BIOMECHANICS OF

POSTURE

TO KNOW ABOUT POSTURE

TO KNOW ABOUT DEFINITION

TO ABOUT TYPES OF POSTURE

TO UNDERSTAND ABOUT BIOMECHANICS OF

POSTURE

KINETICS AND KINEMATICS OF POSTURE

BALACE AND POSTURAL CONTROL

POSTURAL ANALYSIS AND EVALUATIONS

ABNORMAL POSTURES

It is your power foundation- a stacked

framework from your feet through your

legs, hips, spine and shoulders to your

head”

Posture or position of greatest efficiency,

around your center of gravity, with muscles

on all sides, exerting pull.

Posture can be defined as the relative

arrangement of different parts of the

body with line of gravity.

In static postures the body and its

segments are aligned and maintained

in certain positions.

Eg –

Standing, kneeling, lying, and sitting

Dynamic

posture refers to postures in which the

body or its segments

are moving—walking, running, jumping,

throwing,

and lifting.

The study of any particular posture

includes kinetic and kinematic analyses of

all body segments.

Humans and other living creatures have

the ability to arrange and rearrange body

segments to form a large

variety of postures, but the sustained

maintenance of erect bipedal stance is

unique to humans.

Perfect posture pays dividends- by

reducing stress/loads which leads to

tension in the antigravity musculature,

degeneration of weight bearing structures,

less efficient movement, misalignment and

risk for injury.

Erect bipedal stance gives us freedom for the upper extremities, but in comparison with the quadrupedal posture, erect stance has certain disadvantages.

Erect bipedal stance increases the work of the heart

Places increased stress on the vertebral column, pelvis, and lower extremities

Reduces stability

base of support (BOS), defined by an

area bounded posteriorly by the tips of

the heels and anteriorly by a line joining

the tips of the toes, is considerably

smaller than the quadruped base.

center of gravity (COG), which is

sometimes referred to as the body’s center

of mass, is located within the body

approximately at the level of the second

sacral segment, a location that is

relatively distant from the base of support

Without appropriate neuromusculoskeletal

compensation and accommodation, such

actions result in imbalance and often

falling. Thus, postural deviations resulting

in balance problems lead to frequent strain

and injury to antigravity structures.

one's entire weight can be considered as concentrated at a point where the gravitational pull on one side of the body is equal to the pull on the other side. This point is the body's center of gravity, and it constitutes the exact center of body mass When the center of gravity is above the base of support and the pull of gravity is successfully resisted by the supporting members, an equilibrium of forces or a state of balance is reached and no motion occurs.

center of gravity is located in the region just anterior to the top of the second sacral segment; ie, about 55% of the distance for women and 57% for men, from the plantar surfaces to the apex of the head in the erect position. Its location will vary somewhat according to body type, age, and sex, and move upward, downward, or sideward in accordance with normal position movements and abnormal neuromusculoskeletaldisorders.

The accumulation of fat and the loss of soft tissue tone are common factors in altering one's center of gravity. Thus, the center of gravity shifts with each change in body alignment, and the amount of weight borne by the joints and the pull of the muscles vary within reasonable limits with each body movement. Adequate compensation is provided for in the healthy, structurally balanced person.

LINE OF GRAVITY

Reference Points. The vertical A-P line of gravity of the body, as viewed laterally in the erect model subject, falls from above downward through the earlobe, slightly posterior to the mastoid process, through the odontoid process, through the middle of the shoulder joint, touches the midpoint of the anterior borders of T2 and T12, then falls just slightly anterior to S2, slightly behind the axis of the hip joint, slightly anterior to the transverse axis of rotation of the knee (slightly posterior to the patella), crosses anterior to the lateral malleolus and through the cuboid-calcaneal junction to fall between the heel and metatarsal heads. When viewed from the back, the lateral line of gravity passes through the occipital protuberance, the C7 and L5 spinous processes, the coccyx and pubic cartilage, and bisects the knees and ankles. Thus, the A-P and lateral lines of gravity divide the body into four quarters (Fig. 4.6).

Plumb Line Analysis. The plumb line, as used in postural analysis, serves as a visual comparison to the line of gravity. For example, when the plumb line is centered over S1, it should fall in line with the occipital protuberance. In uncompensated scoliosis, however, it will be seen to fall lateral to the occipital protuberance.

BODY BALANCE AND EQUILIBRIUM

Active and Passive States. Positions of the body that require muscular forces to maintain balance are said to be in active equilibrium, while those that do not require muscular effort are in passive equilibrium. In passive equilibrium, all segmental centers of gravity and the centers of all joints fall within the gravity line of the body which must fall within the base of support. This requires complete neutralization of all linear and rotary components of gravitational force by joint surfaces and the base of support. Thus, such a state is impossible in the erect position but possible in the horizontal position.

Balance. When the forces of gravity on a body are in a balanced position, the pull is equal on all sides about the center of gravity; ie, its center of gravity is directly above its base of support and the body is quite stable (Fig. 4.7). The amount of body mass outside this base does not affect the equilibrium unless the center of gravity of the mass is altered. If a part is laterally shifted to one side without a compensatory shift of another part of equal weight, the center of gravity is displaced sideward. The body will topple if the center of gravity is displaced outside its base of support because gravity pulls greater on the side of weight displacement. Because males generally have a larger thorax, broader shoulders, and heavier arms than females, they are toppled with less force than are females of the same size.

Common Torques. In the body, all partial centers of gravity or their axes of motion do not coincide with the common line of gravity. In fact, many partial centers are quite distant from the common line, and this causes active rotary torques in many joints because of gravitational pull which must be neutralized by antigravity muscles. A weight-bearing joint is considered to be in equilibrium if the gravity line of the supported structure is equal to the joint's axis of rotation. If the gravity line is posterior to the joint's axis of rotation, the superior segment tends to rotate posteriorly in compensation. If it is anterior to the axis, the superior segment tends to rotate anteriorly.

Toppling Rate. The rate of movement of an unbalanced body which is toppling depends on the amount of lateral displacement of the center of gravity from its base of support. For this reason, a toppled tree falls slowly at first because of trunk resistance and then rapidly as its center of gravity is further displaced from the tree trunk. A tall person falls harder than a short person. For the same reason, the further the body's center of gravity is displaced from the midline of its base of support, the more force is necessary to return it to the balanced position.

Aging- your body gradually loses its capacity to absorb and transfer forces however its not aging that influences posture as does:

Inactivity/sedentary living/reluctance to exercise -leads to loss of natural movement flow,

Poor postural habits -eventually becomes your structure, Biomechanical compensation → muscle imbalance,

adaptive shortening, muscle weakness & instability within the “core”,

Body composition – increases load, stresses on spinal structure, leads to spinal deviation,

Workspace –ergonomics, Poor movement technique/execution/training , Injury -leads to reduced loading capacity or elasticity, Others:

Weight Bearing. The most economical use of energy in the standing position is

when the vertical line of gravity falls through a column of supporting bones. If the

weight-bearing bony segments are aligned so that the gravity line passes directly

through the center of each joint, the least stress is placed upon the adjacent ligaments

and muscles. This is the ideal situation, but it is impossible in the human body

because the centers of segmental links and the movement centers between them

cannot be brought to accurately meet with a common line of gravity.

Stability. Since the body is a segmented system, the stability of the body depends

upon the stability of its individual segments. The force of gravity acting upon each

segment must be individually neutralized if the body as a whole is to be in complete

gravitational balance. That part of balance contributed by an individual segment is

called the segment's partial equilibrium, as contrasted with the total equilibrium of the

whole body. Thus, each segment has its own partial center of gravity and partial

gravity line.

Position Changes. Any change in position of a partial center of gravity produces a

corresponding change in the common center of gravity. When the arms are raised

overhead and lowered, the center of gravity is respectively raised and lowered within

the body. When the arms are stretched forward or backward, the center of gravity is

respectively moved anteriorly or posteriorly within the body. When the trunk is flexed

severely forward or laterally, the center of gravity shifts outside the body.

Alignment May be tight May be weak Exercises

Mid back flexion Upper abdominals Thoracic extensors

Mid and lower trapezius

Active & passive

thoracic extension

Protracted scapulae Serratus anterior

Shoulder adductors

Shoulder internal

rotators

Mid & lower trapezius

Rhomboids

Stretch Serratus

Stretch Pectoralis minor

Narrowed intercostal

spaces

Intercostals Deep breathing

Multifidus

Quadratus lumborum

Titled scapulae Pectoralis minor Lower trapezius Stretch Pectoralis major

Stretch Latissimus dorsi

Elevated scapulae Upper trapezius

Levator scapulae

Lower trapezius Strengthen Middle &

lower trapezius

Stretch Upper traps &

Levator

Extreme neck

extension’

(Hyperextension)

Long Cervical

Extensors

Short neck flexors Strengthen neck flexors

Alignment May be

tight

May be

weak

Exercises

Anterior tilt Hip flexors Abdominals Stretch hip flexors

Strengthen obliques

for stabilization

Avoid full sit ups

Hip flexion Hip extensors Strengthen

gluteals

Extreme low

back extension

(hyperextension)

Low back

extensors

Stretch low back

extensors

Alignment May be

tight

May be

weak

Exercises

Posterior Pelvic

tilt

Hamstrings Stretch

hamstrings

Low back

flexion

Back extensors Strengthen back

extensors

Hip extension Hip flexors Strengthen hip

flexors

Alignment May be tight May be weak Exercises

Posterior pelvic tilt Hamstrings Hip flexors Stretch hamstrings

Strengthen hip flexors

Long kyphosis Upper abdominals External obliques

Upper back extensors

Strengthen upper back

extensors

Stretch and strengthen

abdominals

Narrowed intercostal

spaces

Intercostals Deep breathing

Hip extension Strengthen hip flexors

Extreme neck extension

(Hyperextension)

Upper trapezius

Levator scapulae

High cervical extensors

Neck flexors Stretch upper traps &

levator, strengthen mid

& lower traps,

strengthen neck flexors

Extreme knee extension

(Hyperextension)

Hamstrings

Calf

Strengthen hamstrings

and calf

1. Static Postural Assessment

2. Dynamic Postural Assessment

3. Gait analysis

4. Flexibility assessment

5. Muscle testing

Once postural alignment is assessed the

focus should be on teaching and training

“Neutral Spine”

Standing on both feet: front, side and

rear views

Standing on one leg

Sitting supported and unsupported

Kneeling

Supine

Sleeping

Performing:

A push- up

A squat- with arms in front, lifting

overhead

A lunge

Walking

Lifting

http://www.chiro.org/ACAPress/Body_Align

ment.html