In 1996, the number of low back pain (LBP) cases totaled 5, 162 in Japan, accounting for 60% of the total number of officially recognized cases of occupational diseases. In recent decades, the number of LBP cases, however, has been gradually decreasing. The rate of this decrease is slower in non-manufacturing industries than in other sectors, while the prevalence rate of LBP has tended to increase among workers in tertiary industries in 1995 and 1996. Epidemiological studies have clarified that workplace factors of LBP include not only the handling of heavy materials, but also unnatural postures, sudden and unexpected motions, and individual worker's characteristics. It was, therefore, suggested that comprehensive countermeasures to prevent LBP be undertaken on the basis of work environmental control, work management practice, and health care. The Labor Ministry of Japan issued guidelines for the prevention of LBP in 1994, in which various factors in the work environment, the importance of readiness for motion, standardization of work procedures, and exercise before work were newly outlined. In addition to the psychophysical and biomechanical models of LBP so far reported, established findings of physiological studies on muscle tone and postural reflexes have been conceptually introduced into the guidelines. Such physiological findings are essential for the mechanistic elucidation of work-related LBP and the preparation of its countermeasures, as LBP can also be caused by sudden and unexpected motions as well as various environmental factors. Physical and mental readiness to cope with changes in voluntary motions is a prerequisite for the prevention of LBP in daily work, which constitutes time-sequential changes in posture and motion under various environmental conditions. This paper critically reviews the workplace factors of LBP, its models for evaluating the workload on the body, and environmental risk factors with reference to the neural control of muscle contraction underlying the voluntary motion of workers.

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Out of the “Report on Workers' Casualties” presented by the employers in the entire nation in 1986 and 1988 to the Labor Standards Inspection Offices, 13, 166 cases diagnosed as low back pain (5, 820 cases in 1986 and 7, 346 cases in 1988) were sampled and studied. This survey revealed that its incidence in men was about 4 times greater than that in women, being noted uniformely in all age groups except the 50 or older age group in men. As to types of industry, it was seen to be high in those working in the mining and cargo industries, as well as those working in the transport, traffic, forestry and agriculture, livestock, and fishing industries. As to the types of occupation, the incidence of low back pain was high in those working in transportation and construction. Onset was noted every month throughout the year, but a little less in December. It was pronounced at the beginning of the week, and seemed to peak immediately after starting the day's work, at 9 a.m. followed by 10a.m. There was a trend toward accidental low back pain being caused frequently when one worked in an unnatural posture, especially in regular work when acting single-handed.

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A cross-sectional questionnaire study was conducted on cooks working for nursery schools n N city in order to verify epidemiological evidence of the work-relatedness of low back pain among them. After female workers aged 30 or more were selected from a study base of 2, 799 workers in social welfare facilities, low back pain prevalence of cooks (n=240) was compared with nursery school teachers (n=955). Age-standardized prevalence ratios (PRs) of low back pain were 1.9 (95% CI: 1.5-2.5) in cooks compared with nursery school teachers. Among cooks, relative risks of low back pain increased with the increase in the number of lunches to be prepared and decreased with the increase in the number of cooks making lunches in a logistic regression model controlling age and body length. Low back pain was also found to be associated with self-estimated job stressors/work load by logistic regression models. Multifactorial effects from ergonomic and psychosocial factors, and individual factors on the low back were suggested. From the viewpoint of epidemiological criteria for work-relatedness, it was concluded that the work-relatedness of low back pain among cooks in nursery schools was partially supported.

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Work-related low back pain and cervicobrachial disorders have become increasingly common among nursing personnel with the increase in the number of social welfare institutions and workers. The aim of this study is to assess the burden on the low backs of personnel caring for children. We measured work content, working time, posture and muscular activity in 16 nursery workers in three different types of institutions for healthy and handicapped children. The working time and posture of 7 nursery teachers in a public nursery school for healthy children (A school), 7 nursing workers (4 nursery teachers and 3 nursery instructors) in a public daycare center for mentally and physically handicapped children (B center), and 2 nursery instructors in a private home for severely handicapped children (C home) were analyzed. The muscular activity of the erectores spinae muscle of three subjects was measured using a newly developed EMG monitor (portable EMG monitor, PEMM). The following results were obtained. The average length of a lesson or activity in A school was greater than that in B center and C home. The time required by care for meals was longest in C home. The arrangement and rearrangement times were longest in the classes of children aged 3-5 in A school. The time occupied for clerical work and other work was relatively longer, while recess including lunch time was approximately one hour. The most commonly observed posture was sitting on the floor in all kinds of classes, with this occurring most often in C home. Hazardous postures such as bending forward, squatting, and kneeling appeared in 11-18% (48-81 min) of a day's working time. The average muscular activity of the erectores spinae muscle of three subjects throughout a day was approximately 10% of the maximum isometric contraction (% maximum work load, %MWL), when muscular activities were measured by PEMM. The relatively high %MWL values (19-27 %MWL) were obtained at a slightly bending posture and a kneeling posture, while lower (1-9 %MWL) values were observed at a sitting posture. The %MWL values at a sitting posture varied according to such conditions as duration of sitting, back rest, weight on the arms, twisting of the trunk, and hip movement. The risky nature of the sitting posture are also discussed.

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Objectives: The purpose of this study was to investigate the prevalence of low back pain (LBP) among various groups of subjects exposed to hand-arm transmitted vibration, and to compare the prevalence of LBP of these subjects with that of non-exposed groups. Methods: The subjects of this study were 13 groups of males and 3 groups of females of working population leaving in a certain city located in the central part of Japan. By means of a questionnaire, interviews, field visits, or annual health examination, information on age, working career, working posture, various types of tools used, and experience of having LBP during the 12 months preceding the completion of the questionnaire were collected. The subjects'age ranged between 22 and 69 years. All subjects were classified into 5 categories, and the prevalence of LBP was obtained for them. Results: On the whole, complaints of LBP among male and female green tea and strawberry farmers were most frequent. There was a large variation (16.0-72.2%) in the prevalence of LBPamong subjects operating vibrating tools. Among three groups of health care professionals, the prevalence of LBP was in the range of 36.5-53.0%. The senior doctors had less complaints of LBP. The prevalence of LBP among subjects who had sedentary jobs was in the range of 41.7-45.9%, and almost as high as that in blue-collar workers using vibrating tools. The prevalence of LBP among females exposed to hand-arm transmitted vibration was between 26.1 and 63%. The prevalence rates of LBP among vibration exposed subjects were plotted against the vibration magnitude of tools used by the same subjects reported in our previous study; however, no significant correlation could be obtained between the prevalence of LBP and vibration values. Conclusions: Exposure to segmental vibration is less likely to be a risk factor in increasing prevalence of LBP. A higher prevalence of LBP in some groups provide strong evidence for a dominant work-related etiology in developing LBP. Regarding data presented in this study and by a review on scientific literature, suggestions for improving working posture were presented. It seemed that to decrease the risk of LBP among these subjects, special attention should be paid to stimulating the adoption of an ergonomic working posture and to ergonomic training.

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To monitor the low back risk imposed by asymmetric postures at workplaces, a method using angular velocity sensors was studied. According to a simple model analysis, trunk rotation could be calculated from the angular velocities measured at both the waist and shoulder and from the inclination of each angular velocity sensor. We thus developed a new detector consisting of an angular velocity sensor (ENC-05D, Murata, Japan) for detecting angular velocity and an acceleration sensor (ADXL05, Analog Devices, USA) for measuring inclination. The precision of the angular velocity sensor was high as the correlation coefficient between the output of the sensor and the true value was 0.9996. When the detectors were affixed to a subject and compared with data measured by a Vicon System 370 (Oxford Metrics, UK), the correlation coefficients between the two methods were 0.949 and 0.815 during model tasks of box transfer and box lifting, respectively. In a model of lifting boxes at different rates, the mean and standard deviation increased according to the task speed. This method was shown to be of practical use for monitoring trunk rotation.

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Back support belts are one of the important measures for preventing low back pain. One theory attributes the effectiveness of such a belt to the intraabdominal pressure it applies. The purpose of this study was to investigate the effect of a pelvic belt on abdominal pressure when the subject held four different weights at four different bending angles. The subjects of the study were ten male students who did not suffer low back pain. They wore a cuff with a blood pressure meter on their abdomens under the pelvic belt. They held a weight for 5s slightly above an adjustable stand at a specified forward bending angle. The external abdominal pressure (EAP) was measured 4s after lifting the weight. The weight was 0, 10, 20 or 30kg; the angle was 0, 30, 60 or 90°; there were 4×4=16 trials/subject. As the weight increased (at all angles), EAP increased significantly. However, at 0kg and 10kg, EAP decreased as the angle increased; at 0kg, EAP decreased significantly. Thus, the belt should be effective for manual material handling due to the sensitive response of EAP for low back load. With light weights such as 0kg and 10kg, it is better to use the belt at small bending angles than at large bending angles because EAP decreases as the angle increases.

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According to the Labor Standard Bureau of Japan, accidental back injuries accounted for about 60% of all occupational injuries and diseases in the last decade. The Ministry of Labor issued guidelines to prevent low back injuries in 1994 to address the problem. The use of back belts is recommended for some special working conditions but details on its proper use were not given. This study was planned to evaluate a newly developed back belt and was done at an express package delivery company where the incidence of low back injury was high. The BackTracker was used to evaluate the effect of the back belt on the range and velocity of torso motion. The results indicated that there were no significant differences in the range of motion (ROM) during flexion/extension, lateral bending, and rotation between with and without the belt. The maximum angular velocity (MAV) of flexion decreased significantly (average decrease: 30±28.3°/sec) when the back belt was worn. The MAV of extension with belt showed a decreasing tendency though not significant. No notable trends were observed in the MAV during lateral bending and rotation of the subjects while wearing and not wearing the belt. The results also indicated that the back belt affected differently the torso motion of each subject. This study suggested that this back belt could be useful for tasks with high velocity of flexion/extension and that proper instruction on the use of the back belt is needed for each worker.

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Low back pain is still a common and serious issue at worksites. In order to evaluate preventive effects on low back pain by providing a participatory occupational safety and health program, we conducted a 10 year follow-up study at the Tokyo Metropolitan Bureau of Waste Management and examined yearly changes in the number of compensated and claimed low back pain. The participatory occupational safety and health program is based on a small-sized group and joint employee-employer involvements. This program includes analysis of occupational accidents, revision of the safety procedure manual, participatory training classes, improving and evaluating working procedures and personal protective equipments, and so on. The number of compensated low back pain from 1984 to 1994 has decreased from 318 to 87, and the number of claimed low back pain has decreased from 343 to 92. These results suggest that the participatory occupational safety and health program is effective in preventin of low back pain.

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This paper reports on a strategy to improve and renovate assembly lines, including countermeasures to prevent low back pain during the past two decades at Toyota Motor Co. Since 1975, there have been problems with low back pain at Toyota's vehicle assembly lines. To deal with these low back pain problems, it was necessary to determine their causes and to quantitatively evaluate the burden on workers. For this purpose, functional burden indexes were developed, that is, a posture burden point and a weight burden point were determined to assess the load on the low back, and a low extremity point and a squatting posture point were determined to assess the burden on the leg. The functional burden index, however, could be applied only to specific human functions, not to human functions in general. Since there are about 400 kinds of working patterns in vehicle assembly lines, comprehensive burden index was required to estimate overall burden of such work. Thus, we developed Toyota's Verification of Assembly Line (TVAL), an index for assessing the physiological stress of an assembly line work, in which an equivalent bicycle ergometer workload is calculated from electromyograms taken of 20 different muscles under actual working conditions. At present, TVAL is used to measure physiological burden of assembly work in order to give priority to improvements, and to objectively demonstrate the effects of such improvements at Toyota.

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Intraocular pressure (IOP) has never been compared between hard working and sedentary subjects. The relationship between physical fitness and IOP is not clearly known. There are only two studies and their results are contradictory. The variability in their results may be due to several factors. Therefore, the present study was planned to investigate the relationship between working style, physical fitness and IOP after taking into account those factors that can affect IOP. One hundred fifty male volunteers of a steel factory were divided equally in two groups. The subjects of group 1 were sedentary worker, whereas group 2 subjects were actively engaged in heavy works requiring exertion. Physical fitness was evaluated by the measurement of maximum oxygen uptake with a Bechman O₂ analyzer. IOP was measured with the Goldmann applanation tonometer. As compared to sedentary subjects, maximum oxygen uptake was significantly higher whereas IOP was significantly lower in those who did moderate or severe exertions. The maximum oxygen uptake difference between groups 1 and 2 was found to be (mean±SD) 5.1±1.1ml/kg/min (p<0.001), whereas, IOP difference was 1.9±0.7mmHg (p<0.001). This study concludes that hard working is associated with physical fitness and physical fitness is associated with reduced resting IOP. It would seem reasonable at present not to discourage subjects who have ocular hypertension from exercise; perhaps, on the contrary, it should be encouraged to increase their physical fitness.

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The aim of this study was to evaluate working conditions using a personal computer with a flat panel display (FPD) in terms of visual and musculoskeletal comfort. Measurements of viewing distance, viewing angle, head angle, neck angle and electromyogram (EMG) activities of the neck, shoulder and back muscles of visual display terminal (VDT) operators were compared at workstations using an FPD and a desktop personal computer (DPC). A notebook personal computer (NPC) with a 10.4 inches FPD, was used in this experiment. Each of 10 healthy subjects performed word processing tasks using both NPC and DPC workstations. Significant differences in the work posture while using the NPC and DPC were seen with viewing distance, viewing angle and head angle. The characteristic features of the work posture using the NPC were a remarkably short viewing distance and a forward inclination of the head. The value of integrated EMG (IEMG) of the neck muscle was greater while using the NPC than when using the DPC. These phenomena were caused by the structure of NPCs; most NPCs have a display and keyboard which cannot be separated and are not adjustable without tilt and swivel mechanisms. VDT devices that cannot be adjusted may potentially make operators assume a poor posture while working, which could cause visual and musculoskeletal disorders. To prevent visual and musculoskeletal problems using NPCs, a more upright head and neck position was recommended. The addition of a mechanism for adjustment of the height of an NPC display would allow a comfortable downward gaze without the loss of correct posture.

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In order to investigate the relationship between occupational exposure to dust/chemicals (toxic gases/fumes) and chronic respiratory symptoms in Vietnam, the questionnaire standardized by the American Thoracic Society was applied to 368 subjects living in Ha Thai district of Vietnam. According to the results of multiple logistic regression analyses, the odds ratios of chronic respiratory symptoms by occupational exposure are over unity, except for the relationship between chronic cough and occupational exposure to chemicals. Especially for chronic breathlessness, significantly higher odds ratios are observed among people with a history of occupational exposure to dust or chemicals: 2.925 (95% CI: 1.130-7.574) for dust, and 3.721 (95% CI: 1.412-9.803) for chemicals. As for the interaction between occupational exposure to dust and cigarette smoking, it is considered that occupational exposure leads to an increase in chronic respiratory symptoms independent of the effects of cigarette smoking.

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2-Bromopropane (2BP) has been implicated to be the reason for the mass intoxication of workers at an electronic company in Korea. A case series study indicated that 2BP was the possible causative chemical for reproductive toxicity, causing severe anemia accompanied by amenorrhea among female workers, and azoospermia or oligospermia among male workers. To clarify the effect of 2BP on the female reproductive function, repeated doses of 2BP were tested on female Sprague-Dawley rats for 21 days. Ten rats were assigned to each treatment group. The rats were maintained in a 12hr:12hr light-dark cycle and vaginal smears were monitored daily for 3 cycles. After the rats had completed 3 estrous cycles, vehicle control olive oil, 300mg, 600mg, and 900mg/kg of 2BP were injected into intraperitoneum for 14 days. The female rats were then mated with male rats on a 1:1 ratio basis. The treatment continued for an additional 7 days. Rats treated with 2BP experienced a significant decrease in body weight gain depending on the dose of 2BP. The estrous cycles of the rats continued at a normal duration of time before the initiation of treatment, showing 4.32 days for the control group, 4.79 days for the low dose, 4.63 days for the middle dose, and 4.75 days of estrous cycle for the high dose group. 2BP treatment, however, induced a significant delay of the estrous cycle in the high dose treated group, showing 11.1±3.82 days of the estrous cycle. 2BP decreased the fertility and tended to decrease in the number of pups born, depending on the dose. A 900mg/kg treatment of 2BP decreased ovarian weight, but 2BP did not affect the length of gestation. Our results indicated that 2BP seemed to be the causative agent for amenorrhea observed in female workers.

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To elucidate the biological effect of static magnetic fields (SMF), we measured lipid peroxidation in the liver, kidneys, heart, lungs and brain of mice exposed to SMF and also evaluated the combined effect of SMF exposure on the hepatotoxicity induced by treatment with carbon tetrachloride (CCl₄). Lipid peroxidation in the liver was significantly increased by exposure to 4.7T of SMF for 3, 6, 24, or 48h, whereas that in the kidneys, heart, lungs and brain was not changed compared to the control. The combination of CCl₄ injection and SMF exposure caused an increase in lipid peroxidation in the liver exceeding that caused by either treatment alone. Furthermore, the increase in activities of both GOT and GPT caused by CCl₄ administration were also enhanced by SMF exposure. These results indicate that the exposure to strong SMF induces lipid peroxidation in the liver of mice and enhances the hepatotoxicity caused by CCl₄ administration.

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Lead is a toxin widely used in industry. Recently, medical investigation into lead exposure has turned to testing organ systems, such as the immune system, that historically were not associated with lead poisoning. We evaluated the effects of doses of 13, 130 or 1, 300ppm of lead on the adherence of mouse peritoneal cells, and particularly on macrophages. Cellular adherence was measured according to the De la Fuente technique. Adherence of macrophages showed significant changes in the 1, 300ppm group, revealing a reduction to 55% of the control group. The macrophage adherence index showed 91% sensitivity and 96% specificity. These results indicate a considerable reduction in the adherence of peritoneal macrophages following exposure to certain levels of lead.

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The fitness of the half facepiece of a gas mask to the face of a worker handling organic solvents was evaluated through the quantitative determination of the concentrations of both organic solvent vapors and airborne dust inside and outside the facepiece. Leakage rates for dust were measured using a mask-fitting tester on a facepiece with a dust filter-covered respirator cartridge of organic solvents. The same facepiece was evaluated for the leakage rate for organic solvent vapors through the determination of the concentrations of the air inside and outside the facepiece. Highly significant correlations were found between the leakage rates obtained for dust and those for organic solvent vapors. The leakage rates for organic solvents were found to be slightly higher than those for dust. The present finding suggested that the leakage of organic solvent vapors from the interstice between the facepiece of gas masks and workers' faces can be evaluated using the leakage rate for dust for the same facepiece of the gas mask attached with the cartridge covered with a high efficiency particulate air (HEPA) filter.

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