Chair Design Beyond Gender and Age
About the Authors:
Anthropometrics and Chair Design
Alan Hedge & Kees Breeuwsma
Anthropometry is the “science of measurement and the art of application that
establishes the physical geometry, mass properties and strength capabilities of the
human body. Anthropometric data helps designers determine the size and shape
of an ideal chair. Anthropometric data for most male and female body dimensions
overlap so designers work to sizes that span the range from a 5th percentile female to
a 95th percentile male. If female dimensions are smaller than the 5th percentile or male
dimensions are larger than the 95th percentile, these chair designs won’t fit. If 50% of
the target population is male and 50% is female, that means these design limits will
not provide a good fit for 5% users.
Alan Hedge is Professor in the Department
of Design and Environmental Analysis
at Cornell University, New York, where
he has directed the Human Factors
and Ergonomics teaching and research
programs since 1987.
Kees Breeuwsma is Vice President for
Seating at Teknion. Kees entered the
contract furniture business in 1982 after
completing his doctoral program at
Michigan State and Erasmus University
in the Netherlands.
Figure 1 Anthropometric dimensions of most importance to chair design.
The Cinderella Chair – is there
such a thing as the right fit?
In the fairytale Cinderella, Prince
Charming uses a glass slipper to find his
mystery princess because it fits only her,
unique foot.
If each of us could choose our own office
chair, it, too, would adjust to our specific
shape. But in the real world, companies
specify only offer one or a few models as a
corporate standard. So the challenge for
designers is to find a visually appealing,
ergonomic chair that fits the dimensions
of most users — and can adjust easily to
their specific needs.1
Using anthropometric data is complicated because a person who is at a particular
percentile for one body dimension will not necessarily be at the same percentile
for other body dimension. In other words, a woman who is at say the 5th percentile
for height will not necessarily be at the 5th percentile for all other body dimensions
and a man who is at the 95th percentile for height will not necessarily be at the 95th
percentile for all other body dimensions. A survey of seven chair design dimensions
for a sample of 778 people found that almost one-third fell outside of the 5th to 95th
1
1
Anthropometry is the “science of measurement and the art of application that establishes the physical geometry, mass properties and strength capabilities of the human body.” 2
percentile range for at least one body
dimension, and between one in six and
one in 12 did not fit the chair on at least
one pertinent body dimension.2
User Diversity
Anthropometric
data
is
further
complicated when workforces are
diverse. In the 2000 U.S. census, more
than one million residents reported
coming from 37 different ancestries,
while 100,000 residents reported
originating from 92 different ancestries.3
Therefore, U.S. anthropometric data
needs to be a composite of all these
ancestries, which can be complicated,
since races may be similar in certain
dimensions, but different in others.
For example, African Americans have
proportionally longer lower limbs than
European Americans, who have longer
lower limbs than Asian Americans.4
Unfortunately, anthropometric data
resources tend to be limited because
they are usually dated, restricted to
young healthy adult samples from certain
ethnic groups and regions, and focus
on skeletal dimensions at the exclusion
of soft tissue contours. Even when a
designer uses the best anthropometric
data available there can be mismatches.
For instance, a study of 30 students
from southern China showed that the
recommended seat depth of 38 cm was
too long for the dimensions of the users
and that seat depths between 31 and
33 cm were appropriate.5
2
Rather than a single chair model that
fits the majority of the population, some
manufacturers offer chairs in different
sizes. However, this complicates inventory
management, especially in environments
with high turnover, or where one chair has
many users (such as 24/7 operations).
Choosing an ergonomic chair
– making an informed choice
Unfortunately, when specifying a
chair for a corporate environment, it’s
impossible to know the body shape of
every individual user. Considering the
following variables can help designers
choose a chair that suits most:
Chair Strength: Must support the weight
of the average user. Body weight can
affect both durability and adjustability —
a lightweight person may have problems
operating controls designed for heavier
users, while a heavy person may exceed
stability limits. Special seating may be
required for exceptionally heavy or light
users.
Seat dimensions: The seat supports the
greatest proportion of body weight and
must provide the following features:
• Seat height - Must support the hips,
buttocks and thighs while the user’s feet
are on the floor or footrest. The height of
the front edge of the chair seat should
align with the popliteal (back of the knee)
height of the user. The seat height may
have to be readjusted whenever the seat
tilt is changed.
• Seat tilt - Should allow a range of tilt
adjustment — either set horizontal for
upright sitting, tilt backward for reclined
sitting, and forward for short-term
inclined sitting. (Note that prolonged
forward sitting compresses the thighs,
knees and lower legs and doesn’t
optimally distribute body weight on
the seat, leaving the user’s torso
unsupported by the chair back.6) Some
chairs have a free-float seat tilt that
adjusts as body weight shifts and some
provide adjustable tension to balance
body weight.
• Seat depth – Must offer clearance
behind the knees. When a user sits back
against the chair backrest, there should
be adequate clearance between the seat
pan and the back of the knees to avoid
any compression problems.
• Seat width – Should be wide enough
to comfortably accommodate the width
of the hips, but not too wide that the
user cannot easily rest their elbows on
the chair arms.
• Seat pan material - Must comfortably
distribute pressure and not restrict
movement. Breathable materials help
prevent heat and moisture buildup and
reduce discomfort.
• Seat-to-back angle – Must allow for
a reclined sitting posture with a thighto-torso angle beyond 90° to reduce
abdominal pressure, promote the lumbar
curve and reduce strain on the lumbar
spine.6.7
Backrest dimensions – Must support
individual body weight and stabilize the
body when reclining. The backrest should
be contoured and adjustable to maintain
a neutral lumbar curve. Backrests that
end below the shoulder blades or are
narrow are ideal for tasks that require
unobstructed upper body mobility. Taller,
wider backrests that end at or are higher
than the shoulder blades, provide better
support for reclined sitting. In addition,
the chair backrest should offer the
following features:
• Backrest height - Must provide
comfortable support for the lower and
upper-back.
• Head/neck support - Must provide
adjustable head/neck support if the back
is high enough to provide head/neck
support for extreme reclined sitting. This
lowers neck muscle activity by more
than 35% and shoulder muscle activity
by more than 64%.8
• Lumbar support - Must allow for
vertical adjustment to accommodate
different lumbar heights and depth
adjustment to accommodate different
lumbar curves. The apex of preferred
lumbar support is about 17 to 23 cm (~710 inches) above the seat pan.9
• Backrest width - Should be wide
enough to allow adequate hip clearance
when the user sits back in the chair. If
the backrest is too wide, it may restrict
comfortable elbow movement and
impede upper body mobility.
3
• Backrest contour - Should be
contoured to the user’s back and should
not restrict comfortable elbow movement
or limit upper body mobility.
• Backrest angle - Should allow for a
range of angles. Most users choose a
reclined posture of 25º.10
• Dynamic backrest - A backrest that
moves and provides support as the user
changes posture is preferred to a static
back.11
Controls – Intuitive control placement
increases usability12 so all controls
should be easy to operate from the
seated position. The ability to correctly
operate chair controls also affects
comfort13. Research shows that most
users tend to prefer controls with long
levers versus short levers and buttons.
Research also demonstrates that use of
adjustments increase with the number
of controls, and that chairs with more
controls are judged to be the most
comfortable. Office workers who receive
training on the use of chair controls
have significantly higher percentages
of adjusting behaviors, and take greater
advantage of chair adjustments.14
Armrests – For many tasks, arm support
reduces upper body fatigue, allows for
easier shifts in body position, and makes
it much easier to enter and exit the
chair. Armrests also help decrease body
flexion, which reduces stress in the knee
and hip joints during sitting-to-standing
transitions. This is especially important
for aging workforces.15
Armrests should be adjustable in height,
width and depth to comfortably support
the forearms or elbows while sitting with
relaxed shoulders. Armrests should not
limit access to the worksurface or any
other chair adjustments.
All too often, users adjust their body to
the chair rather than adjusting the chair
to their body. A recent study found that
61% of 100 Dutch office workers and
24% of 236 Spanish office workers never
made any adjustments to their chairs.16
Fitting Exceptional People
Modern
ergonomic
office
chairs
accommodate most but not all users,
and significant design changes are
sometimes needed to accommodate
people at the extremes of anthropometric
dimensions. For example, the range of
seat height adjustment must change
from 10 cm to 24 cm as the design limits
are increased to 99.9% of people. Even
if a chair had this adjustment range, it
would not accommodate individuals with
some form of dwarfism or gigantism.
Other physical changes can happen to
make normally sized adults exceptional.
For instance, after the first three months
of pregnancy, body mass and shape
changes17 although temporarily. Other
changes, such as significant weight
gain or loss, can be problematic if the
individual is not refitted.
Challenges for Chair Design
Even though a chair may be able to
adjust over the desired range, this does
not guarantee it will always fit a person’s
body.
Anthropometric data gives information
on skeletal dimensions and overall
body characteristics, but it does not
address other important factors, such as
form, appearance and movement. For
example, even though a chair meets all
the adjustment criteria, whether it has
a woven fabric, plastic, leather or mesh
finish can affect comfort.
mass and hip joints anterior to the chair
pivot point while men locate their center
of mass and hip joints posterior to the
pivot point. When a backrest is provided,
women sit with their center of mass
closer to the seat pan center of pressure
than do men. Other variables, such as
age and health can also influence sitting
posture.
User behavior will also affect comfort.
A study observing eight men and eight
women showed that regardless of the
chair or task, the average lumbar and
trunk angles were more flexed for men
than for women, with women sitting with
the pelvis rotated anteriorly and men
sitting with the pelvis rotated posteriorly. 18
Chair image and appearance is also
closely related to customer satisfaction.19
Users distinguish between aesthetics
and comfort parameters more easily
than between ergonomic features20
and perceived chair comfort directly
correlates with ratings of chair
aesthetics.21 Ultimately, the optimal fit
of the chair and the quality of the user’s
experience of chair comfort depend
on the interactions between user
characteristics, the tasks that the user is
performing and the chair design.
A higher lumbar backrest placement
and lower upper-back and neck rest
placement is better for women than
men, and some women need additional
space between the seat and the backrest
for thigh/hip/buttock clearance. When
sitting on a chair with a pivoting seat
pan, women position their center of
Today, users can choose from a wide
variety of ergonomic chairs and while
no chair will be universally well suited to
optimally fit all body types, a good chair
with appropriate adjustability will provide
a comfortable fit for a majority of users.
Choosing the best ergonomic chair for
the greatest number of users requires
knowledge of anthropometric data but
also information on body types, user
preferences and task demands.
Unfortunately, even when given a good
ergonomic chair, many users do not
adjust it appropriately. Instead, they
adjust their postures inappropriately,
increasing the risk of discomfort and
back injury.
Complex and awkward controls deter
users from making adjustments to their
chair.22 Innovative chair designs that
demystify chair adjustments, reduce the
apparent complexity of controls, and are
supplemented with improved training on
the use of chairs and appropriate sitting
postures will result in greater comfort for
everyone.
References
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