Low Back Pain (LBP) Incidence, Ergonomics Risk and Workers' Characteristics in Relations to LBP in Electronics Assembly Manufacturing.

AIMS: Electronics industry workers might have increased the risk of low back pain (LPB). This cohort study aimed to investigate LBP incidence and provide a baseline of ergonomic factors and workers' characteristics associated with LBP.
METHODS: A six-month monitoring phase was designed using 196 electronic workers to identify LBP incidence. Baseline data were collected for ergonomic risk by RULA and lighting intensity measurement. Personal factors and work stress were surveyed by job content questionnaires (JCQ).
RESULTS: Ergonomic risk related to sitting posture was indicated at inspection with lamp (66.7%; change needed). High risk was shown among standing workers at punching and E-check processes. The lighting intensity did not meet the recommended standard in the arm range zone 2 of inspection and E-check stations. Dissatisfaction was reported due to work stress, workload, work rhythm, and job control. The six-month LBP incidence was 52.5%. Work experience less than three years (RR = 1.41; 95% CI: 1.031.90) and chronic diseases (RR = 1.41; 95% CI: 1.091.82) were significantly correlated with LBP incidence.
CONCLUSIONS: Ergonomic and lighting conditions at E-check and inspection should be improved, and the promotion of short break exercise during shiftwork period is suggested. LBP should be closely surveilled in workers who had less job experience and underlying diseases. Copyright:

INTRODUCTION

Low back pain (LBP) is among the most commonly reported health problems in working populations in Thailand.[1] Recent research among workers in one electronics industry in Thailand, showed a high prevalence of musculoskeletal disorders (MSDs) including lower back pain. The highest severity of pain was reported in the following three anatomical areas, i.e. lower back, upper back, and shoulder.[2] This previous study already suggested the prevalence and correlated risk factors for some areas such as shoulder pain were due to the repetitive nature of their work and ergonomic risk conditions.[3] However, there is still no report from a cohort study to identify the incidence of MSDs including low back pain, a chronic symptom among electronic workers.

Electronic workers hold static postures by the nature of their work involving prolonged sitting or standing with repetitive upper limb movement.[4] These work characteristics might induce LBP in the long term as in a previous report among office workers.[5] LBP impacts on health, and can also affect efficiency, effectiveness, and productivity due to work absence.[6] There are various possible risk factors for LBP including individual factors such as age, gender,[7] ergonomic factors such as prolonged sitting and prolonged standing,[8] exposure to working environment factors such as lighting, and seats or station level, and physical factors such as lifting, high workloads, and repetitive tasks.[3678] In addition, psychosocial factors such as co-worker, leader or manager relationships, or work stress, have been reported as risk factors of LBP.[9] According to Thai Labor Regulations,[10] the lighting condition should be also controlled. This study aimed to determine the incidence rate of low back pain among electronic workers. Workers’ characteristics and ergonomics risk were analyzed for their association with LBP among electronic workers.

METHODS

Participants

The prospective cohort group participants were selected from 354 electronic workers in a large electronic assembly manufacturing located in Northeast Thailand. The study was carried out between February and October 2016. The sample size calculation for estimating LBP for the cohort study was based on a hypothesis of relative risk (RR ≠ 1).[11] To test the value of the LBP incidence based on the previous finding of sitting posture workers (83.0%)[5] with a 5% level of significance with a power of 90%, the proportion of non-seated workers to have low back pain at 50%. The minimum sample size requirement was 60 workers per group for standing and sitting. To allow for participant withdrawal and dropout during follow-up, the required sample size was increased by 30% to a total of 156 workers for the cohort group. The participants were screened for no current LBP. Inclusion eligibility was they were full-time employees for work in the next year. Participants were excluded if they had an episode of LBP care or pregnant. The final number was 101 sitting workers of inspection process who used a microscope and a lamp, and 95 standing workers in the assembly line of small items for electronic circuit board of household appliances, i.e. rice cookers and computers.

DATA COLLECTION

Baseline measures and screening data were collected by face-to-face interviews using a structured questionnaire previously used by Chaiklieng et al.[3] The questionnaire collected baseline factors in three parts. Part 1 inquired about personal factors such as gender, age, marital status, job position, work experience, Body Mass Index (BMI) based on the obesity measure for Thai people (BMI >25),[3] ordinary exercise (at least 30 min once and 3 times a week), and chronic diseases (open questions). Part 2 inquired about work characteristics such as working posture, work experience at the current task, appropriateness of workstation, repetitive work. Part 3 focused on work stress questions based on 12 items from the Job Content Questionnaire (JCQ)[12] with a 5-point Likert scale (very satisfied, satisfied, neutral, dissatisfied, and very dissatisfied) with responses categorized into appearing satisfied (very satisfied, satisfied, neutral) or dissatisfied (dissatisfied and very dissatisfied). The details of 12 items relating to aspects of job contents in demand including working time, work hard, workload, and work rhythm. JCQ was also related to job control over their work situation and decision authority to participate in decisions about their work, as shown in Table 1.

Table 1

JCQ appearing dissatisfied items of electronic workers (n=196)

Job contents	n (%)
Job demand
Enough working time to complete	153 (78.1)*
Work hard	128 (65.3)
Excessive workload	150 (76.5)*
Work fast	138 (70.4)*
Job control and decision
High skilled work level	100 (51.0)
Had been learning new things	162 (82.6)*
Variety of work	90 (45.9)
Required creativity	107 (54.6)
Develop always own ability	132 (67.4)
Allow own decisions	133 (67.9)
Lot to say	139 (70.9)*
Decision freedom	144 (73.5)*

*Stress (>70% of workers)

Ergonomic risk factor assessment was performed using Rapid Upper Limb Assessment (RULA) to measure, repetitive movement, force, awkward posture to neck, body, shoulder, arm, hand, wrist, leg, and foot. Total scores were used to classify participants into four risk levels; 1: score 1-2 (acceptable posture), 2: score 3-4 (low risk and further investigation and change may be needed), 3: score 56 (moderate risk, change needed soon), and 4: score 7 (high risk, change needed immediately).[13]

Workstation lighting intensities were measured by using a light meter 407026 (Extech; Serial No. Q431675), and readings were compared with the Thai Labor regulations.[10] When the lighting intensity was higher than 1,000 lux at the inspection or E-checking task, further measurements were considered for focusing point and three zones determination methods. The standard lighting intensity of three zones would be compared to each zone monitoring; when focusing point zone 1 >1,000 lux to <2,000 lux; inner arm-range zone 2 ≥300 lux, outer arm-range zone 3 ≥200 lux; when focusing point ≥2,000–5,000 lux, zone 2 ≥600 and zone 3 ≥300 lux. In case that zone 1 was ≥5,000 lux, zone 2 and zone 3 were ≥1,000 and ≥400 lux.

Cohort participants were followed-up for 6 months by a modified follow-up procedure:[5] every 2 weeks each subject was contacted and asked about any low back pain lasting >24 h during the past fortnight. If the subject reported any onset of LBP, additional information was requested regarding the date of the onset, and he/she continued to be followed up for a further fortnight period for accounting of new cases.

Data analysis

Data were double entry recorded in Epi-info for Windows (Texas, USA, 2007) and the analysis was performed using STATA (version 10.1). LBP monthly incidence was estimated from the 1st month to the 6th month follow-up and accumulated incidence of LBP was calculated for the period of 1, 2, 3, 4, 5, and 6 months LBP incidence ((number of LBP new cases in the period × 100)/196). Correlations between LBP and studied factors were analyzed by simple logistic regression analysis.Statistical significance was set to P value <0.05 for relative risk (RR) at 95% confidence interval (95% CI).

Ethics review

The study received ethical approval from the Khon Kaen University Ethics Committee in Human Research, Khon Kaen University (HE582213). The approval from the ethics committee was obtained on 1 September 2015.

RESULTS

Personal factors and work stress of the cohort group

Most (88.3%) of the 196 electronic workers were female with a mean age of 26.5 ± 5.0 years, and 54.1% were single. In total 90% of the workers were operators. The highest percentage of workers (74.0%) had 1–5 years work experience with the mean being 3.7 ± 3.6 years (min, max: 1, 14). According to the Thai standard for assessing BMI, 11.7% of these workers were classified as obese (>25.0), 55.1% were in the normal range (18.5–23.0). Most of the workers reported no regular exercise (84.7%) and the majority had no chronic diseases (72.5%). Almost all these workers were undertaking repetitive work (97.5%) with sitting posture (55.0%) and standing posture (46.6%) being common.

In regard to work stress, most electronic workers (>50.0%), reported being dissatisfied about job demand in all items. The particularly concerning items (>70.0%) were not enough working time to complete the job, excessive workload, and work speed. Stress related to dissatisfaction over control and decision making on their specific jobs was reported. This particularly concerning items (>70.0%) were dissatisfaction over opportunities to learn new things (82.6%), lot to say (70.9%), lack of decision freedom (73.5%) [see Table 1].

Ergonomic risk

All 196 electronic workers were either sitting (101 workers) or standing (95 workers) during their work. Most of those who were sitting (61.4%) were rated as medium ergonomic risk with change needed, particularly in the inspection stations with lamps. High risk standing workers were in the E-check process (80.0%) and in the Punch process [see Table 2].

Table 2

Ergonomics risk among sitting and standing workers (n=196)

Risk level	Sitting (n=101)		Standing (n=95)
	Lamp (42)	Microscope (59)	Punch (14)	Blank (36)	E-check (10)	Adhesive (19)	Laminate (16)
1:acceptable
2:low	14(33.3)	25(42.4)	5(35.7)	24(66.7)	2(20.0)	7(36.8)	9(56.3)
3:medium	28(66.7)2	34(57.6)	8(57.1)	11(30.6)	8(80.0)1	12(63.2)3	7(43.7)
4:high			1(7.2)	1(2.7)

1,2,3Notification of the top three highest risk ranking level

This study found insufficient lighting in the arm range zone 2 (min–max) of the E-check and Inspection stations. The discomfort condition had occurred as a contrast of lighting intensity when the focusing point zone 1 was >1,000 lux for inspection and E-checking stations, and the arm range zone 2 was lower than the zone standard [see Tables 3 and 4].

Table 3

Lighting intensity and the standard at the main or focusing point zone 1 of workstation

Area	Station line 1 Lux (standard)	Station line 2 Lux (standard)	Station line 3 Lux (standard)
Punch	905 (300-400)	834 (300-400)	902 (300-400)
Blank	766 (300-400)	947 (300-400)	1,183 (300-400)
E-Check	1,470 (800-1,200)*	1,400 (800-1,200)*	2,070 (800-1,200)*
Adhesive	630 (300-400)	672 (300-400)	737 (300-400)
Laminate	811 (300-400)	450 (300-400)	866 (300-400)
Inspection	1,638 (1,200-1,600)a,*	5,125 (≥2,400)b,*	1,620 (1,200-1,600)b,*

aInspection under lamps, bInspection under microscopes. *considering measurement of lighting intensity at the arm range zone 2

Table 4

Lighting intensity (min-max) and the standard at the arm range zone 2 of E-check and Inspection station

Area	Station line 1 Lux; min-max (standard)	Station line 2 Lux; min-max (standard)	Station line 3 Lux; min-max (standard)
E-Check	319-585 (300)	376-486 (300)	293-530 (600)*
Inspection	264-298 (300)a,*	467-530 (1,000)b,*	235-296 (300)b,*

aInspection under lamps, bInspection under microscopes, *Insufficient lighting at the arm range zone 2

LBP incidence and risk factors

The incidence of LBP was highest at the 3rd month follow-up (18.7%). The 6 month LBP incidence was 52.5%, as shown in Table 5. There was no significant difference in LBP incidence rates between sitting posture (54.5%) and standing workers (50.5%).

Table 5

LBP incidence among electronic workers

Period	Number	New cases (n)	Accumulated incidence n (%)	Incidence rate(%)
1st month	196	21	21 (10.7)	10.7
2nd month	175	20	41 (20.9)	16.62
3rd month	155	29	70 (35.7)	18.71
4th month	126	16	86 (43.9)	12.73
5th month	110	11	97 (49.5)	10.0
6th month	99	6	103 (52.5)	6.1

1,2,3The first,the second, and the third ranking of incidence rate, respectively

The univariate analysis of personal factors and work characteristics in correlation with LBP are shown in Table 6. Work experience <3 years and having a chronic disease factors reached statistical significance.

Table 6

Univariate analysis of correlated risk factors to LBP

Factors	LBP cases n (%)	Non-cases n (%)	RR (95% CI)	p
Female	93 (53.8)	80 (46.2)	1.23 (0.76-2.01)	0.353
Age <20 years+	3 (42.9)	4 (57.1)	1.37 (0.72-2.62)	0.328
Age 20-29 years+	76 (55.1)	62 (44.9)	0.84 (0.17-4.15)	0.835
Single status	65 (54.6)	54 (45.4)	1.10 (0.83-1.46)	0.470
Operator/QA position	96 (53.3)	84 (46.7)	1.21 (0.68-2.16)	0.461
Standing posture	48 (50.5)	47 (49.5)	0.92 (0.71-1.21)	0.582
Work experience <3 years	71 (59.2)	49 (40.8)	1.41 (1.03-1.90)	0.019*
BMI ≤23.0	78 (52.4)	71 (47.6)	0.98 (0.72-1.34)	0.919
No regular exercise	90 (54.2)	76 (45.8)	1.25 (0.81-1.92)	0.072
Smoking	100 (53.8)	86 (46.2)	1.79 (0.68-4.66)	0.142
Had chronic diseases	36 (66.7)	18 (33.3)	1.41 (1.09-1.82)	0.015*
Eye focusing work	87 (55.1)	71 (44.9)	1.31 (0.87-1.95)	0.151
Repetitive work	101 (52.9)	90 (47.1)	1.32 (0.26-2.23)	0.569

*Significant correlation at p-value <0.05, +Reference group was age ≥30 years

DISCUSSION

The present study found the 6-month incidence of LBP among electronic workers was 52.5%. The highest rate was found in the 3rd month follow-up. This rate, however, was lower compared to office workers in Thailand (64.8%).[5] However, it was twice as high as the rate reported among informal garment workers (22.7%).[8] The explanation might be that characteristics of electronic manufacturing work involves monotonous multi-task work with prolonged sitting or standing, and repetitive movement of upper limbs under machine rhythm.[4] While some workers had manual handling of materials to input into the machine,[4] risk assessment by RULA indicated that high risk needed immediate change in standing workers. The prolonged and static posture and repetitive tasks contributed to LBP.[8] Moreover, a previous study on automotive industry assembly line workers also showed that higher physical work and awkward posture correlated with LBP.[14] Lighting conditions at E-check station and inspection with lamps or microscopes did not meet the requirement level of the arm range zone 2 when the focusing point of zone 1 was higher than 1,000 lux.[10] Those contrast conditionsmight involve the discomfort, and subsequently impact on the neck, shoulders, and back pain that occur as the previous report.[15]

This study showed that underlying disease and less work experience than 3 years were associated with LBP, confirming an earlier report of school teachers.[16] Work experience of <3 years was related to a significantly higher risk of LBP, maybe related to being less accustomed to workload and repetitive movementwhich associated with shoulder pain among electronic workers.[5] The majority of workers were dissatisfied with job demands and control of work, which would impact on work stress related to the severity of low back pain as a previous report.[3]

CONCLUSION

This paper provided a baseline measurement of lighting intensity, work stress, and ergonomics risk before investigating a prospective cohort for the incidence of LBP. The results provided an indication of health hazards from unacceptable posture risk and contrast of lighting between the high intensity at focusing point zone 1 and the lower intensity than the standard level at arm range zone 2 of E-check or inspection station. LBP incidence among electronic workers was 52.5% at the 6 months follow-up, though with no significant difference between workers predominantly sitting and standing. Less work experience and having chronic diseases were significantly correlated with LBP development. In order to assist in reducing and preventing LBP in this occupation group, steps should be taken to provide working conditions that support good work posture and meet the lighting requirements. These changes may be particularly valuable for workers in the first 3 years of working in this kind of industrial process.

Financial support and sponsorship

National Research Council of Thailand (580064).

Conflicts of interest

There are no conflicts of interest.