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Lecture Notes

Body Mechanics


  1. Body mechanics
    1. the efficient use of the body as a machine and as a means of locomotion
    2. concepts most helpful to the understanding of body mechanics: body alignment, balance, coordinated body movement, joint mobility
    3. body alignment
      1. the geometric arrangement of body parts in relation to each other; synonymous with good posture
      2. benefits of good body alignment:
        1. optimal musculoskeletal balance and operation
        2. healthy physiologic functioning without undue strain on the joints, muscles, tendons, or ligaments in any position, e.g.:
          1. standing
          2. sitting
          3. lying
      3. application of correct body alignment when standing
        1. the head is held erect
        2. the face is in the forward position, in the same direction as the feet
        3. the chest is held upward and forward
        4. the spinal column is upright, and the curves of the spine are within normal limits
        5. the abdominal muscles are held upward and the buttocks downward
        6. the knees are extended - not bent or hyperextended in the knee-locked position
        7. the feet are at right angles to the lower legs
        8. the line of gravity goes through the center of the knees and in front of the ankle joint
        9. the base of support is on the soles of the feet, and weight is distributed through the soles and heels
      4. application of correct body alignment when sitting
        1. the head is held erect, and the neck and vertebral column are in straight alignment
        2. the body weight is distributed on the buttocks and thighs
        3. both feet are supported on the floor; with short patients, a footstool is used
        4. 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
        5. the forearms are supported on the arm rests, in the lap, or on a table in front of the chair
      5. application of correct body alignment when positioning patients
        1. in the Fowler's position
          1. description
            1. position in which the patient is semi-sitting with the head and trunk elevated 45 to 90 degrees
          2. uses
            1. promoting cardiac and respiratory function
            2. eating
            3. conversation
          3. complications of poor alignment in the Fowler's position
            1. flexion contracture of the neck
            2. exaggerated curvature of the spine
            3. dislocation of the shoulder
            4. flexion contracture of the wrist
            5. edema of the hand
            6. flexion contractures of the fingers and abduction of the thumbs
            7. impaired lower extremity circulation and knee contracture, pressure on the heels
            8. external rotation of the hips
            9. footdrop
          4. prevention of complications of poor alignment in the Fowler's position
            1. allow head to rest against the mattress or be supported by a small pillow only
            2. use a firm support for the back; position the patient so that the angle of elevation starts at the hip
            3. support the forearms on pillows to elevate them sufficiently so that no pull is exerted on the shoulders
            4. support the hands on pillows so that they are in natural alignment with the forearms
            5. support the hands so that they are slightly elevated in relation to the elbows
            6. provide hand-wrist splints if necessary
            7. elevate the knees for only brief periods
            8. place one or two pillows under the lower legs from below the knees to the ankles; avoid pressure on the popliteal vessels; avoid using the knee gatch
            9. trochanter rolls
            10. support the feet in dorsal flexion; footboard; high-top sneakers
        2. in the supine (dorsal recumbent) position
          1. description
            1. position in which the patient lies flat on the back with the head and shoulders slightly elevated with a pillow
          2. uses
            1. provide comfort and to facilitate healing following certain surgeries or anesthetics (e.g., spinal)
          3. complications of poor alignment in the supine (dorsal recumbent) position
            1. exaggerated curvature of the spine and flexion of the hips
            2. flexion contracture of the neck
            3. internal rotation of the shoulders and extension of the elbows (hunch shoulders)
            4. flexion of the lumbar curvature
            5. extension of the fingers and abduction of the thumbs
            6. external rotation of the femurs
            7. hyperextension of the knees
            8. footdrop
          4. prevention of complications of poor alignment in the supine (dorsal recumbent) position
            1. provide a firm supportive mattress; bedboard, if necessary
            2. place pillows under the upper shoulders, the neck, and the head so that the head and neck are held in the correct position
            3. place pillows or arm supports under the forearms so that the upper arms are alongside the body and the forearms are slightly pronated
            4. place a rolled towel or small pillow under the lumbar curvature, if necessary
            5. use hand-wrist splints
            6. sandbags or trochanter rolls alongside the hips and upper half of the thighs
            7. place a pillow under the lower legs from below the knees to the ankles
            8. footboard; high-top sneakers
        3. in the lateral position
          1. description
            1. position in which the patient lies on one side of the body
          2. uses
            1. resting and sleeping
            2. relief of pressure on the sacrum and heels
          3. complications of poor alignment in the lateral position
            1. lateral flexion of the neck
            2. inward rotation of the arms and interference with respiration
            3. extension of the fingers and abduction of the thumbs
            4. twisting of the spine
          4. prevention of complications of poor alignment in the lateral position
            1. place a pillow under the head and neck
            2. place a pillow under the upper arms; lower arms should be flexed and positioned comfortably
            3. hand-wrist splints
            4. ensure that the shoulders are aligned with the hips
        4. in the prone position
          1. description
            1. position in which the patient lies on the abdomen with the head turned to one side
          2. uses
            1. prevention of flexion contractures of the hips and knees
            2. promotion of drainage from the mouth
          3. complications of poor alignment in the prone position
            1. flexion of the cervical spine
            2. hyperextension of the spine; impaired respirations
            3. footdrop
          1. prevention of complications of poor alignment in the prone position
            1. place a small pillow under the head
            2. place some suitable support under the patient between the end of the ribcage and upper abdomen if this facilitates breathing and if there is space there
            3. move the patient down in bed so that the feet fall naturally over the edge of the mattress; support the lower extremities on a pillow just high enough to keep the toes from touching the bed
    4. balance
      1. the state of equilibrium in which opposing forces counteract each other
      2. concepts most helpful to understanding balance: base of support, center of gravity, and line of gravity
        1. base of support
          1. the foundation on which an object rests
        2. center of gravity
          1. the point at which all of the mass of an object is centered
          2. located in the center of the pelvis about midway between the umbilicus and symphysis pubis
        3. line of gravity
          1. an imaginary vertical line drawn through an object's center of gravity and base of support
      3. good balance is accomplished by:
        1. a wide base of support
          1. to widen the base of support, spread the feet further apart
        2. a low center of gravity
          1. to lower the center of gravity, flex the hips and knees until a squatting position is achieved
        3. a line of gravity through the center of gravity and base of support
      4. conversely, poor balance is accomplished by:
        1. a narrow base of support
        2. a high center of gravity
        3. a line of gravity which falls near the edge of or outside of the base of support or is constantly changing
    5. coordinated body movement
      1. the production of balanced, smooth, and purposeful movement
      2. coordinated body movements are accomplished through the following:
        1. use of major muscle groups rather than weaker ones, e.g.:
          1. flexors, extensors, and abductors of the thighs
          2. flexors and extensors of the knees
          3. flexors and extensors of the upper and lower arms
        2. use of the arm bones as levers and the elbows as fulcrums to facilitate lifting a weight against resistance (force of gravity)
        3. 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
        4. working close to the object to be moved to decrease the effort involved
      3. coordinated body movements are also accomplished through the integrative function of antagonistic, synergistic, and antigravity muscle groups
        1. antagonistic muscle groups
          1. muscle group that brings about movement at a joint by contraction of a prime mover and relaxation of its antagonist, e.g.:
            1. to flex the arm, the prime mover (biceps brachii) contracts while its antagonist (triceps brachii) relaxes
            2. to extend the arm, the new prime mover (triceps brachii) contracts while its new antagonist (biceps brachii) relaxes
        2. synergistic muscle groups
          1. muscle group that brings about movement at a joint by strengthening the contraction of the prime mover, e.g.:
            1. to flex the arm, the contraction of the prime mover (biceps brachii) is strengthened by contraction of its synergist (brachialis)
        3. antigravity muscle groups
          1. bring about and maintain an upright or sitting posture by contracting and/or relaxing to oppose the effect of gravity on the body
            1. e.g., extensors of the leg, gluteus maximus, quadriceps femoris, soleus muscles, muscles of the back
      4. coordinated body movements are also accomplished through the integrative functioning of postural reflexes, e.g.:
        1. labyrinthine sense
          1. 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
        2. visual or optic reflex
          1. 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
        3. proprioceptive or kinesthetic sense
          1. 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
        4. extensor or stretch reflex
          1. 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
        5. plantar reflex
          1. 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
    6. joint mobility
      1. the complete extent of movement of which a joint (area when bone surfaces come into close contact with another or articulate) is normally capable
      2. types of joints
        1. synarthroidal
          1. immovable joints
          2. examples:
            1. skull sutures, epiphyseal plates, joint between first rib and manubrium of sternum
        2. amphiarthroidal
          1. slightly movable joints
          2. examples:
            1. vertebral joints, joint of the symphysis pubis
        3. diarthroidial
          1. freely movable joints
          2. consistent features of diarthroidial joints
            1. ability to move freely
            2. a fibrous joint capsule
            3. a joint cavity
            4. a synovial membrane that lines the inner surface of the joint capsule
            5. lubricating synovial fluid secreted by the synovial membrane
            6. articular cartilage that covers the bony surfaces
          3. types of diarthroidial joints
            1. ball-and-socket
              1. ball-shaped head fits into concave socket of another bone
              2. examples:
                1. hip joint between the femur and pelvis
            2. condyloid
              1. oval-shaped condyle (protuberance at the end of a bone) fits into elliptical (oval, egg-shaped) cavity of another bone
              2. examples:
                1. wrist joint between the radius and carpals
            3. gliding
              1. articular surfaces; usually flat
              2. examples:
                1. finger joints between carpal bones
            4. hinge
              1. spool-like surface fits into concave surface of another bone
              2. examples:
                1. elbow joint between the humerus and ulna and radius
            5. pivot
              1. arch-shaped structure rotates about rounded, or peg-like, pivot
              2. example:
                1. joint between the atlas and axis
            6. saddle
              1. saddle-shaped bone fits into a socket that is convex on one side and concave on the other
              2. example:
                1. thumb joint between the trapezium and metacarpal
          4. types of diarthroidal joint movements
            1. flexion
              1. decreasing the angle of the joint
              2. e.g., bending the elbow
            2. extension
              1. increasing the angle of the joint
              2. e.g., straightening the elbow
            3. hyperextension
              1. further extension or straightening of the joint
              2. e.g., bending the head backward
            4. abduction
              1. movement of the bone away from the midline of the body
              2. e.g., moving the leg out to the side
            5. adduction
              1. movement of bone toward the midline of the body
              2. e.g., moving the leg back to the other leg
            6. rotation
              1. movement of the bone around its central axis
              2. e.g., turning the head
            7. circumduction
              1. movement of the distal part of the bone in a circle while the proximal end stays fixed
              2. e.g., moving each leg up, to the side, and down in a circle
            8. eversion
              1. turning the sole of the foot outward by moving the ankle joint
            9. inversion
              1. turning the sole of the foot inward by moving the ankle joint
            10. pronation
              1. moving the bones of the forearm so that the palm of the hand faces downward when held in front of the body
            11. supination
              1. moving the bones of the forearm so that the palm of the hand faces upward when held in front of the body
            12. protraction
              1. moving a part of the body forward in the same plane parallel to the ground
              2. e.g., jutting chin out
            13. retraction
              1. moving a part of the body backward in the same plane parallel to the ground
              2. e.g., tucking chin in
    7. principles of body mechanics
      1. the wider the base of support, the greater the stability of the nurse
      2. the lower the center of gravity, the greater the stability of the nurse
      3. the equilibrium of an object is maintained as long as the line of gravity passes through its base of support
      4. the stronger the muscle group, the greater amount of work that can be safely done by it
      5. facing the direction of movement prevents abnormal twisitng of the spine
      6. dividing balanced activity between arms and legs reduces the risk of back injury
      7. leverage, rolling, turning, or pivoting requires less work than lifting
      8. when friction is reduced between the object to be moved and surface on which it is moved, less force is required to move it
      9. reducing the force of work reduces the risk of injury
      10. maintaining good body mechanics reduces fatigue of the muscle groups
      11. alternating periods of rest and activity helps to reduce fatigue
    8. application of the principles of body mechanics
      1. develop a habit of erect posture (correct alignment)
      2. use the longest and the strongest muscles of the arms and the legs to help provide the power needed in strenuous activities
      3. use the internal girdle and a long midriff to stabilize the pelvis and to protect the abdominal viscera when stooping, reaching, lifting, or pulling
      4. work as closely at possible to an object that is to be lifted or moved
      5. use the weight of the body as a force for pulling or pushing
      6. slide, roll, push, or pull an object rather than lift it to reduce the energy needed to lift the weight against gravity
      7. 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
      8. spread the feet apart to provide a wider base of support when increased stability of the body is necessary
      9. flex the knees, put on the internal girdle, and come down close to an object that is to be lifted

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This page was last modified on 6/1/03