Musculoskeletal disorders and stress among footwear industry workers

Abstract

BACKGROUND: Manufacturing footwear requires intense manual labor and high repetitions with low variability in function that may lead to musculoskeletal disorders (MSD) symptoms and psychological stress.

OBJECTIVE: To evaluate a potential association between musculoskeletal disorders (MSD) and perceived stress among footwear industry workers.

METHODS: The Nordic General Questionnaire (NGQ) and the Perceived Stress Scale (PSS-10) were completed by 357 footwear industry workers. The association between MSD and perceived stress was evaluated using the Chi-Square test and Odds Ratios along with their 95% Confidence Interval (95% CI) were calculated.

RESULTS: The twelve-month prevalence of MSD symptoms among the respondents was 66% (n = 236) and the symptoms were significantly associated with perceived stress (p = 0.002, OR: 10, 95% CI: 1.7 to 60.6). The seven-day prevalence of MSD symptoms was 33% and the symptoms were also significantly associated with perceived stress (p = 0.001, OR: 2.7, 95% CI:0.8 to 9.3). The association between perceived stress and MSD symptoms indicates a strong association between MSD symptoms and perceived stress levels.

CONCLUSION: Considering that these problems are important determinants of worker’s health, a combined approach to reduce both stress and MSD symptoms is necessary for prevention and health promotion in the footwear industry.

Keywords

Cumulative trauma disorders occupational health risk factors stress.

1 Introduction

Musculoskeletal disorders (MSD) are one of the leading causes of incapacity for work, and they have significant economical and health-related consequences [1]. The high prevalence of MSD in the footwear industry indicates that it is important to investigate factors that are related to these health problems in this population [2]. Studies have found a relationship between high physical demands and work-related MSD symptoms, such as repetitive motions and carpal tunnel syndrome, awkward postures and neck pain, and manual handling and back pain [3 –5].

Obesity, a sedentary lifestyle, and smoking also seem to be related with MSD symptoms (e.g. low back pain) among different groups of workers such as nurses and steel workers [4]. Some studies also suggested that MSD symptoms might be associated with stress, low job satisfaction, poor emotional support, low degree of decision latitude, excessive cognitive demands and psychological pressure during work [6]. Other studies showed that employees with reduced capacity for work are predisposed to the onset of diseases, long periods of absenteeism, and high levels of psychological stress [7]. On the other hand, Choobineh et al. [8] found no significant correlation between psychosocial factors and MSD symptoms among administrative workers from an oil refinery. The relationship between high physical demands and MSD symptoms is well established [9 –11], but the relationship between stress and MSD is still somewhat unclear [4].

Jobs in the footwear industry present characteristics (e.g. high repetitions, psychological pressure for high productivity) that may lead to MSD symptoms and psychological stress. Manufacturing footwear requires intense manual labor and high repetitions with low variability in function [12]. These factors are physical risks, result of monotonous work and low decision power [13]. However, most of the MSD research conducted in the footwear industry has focused on biomechanical risk factors [5, 14]. Further information is needed on the potential association between MSD symptoms and stress among footwear industry workers. The objective of this study was to evaluate the potential association between MSD symptoms and perceived stress among workers in the production sector of the footwear industry.

2 Material and methods

2.1 Setting and subjects

The study was conducted in the Brazilian footwear manufacturing industry region located in Franca, São Paulo state. Data collection was completed from January to March 2012. The footwear companies were selected according to their size, using a stratified cluster sampling method. Fourteen companies were selected; 14% were large companies, 35% were medium size companies and 50% were small or micro companies. In 2009, there were 17,727 workers in the Brazilian footwear manufacturing industry sector [15]. The sample size was determined based on the target population using calculations for observational studies with a margin of error of 5% (CI = 95%) for MSD symptoms, which results in 377 participants. Employees with less than one year of working experience in the footwear industry were not eligible to participate. Employees of all sectors of the footwear industry were invited to participate in this study. Questionnaires were distributed to 430 workers and 357 (83%) returned completed questionnaires. Fifty one percent of the respondents were male (n = 182) and 49% were female (n = 175). The mean age was 34 ± 10 years. The mean work experience was 9 ± 9 years. All subjects were voluntary participants and signed an informed consent form. The study was approved by the Ethics Committee review board (Ref. 0080-11).

2.2 Perceived stress – assessment

For the analysis of perceived stress the PSS-10 (Perceived Stress Scale – 10) was used; it was developed by Cohen et al. [16] and the Brazilian Portuguese version was validated by Reis et al. [17]. This questionnaire consists of a self-report instrument for general assessment of stress levels. The PSS-10 has ten items, each with five possible answers based on frequency of symptoms. The final perceived stress level score ranges from 0–40, with higher scores meaning higher stress levels. The PSS- 10 questionnaire (Portuguese version) has good internal consistency (Cronbach’s alpha = 0.87), and high test-retest reliability (Intraclass Correlation Coefficient = 0.86) [17].

2.3 Musculoskeletal disorders

To evaluate the prevalence of MSD symptoms, the Nordic General Questionnaire (NGQ) was used; it was developed by Kuorinka et al. [18] and the Brazilian Portuguese version was validated by Barros and Alexandre [19]. The aim of the NGQ is to standardize the analysis of MSD symptoms and allow the comparison of data from different studies. It covers all body areas, with yes or no responses to the presence of MSD symptoms (discomfort, numbness and/or pain) in the different body parts during the last 12 months and last 7 days [19]. The NGQ has adequate psychometric properties, with high reliability [19]. Reliability was assessed by a test– retest procedure at 1-day intervals using the Kappa coefficient in a group of 40 subjects [19]. The Kappa agreement values were calculated for each question of the questionnaire and the agreement among the same observers varied from 0.88 to 1 (Kappa values) [19].

2.4 Procedures

The data collection was done in the footwear companies selected, in which the questionnaires were distributed to workers. The workers took approximately 25 minutes to complete the questionnaires.

2.5 Data analysis

The data were tabulated and the results were presented descriptively including means, standard deviations, and percentages. The association between MSD symptoms and level of perceived stress was evaluated using the Chi-square test for trend (significance level was set to 0.05), and Odds Ratios along with their 95% Confidence Interval were calculated. The perceived stress scores were divided into four ranges: 0 to 9 (Low), 10 to 19 (Moderate), 20 to 29 (High) and 30 or higher (Very high). The MSD symptoms were analyzed to the body in general and divided in upper limb, lower limb and spine. All analyses were performed using the statistical program GraphPadInstat.

3 Results

The twelve-month and the seven-day prevalence of MSD symptoms among the respondents was 66.1% (n = 236) and 33.3% (n = 119), respectively. In the last year, the body regions with the highest prevalence of symptoms were the wrists/hands/fingers, shoulder, neck, lower back and ankles/feet. In the last seven days, higher prevalence were observed in the wrists/hands/fingers, lower back and ankles/feet (Fig. 1).

The mean perceived stress score was 16.3 ± 6.6 (out of 40). Most workers (54.1%) had a moderate score (10 to 19); 28.6% had high scores (20 to 29); 14.3% had low scores (0 to 9) and 3.1% had very high scores (30 or higher).

The perceived stress scores were associated with the presence of MSD symptoms in the last 12 months (p = 0.0017) and in the last seven days (p = 0.0006). The Odds Ratio and 95% confidence intervals presented on Table 1 indicate that workers with higher perceived stress scores were more likely to have had MSD symptoms.

Tables 2 present the Odds Ratios and 95% confidence intervals between perceived stress scores and MSD symptoms in the upper limbs, lower limbs, and back, respectively.

4 Discussion

4.1 Perceived stress

In the last years, the number of studies about stress, depression and anxiety has grown; great importance has been given to the relationship between mental conditions and physical problems [20]. Our results showed that 82.7% of employees reported perceived stress scores between 10 and 30. These findings indicate that the most footwear industry employees have moderate to high levels of stress. Similarly, Cohen and Janicki-Deverts [20] found average scores between 10 and 20 in 1,108 full-time workers in the United States, but high levels of perceived stress were reported among unemployed workers. Significant levels of stress were also found in hospital employees [21]. Strain and stress lead to absenteeism and reduce productivity and thus the success of an organization, leading to additional societal costs [22, 23]. The stressful work can be the combination of two major task characteristics, high demands and low control of decision. In addition, low social support, low rewards, low esteem/recognition, few career opportunities, and job insecurity can also adversely affect the health of workers and lead to health problems [21]. Many of these factors are present in the footwear industry, which may help explain the high rates of stress and MSD symptoms observed in the present study.

4.2 MSD symptoms

The high prevalence of MSD symptoms observed in this study are consistent with previous studies conducted with workers in the footwear industry [5, 14], and in other sectors such as education [24] and construction [25]. We found high prevalence of MSD symptoms in wrists/hands/fingers in the last twelve-months and seven days. These results can be understood by the fact that the jobs in the footwear sector involve manual skills and tasks for the manufacture of footwear [12]. The also high prevalence of MSD symptoms in the neck, shoulder and low back observed in the present study may be explained by the maintenance of standing or sitting postures for long periods of time, repetitive tasks and awkward postures often adopted in the footwear manufacturing [5].

4.3 Perceived stress and MSD symptoms

MSD symptoms were associated with higher levels of perceived stress. Studies conducted in other industries also found associations between psychosocial factors and MSD symptoms [26, 27]. The association between MSD symptoms and stress may be mediated by pain which activates the sympathetic nervous system and the hypothalamic-pituitary-adrenal, causing stress reactions [28]. However, the present results can also be explained by understanding the stages of stress, considering that in the exhaustion stage, the body becomes highly vulnerable to the onset of disease and disorders [29]. Given the cross-sectional nature of our study, cause-effect relationships can not be discussed and we still do not know if the stress leads to MSD symptoms or vice-versa, or if the two simply co-occur. Therefore, longitudinal studies are needed to further clarify the mechanisms mediating the identified association between stress and MSD symptoms.

The association between MSD symptoms and perceived stress was stronger in the last seven days when compared to the last twelve-months which suggests acute responses by high levels of stress and/or MSD symptoms. Vachon-Presseau et al. [30] indicated that acute stress responses can influence the physiological mechanisms involved in the perception of pain and Shahidi et al. [31] demonstrated that acute psychosocial stress causes a high trapezius muscle activation which is associated with pain.

Our results showed that MSD symptoms in upper and lower limbs were strongly associated with higher levels of perceived stress in the last twelve-months; the same tendency was observed for the last seven-days. The hypothesis for this association is that increase of psychological strain may affect the shoulder and wrist/hand. These strain responses can lead to specific MSD symptoms in different body areas [32]. Studies conducted previously found stress to be associated with low back and upper limb MSD symptoms [33]. However, our study identified a stronger association between stress and lower limb MSD symptoms. We did not find in the literature any study that can explain these results, but we believe that some mechanisms increase the strain response in the lower limb. Govindu and Babski [6] suggested that psychosocial factors may increase muscle tension or infuence pain perception and may also impact biomechanical load, causing changes in posture, movement and forces exerted.

In addition, we did not find a strong association between perceived stress and MSD symptoms in the back in the last twelve-months. However, it was observed a high prevalence of symptoms in spine in the four levels of perceived stress, which suggests that these symptoms could be more related with biomechanical factors like the maintenance of standing or sitting postures for long periods of time as opposed to psychosocial factors. Zemp et al. [34] suggested that static sitting increases the risk of back pain and the dynamic posture is important to maintenance the spinal health. Previous studies found that prolonged standing causes a higher gluteus-medius and trunk flexor– extensor muscles co-activation increasing back pain [35, 36]. Another research found that the association of back pain and psychological factors depends on one’s personality and cultural attitudes to illness like tendency to somatization and adverse health beliefs which vary among countries [37]. In addiction, Vargas-Prado et al. suggested that psychological and culturally factors have an important role in musculoskeletal symptoms.

Previous studies found an association between perceived stress and pain in the shoulder, knee, forearm and low back [37, 39]. These results are partly in accordance with the present study. Griffits et al. [39] suggests that the perception of stress can modify the normal muscular tone in repeated movements, which are often performed with the upper limbs in the footwear manufacturing industry. However, we did not find an association between stress and back pain.

Frequent musculoskeletal pain in combination with perceived long-standing stress was found to be associated with decreased work performance and ability [40]. Another studies found associations between occupational stress and musculoskeletal pain with lower work ability [41, 42]. Furthermore, workers with low anxiety and elevated decision latitude have better immunity than those who are submitted to high job strain, which reduce the risk of disease and incapacity [43]. Recently, it was shown that the presence of MSD symptoms associated with perceived stress, increases the risk of incapacity for work [40], which demonstrates the importance of controlling these symptoms and their risk factors among footwear sector workers.

In conclusion, we found high prevalence of the MSD among footwear industry workers, and the MSD, mainly those affecting the upper and lower limbs, were associated with perceived stress. With the objective of changing organizational and physical workplace risk factors, stress and MSD should be considered in developing strategies for prevention and health promotion among footwear industry workers.

4.4 Limitations

The present study has some limitations. The study includes only subjective measures (pain and stress). The lack of direct assessment of physical risk factors, which could be involved in the occurrence of MSD, may have biased results. In addition, there were another potential factors, such as age, gender and duration of work, that were not considered in the analysis.

4.5 Suggestions for future research

For future research, we suggest longitudinal studies to further clarify the mechanisms mediating the association between stress and musculoskeletal symptoms. We also suggest new studies to evaluate the effects of physical, personal, occupational and psychosocial factors as well as their interactions on musculoskeletal symptoms among footwear industry workers. With these results, one may develop more specific and effective strategies in prevention and health promotion in the footwear sector.

Conflict of interest

The authors have no conflict of interest to report.

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