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Muscle
What are muscles?

Machines
– purpose of machines is to help us do work.
Characteristics of Muscle Tissue
Extensibility
 Elasticity
 Contractility
 Irritability
 Amplitude
 Viscosity

What is a muscle contraction?
Types of Contractions

Concentric Contraction

Static Contraction

Eccentric Contraction

Isometric and Isotonic Contractions
Concentric Contractions

development of tension within a muscle
with consequent shortening of the muscle.

the movement is caused by the muscle.
Static Contraction

development of tension within a muscle
with no change in the overall muscle length.

goal is usually to maintain a position.
Eccentric Contraction

development of tension within a muscle
resulting in lengthening of the muscle.

movement is caused by another force

contracting muscle tries to control the
movement.
Mechanical Factors
determining specific movements
structure of the joint or joints muscle
crosses
 the orientation of the muscle’s line of pull to
the axis or axes around which movement is
permitted

Line of Pull

the direct line between the centers of the
muscle’s attachments

one origin, one insertion

one origin, multiple insertions
Mechanical Axis
the straight line drawn connecting the
centers of the joints at each end of the
specific bone, or
 from the center of the joint where the
movement is occurring to the center of the
distal end of the limb, if the limb is moving
as a unit

Axis of Rotation

the angle formed by the line of pull and the
mechanical axis.
Muscle Roles
Individual muscles take on a variety of roles
at different times and under different
circumstances.
 there are six roles a muscle can assume

Muscles and their Roles
Muscles are not selective when stimulated
to contract.
 Resulting actions are partially determined
by functions performed by other muscles
attendant to the agonist.

Muscle Roles
Agonist
 Antagonist
 Fixator
 Regulator
 Neutralizer
 Synergist

Agonist
Prime Mover
 causes a concentric contraction

Antagonist
refers to a muscle whose function is
opposite to that of some muscle tending to
cause a movement.
 Three different functions:

– relax throughout the movement
– relax initially, but contract toward the end of
the movement to prevent injury
– contract throughout the movement
Fixator
any muscle that contracts to anchor or
steady the position of a particular bone
 Two categories of fixators:

– Stabilizing role – Supporting role -
Regulator

used to identify a muscle contracting
eccentrically to control a movement caused
by an external force.
Neutralizer
acts to prevent the undesired action of
another contracting muscle without
interfering with the desired function of that
other muscle
 two types

– mutual neutralizer – true neutralizer -
Synergist
usually assigned to the synchronous action
of two joint muscles
 2 types

– Concurrent pattern – Countercurrent pattern -
Control of Movement
Coordination is an orchestrated sequencing
of binary impulses
 Reciprocal Innervation (Sherrington’s
Principle)

– inhibition of one member of antagonistic pair

Corollary
– inhibition of muscle is inhibited
Conditions for Co-contraction
when an exact amount of tension or
accurate placement of a limb is needed
 deceleration of limb
 to stabilize the wrist for precise hand
movements or for a powerful grip

Ballistic Movements

Three phases:
– Acceleration– Inertial– Deceleration-
Ballistic Movements
muscle initially contracts to move the limb,
but then the limb is carried through space
due to momentum
 antagonistic muscles fire to slow down the
speeding limb

Stretch Reflex
occurs in skilled ballistic movements
 muscle is stretched quickly, resulting in a
stronger contraction

Olson’s Principles

Dealt with free weights only and
considered:
– direction of movement relative to the line of
gravity
– the type of contraction
– the muscle group used
Olson’s 1st Principle

If the movement is against the line of
gravity:
– the muscle causes the movement
– the contraction is concentric
– the muscle group that should perform the
action, performs the action
Olson’s 2nd Principle

If the movement is through the line of
gravity:
– the muscle causes the movement
– the contraction is concentric
– the muscle group that should perform the
action, performs the action
Olson’s 3rd Principle

If the movement is toward the line of
gravity:
– the resistance causes the movement
– the contraction is eccentric
– the muscle group that is opposite to the joint
movement acts to control the movement
Ulibarri’s Corollaries to
Olson’s Principles

These corollaries restate Olson’s Principles
relative to the:
– direction of the weight (resistive force)
– type of muscle contraction
– muscle group used
Ulibarri’s 1st Corollary

If the weight (resistive force) moves against
the line of gravity:
– the muscular force causes the movement
– the contraction is concentric
– the muscle group that should do the action,
performs the action
Ulibarri’s 2nd Corollary

If the weight (resistive force) moves toward
the line of gravity:
– the resistive force causes the movement
– the contraction is eccentric
– the muscle group that is opposite to the joint
action acts to control the movement