postech h uman s ystem d esign lab oratory three evaluations of task-surface heights in elderly...

POSTECHHuman System Design Laboratory

Three evaluations of task-surface Three evaluations of task-surface heights in elderly people’s homesheights in elderly people’s homes

Heli Kirvesoja et al. (1999)Applied Ergonomics

2009. 07. 08. Wed.Lee, Jee-hea


ContentsContents

1. Introductiona. Aged-related changes in bodyb. Evaluation and aims of the study

2. Material and methodsa. Subjectsb. Mock-up simulatorc. Data collection and analysis

3. Resultsa. Score evaluation of task-surface heightsb. Scores on chairsc. Scores on kitchen facilitiesd. Subjective comparison of two different task-surface heightse. Human evaluations by the subjects and the expert vs. anthropometric

compatibility

4. Discussion and recommendationsa. Chairsb. Kitchen facilitiesc. General discussion

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1. Introduction1. Introduction

The number of elderly people ↑ Physiological capabilities ↓

Confine most of their activities to their homes (Meindle and Freivalds, 1992)

The time spent at home & the demands on home conditions ↑

For the ergonomic design of home facilities for the elderly Knowledge about human body size is important Information about functional capabilities, mobility, abilities as a function

of changes in biomechanical, physiological, psychological and mental characteristics is also needed (Kelly and Kroemer, 1990)

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1.1 Age-related changes in body1.1 Age-related changes in body

1. Stature Stature & Sitting height ↓ BUT, no change of the length of BSP (ex. Shoulder-to-elbow length,

elbow-to-middle-finger length) INSTEAD, decrease of functional reach (ex. Arm span)

2. Flexibility of joint of the body Decrease The disability of the elderly and the handicapped• Poor balance, lack of coordination, limited stamina, difficulty in handling and

fingering, in bending and kneeling, and inability to use the lower extremities (Sanders and McCormic, 1993)

3. The condition of musculoskeletal system Ability to maintain balance and stride length and steppage height

Decrease (Kivela et al., 1994) Muscle force Decrease (Rundgren, 1991) Muscle function Change (Berg, 1986) Musculoskeletal capacity Change ( Nygard et al., 1991)

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1.2 Evaluation and aims of the study1.2 Evaluation and aims of the studyEvaluation

The measurements to verify that a product will do what it is supposed to do

Should be done in actual operational situations Difficult to illustrate a work situation using an anthropometric model

• Standard anthropometric measure : static• Human actions : dynamic Full-scale mock-up

Home simulator• Small tasks (daily activities) according to oral instructions

Aims Part of a larger project which aims at improving the possibilities of the

elderly to move safely and to manage independently in their homes by gerontechnological means

Obtaining Static anthropometric measures To define how old people assess various different heights after a short-

term trial with task simulation using furniture or fixtures To compare the subjectively acceptable heights with the

recommendations given in the anthropometric literature

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2.1 Subjects2.1 Subjects

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Represent well the

corresponding Finnish elderly


2.2 Mock-up simulator2.2 Mock-up simulator

Static mock-up simulator A room with furniture and fixtures whose heights could be adjusted

stepwise of with various task-surface heights Perform the task with every task-surface heights, which are from

1. The common heights of the environment the elderly lived in2. Structures that are commercially available

Three video camera record the whole body movements of the subjects

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Chairs Kitchen facilities

350450 550 450

w/ arm rest

The upper cupboard

The work surface heights

The kettle shelf


2.3 Data collection and analysis2.3 Data collection and analysis

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1 2 3 4 5 6 7

Much too high

Too highSlightly too high

SuitableSlightly too low

Too lowMuch

too low

optimal chair seat height (OSH) = popliteal height + shoe height

AC (Δh) = actual seat height - OSH popliteal height


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3.1 Score evaluation of task-surface 3.1 Score evaluation of task-surface heightsheights

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The main statistics of subjects’ score (SS) and experts’ scores (ES)

(N=55)


3.2 Scores on chairs3.2 Scores on chairs

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Condition

SS ES s.d.

350 Too low Lower High

450 (both)

Suitable Low

550Slightly too

highToo high high

The main statistics of SS and ES

The t-test between SS and ES

H0 : there is no difference between the scores

∴ there are difference between the scores except for 45cm with armrests


3.3 Scores on kitchen facilities3.3 Scores on kitchen facilities

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The main statistics of SS and ES

The t-test between SS and ES

H0 : there is no difference between the scores∴ there are difference between the scores except with regard to the work surface height of 900 mm, at the α = 0.01 significance level

Kitchen facilitie

s

conditions

SS ES

Upper cupboard

LowSlightly too high

~ suitableSlightly too

high

High Slightly too high Too high

Work surface

80 cm SuitableSlightly too low

~ too low

90 cm SuitableSuitable ~ slightly too

high

Kettle shelf

16.5 cm Suitable Too low

26.5 cm SuitableSlightly too

high

Usually “too high”


3.4 Subjective comparison of two 3.4 Subjective comparison of two different task-surface heightsdifferent task-surface heightsTo compare the difference between the subjects’ ratings of

two heights of the same furniture or fixtureWilcoxon’s matched-pairs signed-ranks test

H0 : there is no difference between the ratings of the two heights of furniture

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∴ All the differences of SS are statistically significant except 450mm and 450mm w/ armrest


3.5 Human evaluations by the subjects 3.5 Human evaluations by the subjects and the expert vs. anthropometric and the expert vs. anthropometric compatibilitycompatibility

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EScomb

Regression EScomb = -0.19Δh + 4.55

Correlation r = - 0.89 (α = 0.000)

SScomb

Regression SScomb = -0.11Δh + 4.31

Correlation r = - 0.76 (α = 0.000)

Regression relation between score and Δh Correlation the degree to which the actual values agree with the predicted value

• EScomb is changed more by Δh than Sscomb. • The seat height is near the scores for “slightly too low” Seat height should be higher than OSH

• EScomb is changed more by Δh than Sscomb. • The seat height is near the scores for “slightly too low” Seat height should be higher than OSH


Three evaluations of task-surface Three evaluations of task-surface heights in elderly people’s homesheights in elderly people’s homes

1. ES vs. SS (t-test)2. Each height ratings of SS (Wilcoxon’s test)

3. ES or SS vs. AC


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4.1 Chairs4.1 Chairs

The chair height of 400 mm is good Similar to 450mm in the present study

Elderly do not like higher chairs Even though being easier to get up from

The armrests did not affect the suitability scores If they have to sit for a long time on a chair, they prefer to have armrests Do not need armrests as a help for getting up from the chair

Positive relationship between patellar height and stature stature can be used as a reasonable aid to estimate

popliteal height when choosing chair seat height

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4.2 Kitchen facilities4.2 Kitchen facilities

Upper cupboard 1600 mm

Work surface 900 mm Elbow height 850mm Similar to 850mm in the present study

The lowest kettle shelf 300 mm Similar to 265mm in the present study

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4.3 General discussion4.3 General discussion

The Finnish elderly’s main anthropometric measuresMethods are useful and practicable for studying task-

surface heightsStature alone is not an adequate basis for designing task-

surface heights The elbow height, popliteal height, etc. should be measured 5th and 95th percentiles of measures other than mean and s.d. are needed

Classifications made at five-year intervals would be more suitable

Investigation of the static and dynamic anthropometry is necessary

The score of 4.3 is near “suitable” from regression

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Recommendations

1.Every aged person chooses for him/herself a proper fixed-height level

2.Adjustable height

Design for all

More applicable to cognitive characteristics than the basic

human measures


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