Work-related musculoskeletal pain among physical therapists: A cross-sectional study in Kyoto and Shiga Prefectures, Japan.

OBJECTIVES: This study aimed to determine the actual working conditions and prevalence of musculoskeletal pain among physical therapists in Japan, and the risk factors associated with low back pain (LBP) and upper limb pain (ULP). METHODS: A cross-sectional study of physical therapists in the Kyoto and Shiga Prefectures was conducted using a self-administered questionnaire. The survey contents included questions regarding personal, work-related, and musculoskeletal pain factors. Logistic regression models were used to analyze factors associated with LBP and ULP. RESULTS: Responses from 1,479 participants were included in the analyses. The prevalence of LBP at the time of the survey and in the past one year was 40.1% and 74.3% in female, and 37.8% and 69.9% in male, respectively. The prevalence of ULP was 34.8% and 64.2% in female, and 27.2% and 53.3% in male. The number of patients who performed manual therapy per day, worked using a fixed-height bed, performed manual therapy, had job dissatisfaction and stress, were over 40 years old, and slept less than 6 hours were associated with LBP and ULP. Assistance task was a risk factor only for LBP, and female only for ULP. CONCLUSIONS: The prevalence of LBP and ULP among physical therapists in Japan was as high as that in nurses and care workers. Work-related factors associated with LBP and ULP were identified among physical therapists. Thus, to prevent work-related musculoskeletal disorders, measures to reduce the physical burden from the perspective of occupational health are required.

Effects of different bed heights on the physical burden of physiotherapists during manual therapy: an experimental study.

This study aimed to determine the effect of physiotherapists' physical burden caused by different bed heights during manual therapy. Thirty-three male physiotherapists performed tasks simulating lumbar massage and passive hip abduction range-of-motion exercise (ROM) on the beds with low height (LH) and adjusted height (AH), with each task performed three times. The anterior inclination angle of the physiotherapist's trunk was measured, the surface electromyograms of the erector spinae and trapezius muscles were recorded, and perceived stress was assessed. The indexes obtained were statistically compared for different bed heights. Additionally, the lumbar disc compression force and flexion torque were estimated. The lumbar burden caused by the excessive bending and the biomechanical burden and perceived stress were stronger at LH than AH. In ROM tasks using the right hand, the muscle activity was lower at the left lumbar region at LH than at AH. At LH, the anterior inclination angle increased and the lumbar muscle activity declined as the number of tasks increased. The burden on the shoulders was not significantly different by bed heights. Our results showed that, when physiotherapists perform manual therapy, it is necessary to adjust the bed height to reduce physical burden and ensure higher quality of service.

A field study of exposure to whole-body vibration due to agricultural machines in a full-time rice farmer over one year.

OBJECTIVES: The aims of this study were to clarify in detail the levels of whole-body vibration (WBV) exposure from a variety of agricultural machines in a rice farmer over one year, and to evaluate the daily level of exposure compared with European and Japanese threshold limits. METHODS: The subject was a full-time, male rice farmer. We measured vibration accelerations on the seat pan and at the seat base of four tractors with various implements attached, one rice-planting machine, two combine harvesters, produced by the same manufacturer, and one truck used for transportation of agricultural machines. The position and velocity of the machines were recorded in parallel with WBV measurements. In addition, during the year starting in April 2010, the subject completed a questionnaire regarding his work (date, place, content, hours worked, machines used). We calculated the daily exposure to WBV, A(8), on all the days on which the subject used the agricultural machines. RESULTS: The WBV magnitude in farm fields was relatively high during tasks with high velocity and heavy mechanical load on the machine, and had no dominant axis. The subject worked for 159 days using the agricultural machines during the year, and the proportion of days on which A(8) values exceeded the thresholds was 90% for the Japan occupational exposure limit and 24% for the EU exposure action value. CONCLUSIONS: Our findings emphasize the need for rice farmers to have health management strategies suited to the farming seasons and measures to reduce WBV exposure during each farm task.

A field study on the physiological workload of garbage collectors in the Japanese summer.

A field study designed to reveal the physiological workload on garbage collectors (GC) was conducted in Japan. Three drivers who only operated a garbage truck, three loaders who actually collected as a team, three solo collectors, and one clerical worker, totaling 10 male workers participated in this study. The ambient temperature and the relative humidity, activity intensity, and heart rate were measured on the three days in July. The mean heart rate of the workers, excluding the clerical worker, was 97.5 bpm. There were cases in which the heart rate limit, as defined by ACGIH, was exceeded, including a case in which the loader sustainably exceeded this limit for over an hour. There were 10 worker-days in which the 58%HRmax level (corresponding to the permissible limit specified in the Netherlands) was exceeded based on the findings of the 18 worker-days for the loaders and solo collectors. There were many cases in which the energetic load of GC in the humid summertime in Japan exceeded the permissible limits as established in the U.S.A. and the Netherlands. The careful inspection of the actual work conditions and improvements in the work environment should be implemented for the occupational safety and health of GC.

[Relatedness of occupational exposure to whole-body vibration and health, principally back symptoms].

OBJECTIVES: DISCUSSION is continuing about whether or not to update the Occupational Exposure Limit for Whole Body Vibration exposure (OELWBV) which was established in 1975 as a part of the Recommendation of Occupational Exposure Limits (OEL), issued by the Japan Society for Occupational Health. The objectives of this study were to clarify the necessity of the update and the adverse health effects of whole-body vibration by reviewing the literature and to help to compile a for detailed revisions. SUBJECTS AND METHODS: Mainly referring to our preceding review, the current OELWBV exposure was examined. The relatedness of adverse health effects, principally back symptoms and occupational exposure to whole-body vibration (WBV) was examined by reviewing review papers, the original English papers referred to in those papers, and original English and Japanese references from 2002 to 2010 retrieved through a MEDLINE search. RESULTS: The results show the necessity of updating the present OELWBV as soon as possible. The overwhelming majority of the literature consists of epidemiological studies showing the relatedness of WBV to back symptoms. Thirty epidemiological studies out of 28 literatures clearly show the presence of a relationship between WBV and back symptoms. Various indices of exposure to WBV and back symptoms show the dose response relationships. Among these, a few studies used A(sum)(8) (equivalent 8-hour r.m.s. acceleration value for the combined frequency-weighted vibration of three diagonal, that is x, y and z, axes) as the exposure index. All of these studies reported some dose-response relationship between WBV exposure and back symptoms. DISCUSSION: Despite the clear presence or absence of a relationship between WBV and back symptoms, 0.5 m/s(2) seems to be the unconfirmed threshold of risk. Focusing on data of A(sum)(8), we suggest that the risk increases over the magnitude of 0.30 m/s(2). To clarify this, further epidemiological studies and others should focus on A(sum)(8) around 0.30 m/s(2). CONCLUSIONS: The present OEL of WBV should be examined from the viewpoint of the risks of back symptoms referring to the epidemiological studies that show the larger risks of back symptoms in comparison with unexposed referent workers. We conclud that when updating the present OELWBV, A(sum)(8) should be taken into account for back symptoms, referring to the findings of epidemiological studies.

Effectual points of view in occupational health management for persons with cerebral palsy --interventional case approach in VDT work--.

In our previous study, we elicited effectual points of view (POV) in occupational health management for visual display terminals (VDT) operators with disabilities. In order to validate the POV, two VDT operators with cerebral palsy newly-participated in our case study. Problems were ascertained, and in order to attempt to reduce the workload and improve operability, we performed intervention using ergonomic measures. Evaluations were conducted through observations of the equipment used and posture, as well as measurements of sitting pressure distribution and surface electromyogram. For Case 1 (a 33 yr-old male), a trunk support was introduced inside the armrest of his chair to maintain the trunk in a comfortable position. For Case 2 (a 21 yr-old female), in order to improve her unstable sitting position, we changed her chair and adjusted it to an appropriate desk height. For both cases, we confirmed improvements in posture, sitting pressure distribution, myoelectric potential or operability. We were able to confirm that "maintaining of a comfortable trunk" and "alleviation of excessive bending, extension, and curvature of the spinal column and joints" obtained from the previous study as POV in health management are also effective in the present interventional cases.

Effect of mental stress on hemoglobin dynamics in trapezius muscles.

We examined the effect of mental stress on hemoglobin concentrations in the trapezius muscles of 20 healthy, non-smoking women. The participants held their arms out horizontally (physical stimulus) while standing upright for 1 min with 5 min intervals of seated rest, or performed Stroop's Color Word Test (mental stimulus), or both simultaneously. We measured heart rate, muscle tissue hemoglobin (oxy-hemoglobin, OxyHb; deoxy-hemoglobin, DeoHb; total hemoglobin, TotHb) concentrations in, and obtained surface electromyograms from the right upper trapezius muscle. Changes in the hemoglobin concentration (DeltaOxyHb, DeltaDeoHb, DeltaTotHb) induced by physical and/or mental stimuli were calculated. Changes with physical stimulus alone were compared with those induced by physical plus mental stimuli using repeated measures ANOVA. The DeltaDeoHb with physical and mental stimuli was significantly lower (p=0.013) than that with the physical stimulus alone, whereas the DeltaOxyHb and the DeltaTotHb values did not significantly differ (p=0.281, p=0.230). This finding indicates that mental load affects DeltaDeoHb in the trapezius muscle. We think that mental stimulus might provoke a reduction in oxygen consumption by the trapezius muscle. Further investigations using a longer duration of physical and mental stimuli are required.

[Low back load and satisfaction rating of caregivers & care receivers in bathing assistance given in a nursing home for the elderly practicing individual care].

Since the public nursing care insurance system was enacted by the Japanese government, a transition from conventional group treatment to the individual care is required. In Japanese nursing homes for the elderly, bathing assistance methods have shifted from use of traditional mechanical bathtubs or a big bathtub to methods using small homestyle bathtubs, known as "individual bathing assistance". A study on the work load of caregivers with individual bathing assistance has never been conducted. Therefore, in a nursing home for the elderly practicing the individual bathing assistance method, we explored low back load using surface electromyography and trunk inclination angle measurement. Moreover, subjective evaluations by not only the caregivers but also the care receivers were investigated. The individual bathing assistance time per person was about 35 min. When caregiver used the mechanical lift equipment to assist getting into and out of the bathtub, trunk inclination angle and muscle load were lower than with manual handling. Mechanical lift equipment had the advantage of reducing low back load. When caregivers gave assistance with dressing and ablution of the lower limbs, and in setting wheelchair footrests, trunk inclination angle and muscle load showed high values. The satisfaction rating of using the mechanical lift equipment showed the best score, and ratings of perceived exertion were about the same. Thus, the importance of safe and comfortable care for both caregivers and care receivers should be stressed to make effective use of assistance products and care equipment.

[Exposure to whole-body vibration of forklift truck operators in dockyards--actual exposure in Japan and evaluation by EN 13059].

Low-back disorders are well documented as occupational hazards among forklift truck operators. The potential risk factors that may lead to low-back pain include exposure to whole-body vibration (WBV). In Europe, test methods were developed to evaluate WBV in industrial trucks, and the European Standard which defines the methods has been published. We measured the vibrations of forklift trucks operated in the Hanshin harbour area adopting procedures based on the CEN test and report the evaluation results. If the WBV magnitudes of the ride on forklift trucks in the workplace were less than or comparable to those in the CEN test, the CEN test could be considered useful for the risk assessment of forklift truck operators exposed to WBV. In order to verify the applicability of the CEN test to the evaluation of WBV exposure in the field, we conducted measurements of the WBV of four forklift trucks for 19 d. The trucks had already been examined by the CEN test. The truck velocity, driver position (sitting or not), and gear lever position were also measured, and video footage was obtained for the study. The results indicate that the vertical WBV magnitudes of the four forklift trucks were below the CEN test values. No dominant WBV direction was observed on any of the measurement days. The Health value (obtained by combining the values determined from the vibration in orthogonal coordinates) was comparable to that from the CEN test for one truck. The values for the other three trucks were lower. The data obtained for three forklift trucks were analyzed in each operating condition. The vertical WBV magnitudes and Health values for the three trucks were below the CEN test values when the trucks were travelling forwards with a load. The WBV in the anterior-posterior direction had the largest adverse effect on the human body of the three orthogonal directions when the trucks were used for loading and unloading. The results suggest the CEN test can be applied to the evaluation of exposure to WBV from forklift trucks operating in the vicinity of the Hanshin harbour. It was observed that the anterior-posterior WBV is considerable, mostly through exposure occurring in the lifting mode. However, the CEN test is based on the travelling mode, and further WBV measurements under real working conditions with exact descriptions of detailed work situations and operating conditions are required.

Neuro-physiological study in persons with cervico-brachial disorders.

OBJECTIVES: In order to clarify the involvement in the nervous system by cervico-brachial disorders (CBD), we performed neurophysiological tests on the peripheral nervous system (PNS) and the central nervous system (CNS) in patients with CBD, subclinicals and healthy controls. SUBJECTS AND METHODS: We employed antidromic sensory nerve conduction velocities (SCV) in the hands and fingers for PNS function and event-related potentials (P300) for CNS higher function. Subjects for SCV were 27 patients, 14 workers with sign and symptoms of CBD (subclinicals) and 22 controls. Subjects for P300 were 23 patients, 12 subclinicals and 10 healthy controls. CONCLUSIONS: In the PNS, since significant reduction SCV in the index finger among patients was observed, we could not find clear evidence of decrease of conduction function. In the CNS, since the latencies and amplitudes of auditory P300 among patients were significantly delayed and decreased, respectively, and the latencies significantly correlated with symptom score, it was suggested that the dysfunction of the cognition and memory function. However, further investigation is necessary to clarify the mechanism.

[Evaluation of forklift trucks operated in dockyards for reducing exposure to whole-body vibration].

Our preceding study revealed that many fork-lift truck drivers in Japanese dockyards suffer from fatigue symptoms such as low back pain (LBP). It has been suggested that exposure to whole-body vibration (WBV) is a cause of their LBP. Using forklift models manufactured from 1982 to 2000, we measured and evaluated the vibration of forklift trucks operated in dockyards, adopting experimental procedures based on the European Standard. We investigated various factors related to WBV, with the main focus on attenuating seat vibration. This study showed that (1) the seats did not attenuate vibration in the vertical direction, (2) forklift trucks and their seats had not improved in terms of WBV attenuation for a decade, (3) some forklift trucks in which the seat suspension could no longer be adjusted to the driver's weight continued to be used without being repaired, and impractical seat adjustment methods were adopted, and (4) the seats did not attenuate vertical vibration well in the most undesirable frequency range. We conclude that forklift trucks and especially their seats should urgently be improved with regard to WBV attenuation in order to prevent LBP in forklift truck drivers.

Measurement of whole-body vibration in taxi drivers.

In a previous epidemiological study we reported that the prevalence (45.8%) of low-back pain (LBP) and the two-year incidence (25.9%) of LBP in 284 male taxi drivers in Japan was comparable with rates reported for other occupational drivers in which LBP frequently occurs. LBP was significantly related with the level of uncomfortable road vibrations, and, importantly, increased with total mileage. The aim of this study was to measure whole-body vibration (WBV) on the driver's seat pan of 12 taxis operating under actual working conditions. The results were evaluated according to the health guidelines in International Standard ISO 2631-1:1997. Finally, the relation between total mileage and WBV was investigated. The majority of the frequency-weighted r.m.s. accelerations of the taxis fell into the "potential health risks" zone, under ISO 2631-1:1997. It was clear that the taxi drivers were exposed to serious WBV magnitudes. Therefore, occupational health and safety management should be carried out to help prevent adverse health effects in taxi drivers. In particular, reduction of WBV in taxis and shortening of driving time to reduce duration of WBV exposure should be considered. Moreover, because many taxi drivers work 18 h every other day, the shortening of working hours and taking of rest breaks while working should be considered. Frequency-weighted r.m.s. accelerations of taxis had a tendency to decrease as total mileage increased. The relation between total mileage and WBV should be investigated by taking measurements on the floor and the back rest in addition to the seat pan.

[An experimental study on muscle tension reaction induced by voice among sign language interpreters].

The purpose of this study is to ascertain the incidence of cervicobrachial muscle tension induced by voice among sign language interpreters (SLIs). The analyzed subjects included 8 professional SLIs (Case group) who complained of pain in the cervicobrachial muscle when listening to others' talking and 8 other people who have not learned sign language (Control group). Matching sexes, ages, and smoking habits of the Case and the Control groups was carried out. Informed consent to participate in the study was obtained from all subjects. While subjects relaxed in a sitting position, surface electromyographies (EMGs) were recorded from the right and left trapezius muscles and biceps brachii muscles. During this time, all subjects had two listening tasks: to listen to lectures in Japanese and to listen to instrumental music. An inquiry about subjective symptoms was conducted just after each task. Root-mean-square (RMS) values per 100 ms in each of the tasks were calculated for analysis of surface EMG. An original criterion of judgment was that the threshold of RMS values was 3.8 microV, and its threshold continued for more than 1 s. The criterion was used and the muscle tension was confirmed. Results showed muscle tension in the trapezius muscles or the biceps brachii muscles among 5 of 8 subjects in the Case group, and in 1 of 8 in the Control group when listening to the lecture. 3 subjects in the Case group and none in the Control group showed muscle tension in the trapezius muscles when listening not to music but to the lecture. The differences between the Case and Control groups in these results were not statistically significant. Confirmed muscle tension in SLIs when listening to a Japanese lecture is probably induced by the Japanese voice. It is necessary to further investigate whether muscle tension is an acquired reaction from sign language interpreting or a pathological reaction. Listening to Japanese voices may contribute to muscular overload in SLIs so that it may be necessary for SLIs to relax their muscles during break times with an absence of Japanese voices.

[Risk factors for low back pain among taxi drivers in Japan].

We conducted a questionnaire study on low back pain (LBP) and working conditions among male taxi drivers employed in the company in Fukuoka city in order to investigate the occurrence of LBP and occupational factors related to LBP among taxi drivers. The study was undertaken through two questionnaires, the first conducted in 1999 (n = 280, first cross-sectional study), the second conducted in 2001 (n = 284, second cross-sectional study). The questionnaire results were used to conduct two analyses: 1) the one-year prevalence of LBP and the relationship between LBP and occupational factors in the second cross-sectional study, and 2) the incidence of LBP and the relationship between LBP and occupational factors from the first to the second cross-sectional study in the longitudinal study. The incidence cases were defined as subjects who met the following conditions: those who had never experienced LBP at the time of the first study but had experienced LBP during the previous year at the time of the 2nd study. The one-year prevalence (45.8%) of LBP among taxi drivers was comparable to rates reported for other occupational drivers in which LBP occurs frequently. This result indicates that LBP is an important health problem for taxi drivers, and an urgent occupational safety and health management issue. The two-year incidence of LBP among the taxi drivers was estimated at 25.9%. LBP was significantly related with the suitability of the driver's seat pan, total mileage on the taxi (total mileage), the level of uncomfortable vibrations on the road, job stress and time employed as a taxi driver. Importantly, the prevalence of LBP increased with increasing total mileage, a finding which had not previously been reported. The findings of this study also suggest that ergonomic problems with the driver's seat pan, whole-body vibration (WBV) and job stress may contribute to LBP among taxi drivers. Further study is needed to confirm how total mileage contributes to LBP. Furthermore, WBV during normal use of taxies should be measured in order to evaluate the association between WBV and LBP.

[Evaluation of a swiveling seat to reduce the physical load on forklift drivers].

Many forklift drivers have musculoskeletal disorders such as low back pain related to poor work posture and whole-body vibration. With a forklift operator's seat capable of 45-degree swiveling, we evaluated the physical reduction in the load in 10 subjects working in a back-looking position by means of surface electromyography (EMG) and the angle of rotation of the trunk and neck regions. The amplitude of surface EMG on the trapezius, erector spinae, and latissimus dorsi muscles in looking back or maintaining a back-looking position decreased with a swiveling seat compared to the stationary seat. Nevertheless, there was little alleviation of the amplitude of surface EMG on the sternocleidomastoid muscle in maintaining a back-looking posture and no decrease in looking back. The angle of rotation of the trunk maintaining a back-looking position was decreased greatly with the swiveling seat, but no decrease in the rotation angle of the neck was seen. Our study suggests that a swiveling seat is effective in reducing the physical load on the forklift driver during back-looking operations, and this may lead to the prevention of low back pain.