Body Mechanics and Physiology in Function

Body Mechanics and Physiology
in Function

The wider the base of support and the lower the center of
gravity, the greater is the stability of the object.

The equilibrium of an object is maintained as long as the
line of gravity passes through its base of support.

Equilibrium is maintained with least effort when the
base of support is broadened in the direction in which
movement occurs.

Stooping with hips and knees flexed and the trunk in good
alignment distributes the work load among the largest
and strongest muscle groups and helps to prevent back
strain

The stronger the muscle group, the greater is the work it
can

Using a larger number of muscle groups for an activity
distributes the work load.

Keeping center of gravity as close as possible to the center
of gravity of the work load to be moved prevents
unnecessary reaching and strain on back muscles

Pulling an object directly toward (or pushing directly away
from) the center of gravity prevents strain on back and
abdominal muscles.

Facing the direction of movement prevents undesirable
twisting of spine

Pushing, pulling, or sliding an object on a surface requires
less force than lifting an object, as lifting involves moving
the weight of the object against the pull of gravity.

Moving an object by rolling, turning, or pivoting requires
less effort than lifting the object, as momentum and
leverage are used to advantage.

Using a lever when lifting an object reduces the amount of
weight lifted.

The less the friction between the object moved and
surface on which it is moved, the smaller is the force
required to move it.

Moving an object on a level surface requires less effort
than moving the same object on an inclined surface
because the pull of gravity is less on a level surface.

Working with materials that rest on a surface at a good
working level requires less effort

Contraction of stabilizing muscle preparatory to activity
helps to protect ligaments and joints from strain and
injury.

Dividing balanced activity between arms and legs protects
the back from strain

Variety of position and activity helps maintain good
muscle tone and prevent fatigue.

Alternating periods of rest and activity helps prevent
fatigue

Is stability restrain or control?
Your greatest stability is in your mobility.

When you lose the harmony between stability and
mobility you increase your injury potential

Why do people compensate the way they compensate?
The further the attachment from the joint, the more
control / influence it has on the joint

The bigger the force arm the better mechanical
advantage you have. This applies for muscles, ligaments
and tendons, how it attaches (degree of angle)

When the attachment is close to the joint, it is less able to
have control on that joint. When you jam up the pelvis
you screw up the Sacro tuberous ligament, what causes
increased tension on the hamstring muscles.

The main function of the Sacro tuberous ligament is to
stabilize the pelvic girdle and limits upward tilting of the
sacrum and rotation of the pelvis.

Why is one side the muscles bigger than the other side?
Or why is the one side with the smaller muscles smaller in
size. What does it have to do so badly to get to that
size.!!!

Physiological characteristics of a muscle issues leads to
variations in force of contraction.

Recruitment is a Mechanical concept.
The more motor units involved, the more force and the
better the cycle.

Muscle Unit (1) Individual motor axons branch within
muscles to synapse on many different fibres that are
typically distributed over a relatively wide area within the
muscle, presumably to ensure that the contractile force
of the motor unit is spread evenly. this arrangement
reduces the chance that damage to one or a few α
motor neurons will significantly alter a muscle's action.
Because an action potential generated by a motor
neuron normally brings to threshold all of the muscle
fibres it contacts, a single α motor neuron and its
associated muscle fibres together constitute the smallest
unit of force that can be activated to produce
movement.

Muscle Unit (2) Both motor units and the α motor
neurons themselves vary in size. Small α motor neurons
innervate relatively few muscle fibers and form motor
units that generate small forces, whereas large motor
neurons innervate larger, more powerful motor units.
Motor units also differ in the types of muscle fibers that
they innervate. In most skeletal muscles, the small motor
units innervate small “red” muscle fibers that contract
slowly and generate relatively small forces; but, because
of their rich myoglobin content, plentiful mitochondria,
and rich capillary beds, such small red fibers are resistant
to fatigue. These small units are called slow (S) motor
units and are especially important for activities that
require sustained contraction.

Muscle Unit (3) Larger α motor neurons innervate larger,
pale muscle fibres that generate more force; however,
these fibres have sparse mitochondria and are therefore
easily fatigued.
These units are called fast fatigable (FF) motor units and
are especially important for brief exertions that require
large forces, such as running or jumping.
A third class of motor units has properties that lie
between those of the other two.
These fast fatigue- resistant (FR) motor units are of
intermediate size and are not quite as fast as FF units.

Muscle Unit (4) These distinctions among different types
of motor units indicate how the nervous system
produces movements appropriate for different
circumstances.
In most muscles, small, slow motor units have lower
thresholds for activation than the larger units and are
tonically active during motor acts that require sustained
effort (standing, for instance).
The threshold for the large fast motor units is reached
only when rapid movements requiring great force are
made, such as jumping.
The functional distinctions between the various classes of
motor units also explain some structural differences
among muscle groups

Slow Oxidative Muscle Fibre - Capacity to develop tension is
variable, because the nature of the fibre type -Predominate fibre -
Postural fibre -Low force/power/ and speed production -High
endurance -Large amount of myoglobin -Many mitochondria and
blood capillaries

Motor Unit (5) A motor unit is all the motor
fibers it innervates, it’s the all or non-principle.
Maximum strength is when all motor unit’s fire at
once, a safety mechanism stops you from
utilizing all motor units
Fast Oxidative Muscle Fiber
- Fibers are red
- Very high capacity for generating ATP by
oxidative metabolic processes, and split ATP
at a very rapid rate
- Fast contraction velocity
- Resistant to fatigue

Fast Glycolytic Muscle Fiber
-Recruited for very short duration at a high
intensity bust of power
-Contain low content of myoglobin
-Contain relatively few mitochondria
-Contain relatively few blood capillaries
-Contain large amount of glycogen
-White muscle fiber
-Geared to generate ATP anaerobic metabolic
processes

Fast Glycolytic Muscle Fiber -Not able to supply skeletal
muscle fiber continuously with sufficient ATP and fatigue
easily .Split ATP at high rate and have a fast contraction
velocity

Roles in which muscle(s) act - What is the function of a
given muscle if it is activated, what will happen? such
questions cannot be answered directly or exactly,
because many variable factors can regulate, modulate
the result of musculoskeletal contraction.

Depending on the circumstance, a muscle act in one or
several ways.

When a muscle fiber or a whole muscle contracts, it tends
to shorten. If it does shorten is another matter, but it will
tend to.

If it tends to shorten but can’t, it will be something
isometric static contraction happening.

If it tends to shorten depends on numerous of things, it
can even lengthen when it tends to shorten (eccentric
contraction)

When a muscle contracts it tends to do all of its possible
actions. When a muscle crosses a joint it tends to do all of
its possible action.

What does it tend to do on that system?
Both those levers tend to move and come closer
together, not one of them but both of them.
Only one of them will, if something modulates/ happens
to the other lever something comes in and plays havoc,
and then you will have only one of them moving.
If that happens, they both will go in.
If the angle is different, they both will twist and buckle
around, all depending on the angle of pull.

When a particular muscle contract
It tends to pull both ends toward the center
If neither of the bones to which a muscle is attached are
stabilized then both bones move toward each other upon
contraction
More commonly one bone is more stabilized by a variety
of factors and the less stabilized bone usually moves
toward the more stabilized bone upon contraction
Knowing pattern of muscle fascicle pattern/ line of pull, it
tend to want do everything.
So to change what eventuate you have to modulate, so it
does only one thing, the muscle doesn’t do it by itself, it
only creates tension, that’s all it can do.

Some muscles cross more than one joint and in
pretention create movement in all those joints.
Because the muscle can only pull it ends
together, it ends together towards it’s center
contraction will always tend to move all of it’s
joint movements.
Most muscles you come across are not single
muscles, but multi type joint muscles, and some
are even multi, multi type joint muscles.

Multi type muscles have the ability to effect
numerous joints at any time they contract and
that create great complexities.
You need to understand the complexities of that
and can understand that some will be optimal
and some wouldn’t be optimal, and that non-
optimal will be hurting you and causes issues.

What a muscle can do or could do is no indication about
what it will do.
Sometimes a motor program in the brain doesn’t activate
a muscle, which would help in a given moment.

When the gluteus maximus contract one of its tendencies
is hip extension. Angle of pull of gluteus maximus does a
lot of other things too, it has the capacity of doing that, it’s
not ordinary turned on during hip extension and walking

The force exerted by another muscle or by an outside
force can prevent the muscle one or all of its possible joint
movement.

Most people when walking tend not to utilize their glutes,
hamstring use in hip extension, unless you are
mechanically perfect orientated.

Roles in which muscle acts, most of us what utilize the
hamstrings only will be much tighter in the hamstrings,
because they are working harder throughout the day and
during their lift.
The reason for that is, the mechanical priors, the system
driving that requires the hamstring to be more reliant on,
and the glutes harder to utilize.

A posteriorly tilted pelvis make it hard to utilize the glutes,
you have changed the attachment sides relative to the
hip joint.
You have an orientation change, you have reduced the
length of the gluteus maximus.
When you bring one attachment closer, you have
shortened it, it becomes less effective to contract now.
A shortened muscle becomes less effective to contract
now, from a mechanical point of view,
Made it really ineffective to do hip extensions, so now the
hamstrings have to do most of the work, what makes it
very hard to harbor the glutes

Even walking up the stairs, it often times get worse
because you get more posteriorly rotation and it
becomes even worse
In a topline athlete you will never see a posterior rotated
pelvis, you will see good working glutes and you will see
that it works with walking.
Why? Because it has a more powerful angle of pull to
work across the thigh muscle, it will because it can.

A hamstring has to work because it has to, if it shouldn’t
be, that is neither here or there, it does it because it has
to.
At the end of the day it become tighter and tighter, it’s
driven by mechanics, mechanics rules here.
There is a law here, if a bigger muscle can do the job
better than a smaller muscle, the bigger muscles will do
it easier.
Just because you know glutes does hip extension, it
doesn’t mean that they will do that in that case.
The Mechanical prior is different from one person to
another and indicates how muscles behave, it has
nothing to do with your neural input, Mechanics is
running it.

You want to have your glutes contracting, but you can’t,
because they are not in the position to do it, because
Mechanics doesn’t let them.

You should move around with a better pelvic orientation
and that should be maintained.

What to do with abdominal strength when you can’t use
it. It doesn’t protect your back, because it doesn’t. The
transverse abdominis is a dynamic performance muscle
in rotational movements.

Mechanical orientation differentiation from one person to
another is going to dictate how the muscle is going to
function, dynamically and postural rotational movements.

How can you stop from muscles behaving badly?
Maybe you have to change Mechanics if Mechanics rules
so much.

How you going to change how the link system all work
together and get it all working optimally and then the
muscles will behave themselves.
.

Shape of Muscles & Fiber Arrangement
Muscles have different shapes & fiber arrangement
Shape & fiber arrangement affects
Muscle’s ability to exert force
Range through which it can effectively exert force onto
the bones
Cross section diameter
Factor in muscle’s ability to exert force
Greater cross section diameter = greater force exertion

Longer muscles can shorten through a greater range
More effective in moving joints through large ranges of
motion
2 major types of fiber arrangements
– Parallel & pennate
– Each is further subdivided according to shape
Parallel muscles
Fibers arranged parallel to length of muscle produce a
greater range of movement than similar sized muscles
with pennate arrangement

Fiber Arrangement – Parallel
Flat muscles
Usually thin & broad, originating from broad, fibrous,
sheet-like aponeuroses
A
llows them to spread their forces over a broad area – Ex.
rectus abdominus & external oblique
Fusiform muscles
Spindle-shaped with a central belly that tapers to tendons
on each end
Allows them to focus their power onto small, bony targets
. Ex. brachialis, biceps brachii

Strap muscles
- More uniform in diameter with essentially all fibers
arranged in a long parallel manner
- Enables a focusing of power onto small, bony targets –
Ex. Sartorius
Radiate muscles
- Also described sometimes as being triangular, fan-
shaped or convergent
- Have combined arrangement of flat & fusiform
- Originate on broad aponeuroses & converge onto a
tendon – Ex. pectoralis major, trapezius

Sphincter or circular muscles
- Technically endless strap muscles
- Surround openings & function to close them upon
contraction – Ex. orbicularis orris surrounding the
mouth
Pennate muscles
- Have shorter fibers
- Arranged obliquely to their tendons in a manner
similar to a feather
- Arrangement increases the cross-sectional area of the
muscle, thereby increasing the power

Unipennate muscles
- Fibers run obliquely from a tendon on one side only.
Ex. biceps femoris, extensor digitorum longus, tibialis
posterior
Bipennate muscle
- Fibers run obliquely on both sides from a central
tendon Ex. rectus femoris, flexor halluces longus
Multipennate muscles
- Have several tendons with fibers running diagonally
between them • Ex. Deltoid
- Bipennate & unipennate produce strongest contraction

Muscle Tissue Properties
Skeletal muscle tissue has 4 properties related to its
ability to produce force & movement about joints
– Irritability or excitability
– Contractility
– Extensibility
– Elasticity

Irritability or Excitability - property of muscle being
sensitive or responsive to chemical, electrical, or
mechanical stimuli
Contractility - ability of muscle to contract & develop
tension or internal force against resistance when
stimulated
Extensibility - ability of muscle to be passively stretched
beyond its normal resting length
Elasticity - ability of muscle to return to its original length
following stretching

Muscle contractions can be used to cause,
control, or prevent joint movement or
- To initiate or accelerate movement of a body
segment
- To slow down or decelerate movement of a
body segment
- To prevent movement of a body segment by
external forces

Isotonic contractions involve muscle developing
tension to either cause or control joint movement
Dynamic contractions
The varying degrees of tension in muscles result in
joint angles changing
Isotonic contractions are either concentric or
eccentric on basis of whether shortening or
lengthening occurs

Isometric contraction
Tension is developed within muscle but joint
angles remain constant
Static contractions
Significant amount of tension may be developed
in muscle to maintain joint angle in relatively static
or stable position
May be used to prevent a body segment from
being moved by external forces

Movement may occur at any given joint without any
muscle contraction whatsoever. Referred to as passive
Solely due to external forces such as those applied by
another person, object, or resistance or the force of
gravity in the presence of muscle relaxation
Concentric contraction
- Muscle develops tension as it shortens
- Occurs when muscle develops enough force to
overcome applied resistance
- Causes movement against gravity or resistance
- Described as being a positive contraction

Eccentric contraction (muscle action)
- Muscle lengthens under tension
- Occurs when muscle gradually lessens in tension to
control the descent of resistance
- Weight or resistance overcomes muscle contraction but
not to the point that muscle cannot control descending
movement
- Controls movement with gravity or resistance
- Described as a negative contraction
- Force developed by the muscle is less than that of the
resistance

Eccentric contraction (muscle action)
- Causes body part to move with gravity or external
forces (resistance)
- Used to decelerate body
- Results in the joint angle changing in the direction of
the resistance or external force
Isokinetic - a type of dynamic exercise using concentric
and/or eccentric muscle contractions
Speed (or velocity) of movement is constant
Muscular contraction (ideally maximum contraction)
occurs throughout movement

Agonist muscles
- Cause joint motion through a specified
plane of motion when contracting
concentrically
- Known as primary or prime movers, or
muscles most involved

Antagonist muscles
- Located on opposite side of joint from agonist
- Have the opposite concentric action
- Known as contralateral muscles
- Work in cooperation with agonist muscles by
relaxing & allowing movement
- When contracting concentrically perform the
opposite joint motion of agonist

Stabilizers
- Surround joint or body part
- Contract to fixate or stabilize the area to
enable another limb or body segment to exert
force & move
- Known as fixators
- Essential in establishing a relatively firm base
for the more distal joints to work from when
carrying out movements

Synergist
- Assist in action of agonists
- Not necessarily prime movers for the action
- Known as guiding muscles
- Assist in refined movement & rule out
undesired motions

Neutralizers
- Counteract or neutralize the action of another
muscle to prevent undesirable movements
such as inappropriate muscle substitutions
- Referred to as neutralizing
- Contract to resist specific actions of other
muscles

Muscles with multiple agonist actions attempt to
perform all of their actions when contracting
Cannot determine which actions are appropriate
for the task at hand
Actions actually performed depend upon several
factors
- The motor units activated
- joint position
- Muscle length
- Relative contraction or relaxation of other
muscles acting on the joint

Lines of Pull Consider the following
1. Exact locations of bony landmarks to which
muscles attach proximally & distally and their
relationship to joints
2. Planes of motion through which a joint is
capable of moving
3. Muscle’s relationship or line of pull relative to
the joint’s axes of rotation
4. As a joint moves the line of pull may change &
result in muscle having a different or opposite
action than in the original position

Lines of Pull Consider the following
5. Potential effect of other muscles’ relative
contraction or relaxation on a particular muscle’s
ability to cause motion
6. Effect of a muscle’s relative length on its ability
to generate force
7. Effect of the position of other joints on the
ability of a bi-articular or multi-articular muscle to
generate force or allow lengthening

Neural control of voluntary movement
Muscle contraction result from stimulation by the nervous
system

Every muscle fiber is innervated by a somatic motor
neuron which, when an appropriate stimulus is provided,
results in a muscle contraction.

The nervous system 'communicates' with muscle via
neuromuscular (also called myoneural) junctions. (A)
The impulse arrives at the end bulb
Chemical transmitter is released from vesicles (each of
which contains 5,000 - 10,000 molecules of acetylcholine)
and diffuses across the neuromuscular cleft
The transmitter molecules fill receptor sites in the
membrane of the muscle & increase membrane
permeability to sodium.
Sodium then diffuses in & the membrane potential
becomes less negative, and, if the threshold potential is
reached, an action potential occurs, an impulse travels
along the muscle cell membrane, and the muscle
contracts.

The nervous system 'communicates' with muscle via
neuromuscular (also called myoneural) junctions. (A)
The synapse is a specialized structure that allows one
neuron to communicate with another neuron or a muscle
cell.
There are billions of nerve cells in the brain and each
nerve cell can make and receive up to 10,000 synaptic
connections with other nerve cells.
Also, the strength of the synapse is modifiable.
Changes in the strength of synapses endow the nervous
system with the ability to store information

Steps in neuromuscular transmission:
1) Nerve action potential.
2) Calcium entry into the presynaptic terminus.
3) Release of Ach quanta.
4) Diffusion of Ach across cleft.
5) Combination of Ach with post-synaptic receptors and
Ach breakdown via esterase.
6) Opening of Na+/K+ channels (cation channels).
7) Postsynaptic membrane depolarization (EPP).
8) Muscle action potential

Neural control of voluntary movement
The stimulus may be processed in varying degrees at
different levels of the central nervous system (CNS) which
may be divided into five levels of control
– cerebral cortex
– basal ganglia
– cerebellum
– brain stem
– spinal cord

Cerebral cortex
- Highest level of control
- Provides for the creation of voluntary
movement as aggregate muscle action, but not
as specific muscle activity
- Interprets sensory stimuli from body to a
degree for determine of needed responses

Basal ganglia
- The next lower level
- Controls maintenance of postures &
equilibrium
- Controls learned movements such as driving a
car
- Controls sensory integration for balance &
rhythmic activities

Cerebellum
- A major integrator of sensory impulses
- Provides feedback relative to motion
- Controls timing & intensity of muscle activity to
assist in the refinement of movements
Brain stem
- Integrates all central nervous system activity
through excitation & inhibition of desired
neuromuscular functions
- Functions in arousal or maintaining a wakeful
state

Spinal cord
- Common pathway between CNS & PNS
- Has the most specific control
- Integrates various simple & complex spinal
reflexes
- Integrates cortical & basal ganglia activity with
various classifications of spinal reflexes

Functionally
- PNS is divided into sensory & motor divisions
- Sensory or afferent nerves bring impulses from
receptors in skin, joints, muscles, & other
peripheral aspects of body to CNS
- Motor or efferent nerves carry impulses to
outlying regions of body from the CNS

Efferent nerves further subdivided into
- Voluntary or somatic nerves which are under
conscious control & carry impulses to skeletal
muscles
- Involuntary or visceral nerves, referred to as
the autonomic nervous system (ANS) which
carry impulses to the heart, smooth muscles,
and glands

Neurons (nerve cells) - basic functional units of
nervous system responsible for generating &
transmitting impulses and consist of
- A neuron cell body
- One or more branching projections known as
dendrites which transmit impulses to neuron &
cell body
Axon - an elongated projection that transmits
impulses away from neuron cell bodies

Neurons are classified as one of three types according to
the direction in which they transmit impulses
– Sensory neurons
– Motor neurons
– Interneurons
Sensory neurons transmit impulses to spinal cord & brain
from all parts of body
Motor neurons transmit impulses away from the brain &
spinal cord to muscle & glandular tissue
Interneurons are central or connecting neurons that
conduct impulses from sensory neurons to motor neurons

Proprioception & Kinesthesis
- Activity performance is significantly dependent upon
neurological feedback from the body
- We use various senses to determine a response to our
environment
- Seeing when to lift our hand to catch a fly ball
Taken for granted are sensations associated with
neuromuscular activity through proprioception.

Proprioceptors - internal receptors located in
skin, joints, muscles, & tendons which provide
feedback relative to tension, length, &
contraction state of muscle, position of body &
limbs, and movements of joints
Interneurons - are central or connecting neurons
that conduct impulses from sensory neurons to
motor neurons

Proprioceptors work in combination with other
sense organs to accomplish kinesthesis
Kinesthesis – conscious awareness of position &
movement of the body in space
Proprioceptors specific to muscles
– Muscles spindles
– Golgi tendon organs (GTO)

Proprioception
Subconscious mechanism by which body is able
posture & movement by responding to stimuli
originating in proprioceptors of the joints,
tendons, muscles, & inner ear

Muscle spindles
- Concentrated primarily in muscle belly between
the fibers
- Sensitive to stretch & rate of stretch
- Insert into connective tissue within muscle &
run parallel with muscle fibers
- Spindle number varies depending upon level of
control needed
Ex. Greater concentration in hands than thigh

Muscle spindles & myostatic or stretch
reflex
1. Rapid muscle stretch occurs
2. Impulse is sent to the CNS
3. CNS activates motor neurons of muscle and
causes it to contract
Stretch reflex may be utilized to facilitate a greater
response
– Ex. Quick short squat before attempting a jump
– Quick stretch placed on muscles in the squat
enables the same muscles to generate more
force in subsequently jumping off the floor

Golgi tendon organ
- Found serially in the tendon close to muscle
tendon junction
- Sensitive to both muscle tension & active
contraction
- Much less sensitive to stretch than muscles
spindles
- Require a greater stretch to be activated

Tension in tendons & GTO increases as muscle
contract, which activates GTO
1. GTO stretch threshold is reached
2. Impulse is sent to CNS
3. CNS causes muscle to relax
4. Facilitates activation of antagonists as a
protective mechanism
GTO protects us from an excessive contraction by
causing its muscle to relax

Quality of movement & reaction to position
change is dependent upon proprioceptive
feedback from muscles & joints
Proprioception may be enhanced through
specific training

Body Mechanics and Physiology in Function

Body Mechanics and Physiology in Function

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