficiency - cannot actively shorten to

produce full ROM at both joints simultaneously– passive insufficiency - cannot be stretched to

allow full ROM at both joints simultaneously

WholeMuscle

Insufficiency Example

• squeeze the index finger of another student

• move the wrist from extreme hyperextension to full flexion

• What happens to the grip strength throughout the ROM?

• WHY?

WholeMuscle

Movement/Activity Properties of Muscle

• flexibility - the state of muscle’s length which restricts or allows freedom of joint movement

• endurance - the ability of muscles to exert force repeatedly or constantly

WholeMuscle

Movement/Activity Properties of Muscle (cont.)

• strength - the maximum force that can be achieved by muscular tension

• power - the rate at which physical work is done or the force created by a muscle multiplied by its contraction velocity

WholeMuscle

Muscular Strength

• measure absolute force in a single muscle preparation

• in real life most common estimate of muscle strength is maximum torque generated by a given muscle group

WholeMuscle

Strength Gains

from an “untrained state”1st 12 weeks see improvement on the neural side via improved innervation

later see increase in x-sectional area

Training focuses on developing larger x-sectional areaAND developing more tension per unit of x-sectionalarea

Magnitude of strength gainsdependent on

1) genetic predisposition2) training specificity3) intensity4) rest5) volume

WholeMuscle

Training Modalities

IsometricExercise

IsotonicExercise

IsokineticExercise

Close-LinkedExercises

Variable ResistanceExercise

WholeMuscle

Muscle Injury

Greatest Riska) 2-joint musclesb) muscles that limit ROMc) muscles used eccentrically

Soreness v. Damagedamage believed to be in fibersoreness due to connective tissue

Individuals at riska) fatigued stateb) not warmed-upc) new exercise/taskd) compensation

WholeMuscle

Muscular Force Components

• rotary component– causes motion– perpendicular to the

rotating segment

• stabilizing or dislocating component– parallel to rotating segment– stabilizing is toward joint– dislocating is away from joint

WholeMuscle

Muscular Force Components

• components depend on the joint angle

small rotarylarge stabilizing

large rotarysmall stabilizing

medium rotarymedium dislocating

WholeMuscle

What Causes Motion?Force or Torque?

• angular motion occurs at a joint so technically torque causes motion

• torque is developed because the point of application of the force produced by muscle is some distance away from the joint’s axis of rotation

muscle force (Fm)

distance between pt ofapplication and joint axis(dm)

muscle torque (Tm)

WholeMuscle

Calculation of Muscle Torque

60o

400 N

0.03 m

Tm = Fmd*

Torque = 400 N * 0.03 mbecasue Fm is not perpendicularto the forearm!!!

To solve problem we mustresolve the vector Fm intocomponents which areperpendicular (Fm ) and parallel (Fm ) to the forearm.

Fm Fm

Fm

WholeMuscle

Calculation of Muscle Torque

Fm Fm

Fm

FmFm

Fm

Only the perpendicular component will create a torqueabout the elbow joint so only need to calculate this.

WholeMuscle

400 N

0.03 m

400 N

0.03 m

FR = 200 N

T = 200 N * 0.03 m = 6 Nm

FR = 345 N 400 N

0.03 m

T = 345 N * 0.03 m = 10.4 Nm

FR = 345 N

WholeMuscle

Angle of Pull Affects Torque

FR = 345 N 400 N

0.03 m

T = 345 N * 0.03 m = 10.4 Nm

FR = 345 N

FR = 345 N 600 N

0.03 m

T = 520 N * 0.03 m = 15.6 Nm

FR = 520 N

Size of Muscle Force Affects Torque

WholeMuscle

FR = 345 N 400 N

0.03 m

T = 345 N * 0.03 m = 10.4 Nm

FR = 345 N

400 N

0.1 m

FR = 345 N T = 345 N * 0.1 m = 34.5 Nm

Moment Arm Affects Torque

WholeMuscle

Calculation of Muscle Torque

60o

400 N

0.03 m

Fm Fm

Fm

FmFm

Fm

60o

NOTE: The torque created by the muscle depends on1) the size of the muscle force2) the angle at which the muscle pulls3) the distance that the muscle attaches away from joint axis

WholeMuscle

Factors Affecting Torque

Changing any of these 3 factors will change the torque:

1) muscle force - changed by increased neural stimulation

2) d - can’t change voluntarily but use of other muscles insame functional muscle group gives a different d

3) - this changes throughout the ROM

WholeMuscle

Additional Factors Affecting Torque

Muscle Force1) level of stimulation2) muscle fiber type3) PCSA 4) velocity of shortening5) muscle length

Angle of pullMoment arm

WholeMuscle