[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.

Sleeping and working hours of residents at a national university hospital in Japan.

This study aimed to examine the status of time spent working and sleeping by resident doctors before the introduction of the New Training System for Residents in Japan. A time-budget survey was conducted over a 4-wk period on 102 residents at the Shiga University of Medical Science Hospital, and the response rate among residents was 76% of a total of 2,722 person-days. The average number of hours spent sleeping was the lowest and spent in the hospital including commuting time was the highest in residents of the surgery department, at 4.4 h and 18.9 h, respectively. Forty percent of residents reported dozing off at work, with the incidence rate being highest in residents of the surgery department (0.7 times/person-day). Dozing appeared to occur in response to the lack of sleep and fatigue, since the same residents slept longer on nights before days they reported not dozing off than on nights before days when they did doze off. Strong correlations were observed between the number of sleeping and working hours and between working hours and the number of patients in a resident's care. In order to maintain high standards of training and to get sufficient sleep it is therefore necessary for residents to manage their work and the number of patients in their care.

Work schedule differences in sleep problems of nursing home caregivers.

Nursing home caregivers (n=775; 604 women; mean age 33.6 years) were studied to examine how work schedules affect their sleep. The shift group (n=536) worked under a rotating two-shift system (n=365), a rotating three-shift system (n=66), or other types of shifts (n=78). The non-shift group included 222 caregivers. Participants completed a questionnaire about working conditions, sleep problems, health, lifestyle, and demographic factors. The two-shift caregivers reported the highest levels of difficulty initiating sleep (DIS, 37.6%), insomnia symptoms (43.0%), and poor quality of sleep (24.9%) among the groups. Adjusted odds ratios for these problems were significantly greater for the two-shift caregivers than for non-shift counterparts: DIS (odds ratio 2.86, 95% confidence interval 1.57-5.20), insomnia symptoms (2.33, 1.36-4.02), and poor sleep quality (2.15, 1.09-4.22). Our data suggest that working under a rotating two-shift system, which has a longer night shift, is associated with an elevated risk of sleep problems for nursing home caregivers.

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.

[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.

Dependency of temporary threshold shift of vibratory sensation in fingertip on 1/3 octave-band hand-arm vibration exposure period.

OBJECTIVES: To investigate the dependency of temporary threshold shift of vibratoty sensation (TTS(v)) in fingertip on hand-arm vibration exposure period. METHODS: Six healthy students were instructed to grip a vibrating or nonvibrating handle in the experimental room. The gripping force was 40 N. The vibratory sensation threshold at 125 Hz was measured before and after the exposure in the exposed middle fingertip. The exposure vibration was vertical and the 1/3 octave-band vibration with had a central frequency of 200 Hz and an intensity of 39.2 m/s(2). The exposure periods were 8, 15, 30, 60, 120, 240 and 600 s. TTS(v,t) was evaluated as the difference in vibratory sensation threshold between immediately before and t seconds after the exposure. RESULTS: TTS(v) recovered exponentially as in several previous studies and its use enabled us to estimate the time constant and TTS(v,0). TTS(v,0) with vibration exposure was significantly larger than that without it. The regression analysis of the relationship between vibration exposure period (T) and TTS(v,0) (T) for each subject confirmed the good fit of the equation TTS(v,0)(T)=B(0)+B(1) (*)Log(10)(T), where B(0) and B(1) are the calculated constants (adjusted R(2)=0.56-0.87). The time constants did not show such a clear dose effect relationship of exposure period as TTS(v,0). CONCLUSION: The dependency of TTS(v,0) on vibration exposure period was asymptotically proportional to the logarithm of gripping period. To more quantitatively confirm the relationship of the time constants for recovering time course of TTS(v), it may be necessary to improve the measurement method for TTS(v).

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.