Gender differences in prevalence of musculoskeletal disorders and physiological stress among the brick field workers of West Bengal,India

Abstract

BACKGROUND:

The manual brick field industry is one of the most important and oldest industries in India, where millions of male and female workers make their livelihood.

OBJECTIVE:

To estimate the different ergonomic risk factors associated with brick making, identify potential gender differences and the prevalence of Work-related musculoskeletal disorders (WMSDs), physiological and psychological stress among the brickfield workers.

METHODS:

Brickfield workers - 152 male and 148 female were randomly selected from the 12 brickfields. The Modified Nordic Questionnaire was applied to assess the discomfort reported among both groups of brickfield workers. Objective measurement of physiological parameters and lung function values were also recorded.

RESULTS:

From this study, it was revealed that there is significantly higher discomfort reported in hands, lower back and knees among female brick molders than male brick molders. The physiological parameters did not show any significant change between male brickfield workers and female brickfield workers. The mean values of FVC, FEV1 and PEFR for females were lower than those for male brickfield workers.

CONCLUSION:

This study concludes that female brickfield workers reported more discomfort than male brickfield workers; perhaps in part due to their additional domestic work responsibilities.

Keywords

Gender difference WMSDs REBA brickfield workers physiological stress psychological stress

1 Introduction

The manual brick field industry is one of the most important and oldest industries in India, where millions of male and female, skilled and unskilled workers make their livelihood [1]. Workers in this industry report work-related musculoskeletal disorders (WMSDs) [2]. WMSDs are a common cause of pain in both male and female brickfield workers in brick field industries involved in molding, carrying and stacking process [3]. In the brickfield industry, the workers felt severe pain due to performing various types of hard and strenuous work [4]. Studies of the epidemiology of pain in different body parts have implicated mechanical risk factors, such as manual handling, carrying heavy loads and work-related posture [5, 6].

Manual brick making is one of the strenuous types of work in which the prevalence of WMSDs were found among brickfield workers [7]. WMSDs were caused by multifactorial operations of various risk factors, such as working posture, repetitive work, forceful activities and static muscle load [8]. WMSDs attributed to work include a group of conditions that involve the nerves, tendons, muscles and supporting structures of the body such as intervertebral discs. Often attributed to or exacerbated by the work environment, these disorders are also referred to as WMSDs which can cause symptoms such as pain, numbness, and tingling, as well as reduced worker productivity, lost time from work, temporary or permanent disability [9]. These disorders lead to financial losses associated with workers’ compensation insurance or similar forms of social security in place. Highly repetitive work, forceful exertions, lifting and forceful movements, and whole-body vibration are examples of risk factors that have been associated with increased reporting of WMSDs [10]. Poor working conditions in heavy manufacturing often expose workers to multiple risk factors for musculoskeletal disorders. The level of risk depends on the duration a worker is exposed to risk factors, the frequency at which they are exposed, and the magnitude of the exposure.

Brickfield workers generally perform rigorous hand-intensive jobs for a sustained period of time and are forced to carry various loads during their work, and as a result they may suffer from WMSDs and other occupational health problems. WMSDs can be caused by heavy physical work, static work postures, frequent bending and twisting, lifting, pushing and pulling, repetitive work, vibration and psychological and psychosocial stress [11]. In the brick field industry, the workers perform heavy manual tasks in a repetitive manner for a prolonged period of time, which may lead to severe physical stress. Das [1] stated that brickfield workers reported discomfort in different parts of the body due to working in awkward postures for extended periods of time. According to Burdorf and Sorock, [12] manual material handling, awkward back postures and heavy physical work are work-related physical risk factors for low back pain. Inbaraj et al. [13] stated that awkward postures adopted by brick kiln workers during work are directly related to their WMSDs

Brickfield workers perform several types of strenuous activity, such as i) cutting mud with a spade, ii) carrying mud, iii) preparation of clay, iv) carrying clay, v) molding, vi) stacking (loading and unloading bricks), vii) carrying bricks (green and baked bricks), and viii) baking bricks in a kiln. During this process, brick field workers face many hazards. For instance, molders are directly exposed to dust which contains a mixture of inorganic compounds including free silica, iron oxide, etc. On the other hand, brick kiln workers (firemen) are exposed to very high temperatures along with more proximal exposure to smoke and some toxic gases such as sulfur dioxide, hydrogen sulfide, carbon dioxide and carbon monoxide, as well as particulate air pollutants while burning biomass fuels [14].

Adverse environmental and physical conditions affect the health status of brickfield workers who also perform other types of activities (e.g. walking on a hot surface (top of the furnace) while monitoring and regulating the fire). Physiological responses to such activities mainly involve the musculoskeletal and cardiovascular systems. Since the environment is adverse, it hinders excess heat elimination by the circulatory system, making the heart work harder to transport energy to the muscles for successful completion of the job. An increase in age concurrently deteriorates the functional capacity of workers [15].

The present study deals with (i) the assessment and identification of the risk factors leading to the development and prevalence of musculoskeletal disorders (MSDs) during brick production among male and female brickfield workers, (ii) to analyze the relationship of discomforts associated with awkward postures and (iii) to assess physiological and psychosocial stress among male and female brickfield workers.

2 Methods

2.1 Selection of participants

A total of 300 participant (152 male and 148 female) brickfield workers were randomly selected from the 12 Brickfields, working in a selected brick field unit of Bhadrakali in Hooghly District, which is situated in the side of the Hooghly River of West Bengal, India. Before the survey, consent was obtained from brick field owners as well as each individual subject. Written permission for the project was obtained from the Institutional Human Ethical Clearance Committee of the Indian Council of Medical Research Guidelines.

2.2 Physical characteristics

Physical characteristics of male and female brickfield workers participating in this study were recorded using an anthropometer and a weighing machine. The Body Mass Index (BMI) [16] of all the subjects was also computed.

2.3 Questionnaire study

A modified Nordic Questionnaire [17] was completed by male and female brickfield workers. The questionnaire consisted of a number of objective questions, with multiple choice answers identifying the participant’s personal viewpoints, pattern of work, duration of work, and discomfort levels in different parts of the body.

2.4 Posture analysis

The maintenance of working posture and the support of load are particular examples of static work. To analyze working postures, measurement of the angles between the body parts, distribution of masses of the body parts, the forces exerted on the environment during the posture, the length of time for which the specific posture is held, and the effect on the person were measured. The working postures were analyzed by the Rapid Entire Body Assessment (REBA) tool [18]. The working postures were recorded with the help of a digital video camera (Sony Handycam). Later, stick diagrams were drawn from frozen frame video recordings and then analyzed. The most frequently repeated postures or the postures that were held for the longest amount of time of the work cycles were chosen for assessment. The REBA method was also carried out to assess critical tasks of a job and for each task, to assess the postural factors by assigning a score to each region REBA Score = 11– 15 (Risk Level – Very High; Action Category – Work must cease until a safer solution can be found); REBA Score = 08– 10 (Risk Level – High; Action Category – Action needs to be taken very soon); REBA Score = 04– 07 (Risk Level – Medium; Action Category – Further consideration should be given as how risk can be lowered); REBA Score = 02-03 (Risk Level – Low; Action Category – Action has already been taken to get to this level) and REBA Score = 01 (Risk Level – Negligible; Action Category – No need for any action) [18].

2.5 Discomfort level scale

The intensity of pain/discomfort was measured by the Body Part Discomfort Scale [19]. A scale of 1 to 10 was used to indicate the level of discomfort where 1 = just noticeable pain, 5 = moderate pain or discomfort and 10 = intolerable pain or discomfort.

2.6 Assessment of physiological parameters

The heart rates of participants were taken prior to work and just after finishing work. The resting or prior to work heart rate was taken from the radial pulse for one minute. The heart rate just after finishing work was recorded from the carotid pulse by 10 beats method [20]. Resting heart rate was measured manually from the radial pulse because at rest, the heart rate measured from the radial pulse (by three finger method) for 60 sec which is the required time for measurement (available in resting), whereas in the case of just after exercise heart rate was measured from the carotid pulse because here we calculate the time taken for the first 10 beats. The blood pressures of the male and female participants were measured with a sphygmomanometer and stethoscope before and just after completion of work.

Maximum heart rate (MHR) was considered to be 220 less the age of the subjects in years. Heart Rate Reserve (HRR) was obtained as the difference between MHR and RHR. From the resting heart rate (RHR) and working heart rate (WHR), Net Cardiac Cost (NCC) and Relative Cardiac Cost (RCC) (two indices of cardiac strain) were derived as follows: NCC = WHR – RHR; RCC = (NCC/RHR)×100. Energy expenditure for any kind of job is normally measured by different calorimetric methods. It has also been determined by the predictive formula: [0.159× Heart rate (beats/min) – 8.72] [25].

Table 1
Demographic Characteristics of the brickfield Workers (N = 300)

Characteristics Brick Molders Brick Carriers

Male (N = 64) Female (N = 82) Male (N = 88) Female (N = 66)

Age (yrs) 33.2 (±6.35) 30.5 (±10.9) 33.8 (±6.33) 30.1 (±10.3)

BMI (Kg/m²) 20.7 (±1.9) 18.7 (±1.6) 21.3(±1.8) 19.5 (±2.0)

Duration of work / day (hrs) 8.1 (±1.6) 6.8 (±2.1) 7.8 (±1.4) 6.2(±1.8)

Years of experience of work 14.2 (±4.8) 5.7 (±8.3) 14.0 (±5.0) 5.6 (±8.2)

Number of working days per week 7 6 7 6

Literacy (%)

Illiterate 35.6% 19.6% 32.4% 19.5%

Primary 48.1% 49.3% 41.9% 49.2%

Junior high school 16.3% 31.1% 25.7% 31.3%

Smokers (%) 98% 38% 92% 33%

Tobacco Chewers (%) 89% 10% 81% 07%

Characteristics	Brick Molders	Brick Carriers
Age (yrs)	33.2 (±6.35)	30.5 (±10.9)	33.8 (±6.33)	30.1 (±10.3)
BMI (Kg/m²)	20.7 (±1.9)	18.7 (±1.6)	21.3(±1.8)	19.5 (±2.0)
Duration of work / day (hrs)	8.1 (±1.6)	6.8 (±2.1)	7.8 (±1.4)	6.2(±1.8)
Years of experience of work	14.2 (±4.8)	5.7 (±8.3)	14.0 (±5.0)	5.6 (±8.2)
Number of working days per week	7	6	7	6
Literacy (%)
Illiterate	35.6%	19.6%	32.4%	19.5%
Primary	48.1%	49.3%	41.9%	49.2%
Junior high school	16.3%	31.1%	25.7%	31.3%
Smokers (%)	98%	38%	92%	33%
Tobacco Chewers (%)	89%	10%	81%	07%

2.7 Assessment of pulmonary function test (PFT)

An RMS Hellios spirometer was used to make three successive recordings of forced vital capacity (FVC) and forced expiratory volume in the first second (FEV1).Forced expiratory ratio (FEV1/FVC (%)) was performed with participants in the standing position and the highest of the three ratings was recorded. Measurement of peak expiratory flow rate (PEFR) used a mini-Wright peak flow meter (Clement Clarke International, UK). Prior to recording the subjects’ PEFR, the use of the instrument was demonstrated and explained. The PEFR test was performed with the participant in the standing position and the peak flow meter was held horizontally. All participants were asked to inhale as deeply as possible and then to exhale as hard and as quickly as possible. The best of three ratings was recorded.

2.8 Statistical analysis

A two-tail chi-square test of independence was applied to determine whether or not the test item had any significant association with gender effect on brickfield workers in contrast to the subjective assessment of discomfort in different parts of the body. A two-tail chi-square test of independence was also applied to determine whether there were any significant gender effects related to discomfort during different brick production activities. The computed χ2 was next compared with the critical χ2 values for the chosen level of significance (p < 0.05). The adjusted prevalence odds ratios (OR) with 95% confidence intervals (CI) were used to indicate the strength of the association between MSD and the independent variables. ANOVA was performed to compute the F ratio to determine whether there were any significant differences between the physiological stresses among the two groups of brick field workers. Student “t” tests were performed to determine whether there were any significant gender-related differences in lung function values for male and female. Statistical analysis was performed using the statistical package Primer of Bio-Statistics (Primer of Biostatistics 5.0.msi, Msi Version 1.20.1827.0, Primer for Windows, McGraw-Hill).

3 Results

The mean values of the demographic characteristics age and physical parameters (BMI) for male and female brickfield workers are shown in Table 1. Table 2 shows the gender-related differences for the measures of discomfort in different parts of the body. This study indicated that there was significantly higher discomfort reported in hands, lower back and knees among the female brick molders than male brick molders. Whereas the female brick carriers felt significantly more discomfort in wrists, lower back and knees than male brick carriers.

Table 2
Gender effect on brickfield workers in subjective assessment of discomfort feeling during different parts of the body

Different Body Parts Gender Brick Molders (Male = 64; Female = 82) Brick Carriers (Male = 88; Female = 66)

NDF DF OR 95% CI P value NDF DF OR 95% CI P value

Neck Male 21 43 0.8981 0.4449 to 1.8128 0.904 29 59 0.8846 0.4446 to 1.7598 0.861

Female 25 57 20 46

Shoulder Male 14 50 0.7996 0.3538 to 1.8069 0.742 18 70 0.5364 0.2175 to 1.3228 0.251

Female 15 67 08 58

Elbow Male 38 26 1.186 0.606 to 2.3209 0.744 50 38 0.8581 0.4517 to 1.6299 0.761

Female 52 30 35 31

Wrists Male 11 53 0.4497 0.1637 to 1.2357 0.186 25 63 0.1626 0.0535 to 0.4944 0.000^*

Female 07 75 04 62

Hands Male 05 59 4.0623 1.4374 to 11.4806 0.010^ 11 77 0.3333 0.0891 to 1.247 0.157

Female 21 61 03 63

Upper back Male 56 08 0.6071 0.2421 to 1.5227 0.398 81 07 1.3395 0.3753 to 4.7805 0.892

Female 68 16 62 04

Lower back Male 08 56 0.0864 0.0105 to 0.7104 0.014^ 17 71 0.1305 0.029 to 0.5871 0.005^

Female 01 81 02 64

Knees Male 13 51 0.2547 0.0856 to 0.758 0.019^ 18 70 0.3188 0.1117 to 0.9097 0.047^

Female 05 77 05 61

Ankles Male 60 4 1.7556 0.3786 to 8.1411 0.736 82 06 0.8927 0.2603 to 3.0609 0.892

Female 79 3 61 05

Feet Male 55 09 0.7948 0.32 to 1.974 0.790 73 15 1.0274 0.4378 to 2.4113 0.877

Female 68 14 55 11

Different Body Parts	Gender	Brick Molders (Male = 64; Female = 82)	Brick Carriers (Male = 88; Female = 66)
Neck	Male	21	43	0.8981	0.4449 to 1.8128	0.904	29	59	0.8846	0.4446 to 1.7598	0.861
	Female	25	57				20	46
Shoulder	Male	14	50	0.7996	0.3538 to 1.8069	0.742	18	70	0.5364	0.2175 to 1.3228	0.251
	Female	15	67				08	58
Elbow	Male	38	26	1.186	0.606 to 2.3209	0.744	50	38	0.8581	0.4517 to 1.6299	0.761
	Female	52	30				35	31
Wrists	Male	11	53	0.4497	0.1637 to 1.2357	0.186	25	63	0.1626	0.0535 to 0.4944	0.000^***
	Female	07	75				04	62
Hands	Male	05	59	4.0623	1.4374 to 11.4806	0.010^**	11	77	0.3333	0.0891 to 1.247	0.157
	Female	21	61				03	63
Upper back	Male	56	08	0.6071	0.2421 to 1.5227	0.398	81	07	1.3395	0.3753 to 4.7805	0.892
	Female	68	16				62	04
Lower back	Male	08	56	0.0864	0.0105 to 0.7104	0.014^**	17	71	0.1305	0.029 to 0.5871	0.005^**
	Female	01	81				02	64
Knees	Male	13	51	0.2547	0.0856 to 0.758	0.019^**	18	70	0.3188	0.1117 to 0.9097	0.047^**
	Female	05	77				05	61
Ankles	Male	60	4	1.7556	0.3786 to 8.1411	0.736	82	06	0.8927	0.2603 to 3.0609	0.892
	Female	79	3				61	05
Feet	Male	55	09	0.7948	0.32 to 1.974	0.790	73	15	1.0274	0.4378 to 2.4113	0.877
	Female	68	14				55	11

Level of Significance ^**=P < 0.05; ^***=P < 0.001. NDF = No Discomfort Feeling; DF = Discomfort Feeling. OR = Odd Ratio; 95% CI = 95% Confidence Interval.

Table 3 shows the gender-related differences related to each individual brickfield activity. Significant gender-related effects were found for shoveling for mud collection, carrying mud, preparation of clay, molding, setting bricks in the kiln, loading and unloading bricks and carrying bricks. Table 4 shows severity of pain, remedial measures and causes of MSD as reported by the brickfield workers. This study showed that rest from work (OR 0.4; P < 0.03), job rotation (OR 3.5; P < 0.02) and short rest breaks during work scheduled (OR 3.7; P < 0.009) were significantly different between male and female brick carriers. Table 4 also shows that awkward posture (OR 0.12; P < 0.001), manual material handling (OR 0.01; P < 0.001), repetitiveness of work (OR 0.24; P < 0.001) and long duration of work (OR 0.27; P < 0.001) were significantly different between male and female brick carriers. Whereas repetitiveness of work (OR 0.15; P < 0.001), deficiency of ergonomically design equipment (OR 5.71; P < 0.04) and long duration of work (OR 0.35; P < 0.007) were significantly different between male and female brick molders.

Table 3

Gender effect on brickfield workers in subjective assessment of discomfort feeling during different brickfield activities in brick field production

Activities in Brickfield	Gender	Brickfield Workers (n = 300) (Male = 152; Female = 148)
		NDF	DF	OR	95% CI	P value
Spading for mud collection	Male	109	43	0.5178	0.3204 to 0.8367	0.010^**
	Female	84	64
Loading mud	Male	130	22	0.7584	0.41 to 1.4028	0.467
	Female	121	27
Carrying mud	Male	108	44	0.5811	0.3597 to 0.9387	0.035^**
	Female	87	61
Preparation of clay	Male	134	18	0.4337	0.233 to 0.8071	0.011^**
	Female	113	35
Carrying clay	Male	103	49	1.5359	0.9229 to 2.5561	0.127
	Female	113	35
Moulding	Male	112	40	0.3873	0.2387 to 0.6285	0.000^***
	Female	77	71
Setting bricks in the kiln	Male	131	21	0.464	0.2572 to 0.8373	0.015^**
	Female	110	38
Loading &unloading bricks	Male	110	42	0.4744	0.2932 to 0.7675	0.003^**
	Female	82	66
Carrying bricks	Male	106	46	0.5855	0.364 to 0.9418	0.036^**
	Female	85	63

Level of Significance ^**=P < 0.05; ^***=P < 0.001. NDF = No Discomfort Feeling; DF = Discomfort Feeling. OR = Odd Ratio; 95% CI = 95% Confidence Interval.

Table 4

Severity of pain, remedial measures and causes of MSDs as reported by the brick field workers

	Brick Molders (Male = 64; Female = 82)					Brick Carriers (Male = 88; Female = 66)
	Male	Female	OR	95% CI	P value	Male	Female	OR	95% CI	P value
Pain severity (%)
Severe	28	32	1.21	0.62– 2.36	0.684	29	23	0.91	0.46– 1.80	0.941
Moderate	33	38	1.23	0.64– 2.37	0.646	42	32	0.97	0.51– 1.83	0.944
Mild	03	12	0.28	0.07– 1.06	0.091	17	11	1.19	0.51– 2.76	0.833
Subject selection of Remedial measure (%)
Rest from Work	08	03	3.76	0.95– 14.81	0.091	15	22	0.411	0.19– 0.87	0.032^**
Job rotation	17	12	2.10	0.92– 4.82	0.113	11	19	0.353	0.15– 0.80	0.020^**
Short rest breaks during Work scheduled	31	25	2.14	1.08– 4.22	0.041^**	20	29	0.375	0.18– 0.75	0.009^**
Different types of stretching exercises practiced during the breaks	22	18	1.86	0.89– 3.88	0.138	18	11	1.285	0.56– 2.94	0.699
Self Medication	10	21	0.53	0.23– 1.24	0.208	10	18	0.341	0.14– 0.80	0.020^**
Doctor Consultancy	08	20	0.44	0.18– 1.08	0.110	08	18	0.266	0.10– 0.66	0.006^**
Use of trolley during Carrying	—-	—-	—-	——	—–	25	32	0.421	0.21– 0.82	0.017^**
No remedial measures	07	02	4.91	0.98– 24.52	0.076	04	08	0.345	0.09– 1.20	0.152
Subject Perception to the cause of pain (%)
Awkward Posture	42	50	1.22	0.61– 2.41	0.686	41	58	0.12	0.05– 0.28	0.000^***
Manual Material Handling (MMH)	31	44	0.81	0.42– 1.56	0.646	44	65	0.01	0.002– 0.11	0.000^***
Repetitiveness of Work	45	77	0.15	0.05– 0.44	0.000^***	12	26	0.24	0.11– 0.53	0.000^***
Work Method	12	10	1.66	0.66– 4.13	0.387	05	01	3.91	0.44– 34.34	0.367
Deficiency of ergonomically design equipment	08	02	5.71	1.16– 27.92	0.040^**	02	05	0.28	0.05– 1.51	0.241
Long duration of work	15	38	0.35	0.17– 0.73	0.007^**	18	32	0.27	0.13– 0.55	0.000^***

Level of Significance ^**=P < 0.05; ^***=P < 0.001. OR = Odd Ratio; 95% CI = 95% Confidence Interval.

Table 5 shows the psychosocial variables and their association with WMSDs. About 48% females (OR 2.2) in brick molding and 58% males (OR 1.9) in brick carrying had poor job satisfaction, with the positive association to developing musculoskeletal disorders in any body parts region. Monotony at work had a significant effect on the occurrence of WMSDs among males (OR 3.2; p < 0.005) and females (OR 3.6; p < 0.001) in brick molding, whereas male brick carriers (OR 4.38; p < 0.001) and female brick carriers (OR 3.28; p < 0.003) had a significant effect on the occurrence of WMSDs. Poor relationships with managers of the brick field among female workers (molders: 10% and carriers 21%) had no significant impact on musculoskeletal disorders. Perceived inadequacy of income had a significant effect on the occurrence of WMSDs among males (OR 52.2; p < 0.001) and females (OR 20.9; p < 0.001) in brick molding, whereas male brick carriers (OR 17.9; p < 0.001) and female brick carriers (OR 9.41; p < 0.002) had significant effects on the occurrence of WMSDs. Unpleasant work environment had a significant effect on the occurrence of musculoskeletal disorders among males (OR 0.36; p < 0.01) and females (OR 0.44; p < 0.01) in brick molding. Table 5 also shows that the responses are participatory in nature (i.e., gathered from the subjects through interview). Among the psychosocial variable factors, such as got tired easily by doing strenuous jobs (molding) which had a significant effect on the occurrence of musculoskeletal disorders among males (OR 0.22; p < 0.001) and females (OR 0.37; p < 0.02) in brick molding. The same findings were also observed in case of male brick carriers (OR 3.53; p < 0.006) and female brick carriers (OR 5.81; p < 0.002) which had a significant effect on the occurrence of musculoskeletal disorders. Other psychosocial factors, such as whether they were annoyed and irritated easily in which occurrence of MSD has been correlated among both brick molding (OR 0.35; p < 0.008) and brick carrying (OR 1.98; p < 0.04) activities. Mental overload had a significant effect on the occurrence of WMSDs among males (OR 0.27; p < 0.002) and females (OR 0.28; p < 0.001) in brick molding. Another important psychosocial variable factors, such as the job requires knowledge of skillful activity in both brick molding (OR 7.855; p < 0.001) and brick carrying (OR 0.15; p < 0.001) among males were the significant predictors of symptom development on WMSDs occurrence.

Table 5

Psychosocial variables and their association with MSDs as indicated by risk estimated

Psycho-social Variables	Brick Molders								Brick Carriers
	Male				Female				Male				Female
	%	OR	95% CI	P	%	OR	95% CI	P	%	OR	95% CI	P	%	OR	95% CI	P
Job dissatisfaction	44	0.184	0.88 to 3.88	0.142	48	2.19	1.15 to 4.17	0.025^**	58	1.89	1.04 to 3.45	0.050^**	58	1.44	0.72 to 2.86	0.383
Monotony at work	80	3.250	1.48 to 7.11	0.005^**	83	3.61	1.75 to 7.45	0.000^***	86	4.38	2.08 to 9.21	0.000^***	79	3.28	1.53 to 7.05	0.003^**
Poor relationship with managers of the brick field	20	1.228	0.50 to 2.99	0.821	10	0.77	0.29 to 2.08	0.803	43	2.76	1.42 to 5.34	0.004^**	21	1.21	0.51 to 2.86	0.827
Perceived inadequacy of income	91	52.2	17.76 to 153.4	0.000^***	88	20.9	9.14 to 47.8	0.000^***	93	17.9	7.09 to 45.5	0.000^***	97	9.41	2.05 to 43.0	0.002^**
Unpleasant work Environments	27	0.361	0.172 to 0.758	0.011^**	34	0.44	0.23 to 0.84	0.018^**	81	4.57	2.33 to 8.98	0.000^***	73	1.33	0.63 to 2.80	0.57
Have you got tired Easily	38	0.222	0.105 to 0.466	0.000^***	71	0.37	0.16 to 0.82	0.022^**	91	3.53	1.48 to 8.43	0.006^**	94	5.81	1.84 to 18.3	0.002^**
Have you been Annoyed and irritated easily	33	0.353	0.171 to 0.728	0.008^**	56	0.28	0.23 To 0.84	0.000^***	70	1.98	1.06 to 3.69	0.043^**	76	1.78	0.84 to 3.79	0.185
Mental overload	19	0.278	0.125 to 0.618	0.002^**	45	0.28	0.14 to 054	0.000^***	84	1.45	0.67 to 3.12	0.44	77	0.16	0.04 to 0.59	0.005^**
Job requires know-Ledge of skilful Activity	94	7.857	2.522 to 24.46	0.000^***	95	3.34	1.03 to 10.8	0.065	14	0.15	0.07 to 0.31	0.000	27	0.80	0.37 to 1.70	0.703
Rigidity in work Methods and Procedure	89	2.075	0.768 to 5.605	0.224	80	0.77	0.34 to 1.73	0.682	51	0.54	0.29 to 0.99	0.066	15	0.44	0.18 to 1.04	0.093
Work demand targets specific productivity	86	0.750	0.261 to 2.150	0.789	76	1.35	0.68 to 2.70	0.484	76	1.19	0.60 to 2.35	0.73	91	3.2	1.16 to 8.79	0.036

Level of Significance ^**=P < 0.05; ^***=P < 0.001. OR = Odd Ratio; 95% CI = 95% Confidence Interval.

Table 6

Analysis of working posture by using REBA method for assessing risk level of Musculoskeletal Disorder

Sl No	Activities	Posture	Posture details	REBA score	Risk Level	Action categories
1	Carrying mud		Back bent backward, both arms above shoulder level, walking or moving, weight or force needed exceeds 20 kg	10	High	Action needs to be taken very soon
2	Moulding		Bent forward, both arms below shoulder level, legs bent forward, weight or force needed >20 kg	08	High	Action needs to be taken very soon
3	Carrying raw bricks to kiln		Neck inclined, Back straight, both arms are below shoulder level, walking or moving, weight or force below 20 kg	06	Medium	Further consideration should be given as how risk can be lowered
4	Unloading raw bricks		Bent forward, both arm is below shoulder level, standing or force needed below 10 kg	06	Medium	Further consideration should be given as how risk can be lowered
5	Picking up baked bricks from kiln		Back bent forward, both arms are below shoulder level, weight or force needed is 10 kg or less	10	High	Action needs to be taken very soon
6	Carrying baked bricks from kiln to storage		Back bent forward, both arms are above shoulder level, walking or moving, weight or force above 20 kg	11	High	Action needs to be taken very soon

From the analysis of working postures (Table 6), it was found that most of the working postures were of high risk and required immediate corrective measures, as indicated by the REBA analysis (by comparing the REBA score with REBA risk level). These types of working postures are frequently adopted by brickfield workers, and often, they report musculoskeletal complaints in the lower back pain and upper extremities. The posture codes of the REBA indicated that all postures in different brick making activities were at a high-risk level and required immediate attention (i.e., change of posture necessary soon).

Table 7

Assessment of Average Discomfort Feeling (Pain) According to Body Part Discomfort (BPD) Scale among Male and Female brick field workers

Sex	No. of Subjects	Average Results Of Discomfort Feeling (Pain) In Body Part Discomfort Scale (BPD) SCALE	Remarks
Male Molders	64		t = 23.33 So Female molders has Significantly (P < 0.001) higher discomfort feeling than Male molders
Female Molders	82
Male Carriers	88		t = 32.99 So Female carriers has Significantly (P < 0.001) higher discomfort feeling than Male carriers
Female Carriers	66

Table 8

Physiological stress difference between male and female brick field workers

Physiological parameters	Male Brick field Workers (n = 152)		Female Brick field Workers (n = 148)		F value	P Value
	Mean	SD	Mean	SD
Heart rate (beats/min)
Resting cond.	74.2	±5.60	75.0	±5.44	1.57	0.211
Just after work cond.	132.4	±8.30	133.4	±6.84	1.29	0.256
Maximum heart rate (HRmax)	188.8	±7.62	189.5	±6.48	0.73	0.393
Heart rate reserve (HRR)	114.6	±10.1	114.5	±7.65	0.01	0.923
Net cardiac cost (NCC) (beats/min)	58.1	±6.79	58.3	±5.35	0.08	0.777
Relative cardiac cost (RCC) (%)	78.8	±11.6	77.8	±9.77	0.65	0.421
Cardiovascular Stress Index (CSI)	30.9	±4.27	32.8	±3.11	19.32	0.000

Table 7 presents the discomfort reported according to the BPD scale [16]. It was revealed from the BPD scale that the male brick molders and the female brick molders rated their discomfort as 6.9 and 7.5 respectively. This indicates that female brick molders reported more strong body part discomfort than male brick molders (p < 0.001). Whereas Table 7 also showed that male brick carriers and female brick carriers rated their discomfort as 7.3 and 8.0 respectively. This indicates that female brick carriers reported more strong body part discomfort than male brick carriers (p < 0.001).

Physiological stress levels for male and female are shown in Table 8. The resting heart rates and just after work heart rates of male and female participants did not show any significant change. The other physiological parameters (HR max, HRR, NCC, RCC and CSI) did not show any significant change between male brickfield workers and female brickfield workers. The lung function parameters between male and female participants are compared in Table 9. There were significant differences in spirometry readings (FVC, FEV1 and PEFR value) between male and female brickfield workers. The mean values of FVC, FEV1 and PEFR for females were lower than those for male brickfield workers.

Table 9

Comparison of lung function values among male and female brick field workers

Average lung function parameters	Male Brick field Workers (n = 152)		Female Brick field Workers (n = 148)		t value	P value
	Mean	SD	Mean	SD
FVC (lit)	4.23	±0.15	4.51	±0.18	14.65	0.000
FEV1 (lit)	3.20	±0.17	3.52	±0.24	13.35	0.000
FEV1/FVC%	75.72	±2.24	77.28	±1.98	6.38	0.000
PEFR (lit/min)	398.25	±38.42	422.01	±40.52	5.21	0.000

Figure 1 shows the comparative Study of discomfort feeling in different body parts among male and female brickfield workers, in which it was found that females had significantly higher discomfort than males in different body parts. Figure 2 shows the types discomfort among male and female brickfield workers. The predominant type of discomfort was pain followed by tingling, numbness and stiffness. Figure 3 represents that both groups of brickfield workers felt trouble during work, after work, last for 7 days and last for 12 months. This figure indicates that a greater percentage of both groups of brickfield workers felt trouble after completion of work (91%, in case of male and 97% in case of female) than during work (80%, in case of male and 86% in case of female). This figure also indicates that 62% and 30% male brickfield workers trouble for last 7 days and last 12 months respectively. Whereas, the female brickfield workers felt trouble 73% and 44% for last 7 days and last 12 months respectively.

Fig.1

Comparative study of discomfort feeling in different body parts among male and female brickfield workers.

Fig.2

Types of discomfort among male and female brickfield workers.

Fig.3

Comparative study of feelings of discomfort (pain) at different times among the male and female brickfield workers.

4 Discussion

The results of this study revealed that both groups of brickfield workers (brick molders and brick carriers) are engaged in rigorous hand-intensive jobs. Brickfield workers (molders and carriers) suffered pain in different parts of the body especially low back, shoulder, wrist, and knee pain when making bricks [21]. Male and female brick molders performed their high hand intensive job, in which wrist, hand and shoulder were affected most. The results of this study showed that the hand is the region which had a significant difference between male and female workers. Female brickfield workers may have less muscle mass, which can lead to significantly more pain in the hands while performing the molding activity. Brick molders perform their work in kneeling and squatting postures for a prolonged period of time, which can lead to low back and knee pain. So, the kneeling and squatting posture in brick molding activity for long period of time may lead to low back pain and knee pain among brick molders [22]. So, it was suggested that they try to avoid static work posture for prolonged period of time [23]. The results of the study also showed that female brick molders suffered significantly more pain in the low back and knee than male brick molders. The study showed a high prevalence of self-reported WMSDs among brick molders and brick carriers which may be influenced by various types of stress. Female brick carriers suffered significantly more pain in their wrists, low back and knees than male brick carriers due to loading and unloading of baked bricks from a kiln. Awkward postures for a prolonged period of time may lead to WMSDs among the brickfield workers. It is also well known that brick making works are associated with high rates of occupational injury, disability and illness [24, 25]. Interim rest pauses should be enhanced to avoid excessive physical stress among the both group of brickfield workers. In a study by Chakraborty et al. [26], they stated implementation of rest break schedules, including brief rest breaks may reduce workers’ musculoskeletal discomfort.

Wrist pain mainly found in molding activity among both groups of male and female brickfield workers. It was also noted that during the molding activity both groups of brickfield workers pull the wooden make dice forcefully, which imposed a jerk in their shoulder joint along with the shoulder muscles, which may be responsible for shoulder pain among the brickfield workers. Knees, ankles and feet of both groups of brickfield workers (male and female) had problems during and after the molding activity. During picking burned bricks from a kiln, the workers remain in squatting and stooping posture with a repetitiveness of work that may be responsible for the feeling of discomfort in the knees, ankles and feet regions of the body. This mainly occurred due to the male and female brickfield workers performing these jobs in an inappropriate kneeling and bent posture (squatting and stooping posture). One of the risk factors of WMSDs is repetitiveness of work. Gangopadhyay et al. [27] also stated that repetitiveness of work is the main causative factor in WMSDs. Ghosh et al. [28] suggested that trying to avoid the repetitiveness of work can help to prevent WMSDs among black smith workers. This study also shows that repetitiveness of work in brick molding and brick carrying activities which has a high tendency to cause WMSDs among both group of brickfield workers.

Male and female brickfield workers are engaged in different types of intensive work including forwarding bending, awkward postures and frequent twisting at the waist for prolonged periods of time which may lead to discomfort in different parts of the body especially in the lower back and knees. This result supports the previous findings of Das [25]. The author also found that brickfield workers suffered from low back pain and pain in upper extremities due to working in awkward postures and carrying heavy loads. Punnet et al. [29] also found that low back pain has been associated with lifting heavy materials in awkward postures. According to Kivi and Mattila, [30] awkward working postures are mainly associated with the development of WMSDs.

The result of this study showed that among all the activities in brick making, molding is the activity in which there is a significant difference in discomfort feeling (pain) between male and female brickfield workers. Besides molding, shovelling for mud collection, carrying mud, setting bricks in the kiln, loading and unloading bricks and carrying bricks are the activities in which there is a significant difference in discomfort feeling (pain) between male and female brickfield workers were also observed. The result also revealed that posture analysis study shows that postures adopted by both groups of brickfield workers in most of the activities in brick making were vulnerable to WMSDs which were high risk and require immediate corrective measures, as indicated by the REBA analysis by ergonomics design intervention. The result of this study demonstrated that most of the male and female brickfield workers had a discomfort feeling (mainly pain) during Carrying mud, molding, Loading raw bricks, Carrying raw bricks to Kiln, Unloading raw bricks to a kiln, Picking burned bricks from a kiln, Carrying burned bricks from kiln to storage. Awkward posture for a prolonged period and frequently twisting of the waist was noted in the case of these activities which may also lead to WMSDs among them.

The brickfield industry is filled with tasks that require high physical demands. Furthermore, manual lifting and handling of heavy supplies and other material are still common place in the brick field. A number of risk physical factors for low back pain (LBP) have been identified such as manual material handling (MMH), awkward lifting, constant sitting static posture, awkward working posture and repetitive work and frequent bending and twisting. This study corroborated with the work of Bernard [31]. He stated several risk factors for low back pain. These risk factors include manual materials handling, frequent bending and twisting and heavy physical load. These results also echo the findings of a comprehensive review by the US National Institute for Occupational Safety and Health [32], which found strong evidence for a causal relationship between low back pain and lifting/forceful movement and evidence for a causal relationship between awkward postures and heavy physical work and low back pain. Devereux et al. [33] and Waters et al. [34] stated that the combination of workplace stress and physical work demands increase rates of low back pain.

From this study, it was revealed that the feeling of discomfort is much higher in female brickfield workers than male brickfield workers. This study also showed that female brickfield workers have a significant change in discomfort feeling in respect to awkward posture, manual material handling and repetitiveness of work than male brickfield workers. The reason behind this may be that the female brickfield workers, apart from their regular work activity in the brickfield, they have to perform numerous household activities which further enhanced their discomfort feeling in their different body parts. The same findings are found in the work of other researchers [35, 36]. They stated that the female subjects suffer more discomfort than male subjects. Females experience higher prevalence of upper extremity musculoskeletal disorders (UEMSDs) than males [37]. This result was further supported by Smith et al. [38]. According to them, females are at substantially greater risk of discomfort than males. This gender difference seems to be more distinct for lower extremity complaints than for upper-extremities complaints. The prevalences of upper and lower extremities complaints have been found to be consistently higher for females than for males. This result was supported by De Zwart et al. [39]. According to them, neck and upper-extremity complaints have been found to be consistently higher for females than for males. While the prevalence of back complaints has been shown to be markedly higher for females or slightly higher for females [39]. This study shows that the prevalence of WMSDs has been higher in case of female brickfield workers in compare to male brickfield workers. Das [25] also explained that female rice farmers had a higher prevalence of WMSDs than male rice farmers.

This study showed that some psychosocial factors, such as job dissatisfaction, monotony at work, perceived inadequacy of income, unpleasant work environment, tire easily, easily annoyed and irritated and mental overload, have a relationship between WMSDs. The study of Snook et al. [40] also stated that the psychological factors e.g. job dissatisfaction, poor relationship with immediate supervisors, perceived inadequacy of income, lack of control over one’s job, and unpleasant work environment seem to have an impact on WMSDs. Hoogendoorn et al. [41] stated that one of the consistent findings related to workplace psychosocial stressors is that low job satisfaction is associated with WMSDs. Monotony at work is also usually associated with higher levels of low back pain. Svensson and Andersson [42] stated that monotony was found to have a direct relationship to low back pain. Davis and Heaney [43] showed that job dissatisfaction and stress are more consistently and strongly associated with the development of mainly WMSDs in the lower back. Dissatisfaction with a work situation, a supervisor, or a dead-end job and boredom contribute greatly to the onset and persistence of WMSDs. Job or work rotation policy should be implemented in brick making so that activities of brick manufacturing reduce the boredom and monotony of a job and also reduce the fatigue. Konz [44] and Raina and Dickerson [45] stated that job rotation reduces the muscle fatigue and monotony of a job.

Carrying heavy loads are the most common human activities in several occupations involving manual material handling. During brick making, female brickfield workers perform several types of manual material handling that may be causative factors for the development of low back pain among them. The present study deals with manual material handling in which female brickfield workers carry, loading and unloading heavy loads (mud, raw bricks and burned bricks) in a repetitive manner is also a causative factor of low back pain among them. This study was supported by the study of Cole and Grimshaw [46] who also stated that carrying heavy loads in a repetitive manner is a causative factor of low back pain.

To avoid physical stress among the brickfield workers, brickfield workers are suggested to carry the brick making materials (mud, bricks, etc) with wheel barrow or other carrying vehicles which reduces physical stress among them. Besides this, different types of stretching exercises during lunch break should be included in their work scheduled for the brickfield workers which also reduces musculoskeletal pain among them. This study results are also supported by Lee [47]. They also recommended some physical exercises during work schedule to reduce musculoskeletal pain.

This study found that both male and female brickfield workers suffered from acute WMSDs due to working in an awkward (stooping and kneeling) and static posture in a brick field. One of the main causative factors of WMSDs is manual material handling of bricks and loading and unloading of bricks from the kiln. Repetition of work is the main causative factor of WMSDs and also the pain in the upper extremities of the body. REBA posture analysis suggested that working in an awkward posture for a prolonged period of time is one of the leading causative factors for WMSDs among both male and female brickfield workers.

Psychophysical study (BPD Scale) shows that the intensity of discomfort feeling (pain) is higher among the female workers than male workers due to more domestic work at home. This results agreed with those by Gangopadhyay et al. [48] According to them, female prawn seed collectors (prawn seed collection is a collection of a seed of tiger prawn) has a higher discomfort feeling than male workers in according to BPD scale due to same reason.

Respiratory disease is the main chronic health conditions affecting brickfield workers. This study showed that the FVC, FEV1, PEFR values are much less (p < 0.001) among the female brickfield workers than male brickfield workers due to lesser volume of lungs, thoracic cavity and smaller diameter airways, lung volumes, diffusion surface. Das [21] stated that PEFR value was less among the brickfield workers than the other group of workers e.g., domestic workers, who perform household activities. The same result also had been found among preadolescent brickfield workers. The lung function values of preadolescent brickfield workers were lower in compare to preadolescent control subject [4].

Heart rate increases linearly with the work performed. The heart rate increases quickly to a level appropriate to the effort and then remains constant during the work. The researcher also stated that with more strenuous work, however, the heart rate goes on increasing until either the work is interrupted or the workers are forced to stop from exhaustion. Astrand and Rodahl [16] also explained that increase in heart rate is linear with the increase in the rate of activities. Thermal stress also influenced the heart rate and other physiological parameters among both groups of brick field workers. This result corroborates with the work Das [49] in which he stated that thermal stress and cardiovascular stress has a high influence in both groups of brickfield workers’ productivity.

5 Conclusion

From this study it was concluded that both groups of brickfield workers (male and female) work in awkward or stressful postures during different brick making activities in brick manufacturing, by which they suffered from discomfort or pain in different parts of their bodies – specifically in the lower back, knees, shoulders, neck and hands. This study shows that female brickfield workers suffered more discomfort than male brickfield workers; perhaps in part due to their additional domestic work responsibilities. This study also indicates that both male and female suffered maximum discomfort when molding, carrying mud, carrying raw bricks, loading and unloading burned bricks and carrying burned bricks. Both males and females suffered from severe physiological stress due to the hazardous working conditions. Increased heart rates also affected their health and overall work performance. There were significant differences in spirometry readings (FVC, FEV1 and PEFR value) between male and female brickfield workers.

6 Limitations of study

This study had some limitations, including a small sample size (n = 300). The study was performed in only in 12 brickfields. But these brickfields are in the same area and this does not reflect any change of the results. These workers are highly prone to WMSDs because of the heaviness of the loads they carry overhead and the adoption of harmful postures during lifting of the same load overhead. Ergonomics design interventions are urgently needed to improve the health of these workers. Barring these limitations, this study of electromyography needs to implicate during the various strenuous activities in brick making activities. Participants’ heart rates were only gross estimates taken from a manual pulse. Resting heart rate measured manually from the radial pulse because in resting condition, the heart rate measured from the radial pulse (by three finger method) for the 60 sec which was time consuming (available in resting condition), whereas in case of just after exercise heart rate beats very fast; that was the reason it was measured for the first 10 beats and calculated for 60 seconds from carotid pulse.

Conflict of interest

None to report.

Footnotes

Acknowledgment

The author express his sincere gratitude to all those male and female brickfield workers and brickfield owners who rendered immense co-operation during the completion of this study.

References

Das

. Prevalence of work related musculoskeletal disorder among the brick field workers of West Bengal, India. Arch Environ Occup Health. 2014;69:231–40.

Trevelyan

, Haslani

. Musculoskeletal disorders in a handmade brick manufacturing plant. Int J Ind Ergon. 2001;27:43–55.

Mukhopadhyay

. Risk factors in manual brick manufacturing in India. HFESA J Ergon Aust. 2008;22(1-2), 16–25.

Das

. Health hazards and risks for musculoskeletal problems among child labourers in the brickfield sector of West Bengal, India. Int Health. 2018. doi: 10.1093/inthealth/ihy071 [Epub ahead of print].

Bakker

, Verhagen

, Lucas

, Koning

, Koes

. Spinal mechanical load: A predictor of persistent low back pain? A prospective cohort study. Eur Spine J. 2007;16:933–41.

Das

, Gangopadhyay

. Prevalence of musculoskeletal disorders and physiological stress among adult, male potato cultivators of west bengal, India. Asia Pac J Public Health.NP. 2015;27(2):1669–82.

Sahu

, Sett

, Gangopadhyay

. An ergonomic study on teenage girls working in the manual brick manufacturing units in the unorganized sectors in West Bengal, India. J Hum Ergol. 2010;39(1):23–33.

Das

, Ghosh

, Gangopadhyay

. Assessment of ergonomic and occupational health related problems among female prawn seed collectors of Sunderbans, West Bengal, India. Int J Occup Saf Ergon. 2012;18(4):531–40.

Das

, Gangopadhyay

. An ergonomics evaluation of posture related discomfort and occupational health problems among rice farmers. Occup Ergon. 2011;10:25–38.

10.

Das

, Ghosh

, Gangopadhyay

. Child work in agriculture in west bengal, India: Assessment of musculoskeletal disorders and occupational health problems. J Occup Health. 2013;55:244–58.

11.

Andersson

GBJ

. Epidemiological aspects on low back pain in industry. Spine. 1981;6:53–60.

12.

Burdorf

, Sorock

. Positive and negative evidence of risk factors for back disorders. Scand J Work Environ Health. 1997;23(4):243–5.

13.

Inbaraj

, Haebar

, Saj

, Dawson

, Paul

, Prabhakar

, Mohon

, Alex

. Prevalence of musculoskeletal disorders among brick kiln workers in rural Southern India. Ind J Occup Env Med. 2013;17(2):71–5.

14.

Shaikh

, Nafees

, Khetpal

, et al. Respiratory symptoms and illnesses among brick kiln workers: A cross sectional study from rural districts of Pakistan. BMC Public Health. 2012;12:999–1004.

15.

Garg

. Ergonomics and the older worker: An overview. Exp Aging Res. 1991;17(3):143–55.

16.

Cole

, Bellizzi

, Flegal

, Dietz

. Establishing a standard definition for child overweight and obesity worldwide: International survey. BMJ. 2000;6:1240–3.

17.

Dickinson

, Campion

, Foster

, Newman

, O’Rourke

AMT

, Thomas

. Questionnaire development: An examination of the Nordic Musculoskeletal questionnaire. Appl Ergon. 1992;23(3):197–201.

18.

Hignett

, McAtamney

. Rapid entire body assessment (REBA). Appl Ergon. 2000;31:201–5.

19.

Jacquelin , LR , Drury , G , Richard , LB . A field methodology for the control of musculoskeletal injuries. Appl Ergon. 1994;25:3–16.

20.

Astrand

, Rodhall

Textbook of work physiology, 3rd edition, McGraw-Hill, New York, (1986), pp. 501–2.

21.

Das

. Assessment of occupational health problems and physiological stress among the brick field workers of West Bengal, India. Int J Occup Med Environ Health. 2014;27(3):413–25.

22.

Das

. An evaluation of low back pain among female brick field workers of West Bengal, India. Environ Health Prev Med. 2015;20:360–8.

23.

Gangopadhyay

, Das

, Ghoshal

, Ghosh

. An ergonomics study on posture-related discomfort and occupational-related disorders among stonecutters of West Bengal, India. Int J Occup Saf Ergon. 2010;16(1):69–79.

24.

Ray

Chaudhuri S

, Biswas

, Roy

. A subjective and objective analysis of pain in female brick kiln workers of West Bengal, India. Int J Occup Saf Health. 2012;2:38–43.

25.

Das

. Gender differences in prevalence of musculoskeletal disorders among the rice farmers of West Bengal, India. Work. 2015;50:229–40.

26.

Chakrabarty

, Sarkar

, Dev

, Das

, Mitra

, Sahu

, Gangopadhyay

. Impact of rest breaks on musculoskeletal discomfort of Chikan embroiderers of West Bengal, India: A follow up field study. J Occup Health. 2016;58(4):365–72.

27.

Gangopadhyay

, Ghosh

, Das

, Ghoshal

, Das

. Prevalence of upper limb musculoskeletal disorders among brass metal workers in West Bengal, India. J Ind Health. 2007;45:365–70.

28.

Ghosh

, Das

, Gangopadhyay

. A comparative ergonomic study of work-related upper extremity musculoskeletal disorder among the unskilled and skilled surgical blacksmiths in West Bengal, India. Indian J Occup Environ Med. 2011;15(3):127–32.

29.

Punnett

, Fine

, Keyserling

, Herrin

, Chaffin

. Back disorders and non-neutral trunk postures of automobile assembly workers. Scand J Work Environ Health. 1991;17:337–46.

30.

Kivi

, Mattila

. Analysis and improvement of work postures in the building industry: Application of the computerized OWAS method. Appl Ergon. 1991;22:43–8.

31.

Bernard

BP.

Musculoskeletal disorders and workplace factors: A critical review of epidemiologic evidence for workrelated musculoskeletal disorders of the neck, upper extremity, and low back. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) 1997; Publication No. 97–141.

32.

NIOSH.

Simple Solutions: Ergonomics for Construction workers (DHHS (NIOSH), Publication No. 2007-122). National Institute for Occupational Safety and Health, (2007); Cincinnati, OH.

33.

Devereux

, Rydstedt

, Kelly

, Weston

, Buckle

The role of work stress and psychological factors in the development of musculoskeletal disorders. Norwich, U.K.: Health and Safety Executive Research Report 273; 2004.

34.

Waters

, Dick

, Davis-Barkley

, Krieg

. A cross-sectional study of risk factors for musculoskeletal symptoms in the workplace using data from the general social survey (GSS). J Occup Environ Med. 2007;49:172–84.

35.

Alcouffe

, Maniller

, Brehier

, Fabin

, Faupin

. Analysis by sex of low back pain among workers, from small companies in the Paris area: Severity and occupational consequences. Occup Environ Med. 1999;5:696–701.

36.

Treaster

, Burr

. Gender differences in prevalence of upper extremity musculoskeletal disorders. Ergonomics. 2004;47:495–526.

37.

Hooftman

, van

Poppel MN

, van

der Beek AJ

, Bongers

, van

Mechelen W

. Gender differences in the relations between work-related physical and psychosocial risk factors and musculoskeletal complaints. Scand J Work Environ Health. 2004;30(4):261–78.

38.

Smith

, Zhang

, Zheng

, Zhang

, Wang

. Musculoskeletal disorders and their after-effects among health professionals in Beijing. Occup Ergon. 2006;6(1):25–34.

39.

DeZwart

BCH

, Frings-Dresen

MHW

, Kilbom

. Gender differences in upper extremity musculoskeletal complaints in the working population. Int Arch Occup Environ Health. 2000;74:21–30.

40.

Snook

SH.

Secondary intervention for low back pain. In: Karwowski W, Marras WS, editors. The occupational ergonomics handbook. 2nd ed. Interventions, controls, and applications in occupational ergonomics. Boca Raton, FL: Taylor and Francis. 2006;24:1–15.

41.

Hoogendoorn

, Bongers

, de

Vet HCW

, Houtman

ILD

, Ariens

GAM

, van

Mechelen W

, Bouter

. Psychosocial work characteristics and psychological strain in relation to low-back pain. Scand J Work Environ Health. 2001;21:258–67.

42.

Svensson

, Andersson

GBJ

. Low-back pain in 40- to 47-year old men: Work history and work environment factors. Spine. 1983;8:272–6.

43.

Davis

, Heaney

. The relationship between psychosocial work characteristics and low back pain: Underlying methodological issues. Clin Biomech. 2000;15:389.

44.

Konz

Work Design. USA: 4th Edition, Publishing Horizons, Inc. Scottsdale, Arizona; 1990.

45.

Raina

, Dickerson

. The influence of job rotation and task order on muscle fatigue: A deltoid example. Work. 2009;34:205–13.

46.

Cole

, Grimshaw

. Low back pain and lifting: A review of epidemiology and aetiology. Work. 2003;21:173–84.

47.

Lee

, Swanson

, Sauter

, Wickstorm

, Waiker

, Mangum

. A review of physical exercises recommended for VDT operators. Appl Ergon. 1992;23(6):387–407.

48.

Gangopadhyay

, Das

, Ghoshal

, Ghosh

, Ganguly

, Samanta

. The prevalence of musculoskeletal disorder among the prawn seed collectors of Sundarbans. J Hum Ergol. 2008;37(2):83–90.

49.

Das

. Thermal stress, cardiovascular stress and work productivity among the female brick field workers of West Bengal, India. J Hum Ergol. 2018;47:1–11.