M.G.Mohamed Thariq et al. AJE Vol.9 2009 79-98
84
for analysis. The posture change frequency i.e., the number of posture changes per minute was calculated. The questionnaire survey data and the posture change
frequency data were analyzed using SPSS version 13.0 software.
3 Results and Discussions
3.1 Factor separation
We verified the factor structure of sitting comfort and discomfort before investigating the interactions between underlying factors of sitting comfort and
discomfort. The factor analysis was conducted with Varimax rotation to separate main factors for data collected using rating questionnaires; the results separated the
underlying factors rated in the questionnaires into two main factors Table 2. Factor 1 discomfort factor consists of neck pain, upper back pain, mid back pain, low back
pain, upper leg pain, lower leg pain, upper arm pain, lower arm pain, wrist pain, and fatigue. Factor 2 comfort factor consists of impression, relaxation, and relief.
This result confirmed the factor structure obtained by Zhang et al. 1996 and Helander and Zhang 1997. The results obtained were also similar to those obtained
in class room settings by Thariq and Munasinghe under review.
3.2 Chair and time effect
MANOVA was conducted to identify the Chair, Time, and Chair x Time interaction effects on comfort and discomfort factors, as well as on overall comfort
and discomfort perception Table 3.
Table 2 . The results of factor analysis
Underlying factors of sitting comfort and discomfort
Factor 1 discomfort factor Factor 2 comfort factor
Neck pain 0.797 -0.213
Upper back pain
0.810 -0.186
Mid back pain 0.715 -0.384
Low back pain 0.622 -0.372
Upper leg pain 0.725 -0.398
Lower leg pain 0.701 -0.283
Upper arm pain 0.640 -0.156
Lower arm pain 0.712 0.076
Wrist pain 0.733 0.015
Fatigue 0.730 -0.093
Impression 0.072 0.784
Relax -0.277 0.723
Relief -0.232 0.839
Laboratory Study of Factors Affecting Sitting Comfort and Discomfort
85
3.2 Chair and time effect
MANOVA was conducted to identify the Chair, Time, and Chair x Time interaction effects on comfort and discomfort factors, as well as on overall comfort
and discomfort perception Table 3. Chair type had no significant effects on discomfort factors or on discomfort
perception. Helander and Zhang 1997 found that biomechanical discomfort factors e.g. pain increased as a function of time of day, and that chair design did not seem
to matter. Discomfort perception and all discomfort factors were significantly affected by sitting Time. The Chair x Time interaction effect did not significantly
affect overall discomfort factors or discomfort perception. The results suggest that discomfort perceived in this study was caused by the passage of time while sitting.
These results are similar to those obtained by Helander and Zhang 1997; they believed that the time dependency is a fatigue effect.
Chair effect had no significant effect on relaxation and relief but a significant effect on impression. Further, the results showed that the overall comfort perception
was not significantly affected by the chair. These result may suggest that a significant chair effect on impression comfort factor alone may not be sufficient to
rate the chair as comfortable. However, Helander and Zhang 1997 obtained significant chair effects for all comfort factors measured. In a study under class room
settings conducted by Thariq and Munasinghe under review, impression, relaxation and relief were affected by chair type. The present experiment was
conducted in 1.5-h session whereas the study under class room settings was conducted for 3-h time periods. In the class room experiment by Thariq and
Munasinghe under review, relaxation and relief were affected by the time, but relaxation and relief were unaffected by the time factor in the present experiment.
Therefore the duration effect may be the possible reason for the chair effects not being significant except for impression.
Overall comfort perception and comfort factors impression, relax and relief were unaffected by the Time or the Chair x Time interaction in the present study.
This indicates that comfort perception as well as impression, relaxation, and relief did not change over time while sitting. Similar results were obtained by Helander
and Zhang 1997 for time the Time and Chair x Time interaction effects on comfort factors.
In a separate analysis data not presented, age and gender did not affect comfort factors, discomfort factors, overall comfort or discomfort. This means that
age and gender effects are immaterial in comfort and discomfort perception while sitting, although this conclusion may be due to the fact that all subjects tested were
of a limited age range and were university students who were all used to sitting and carrying out similar type of activities. We also analyzed the effects of overall
comfort and discomfort on typing speed and accuracy because these values may indicate the level of typing skills between subjects; we observed no significant
effects.
