Trunk postural demands of physical occupational activities for women in Benin
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Women in Benin commonly participate in physically demanding activities that involve the carriage of heavy loads on the head and back. These strenuous tasks combined with pregnancy can result in back pain that may persist after delivery in some cases. The objective of this study was to examine how the trunk postures of pregnant women in Benin were affected by their occupational activities. This study also examined trunk postures, as well as postures of the head relative to the trunk, in the specific task of carrying loads on the head. Finally, the instrument used in this study to measure trunk postures, the Virtual CorsetTM (VC) (Microstrain, Williston, VT, USA), was validated against a system of potentiometers. Questionnaires completed by 26 pregnant and 25 non-pregnant subjects revealed that 58% of pregnant women suffered from back pain since the start of pregnancy. An average of 328 instances of trunk flexion at angles larger than 60° were recorded during the workdays of 17 pregnant women, while 66 of those flexions events were held for more than four seconds. Furthermore, an average of 36% of the recorded workday was spent in trunk flexion at angles exceeding 20°. Trunk postural data, at C7 and S1, as well as sagittal positions of the head relative to the trunk were compared between pregnant and non-pregnant subjects and between unloaded and loaded walking conditions for the specific task of head load carriage. These comparisons showed that load on the head significantly increased upper trunk extension and lateral bending of the upper trunk towards the left during walking. Motion of the head relative to the trunk and motion of the upper trunk significantly decreased in the loaded condition and was compensated by increased motion at the sacrum level. In the validation study, the VC was moved at different speeds to observe the effects of accelerations on the angle measurements. Root mean square difference between the angles measured by the VC and the potentiometers were all below 5° and 6° for flexion-extension and lateral bending, respectively, with the exception of rapid movements where errors were slightly larger.