Download Human Muscular System

Human Muscular System
Common Characteristics
 Excitability
- receives & responds to
nerve impulses
 Contractility - can shorten, thicken &
generate force
 Extensibility - can be stretched
 Elasticity - returns to original shape
after contraction or stretch
Skeletal Muscle
Composition
 Basic
unit - Muscle cell (fiber); can
be up to 70 cm long
» bound together to form a fascicle
» fascicles bound together to form entire
muscle
» layer of tough connective tissue
surrounds each “level”
» this tough tissue extends beyond the
muscle as a tendon
Terminology of Muscle
Action
 Prime
mover - contributes the most
to the movement
 Synergist - assists the prime mover
 Agonist - same as prime mover
 Antagonist - opposes the agonist
 Agonist/Antagonist Patterns
» flexors / extensors
» adductors / abductors
» medial / lateral rotators
» etc . . .
Terminology of Muscle
Contraction
3
Types of skeletal muscle contraction
» Isometric - “no movement”
equal opposition of agonist/antagonist OR
 immovable weight

» Concentric - shortening contraction of muscle
with “expected” osteokinematic motion
» Eccentric - lengthening contraction of muscle
for “controlling” the opposite osteokinematic
motion; such as controlled lowering of
forearm against gravity (brachialis)
Muscle Contraction related
to Exercise
 Isometric
exercise
» no movement (immovable weight or end of
AROM)
» isometric contraction
 Isotonic
exercise
» “same weight”, ex. Free weights
» muscle contraction force varies as
direction of object movement changes
relative to the gravity line
» speed of movement can vary
» concentric or eccentric contractions
 Isokinetic
Exercise
» accommodating/variable resistance
 muscle force production can stay at max
because the machine will accommodate to the
force output
» “same speed of movement”
» concentric or eccentric contractions
» why does muscle force production vary
at different parts of the AROM?
Physical Factors Impacting
Muscle Force Production
 Age
 Gender
 Speed
of Contraction
 Type of Contraction
 Length - Tension Relationship
AGE
 Strength
peaks between age 20
& 40 years of age
» with aging comes a decrease in the
number of muscle fibers (results in
decreased mass & strength)
 Loss
of muscle fibers & ms mass
by
decade of life
 Fiber type changes: less Type II
6th
GENDER
 males
have greater strength than
females after onset of puberty
 greatest difference in muscle strength
between genders is ages 30 - 50.
 Differences due primarily to greater
muscle mass
» males can have up to 50% more muscle
mass than females. Male and female
muscle produce the same amount of force
per cross-sectional area.
SPEED OF CONTRACTION
 With
concentric contractions,
maximal force production
decreases with increasing speed
of contraction (ie. force
production decreases with faster
movement)
TYPE OF CONTRACTION
 Maximal
contraction force can be
produced with eccentric
contraction, followed by
isometric and then concentric.
Theoretic forcevelocity curve of an
activated muscle is
shown. Concentric
activation is shown
on the right and
eccentric activation
on the left. Isometric
activation occurs at
the zero velocity
point on the graph.
LENGTH – TENSION
RELATIONSHIP
The force that a muscle can generate is
dependent on the number of cross bridges
that can be formed during contraction.
 This is dependent on the amount of overlap
of actin & myosin in a muscle fiber.
 The amount of overlap is dependent on
muscle length (ie. the position of the muscle
as related to it's range of excursion).

Length-Tension . . .
Example: the maximally lengthened position
for the brachialis is full extension of the elbow
& the maximally shortened position is full
elbow flexion.
 The length at which a muscle can produce it
maximal force or tension is called the optimal
length. This is the length at which the actin &
myosin can form the most cross bridge links.
At lengths shorter or longer than the optimal
length, a muscle cannot develop its maximal
force when stimulated to contract.

Active Insufficiency
 is
the decreased force production of
a muscle when the muscle
attachments are either too close OR
too far apart (puts the sarcomeres in
the ascending or descending parts of
the length-tension curve).
 Most common in two-joint muscles
 Examples . . . .
Passive Insufficiency
 When
the ANTAGONIST MUSCLE is
being STRETCHED by contraction of
the AGONIST, the PASSIVE STRETCH
may become too great and limit joint
motion
 Occurs primarily in two-joint muscles
 May cause movement at some joints
crossed by the muscles
» Examples . . .
Why max eccentric contraction is the
greatest of all?
A generalized passive
length-tension curve is
shown. As a muscle is
progressively stretched,
the tissue is slack during
its initial shortened
lengths until it reaches a
critical length where it
begins to generate
tension. Beyond this
critical length, the
tension builds as an
exponential function.