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Anthropometry

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REBA (Rapid Entire Body Assessment )

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Anthropometry

  • Initiative
  • Imagination
  • Needs
  • Dexterity
  • Intelligence
  • And so forth

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  • Visual acuity
  • Determination
  • Upper back strength
  • Age
  • Leg length

Anthropos (human) + metrein (to measure)�The study of how people vary in

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Engineering Anthropometry

  • Physical body size
    • Static
      • Two dimensional
      • Three dimensional
    • Functional

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  • Strength
    • Isometric
    • Dynamic – isotonic, iso- kinetic, iso-inertial etc.
    • MVC joint torques
  • Biomechanical / inertial properties
    • Segment mass
    • Segment center of gravity locations
    • Muscle attachment sites and lever arms
    • Failure stresses of ligaments, tendons, bones etc.

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Selection vs. Job Modification

  • Two basic strategies:
    • Selection—fit the person to the job.
    • Job modification—fit the job to the person
  • Follow the second strategy: the key to progress has been to challenge the environment.

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Exclude as Few as Possible

  • Minimizes the number of people excluded, which tends to make the job easier for everyone
  • Balance seriousness of exclusion with cost of inclusion

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Excluded Percentile

  • May be:
    • Upper (a door tall people can’t fit under)
    • Lower (a task requiring manual dexterity)
    • Both (intelligence test for factory job)
  • Designing for the mean may exclude half the population.

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Population Dimensions

  • Define the user population.
  • Consider the source of population dimensions
    • Male/female
    • Military/civilian
    • Age
    • Ethnicity
    • Occupation

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Body Position Descriptions

  • Planes
    • Saggital – divides the body into left and right half (medial/lateral)
    • Coronal – divides the body into front and back half (anterior/posterior)
    • Transverse – divides the body into top and bottom half (superior/inferior)
  • Limbs
    • Proximal: close to torso
    • Distal: further from torso

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Wrist/Hand Motions

  • Flexion – closes the joint angle from neutral position.
  • Extension – opens the joint angle from neutral position.
  • Adduction/ abduction – opens and closes laterally

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Wrist/Hand Motions

  • Radial deviation/ulnar deviation

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Wrist/Hand Motions

  • Pronation/supination

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Body Dimensions

  • Sample 95th percentile dimensions (cm) of nude U.S. adult civilians.

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Female

Male

Stature (height)

173.73

186.65

Eye height

162.13

174.29

Thigh height (sitting)

18.02

18.99

Forward reach

79.67

86.70

Hip breadth (sitting)

43.22

41.16

Weight (kg)

84.8

99.3

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Variations in body dimensions

  • Most body dimensions do not correlate well with stature, coefficient of determination R2 is less than 50%. So be careful when predicting other dimensions from stature.
  • Individual segment weights are calculated from total body weight.
  • In absence of data female may be estimated as 93% of male if no data available

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Variations in Strength

  • Females average 63% isometric strength of males.
  • Strength of specific muscle groups varies depending on
    • Limb: Leg approx. 3 times strength of arm
    • Direction exerted: Strength may decrease by 50%
    • Preferred hand/arm/leg: Strength may vary by 40–50%
  • Left and right leg strengths do not differ appreciably.

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Other Characteristics

  • Age
  • Personal space

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Age of Workforce

  • Birth rate is declining.
  • Additional workers must come from immigration
  • Longer work hours
  • Delayed retirement
  • Older workers must be considered.

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Personal Space

  • Intimate (0 – 18 in.)
  • Personal (18 – 48 in.)
  • Social (4 – 12 ft)
  • Public (> 12 ft)
  • Boundaries vary with gender, familiarity, and culture.

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Statistical Calculations

  • Normal distribution provides a close approximation.
  • Mean (average) is 50th percentile.
  • Normal distribution is symmetrical.
  • Absolute variability given by standard deviation.
  • Relative variability given by coefficient of variation.

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Normal Distribution

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Distribution Calculations

  • To Find Percentile
    • Find difference from the mean (subtract).
    • Convert to standard units (divide by standard deviation).
    • Use table to find percentile.

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Distribution Calculations

  • To Find Dimension
    • Use table to find number of standard units from mean.
    • Convert to dimension measure (multiply by standard deviation).
    • Add or subtract mean.

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Anatomical Landmarks

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Measurement Postures

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Ergonomics is based on:

  • Anthropometric data
    • For adults of a specific ethnic group
      • Maximum: 95% men
      • Minimum: 5% woman
  • Neutral position
  • Middle of range of motion
  • Empirically verified

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Mistakes

  • Do not design for yourself and assume it will be satisfactory for everyone else.

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  • Do not design for the average person and assume it is satisfactory for those at the outer ranges.

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  • Ergonomic designs are not based on intuition -- they are based on data.

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Seats

  • Seat Depth:
    • Buttock-popliteal length (440 mm for 5% woman)
  • Seat Width:
    • Minimum: 25 mm less than maximum breadth of hips (typical 385 mm)
    • Wider necessary for arm rests.
  • Seat Height:
    • Popliteal height (380 mm minimum)

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Backrest Angle

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Handles

  • Handle Diameter:
      • 30-50 mm for power grip
      • 8 – 16 mm for fine work
  • Handle Length: 100-120 mm long for power grip
  • Clearance:
      • 115 x 50 mm for handles (eg. Suitcases)
      • 35 mm for finger or thumb affordance (ok, this is a rule of thumb….)
  • 25 mm radii where hand might engage
  • For high torque use 70 mm (for turning such as a screwdriver)
    • Note that this increases with diameter
    • Optimal shear force on handle occurs at 30-50 mm

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Handles

  • Rounded cross section
  • Support surfaces for palm/finger as appropriate
  • Texture (not too smooth or rough)

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Neutral Position

Neutral wrist position (as always!) occurs at 110- 110 degrees

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