Occupational Therapy Optimizing abilities and capacities

Occupational Therapy
Optimizing Abilities and Capacities

Three capacities necessary for performing physical activity
- Range of Motion
- Strength
- Endurance
Occupational Therapist helps client improve these basic
capacities as a preparatory means for developing higher level
skills needed for the performance of everyday activities or
occupations
The underlying biomechanical and physiological principles
that pertain to motion, strength, and endurance are the
building blocks upon which treatment for physical
dysfunction is built.

The principles that are applied to the remediation of
impairments for acute injuries; the prevention of illnesses
and conditions caused by repetitive motion, cumulative
trauma, or poor biomechanics ; and as compensation for or
adaptation to chronic disability
Biomechanics is broken down into static and dynamic
systems, and the dynamic system can be further broken down
as kinematics and kinetics.
Kinematics analysis describes human motion in relation to
the location and the direction of the movement, the
magnitude and velocity of the motion, and the type of motion
that is occurring such as translator or rotary motion.

Kinematic analysis of movement involves the measurement of
position, velocity, and acceleration of one or more body parts.
Linear measurements of specific parts, angular
measurements at joints, or a combination can be performed
in order to quantify the special and temporal properties of
movements of multiple body parts simultaneously.

Kinematic assessment can also be used to identify bilateral
differences in upper and lower extremity movement.
Kinematic assessment involves using media such as video
cameras, high-speed video, or three-dimensional motion
analysis systems, with markers on the body to be tracked
through the movement.
Using this tracked data in either two-dimensional or three-
dimensional space, joint and body segment positions,
velocities, and accelerations can be calculated and compared
between sides of the body.

Closed Kinematic Chain
- When the motion of one joint directly affects motion at
another joint, it is considered a closed kinematic chain.
- To visualize this, picture a person squatting down to pick
up a heavy box. The feet are solid on the ground, locking
the position of the foot.
- The person, with correct body mechanics, bends his or her
knees to reach the box. As the person gets lower, both the
ankles and the hips must change their angles to allow
motion to occur.

- These joint movements are linked together and can be
predicted based on the movements necessary to perform the
action.

- Looking at these movements allows the therapist to note
any kind of compensation that may need to be made
because of a limiting factor, injury, or pain.
- Ideally, in the squatting motion, the back should remain
straight and hips, knees, and ankles should travel along
the same plane.
- If there is a restriction in the knee, the hip, or the ankle,
the body will make a minor adjustment to allow the
motion to occur.
- If the medial aspect of the knee is sore it may pry
outward, causing the toes to turn out during the motion.

Open Kinematic Chain
- Open kinematic chains are noted at the ends of the limbs
or at the joint where it is free to move without causing
motion at another joint.
- This can be easily observed by sitting in a chair and
extending the knee.
- When a person is sitting and is asked to tighten the
quadriceps to extend his or her knee, the only joint that is
moving is the knee joint.
- Motion of the ankle and hip do not need to change their
angles to allow knee extension to occur.

Open Kinematic Chain
- The open chain allows joints to function independently
from each other.
- The joints above and below the moving joint do not need to
compensate and their motions are not predictable.
- These joints have freedom to move or stabilize the joint
without affecting the action of the other.
- Open chains can be beneficial to help pinpoint pain,
discomfort, and potential injuries or restrictions.
- Open kinematic chains do not represent most motions in
the activities of daily living

Musculoskeletal System: Biomechanical Aspect
Kinematic analysis: Describes the amount and direction of
movement, speed, and acceleration of body segments and joint
angles
Kinetics: Addresses the forces the cause motion or maintain
stability
Torque: Tendency of a force to produce rotation about an axis
Lever systems: Effort is the force that causes movement and
resistance is the force that tends to keep the object moving
- First-class lever
- Second-class lever
- Third-class lever

Kinetics: is a description of motion with regards to the forces
that cause motion. The forces that provide movement or
stability are both internal and external to the body.
Internal force consists of muscle contractions that enable us
to engage in our daily occupations or the elasticity of
structural and connective tissue that prevent unwanted
movement
Nearly all purposeful activity can be broken down into a
series of coordinated movements. Understanding the different
types of movement and forces behind the motion helps
therapist design the most effective exercise programs and
structure therapeutic occupation.

Dynamic joint stiffness is defined as the dynamic relation
between the angular position of a joint and the torque acting
about it.
It determines the resistance of the joint to external
perturbations before voluntary interventions in postural tasks
and the properties of the load and actuator that the central
nervous system must control to perform movements

Studying joint stiffness is significant for a number of reasons:
- It provides valuable functional insight into the
neuromuscular system
- It helps in diagnosis, assessment, treatment prescription
and monitoring of neuromuscular diseases that change
muscle tone
- Quantitative characterization of stiffness is important in
the design of rehabilitation devices to restore lost limb
functions

Torque is the tendency of a force to produce rotation about an
axis.
In rotary movements, torque depends on:
- The amount of force applied
- The distance of the force from the axis of movement
(moment arm)
Torque is equal to the magnitude of a force times the
perpendicular distance between the line of force and the axis
of rotation.
The concept of torque explains why the placement of an
object either closer to or farther from the axis of rotation
changes the effort needed to make the movement, even tough
the object’s weight remains constant.

Rotational inertia
- Rotational inertia is a property of any object which can be
rotated.
- It is a scalar value which tells us how difficult it is to
change the rotational velocity of the object around a given
rotational axis.
- Rotational inertia plays a similar role in rotational
mechanics to mass in linear mechanics. Indeed, the
rotational inertia of an object depends on its mass. It also
depends on the distribution of that mass relative to the axis
of rotation.

Rotational inertia
- When a mass moves further from the axis of rotation it
becomes increasingly more difficult to change the
rotational velocity of the system.
- Intuitively, this is because the mass is now carrying more
momentum with it around the circle (due to the higher
speed) and because the momentum vector is changing
more quickly. Both of these effects depend on the distance
from the axis

The skeletal system
- The skeletal system consists of 206 bones of strikingly
varying shapes, sizes, and functions. More than with any
other organ, the specific shapes and sizes of these bones
are crucial to their functions of providing levers for
movement and protection of soft tissues.
- Despite the striking diversity of the sizes and shapes of
individual bones, all bones form through one of two
distinct processes: endochondral bone formation, used for
the generation of most bones, and intramembranous bone
formation, used to form the flat bones of the skull and
parts of several other bones.

The skeletal system
- In each of these processes, local paracrine signals and
systemic hormonal signals trigger characteristic
transcription programs and activation of kinase cascades
that orchestrate the generation of the skeleton.

Levers and Torque
- The skeletal system provides the levers and axes of
rotation about which the muscular system generates
movement.
- A lever is a simple machine that magnifies the force or
speed of movement, or both.
- The levers are primarily the long bones of the body, and
the axes are the joints where the bones meet. Human
skeletal levers can be one of three types .

Levers and Torque
- Human levers serve many different functions, including
movement, manipulation of objects, and weight bearing.
- If a joint is misaligned, the lever structure is altered, and
mechanical stress to the joint caused by external and
internal forces increases, all of which result in injury to
the joint or soft tissue.

Levers and Torque
- When a force is applied to a lever, the lever rotates about
the fulcrum.
- Torque is an expression for how a force changes the
angular motion of a lever, which signifies the angular
velocity.
- To calculate the torque M, the magnitude of the force F is
multiplied by the distance l between the force and the
rotating point.
- Equilibrium is achieved when the torque on the left equals
that on the right:

Levers
A lever system consists of a rigid bar (bone), an axis of
rotation (joint), and two forces: effort and resistance
Effort is the force that causes movement, and resistance is
the force that tends to keep an object from moving.
First-class lever is a system where the axis of rotation lies
between the effort and the resistance forces
Second and Third-class levers, the effort and resistance force
lie on the same side of the axis.
Second-class lever systems explain the type of tools used
frequently in occupations when mechanical advantage is
required, such as an extended handle on a faucet.

In third-class lever systems, the effort force lies closer to the
axis than does the resistance force
In contrast to the stability of first-class levers and the
mechanical advantage of the second-class levers, third-class
levers produce greater velocity and ROM.
The potential work capacity of the various muscles of the
body also depends on the amount of force they can generate
and the distance over which the muscles can shorten.
The ability to fully function, move, and engage in occupation
depends not only on the biomechanics of the musculoskeletal
system but also the physiologic principles of the muscles
themselves.

The Lever System: 1st , 2nd, 3rd Class Levers

Musculoskeletal System: Physiological Aspects
Strength
Muscle hypertrophy
- Development of more effective neural patterns and
neuromotor connections

Biomechanical Approach to Treatment: Maintaining or
Preventing Limitation in Range of Motion
- An individual’s actual ROM at any joint is determined by
the structures surrounding the segments that are moving
- Functional ROM is the range necessary to perform daily
activities
- Occupational therapists are concerned with providing
treatment that helps clients maintain functional motion or
to help patients gain motion when there are limitations
that interfere with occupation.

Physiological Aspects
- Skeletal muscle provides the power to produce movement
of a bony lever around its joint axis
A muscle’s strength and endurance to perform this activity
depends on multiple factor
- The size and type of muscle fibers
- The number and frequency of motor units firing
- The length-tension relationship of the muscle
- The sarcomere, made up of actin and myosin, is the main
contractile portion of skeletal muscle and is located within
the myofibrils of the muscle

- A nerve impulse sent to a motor unit, which consists of
motor neuron, an axon, and the muscle fibers supplied by
the neuron, initiates a chemical reaction and the release of
calcium throughout the muscle fibers
- The calcium ions release the inhibition that prevents actin
and myosin filaments from combining. When these thin
and thick filaments are allowed to combine, cross-bridges
are created.

- Muscle contraction occurs when these cross-bridges are
broken, actin is pulled over the myosin, and new cross-
bridges are formed.
- As this sequence continues, tension is generated, and the
muscle shortens (concentric contraction)

- In a lengthening position (eccentric contraction), cross-
bridges are broken down and reformed as the actin is
pulled away from the myosin filaments
- The strength of a contraction depends on the number and
type of muscle fibers found in a motor unit
- Muscles that produces large contractions typically are
composed of motor units that have large axons, large cell
bodies, and many muscle fibers. (responsible for activities
for large movements)

- Muscles that contain motor units with small axons, small
cell bodies, and fewer muscle fibers are more adept at
smaller movements, stabilizing actions and fine motor
activity.

- Other contributing factors for regulating the force of a
muscle contraction are the number of motor units that are
recruited and the modulation of firing rates of active
motor units
- Large motor units are innervated by large motor neurons,
and smaller motor units are innervated by smaller motor
neurons. The small motor neurons are more excitable, so
these are recruited first.

- This corresponds to our everyday experience. When trying
to perform delicate movements that require dexterity but
little force, control of muscle force must be fine. This is
accomplished by recruiting small numbers of muscle
fibers.
- When performing gross motor movements involving a lot
of force, the increments of force are large and we recruit
successively larger motor units. The recruitment of motor
units in order of their sizes is accomplished through other
nerves that make connections to the lower motor neurons.

Motor Unit Involvement different exercises

- Each motor unit comprises a motor neuron and the group
of muscle fibers it innervates.
- Motor units exhibit great diversity in their mechanical,
energetic and fatigue properties, and the types of motor-
units in a skeletal muscle are critically important in
determining the overall functional capacity of the muscle
in accomplishing specific motor behaviors.
- Structural and functional diversity is evident at each level
of the motor unit, including motor-neurons,
neuromuscular junctions and muscle fibers

Motor units are categorized into four types based on
mechanical and fatigue properties of muscle fibers:
- (1) slow-twitch, fatigue resistant (type S)
- (2) fast-twitch, fatigue resistant (type FR)
- (3) fast-twitch, fatigue-intermediate (type FInt)
- (4) fast-twitch, fatigable (type FF)

The size principle states
That Motor Units Are Recruited in the Order of Their Size
- Large motor units are innervated by large motor neurons,
and smaller motor units are innervated by smaller motor
neurons.
- The small motor neurons are more excitable, so these are
recruited first.
- This corresponds to our everyday experience. When trying
to perform delicate movements that require dexterity but
little force, control of muscle force must be fine. This is
accomplished by recruiting small numbers of muscle
fibers.

- When performing gross motor movements involving a lot
of force, the increments of force are large and we recruit
successively larger motor units.
- The recruitment of motor units in order of their sizes is
accomplished through other nerves that make connections
to the lower motor neurons.

- Muscle either shorten or produce force
- Muscles perform diverse functions
- Muscles are classified according to fine structure, neural
control and anatomical arrangement
- Isometric force is measured while keeping muscle length
constant
- Muscle force depends on the number of motor units and
the recruitment patterns of its fibers

- Size principle states that under load, motor units are
recruited from smallest to largest.
- In practice, this means that slow-twitch, low-force,
fatigue-resistant muscle fibers are activated before fast-
twitch, high-force, less fatigue-resistant muscle fibers.

- Muscle force can be graded by the frequency of motor
neuron firing
- Muscle force depends on the length of the muscle
- Recruitment provides the greatest gradation of muscle
force
- Muscle fibers differ in contractile, metabolic and
proteomic characteristics
- Motor units contain a single type of muscle fiber

- The innervation ratio of motor units produces a
proportional control of muscle force
- Muscle force varies inversely with muscle velocity
- Muscle power varies with the load and muscle type
- Eccentric contractions lengthen the muscle and produce
more force
- Concentric, isometric and eccentric contractions serve
different functions

- Muscle architecture influences force and velocity of the
whole muscle
- Muscles decrease force upon repeated stimulations

Local and global muscle characteristics and general features
Implications of stabilizer–mobiliser characteristics
- Muscles with predominantly stability role characteristics
(one-joint) optimally assist postural holding/anti-
gravity/stability and control function.
- Muscles that have a stability function (one-joint
stabilizer) demonstrate a tendency to inhibition, excessive
flexibility, laxity and weakness in the presence of
dysfunction ‘phasic’ muscles.

Implications of stabilizer–mobiliser characteristics
- Muscles with predominantly mobility role characteristics
(multi-joint) optimally assist rapid/accelerated movement
and produce high force or power.
- Muscles that have a mobility function (two-joint or multi-
joint mobiliser) demonstrate a tendency to over activity,
loss of extensibility and excessive stiffness in the presence
of dysfunction ‘postural’ muscles

Characteristic of muscles with stabilizer and mobiliser role
Muscle control of load transfer across the lumbar spine

Implications of local and global characteristics
- The small deep segmental muscles in the local muscle
system are responsible for increasing the segmental
stiffness across a joint and decreasing excessive
intersegmental motion. The relevance of this is that these
muscles are ideally situated to control displacement of the
path of the instantaneous center of motion and reduce
excessive intersegmental translatatory motion during
functional movements.
- At end range of motion the passive restraints of motion
(e.g. ligaments and joint capsules) contribute
significantly to controlling translatatory or accessory
motion.

- Local muscles maintain this translatatory control during
all functional activities such as postural control tasks,
non-fatiguing functional movements, fatiguing high load
and high speed activities.
- Local muscles maintain activity in the background of all
functional movements. Their recruitment is independent
of the direction of loading or movement and is biased for
non-fatiguing low load function, although they maintain
the role of controlling intersegmental displacement
during fatiguing high load function as well.

- The local muscles do not significantly change length
during normal activation and therefore do not primarily
contribute to range of motion.
- The one-joint (monoarticular) global muscles have a
primary stability role, while the multi-joint (biarticular)
global muscles have a primary mobility role.

- The muscles that make up the global muscle system are
responsible for the production and control of the range
and the direction of movement.
- The global muscles can change length significantly and
therefore are the muscles of range of motion.
- The global muscles participate in both non-fatiguing low
load and fatiguing high load activities.

- Both the local and global muscle systems must work
together for efficient normal function.
- Neither system in isolation can control the functional
stability of body motion segments.

Threshold Strategies
- It’s important to understand that most local stabilizing
muscles have a higher portion of low-threshold motor
units, where as global moving muscles have a higher
portion of high-threshold motor units. Further more,
motor units are recruited sequentially from low to high.
It’s the body’s way of being efficient and trying to
perform a task with the easiest motor program possible.
- So before high-threshold motor units are recruited, all of
the other motor units must be recruited (high-threshold
on top of low-threshold). This increases the mechanical
advantage of the global movers and centrates the joint,
thus making it more efficient to perform the task.

- Working within the edge of ability and gaining
fundamental stability is paramount for developing
efficient stability and power
What Goes Wrong?
- The body moves very efficiently when the low-threshold
precedes the high-threshold. It’s when people skip the
low-threshold step that things start to go very wrong.
- This dysfunctional high-threshold only strategy will
plague the body compensations and inefficient
movement.

- When the body fatigues and the local stabilizers stop
firing, the body goes into a dysfunctional high-threshold
strategy.
- This is filled with poor movement patterns. To make
matters worse, it teaches the body how to incorrectly use
global mobilizing muscles (as movers AND stabilizers).
- So now these muscles are always on and always trying to
do everything, even for low-load activities.

Abnormal recruitment sequence
Hip extension Normal Recruitment sequence
- Hamstrings
- Gluteals
- Contralateral erector spinae
Hip Extension Low Back Pain Recruitment Sequence
- Hamstrings
- Delayed gluteals
- Ipsilateral erector spinae
- Thoraco-lumbar erector spinae
- Lumbar erector spinae
- Hamstrings
- Variable gluteals

Hip Abduction Normal Recruitment Sequence
- Gluteus medius
- Tensor fascia latae
- Ipsilateral quadratus lumborum
Hip Abduction Low Back Pain Recruitment Sequence
- Gluteus medius
- Ipsilateral quadratus lumborum
- Quadratus lumborum
- Gluteus medius

Shoulder Abduction Normal Muscle Recruitment
- Deltoids
- Contralateral upper trapezius
- Ipsilateral upper trapezius
- Lower scapula muscles
Shoulder Abduction Neck and Shoulder pain Muscle
Recruitment
- Deltoid
- Lower scapula muscles
- Deltoid

Muscle imbalance
Active straight leg raise
- Contralateral hamstrings (dominant mobilizer)
- Abdominals (inefficient stabilizer
Forward bending (standing)
- Hamstrings (dominant mobilizer)
- Back extensors (inefficient stabilizer0
Knee extension (sitting)
- Medial hamstrings (dominant mobilizer)
- Lateral hamstrings (inefficient stabilizer)

Muscle imbalance
Hip extension (prone)
- Hamstrings (dominant mobilizer)
- Gluteals (inefficient stabilizer)
Hip flexion
- Tensor facia latea & ITB (dominant mobilizer)
- Illiacus & psoas (inefficient stabilizer)
Hip abduction
- Tensor facia latea & ITB (dominant mobilizer)
- Posterior gluteus medius (inefficient stabilizer)

Muscle imbalance
Shoulder abduction or flexion
- Scapular elevators (dominant mobilizer)
- Lower trapezius (inefficient stabilizer)
Shoulder medial rotation
- Latissimus dorsi (dominant mobilizer)
- Subscapularis (inefficient stabilizer)
Elbow flexion
- Extensor carpi radialis longus (dominant mobilizer)
- Brachialis & biceps (inefficient stabilizer)

Functional efficiency
- The functional efficiency of a muscle is related to its
ability to generate tension.
- A muscle’s tension is not constant throughout a
contraction, especially if the muscle is changing length to
produce movement.
- Length and tension properties of a muscle are closely
related. The tension or force a muscle produces is the
resultant force arising from a combination of both active
and passive components of the muscle.

Functional efficiency
- The active component of muscle tension is determined by
the number of actin–myosin cross-bridges that are linked
at any point in time.
- The passive tension property of muscle is largely due to
the elastic titin filaments which anchor the myosin chain
to the Z band. Other connective tissue structures within
muscle only contribute partially to passive tension

Actin-myosin filament cross-bridge and titin attachments

Actin–myosin filaments within the sarcomeres
- The position in range (usually mid-range) where the
active length–tension curve is maximal is known as the
muscle’s resting length. In this position, the maximum
number of actin–myosin cross-bridge links can be
established.
- In a muscle’s shortened or inner range position, the
passive elastic components do not contribute to muscle
tension.
- Passive tension only begins to play a role after a muscle
starts to lengthen or stretch into the muscle’s outer range,
beyond its resting length or mid-range position.

Actin–myosin filaments within the sarcomeres
- Muscles are most efficient and generate optimal force
when they function in a mid-range position near resting
length.
- Muscles are less efficient and appear functionally weak
when they are required to contract in a shortened or
lengthened range relative to their resting length because
of physiological or mechanical insufficiency

Contractile component of a muscle length-tension curve changes
when muscles change length.
Changes in muscle length affect force efficiency in different positions
of joint range

- Physiological insufficiency occurs when a muscle actively shortens
into its inner range where the actin filaments overlap each other,
thus reducing the number of cross-bridges that can link to the
myosin filament.
- As the muscle progressively shortens, there are fewer cross-bridges
able to be linked, and the muscle is unable to generate optimal
force.
- Mechanical insufficiency occurs when a muscle actively contracts
in its lengthened or outer range. In this range, the actin filaments
do not adequately overlap the myosin filament and again a reduced
number of cross-bridges are linked. Consequently the muscle
cannot generate optimal force.
- Mechanical insufficiency during an outer range contraction is
offset somewhat by the increase in passive tension from titin
filaments.

- When a muscle habitually functions at an altered length (either
lengthened or shortened), its length–tension relationships adapt
accordingly.
- The position in range where it generates optimal force efficiency
changes to match the subsequent lengthening or shortening
- When a muscle is persistently elongated or lengthened, it adds
sarcomeres in series.
- Because the sarcomeres are the force generating units within a
muscle, a lengthened or elongated muscle is stronger and is able to
generate a higher peak force than normal.
- This higher peak force, however, is produced in an outer range
position and not at its usual resting length, mid-range position.

- At the muscle test position (inner to middle range), the
lengthened muscle is inefficient due to physiological
insufficiency, and consequently tests ‘weak’ during muscle
testing and fatigues more readily in postural control tasks.
- A persistently shortened muscle, on the other hand, loses
sarcomeres in series and increases in connective tissue.
- Because of the reduced number of sarcomeres, the
shortened muscle generates less peak force than normal..

- Even though the shortened muscle is weaker than its
normal control, muscle testing is performed at the point in
range where it is optimally efficient. Consequently,
shortened muscles frequently demonstrate good strength
during muscle testing. This explains the clinical
observation that ‘short muscles test strong and long
muscles test weak’.

- A muscle’s structure also affects its ability to generate
force.
- Muscles that have long lever arms, such as the multi-joint
rectus femoris or hamstrings, can contract through a
greater range and are biomechanically advantaged to
produce range of movement during concentric shortening.
These muscles primarily have a mobility role. These multi-
joint mobilisers are not particularly efficient at preventing
or controlling excessive movement during eccentric
lengthening.
- When a muscle has such a short lever arm that it
produces minimal length change when contracted, it has a
greater potential to control intersegmental translation, for
example the single segment fibres of lumbar multifidus.

- The smaller one-joint muscles with short lever arms, such
as subscapularis or iliacus, are not biomechanically
efficient to produce forceful or high speed movement
during concentric shortening. However, they are more
efficient during eccentric lengthening to control excessive
movement and to decelerate momentum and therefore are
more able to protect tissues from overstrain. These
muscles primarily have a stability role.
- When a muscle has such a short lever arm that it
produces minimal length change when contracted, it has a
greater potential to control intersegmental translation, for
example the single segment fibres of lumbar multifidus.

Classification of muscle functional roles in terms of function

Classification of muscle functional roles characteristics and
dysfunction

- Postural adjustments are anticipatory and ongoing and all
muscles can have an anticipatory timing to address
displacement and perturbations to equilibrium.
- All muscles provide reflex feedback reactions under both
low and high threshold recruitment tasks and demonstrate
anticipatory feedforward recruitment when appropriate.
- However, only muscles with a local stability role exhibit
anticipatory timing that is independent of the direction of
loading or displacement. Muscles recruited in a global
range related role are direction-specific in their
anticipatory feedforward response

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