The objective of this study is to clarify the prevalence of and risk factors for low back pain (LBP) in schools for physically and mentally handicapped children. This study design is a cross-sectional study. The subjects included were 1,869 staff members from 19 prefectural schools for children in Shizuoka Prefecture, Japan, which included schools for the blind, deaf-mutes, physically handicapped, and mentally retarded children. A total of 975 subjects completed two postal questionnaires which included morbidity, demographic factors, nursing activity, and psychosocial factors. The answer rate was 52%. The one-month prevalence of LBP was 45%. According to the classification of nursing activity, assistance in movement 1.67 (95% CI 1.27-2.14), excretory function 1.45 (1.11-1.88), and feeding 1.44 (1.10-1.90) showed significant increases in the odds ratio. The adjusted odds ratio significantly increased by 2.35 (1.78-3.11) in the group with depression symptoms as well as in the group with job stressors such as quantitative, qualitative, and physical work loads, job control, utilization of technique, interpersonal conflicts, and degree of satisfaction with their work/home life.

A head-mounted display (HMD) with inappropriate mass and center of mass (COM) increases the physical workload of HMD users. The aim of this study was to investigate the effects of mass and COM of HMD on physical workload. Twelve subjects participated in this study. The mass and posteroanterior COM position were 0.8, 1.2, or 1.6 kg and -7.0, 0.0, or 7.0 cm, respectively. The subjects gazed at the target objects in four test postures: the neutral, look-up, body-bending, and look-down postures. The normalized joint torques for the neck and the lumbar region were calculated based on the measured segment angles. The results showed that the neck joint torque was significantly affected by mass and COM and it increased as the HMD mass increased for all test postures. The COM position that minimized the neck joint torque varied depending on the test postures, and the recommended ranges of COM were identified.

Estimation of Trunk Muscle Parameters for a Biomechanical Model by Age, Height and Weight: Akihiko Seo, et al. Department of Intelligent Systems, Graduate School of Engineering, Tokyo Metropolitan Institute of Technology—To establish more accurate equations for estimating the moment arm length and cross‐sectional area of the erector spinae and rectus abdominis muscles, the effects of height, weight and age on those muscles were analyzed by using a high‐order polynomial equation. Data on the moment arm length and cross‐sectional area at L3/ 4 were obtained from MRI images of 152 males and 98 females. The statistical model used in this study has any combination of up to third‐order independent variables for age, height and weight. The effective independent variables were selected by the forward step method of multiple regression analyses. The results of multiple regression analyses showed that the polynomial equations for the moment arm length of erector spinae in both genders, and that for the rectus abdominis in males, contained all three variables of age, height and weight. That for the moment arm length of female rectus abdominis contained the variables of weight and age. The multiple correlation coefficients of the erector spinae and rectus abdominis were 0.355 and 0.650 for males, 0.364 and 0.411 for females, respectively. The equations for the cross‐sectional area of the erector spinae in both genders, as well as that for male rectus abdominis contained only one variable (weight). The multiple correlation coefficients of the cross‐sectional area of the erector spinae were 0.576 for males and 0.469 for females. The cross‐sectional area of the female rectus abdominis had no effective variables.

Leg Swelling during Continuous Standing and Sitting Work without Restricting Leg Movement: Akihiko Seo, et al. Department of Public Health, Hiroshima University School of Medicine—To clarify the dynamics of leg swelling during standing and sitting work without restricting leg movement, lower leg swelling and subjective complaints were measured during work under three working conditions: Straight standing, buttock chair sitting and ordinary chair sitting. Twelve subjects (eight males and four females) were assigned jigsaw puzzles as a task for an hour. The lower leg swelling and subjective complaints were recorded every two minutes. The lower leg swelling was measured by the bioelectrical impedance method. The results were as follows: (1) The lower leg swelling increased during the work under all working conditions. The swelling was least for straight standing and greatest for ordinary chair sitting. The mean and standard deviations for leg swelling after one hour's work were 5.8±3.9% for straight standing, 8.2±4.7% for buttock chair sitting and 9.7 + 7.5% for ordinary chair sitting. (2) The subjective complaints also increased during work. Complaining of lower leg dullness was least for ordinary chair sitting and greatest for straight standing. The relation to the leg swelling was reversed. Complaining of low back pain was more common for buttock chair sitting than for other working postures. It is reasonable that prolonged standing is more likely to cause leg swelling than sitting because of high hydrostatic pressure. This theory has been supported by studies on motionless standing and sitting. Our results obtained without restricting leg movement, however, showed a reversed relation. It was considered that leg swelling factors such as low muscle activity and lymph pumps, low interstitial pressure brought on by low muscle activity, and the seat pressure during prolonged sitting may be dominant in the sitting posture although the hydrostatic pressure was low compared with the standing posture.

PKC-alpha may help to modulate the right ventricular hypertrophy caused by pulmonary hypertension in HHE.