Skilled Work

1
Skilled Work

• Usually hand and finger work
• Coordinated muscle activity
• Precise movements
• Learning is 2 phase process
• Learning movements-conscious control
• Adaptation of organs involved
• From conscious to automatic
• Gradually eliminate unnecessary muscle
  decrease energy requirements

2
Skilled Work

• Phase I Training
• Short training sessions
• Requires high concentration
• Split job into separate components
• Set performance expectations for most difficult
  components
• Practice important components alone and later put
  in sequence
• Strict control and good examples
• Avoid bad learning habits
• Young people learn by example
• Older people learning depends more on visual
  aids

3
Skilled Work

• Phase II Body Adaptation
• Gradual changes in muscles and other organs
• Build muscle strength
• Reduce internal friction
• Eliminate connective tissue and fat
• Develop sensitivity of neural pathways (reflex
  arc)
• Maximum Control of Skilled Movement
• Max speed of manual operation is in front of the
  body, elbows at side, and 90 degree elbow angle
• Best working metabolism with shoulder abducted
  8-23 degrees
• Precision of movement
• Outward movement more precise
• Speed max at 45 degrees to right with right hand
• Lowest oxygen consumption 60 degrees from
  sagittal
• Decreses as distance increases
• Highest precision and fastest movement if forearm
  the primary limb

4
Hand Tool Design

• Tools are useless by themselves
• Tools link workers with their job
• Tools extend the capabilities of the worker
• Optimal tool design involves
• anthropometry
• anatomy
• functional considerations
• mechanical considerations

5
Hand Tool Design

• Hand Grips poor design can lead to poor
  performance and injury
• Max grasp force quadrupled by changing from
  finger grasp to whole hand
• Finger power maximized when bent slightly upwards
  (dorsal flexion)
• Grasp power ( skill) reduced if hand bent
  downward or turned to side
• Ulnar/radial deviation reduces rotational ability
  50 percent and may inflame tendons if repeated
• Grip Guidelines
• Shape handle for grip assist
• Distribute forces across hand
• Palm not suitable for stress concentration
• Wider and cushioned handles all for wider area to
  bear resultant forces
• Add stops to prevent tool slippage

6
Hand Tool Design

• Design of hand grips
• Cylindrical, ? 100 mm long, effective up to 30-40
  mm thick
• Guidelines Grip
• Consider hand clearance for optimal grip span
• If too small or too large, forces cant be
  applied (7.5 cm measured at center of hand best)

Strength (N)
Grip Span (cm)
7
Hand Tool Guidelines

• Guidelines Grip
• Consider finger clearance
• Use analysis of how tools is used and placement
  of hands and fingers
• Finger anthropometry
• Minimizing concentrated stress over soft tissue
• Palm
• Fingers
• Protect hand from external energy
• Heat, cold
• Vibration
• Electric shock

8
Hint and Equipment for Max Skill

• Manual operations elbows lowered and forearm
  angle 85-100 degrees
• Delicate work raise working field to visual
  field, support forearm
• Skilled operations with minimize force (heavy
  force more difficult to control)
• Avoid imposing static stress at same time
• Improve concentration on manual operations
• Support work, foot pedals, chutes and conveyors
• Try prevent doing multiple things at same time
• Arrange operations in rhythmic sensible sequence
• Allow free rhythm rather than imposed pace
• Less energy, motor control easier, reduced
  fatigue, less monotony boredom
• Too slow requires support, too fast creates
  nervous stress
• If using both hand, work field should extend
  little as possible to side (best visual control),
  symmetrical motion (begin and end together)

9
Hint and Equipment for Max Skill

• Forearms and hands at most skillful in precision
  and speed if take place in 45-50 degree arc to
  each side
• For grasping working optimum is 2/3 of
  maximum reach
• Horizontal movement easier than verticle control
• Circular easier than zig zag
• Each operation should end in position to start
  next one
• Handle shaped to fit hand and operate when hand
  held in line with forearm

10
HT Guidelines

• Maintain straight wrist (neutral position)
• Use gloves with caution
• Extra clearance required
• Forces applied are less than bare hand
• Safety hazard caught in rotating parts
• Prevent tool slippage during use
• Flat metal and smooth plastic tool handle can
  slip
• Best compressible rubber hadles that do not
  absorb liquids and oils
• Avoid repeated finger activities
• Finger not used to open or close a tool, use a
  spring
• Trigger mechanisms should use multiple fingers to
  minimize trigger finger syndrome
• Minimum static loading on hand arms
• No heavy tools for extended periods
• Extended use tool not to exceed 0.5 kg
• CoG close to hand to minimize slipping turning
  during use
• Elbows close to body not elevated when in use