human factors lectures 3a-3c anthropometry

Anthropometry

Measurement of human body dimensions used in engineering design and ergonomics.

Structural (Static) Anthropometry

Measurement of body dimensions in standard, still postures (e.g., sitting height, stature). Used for clearance and fit.

Functional (Dynamic) Anthropometry

Measurement of body dimensions during movement or activity (e.g., forward reach, overhead reach). Used for reach and performance.

Popliteal Height

Vertical distance from the floor to the underside of the thigh next to the knee while seated; determines chair height.

Acromial Height

Vertical distance from the floor to the acromion (shoulder) process when standing upright.

Eye Height

Vertical distance from the floor to the inner corner of the eye when standing or sitting erect.

Hip Breadth (Sitting)

Maximum horizontal distance across hips while sitting erect; used for seat width.

Elbow-to-Elbow Breadth

Horizontal distance between elbows when sitting erect with arms at sides; used for workspace clearance.

Thigh Clearance

Vertical distance between the seat surface and the thigh-abdomen intersection; affects under-desk clearance.

Arm Reach

Horizontal distance between the tip of the middle finger and the shoulder; used for reach envelope design.

Morant Technique

A method using perpendicular grids to project body landmarks for measurement. Useful for capturing accurate anthropometric data in research or when direct caliper measurement is impractical

Anthropometer

Device for measuring human body dimensions such as height and reach.

Percentile

Value of a variable below which a specific percentage of a population falls (e.g., 95th percentile).

Z-Score

Standardized value used to calculate percentiles in normally distributed anthropometric data.

Mean (μ)

Average value of a dataset; measure of central tendency.

Standard Deviation (σ)

Measure of dispersion or variability in a dataset.

Design for the Mean

Design approach accommodating the 50th percentile user when adjustability is not critical.

Design for One Extreme (short or small user)

Design for 5th percentile users when reach is primary concern (smallest users).

Design for the Other Extreme (tall or large user)

Design for 95th percentile users when clearance is primary concern (largest users).

Design for Adjustability

Design that accommodates a range of users (typically 5th percentile female to 95th percentile male). Consumer product – very common

 Workplaces – not that common

 Not practical or desirable in many design situations:

 Economically infeasible

 Design constraints

Radius of Gyration (k)

Distance from axis of rotation where the entire mass could be concentrated without changing MOI; reflects mass distribution.

Moment of Inertia (MOI)

Resistance of an object to changes in rotational motion; depends on mass and distance from rotation axis.

Center of Mass (CoM)

Point at which a body’s mass is equally balanced in all directions.

Parallel Axis Theorem

Used to calculate MOI about an axis not through the center of mass.

Dempster’s Body Segment Parameters

Biomechanical data giving average segment mass (% body mass), CoM, and radius of gyration for body parts.

ANSUR Database

Anthropometric survey of U.S. Army personnel providing standardized human measurements.

Active Range of Motion (ROM)

Extent of movement produced by muscle contraction; usually less than passive ROM.

Passive Range of Motion (ROM)

Extent of movement achieved with external assistance (e.g., another person).

Correlation Coefficient (ρ)

Measures relationship strength between two body dimensions (e.g., stature and arm reach).

Human Variability

Natural differences within and between populations that require adjustability in design.

Design Principle Conflict

Occurs when designing for small reach and large clearance simultaneously; resolved with adjustability or zoning.

Design for Clearance

Ensures adequate space for movement or equipment use; typically based on 95th percentile male.

Design for Reach

Ensures smallest users can reach; typically based on 5th percentile female.

Static Dimension

Measurement of body while still; examples: stature, sitting height.

Dynamic Dimension

Measurement of body while moving; examples: reach or bending postures.

Ergonomics

Application of human measurements and capabilities in design to optimize comfort, safety, and performance.

Adjustability Range

Span between smallest (5th) and largest (95th) user dimensions a design can accommodate.

Moment

Rotational effect of a force acting at a distance from an axis.

Mass

Amount of matter in an object; proportional to inertia.

Normal Distribution

Bell-shaped statistical distribution describing most anthropometric data.

manikins

lifelike human models (2D or 3D) and computerized models can be used to simulate the anthropometric characteristics of a user population and evaluate proposed designs.

factors that affect anthropometric data

age, gender, ethnic background, body position, clothing

Tragion – Top of Head

The vertical distance between the right tragion landmark and the horizontal plane tangent to the top of the head.

Bitragion Chin Arc

The surface distance between the right and left tragion landmarks across the chin landmark

Bitragion Submandibular Chin Arc

The surface distance between the right and left tragion landmarks across the submandibular landmark

Bizygomatic Breadth

The maximum horizontal breadth of the face (between the zygomatic arches) at the left and right zygion landmarks.

Head Breadth

The maximum horizontal breadth of the head above the plane of attachment of the ears.

Head Circumference

The maximum circumference of the head above the attachment of the ears is measured with a tape passing just above the ridges of the eyebrows and around the back of the head.

Head Length

The distance from the glabella landmark to the opisthocranion landmark

inertia

refers to an object’s tendency to maintain its state of motion. The greater the mass, the greater this

force

a push or pull that can cause an object to accelerate or decelerate.

Newton’s Laws of Motion

An object will remain at rest or move with a constant velocity unless acted upon by an external force. This equation also describes how forces cause changes in an object’s motion

Newton’s Laws of Equilibrium

An object is in equilibrium when the sum of all forces acting on it is zero, and the sum of all moments acting on it is zero.

Dempster’s Body Segment Parameters

a gold-standard source in

biomechanics and ergonomics for

estimating:

 Segment mass as a % of total body mass (P)

E.g.,

 Center of mass (COM) location from the

proximal end (R_proximal)

 Radius of gyration (K_proximal) to calculate

moment of inertia