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Table 3. MANOVA for the chair type, Time and Chair Type x Time interactions effects, p
values were given in the table p; values p 0.05 are significant. Items
Chair Type p Time p
Chair Type x Time p Discomfort factors
Neck pain 0.082 0.000
0.982 Upper back pain
0.232 0.000 0.832
Mid back pain 0.269 0.000
0.973 Low back pain
0.215 0.000 0.990
Upper leg pain 0.144 0.001
0.952 Lower leg pain
0.153 0.006 0.378
Upper arm pain 0.206 0.000
0.914 Lower arm pain
0.640 0.003 0.882
Wrist pain 0.916 0.002
0.986 Fatigue
0.759 0.000 0.662
Comfort factors
Impression 0.013 0.598
0.803 Relaxation
0.925 0.851 0.630
Relief 0.976 0.977
0.926
Comfort 0.831 0.490
0.946
Discomfort 0.802 0.000
0.635 Note: p values were given in the table; values p 0.05 are significant.
3.3 Effect of chair, time, overall comfort and discomfort on body posture movements
Body posture movements were not significantly affected by the chair type Table 4 in this study. The subjective ratings were unaffected by the chair type
except for impression. Subjects’ frequency of movement was greatest in Chair ‘Q’ Figure 2; this was also the most uncomfortable chair in the analysis of subjective
data. Liao and Drury 2000 found that the subjects increased their frequency of overall postural shifts as body-part discomfort increased. In the present study, the
results of the body posture movements confirmed the results obtained in the subjective ratings. Further we plotted the body posture movements against
discomfort ratings in which positive relationship between discomfort and body posture movements Figure 3 existed. The frequency of movement increases
rapidly between discomfort levels 2 and 3. However, it was not significant. These results obtained are consistent with those obtained by Liao and Drury 2000.
Body posture movements were significantly affected by the time factor, with increase of time on task, postural shift frequency increased. Liao and Drury 2000
found that frequency of postural shifts associated with progression of time. There was no significant Chair x Time interaction effect indicating that the body postural
movements caused by the passage of time was not affected by the chairs selected in this study. The frequency of body posture movements increased with the
development of discomfort and fatigue. These results on the body posture movements again confirmed the results obtained in the subjective rating.
Laboratory Study of Factors Affecting Sitting Comfort and Discomfort
87
Table 4. ANOVA for the chair, Time and Chair x Time interaction as well as Comfort,
Discomfort effects on posture
Factors Body posture movements p values
Chair 0.054
Time 0.000
Chair x Time 0.938
Comfort 0.148
Discomfort 0.935
Note: p values were given in the table; values p 0.05 are significant.
6 5
4 3
2 1
1.00 0.90
0.80 0.70
0.60 0.50
Mean posture changesmin
Discomfort levels
Figure 2. Body posture movement ratio against time for chair type P, Q and S
0.02 0.04
0.06 0.08
0.1 0.12
0.14 0.16
0.18
30 60
90
Time minutes
B o
d y
p o
s t
u r
e m
o v
e m
e n
t s
r a
t i
o
Chair P Chair Q
Chair S
Figure 3. Relationship between body posture movement frequency and discomfort level
