BODY MECHANICS

Body mechanics

• the efficient use of the body as a machine and as a means of locomotion

• concepts most helpful to the understanding of body mechanics:

– body alignment, – balance, – coordinated body movement, and– joint mobility

Body Alignment• the geometric arrangement of body parts in

relation to each other; • synonymous with good posture

• benefits of good body alignment: – optimal musculoskeletal balance and operation – healthy physiologic functioning without undue

strain on the joints, muscles, tendons, or ligaments in any position, e.g.:

• standing • sitting • lying

application of correct body alignment when standing

• the head is held erect • the face is in the forward position, in the

same direction as the feet • the chest is held upward and forward • the spinal column is upright, and the

curves of the spine are within normal limits

• the abdominal muscles are held upward and the buttocks downward

application of correct body alignment when standing

• the knees are extended - not bent or hyperextended in the knee-locked position

• the feet are at right angles to the lower legs

• the line of gravity goes through the center of the knees and in front of the ankle joint

• the base of support is on the soles of the feet, and weight is distributed through the soles and heels

application of correct body alignment when sitting

• the head is held erect, and the neck and vertebral column are in straight alignment

• the body weight is distributed on the buttocks and thighs

• both feet are supported on the floor; with short patients, a footstool is used

• a 2.5 cm - 5 cm (1 - 2 in) space is maintained between the edge of the seat and popliteal space on the posterior surface of the knee

• the forearms are supported on the arm rests, in the lap, or on a table in front of the chair

balance

• the state of equilibrium in which opposing forces counteract each other

• concepts most helpful to understanding balance:

– base of support, – center of gravity, and – line of gravity

Balance

– base of support • the foundation on which an object rests

– center of gravity • the point at which all of the mass of an object is

centered • located in the center of the pelvis about midway

between the umbilicus and symphysis pubis

– line of gravity • an imaginary vertical line drawn through an

object's center of gravity and base of support

Balance

• good balance is accomplished by: – a wide base of support

• to widen the base of support, spread the feet further apart

– a low center of gravity • to lower the center of gravity, flex the hips and

knees until a squatting position is achieved

– a line of gravity through the center of gravity and base of support

Balance

• conversely, poor balance is accomplished by: – a narrow base of support

– a high center of gravity

– a line of gravity which falls near the edge of or outside of the base of support or is constantly changing

coordinated body movement

• the production of balanced, smooth, and purposeful movement

– coordinated body movements are accomplished through the following: • use of major muscle groups rather than weaker

ones, e.g.: – flexors, extensors, and abductors of the thighs – flexors and extensors of the knees

– flexors and extensors of the upper and lower arms

coordinated body movement

• use of the arm bones as levers and the elbows as fulcrums to facilitate lifting a weight against resistance (force of gravity)

• use of a pull sheet and smooth, dry, firm bed foundation to decrease the effect of friction which increases the amount of effort required to move an object

• working close to the object to be moved to decrease the effort involved

coordinated body movements• coordinated body movements are also

accomplished through the integrative function of antagonistic, synergistic, and antigravity muscle groups

– antagonistic muscle groups • muscle group that brings about movement at a

joint by contraction of a prime mover and relaxation of its antagonist, e.g.: – to flex the arm, the prime mover (biceps brachii)

contracts while its antagonist (triceps brachii) relaxes – to extend the arm, the new prime mover (triceps

brachii) contracts while its new antagonist (biceps brachii) relaxes

coordinated body movements

• synergistic muscle groups – muscle group that brings about movement at

a joint by strengthening the contraction of the prime mover, e.g.:

• to flex the arm, the contraction of the prime mover (biceps brachii) is strengthened by contraction of its synergist (brachialis)

coordinated body movements

– antigravity muscle groups • bring about and maintain an upright or

sitting posture by contracting and/or relaxing to oppose the effect of gravity on the body

• e.g., extensors of the leg, gluteus maximus, quadriceps femoris, muscles of the back

postural reflexes

• coordinated body movements are also accomplished through the integrative functioning of postural reflexes, e.g.:

– labyrinthine sense • assists in producing coordinated body movement

by alerting an individual to movement of the head in relation to gravity through stimulation of receptors in the semicircular canals in the inner ear

postural reflexes

• visual or optic reflex – assists in producing coordinated body

movement by alerting the brain of the spatial relationships within the environment (e.g., nearness of ceilings, walls, furniture, condition of floor) through stimulation of receptors in the visual special sense

postural reflexes

• proprioceptive or kinesthetic sense

– assists in producing coordinated body movements by alerting the brain of the location of a limb or body part in space through stimulation of proprioceptive receptors in muscles, tendons, and fascia

postural reflexes

• extensor or stretch reflex – assists in producing coordinated

body movement by alerting the brain of the need to stimulate extensor muscles to reestablish an erect posture through stimulation of receptors in antigravity muscle groups

postural reflexes

• plantar reflex – assists in producing coordinated

body movement by alerting the brain of the need to stimulate extensor muscles of the lower legs though the stimulation of receptors in the soles of the feet

joint mobility • the complete extent of

movement of which a joint (area when bone surfaces come into close contact with another or articulate) is normally capable

types of joints

• synarthroidal

– immovable joints

– examples: • skull sutures, • epiphyseal plates,• joint between first rib and manubrium of

sternum

types of joints

• amphiarthroidal – slightly movable joints

– examples: • vertebral joints,

• joint of the symphysis pubis

types of joints

• diarthroidial – freely movable joints

• consistent features of diarthroidial joints – ability to move freely – a fibrous joint capsule – a joint cavity – a synovial membrane that lines the inner surface of the

joint capsule – lubricating synovial fluid secreted by the synovial

membrane – articular cartilage that covers the bony surfaces

types of diarthroidial joints

• ball-and-socket • ball-shaped head fits into

concave socket of another bone

• examples: – hip joint between the femur and

pelvis

types of diarthroidial joints

• condyloid – oval-shaped condyle

(protuberance at the end of a bone) fits into elliptical (oval, egg-shaped) cavity of another bone • examples:

– wrist joint between the radius and carpals

types of diarthroidial joints

• gliding – articular surfaces; usually

flat • examples:

» finger joints between carpal bones

types of diarthroidial joints

• hinge – spool-like surface fits into

concave surface of another bone • examples:

– elbow joint between the humerus and ulna and radius

types of diarthroidial joints

• pivot – arch-shaped structure rotates

about rounded, or peg-like, pivot • example:

» joint between the atlas and axis

types of diarthroidial joints

– saddle • saddle-shaped bone fits into a

socket that is convex on one side and concave on the other – example:

» thumb joint between the trapezium and metacarpal

types of diarthroidal joint movements

• flexion – decreasing the angle of the joint

• e.g., bending the elbow

• extension – increasing the angle of the joint

• e.g., straightening the elbow

types of diarthroidal joint movements

• hyperextension – further extension or straightening of

the joint • e.g., bending the head backward

• abduction – movement of the bone away from the

midline of the body • e.g., moving the leg out to the side

types of diarthroidal joint movements

• adduction – movement of bone toward the midline

of the body • e.g., moving the leg back to the other leg

• rotation – movement of the bone around its

central axis • e.g., turning the head

types of diarthroidal joint movements

• circumduction – movement of the distal part of the bone in a

circle while the proximal end stays fixed • e.g., moving each leg up, to the side, and down

in a circle

• eversion – turning the sole of the foot outward by

moving the ankle joint

• circumduction – movement of the distal part of the bone

in a circle while the proximal end stays fixed • e.g., moving each leg up, to the side, and

down in a circle

• eversion – turning the sole of the foot outward by

moving the ankle joint

• supination – moving the bones of the forearm so

that the palm of the hand faces upward when held in front of the body

• protraction – moving a part of the body forward in

the same plane parallel to the ground • e.g., jutting chin out

• retraction – moving a part of the body

backward in the same plane parallel to the ground • e.g., tucking chin in

principles of body mechanics

• the wider the base of support, the greater the stability of the nurse

• the lower the center of gravity, the greater the stability of the nurse

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

• the stronger the muscle group, the greater amount of work that can be safely done by it

• facing the direction of movement prevents abnormal twisting of the spine

• dividing balanced activity between arms and legs reduces the risk of back injury

• leverage, rolling, turning, or pivoting requires less work than lifting

• when friction is reduced between the object to be moved and surface on which it is moved, less force is required to move it

• reducing the force of work reduces the risk of injury

• maintaining good body mechanics reduces fatigue of the muscle groups

• alternating periods of rest and activity helps to reduce fatigue

application of the principles of body mechanics

• develop a habit of erect posture (correct alignment) • use the longest and the strongest muscles of the arms

and the legs to help provide the power needed in strenuous activities

• use the internal girdle and a long midriff to stabilize the pelvis and to protect the abdominal viscera when stooping, reaching, lifting, or pulling

• work as closely at possible to an object that is to be lifted or moved

• use the weight of the body as a force for pulling or pushing

• slide, roll, push, or pull an object rather than lift it to reduce the energy needed to lift the weight against gravity

• use the weight of the body to push an object by falling or rocking forward and to pull an object by falling or rocking backward

• spread the feet apart to provide a wider base of support when increased stability of the body is necessary

• flex the knees, put on the internal girdle, and come down close to an object that is to be lifted