1. Background
Musculoskeletal disorders allocate a dominant part of work-related diseases. According to the definition, musculoskeletal disorders are disorders of muscles, tendons, nerves, joints, bones, ligaments, and blood vessels that are created as the result of repetitive stress or immediate to acute trauma (e.g. slip and fall) (1). Despite the spread of mechanized and automated processes, work-related musculoskeletal disorders account for the most common cause of work time loss, increase of costs, and human diseases (2). Currently, the factors that increase the probability of experiencing musculoskeletal disorder should be studied in detail. As most health consequences, musculoskeletal disorders have multifactorial source (3). Individual factors are often interpreted as non-occupational factors that will participate in the prevalence of musculoskeletal disorders. Individual traits influence the individual’s response to environmental exposures (4). Individual factors include demographic data (gender and different reactions to stress), age, anthropometric (height and weight), psychological traits (character), lifestyle people (i.e. physical activity, exercise, smoking, drugs), disease (i.e. Diabetes, confusion, depression), past history (musculoskeletal disorders), as well as social features (i.e. divorce, segregation and poverty) (5). Studies have pointed out that there is significant relationship between psychosocial factors and musculoskeletal disorders. Bongers et al. concluded that many psychological factors have been interrelated in emerging of such disorders including: stable work, time pressure, high load work, low control over work, poor social support from colleagues, worry, tension, anxiety, and anger with pain in the back, neck and shoulders (6). The relationship between the physical and psychosocial factors and its contribution to the development of musculoskeletal disorders has not yet been completely understood. It has been proved that these factors have interaction by the risk of musculoskeletal disorders, effectively. To help better understand this interaction, it may be important to determine whether individuals show different reactions when exposed to psychosocial factors or whether they prefer workplace as stressful or better. The personality theory helps understand this matter. It dictates adaptability for many life situations, such as work. Theorist gordon allport (1937) has defined personality as the dynamic organization within the individual that determines his/her unique adaptation to the environment. This subject reflects the idea within which a person’s character is a system that integrates both physical and mental aspects and people are active to get adjusted with their surroundings. Personality traits are psychological factors that have been hidden to affect the physical illness over time and thereby reflect individual differences. Amongst these variables, some of the important personality traits may be named as neuroticism and extraversion (7, 8).
Many psychologists believe that the main basis of the human character can be observed through 5 main traits including: extraversion, agreeableness, conscientiousness, neuroticism, and openness. Extraversion represents a dynamic approach inside a person towards the material and social world whose traits can be stated as sociability, activeness, decisiveness, courage and more. Agreeableness represents the social and prosocial orientation against hostile feedback to others. Some of these features may be depicted as altruism, kindness, trust, humility, etc. Conscientiousness describes the power impulses so that the society knows it as an ideal behavior and facilitates it as task-oriented and goal-oriented behavior. The adjective traits may be described as traits such as thinking before acting, delay of desire gratification, compliance with rules and norms as well as organize and prioritize tasks. Neuroticism can be defined as the tendency to represent negative emotions and experiences against emotional stability and calm. This dimension also includes sensitivity to the unreal beliefs, poor control of individual desires and ineffective strategies against the stress. Openness also describes the breadth, depth, complexity and creativity of the mind and experience of the person towards the finite subjective (9). Each of these personality traits have certain advantages that may be answered by a person in a work situation and a task with certain conditions that can affect a person’s energy and stress (10). Neuroticism, extraversion and conscientiousness have reliable relationships with the physical activity (11-14). Previous studies have shown a lot of evidence that people with high neuroticism scores are more likely to suffer with a disability (9). High levels of neuroticism personality traits related with high levels of diseases, including heart disease, asthma, arthritis, autoimmune, and infection (15-18). Individuals with high extraversion levels are usually active and bolder and with more energy in comparison to those who are introvert (that are usually quiet, shy and dissociable) (19). More diseases have been reported for the individuals with high extraversion traits compared with introverts (20-22). Individual differences are very important in determining how people behave in the workplace. Personality traits have an important role in the prevalence of musculoskeletal disorders.
2. Objectives
The purpose of the present study is to identify the personality traits used to determine the relationship between different personality traits and the prevalence of musculoskeletal disorders in 2 different companies including petrochemical repair and dairy factory workers in Tabriz, Iran (in 2015).
3. Methods
The present study has been implemented in 2 different companies. In the study there were 136 people of the petrochemical repair workers (n = 84) and dairy factory workers (n = 52) that were involved in census method. For this purpose, all repair workers in petrochemical company and all workers in dairy factory were studied. The permanent workers with at least 1 year experience were included in study. In order to measure personality traits of people, Goldberg’s big five personality scale was used. The Goldberg (1999) designed scale is based on a five-factor pattern of personality, which measures five factors including emotional stability, extraversion, openness, agreeableness, and conscientiousness (Goldberg, 1999). In the present study, the 50-item question version of the Goldberg questionnaire was used. The questionnaire, which any 10 questions were related to a feature of neuroticism, extraversion, openness of experience, agreeableness, and conscientiousness, meet the appropriate validity and reliability index and they are based on the five-point scale (from 1 to 5).
The Scoring of Goldberg’s Five Personality Factors Questionnaire:
As stated, the utilized questionnaire consists of 50 sections within which, 10 sections are devoted into the personality traits. The scoring method is based on the Likert five-degree scale. Score one belongs to the first option (mostly not-correct) and the score of five to the fifth option (mostly correct). The sub-scales are as follows:
Questions No. 1, 6, 11, 16, 21, 26, 31, 36, 41 and 46: extraversion
Questions No. 2, 7, 12, 17, 22, 27, 32, 37, 42 and 47: agreeableness
Questions No. 3, 8, 13, 18, 23, 28, 33, 38, 43 and 48: conscientiousness
Questions No. 4, 9, 14, 19, 24, 29, 34, 39, 44 and 49: Emotional stability
Questions No. 5, 10, 15, 20, 25, 30, 35, 40, 45 and 50: Openness
Questions No. 2, 4, 6, 8, 10, 12, 14, 16… 48: converse questions
Goldberg has reported Cronbach’s alpha as 0.65 to 0.85 for traits of the big five personality factors in this questionnaire (23). The value of 0.82 for agreeableness, 0.79 for conscientiousness, 0.86 for emotional stability, 0.8 for openness, and 0.87 for extraversion were reported (24). The persian version of this scale was a translation and prepared with standard methods by Ghorbani et al. (2005) (25). Aghababaie (2012) reported the alpha coefficient factor (of correlation) from 0.70 to 0.79. Khormaei revealed the validity and reliability of the test and Cronbach’s alpha coefficient of conscientiousness and agreeableness as 0.8, openness as 0.78, extraversion as 0.77, and emotional stability as 0.88 (26).
The Nordic questionnaire was used to evaluate the prevalence of musculoskeletal disorders. In the present study, the Nordic questionnaire (that was designed by Kurinka et al. at the Scandinavian institute of occupational health) was incorporated to investigate the wide spread rate of musculoskeletal disorders. This questionnaire has been widely used as standard tool to conduct the epidemiologic researches for evaluation of the musculoskeletal disorders at different industries. It consists of personal information such as age, gender, weight, height, marriage, education, job experience, work shift, and the dominant hand besides the musculoskeletal disorders such as neck, shoulder, elbow, wrist and hand, reins, hips and thigh, knee, ankle, and feet-related diseases. The first part of the questionnaire concerns the demographic information. Other parts are regarding the prevalence of musculoskeletal disorders in different body parts during a week and 12 months. To analyze the data, chi-square test were used and the p-value lower than 0.05 is considered as a significant association. Finally, logistic regression test was used to study the factors affecting the upper and lower body pain.
4. Results
4.1. Subjects Demographic Characteristics
All of the subjects were male at the overall samples. They worked in part of repairing the petrochemical industry (n = 84) and dairy company (n = 52). The workers mean age for the petrochemical and dairy companies were 42.4 ± 6.31 and 50 ± 6.24, respectively. BMI mean weights of the workers in the petrochemical industry were 26.56 ± 3.6 and 25.5 ± 3.4, respectively. The workers average heights in petrochemical and dairy company were 174.4 ± 6.58 and 169.7 ± 8.49cm, respectively. The average workers job tenure in petrochemical and dairy company was 16.4 ± 4.9 and 11.9 ± 6.7, respectively. Other demographic traits are shown in Table 1. Furthermore, most of the people were married. The majority of the people were right handed in 2 companies (89.2% for petrochemical company and 86.8% for dairy company). Additionally, the majority of people had a bachelor degree (45.3%) in petrochemical company and high school diploma (38.6%) in the dairy company.
Table 1. Demographic Traits of the Individual (Subjects)a
| Demographic Traits | Company | ||
|---|---|---|---|
| Petrochemica | Dairy | ||
| Age | 30 and under | 2 (2.4) | 10 (18.9) |
| 31 - 35 | 11 (13.3) | 14 (26.4) | |
| 36 - 40 | 17 (20.5) | 14 (26.4) | |
| 41 - 45 | 30 (36.5) | 10 (18.9) | |
| 46 - 50 | 15 (18.1) | 5 (9.4) | |
| 51 and above | 8 (9.6) | 0 | |
| Education | Under diploma | 20 (24.1) | 1 (1.9) |
| Diploma | 32 (38.6) | 8 (15.1) | |
| Upper diploma | 10 (12) | 7 (13.2) | |
| Bachelor | 21 (25.3) | 24 (45.3) | |
| Post graduate | 12 (22.6) | - | |
| Dominant hand | Right | 74 (89.2) | 46 (86.8) |
| Left | 9 (10.8) | 7 (13.2) | |
| Work experience | 1 - 5 | 2 (2.4) | 12 (22.6) |
| 6 - 10 | 9 (10.8) | 12 (22.6) | |
| 11 - 15 | 22 (26.5) | 14 (26.4) | |
| Above 16 | 50 (60.2) | 15 (28.3) | |
| BMI | Under 25 | 28 (33.7) | 26 (49.1) |
| 26 - 30 | 42 (50.6) | 22 (41.5) | |
| Above 31 | 13 (15.7) | 5 (9.4) | |
| Marital status | Single | 4 (4.8) | 9 (17) |
| Married | 79 (95.2) | 43 (81.1) | |
| Personality traits | Extraversion | 32.3 ± 4.6 | 33.41 ± 5 |
| Agreeableness | 38.73 ± 5.33 | 41.8 ± 4.2 | |
| Conscientiousness | 40.87 ± 5.3 | 40.67 ± 4.6 | |
| Emotional stability | 32.9 ± 4.5 | 33.07 ± 5.7 | |
| Openness | 36.56 ± 5.2 | 36.39 ± 4.9 | |
aValue are expressed as number percent.
4.2. Personality Traits
Extraversion trait average scores were as 32.3 ± 4.6 and 33.41 ± 5 for petrochemical and dairy companies, respectively. Emotional stability trait average score were as 32.9 ± 4.5 and 33.07 ± 5.7 for the petrochemical and dairy companies, respectively. Openness trait average score were as 36.56 ± 5.2 and 36.39 ± 4.9 for the petrochemical and dairy companies, respectively. Agreeableness trait average score were 38.73 ± 5.33 and 41.8 ± 4.2 for the petrochemical and dairy companies, respectively.
4.3. Musculoskeletal Disorders
Distribution of the musculoskeletal disorders is presented in Table 2 in different parts of the body in 2 companies. Based on Table 2, prevalence of musculoskeletal disorder in low back (petrochemical; 49.4% and dairy; 58.5%) was higher than its prevalence in other parts of the body at both companies. The second part of the body that had high prevalence of disorder (52.8%) was the shoulder in dairy company and knee (with prevalence of 39.8%) in petrochemical company.
Table 2. Distribution of Musculoskeletal Disorder in Different Part of Body in Two Companya
| Limb | Musculoskeletal Prevalence | Company | P Value | |
|---|---|---|---|---|
| Petrochemical | Dairy | |||
| Neck | No | 54 (65.1) | 30 (56.6) | 0.209 |
| Yes | 29 (34.9) | 23 (43.4) | ||
| Shoulder | No | 63 (75.9) | 25 (47.2) | 0.001 |
| Yes | 20 (24.1) | 28 (52.8) | ||
| Elbow | No | 60 (72.3) | 43 (81.1) | 0.167 |
| Yes | 23 (27.7) | 10 (18.9) | ||
| Wrist | No | 63 (75.9) | 40 (75.5) | 0.556 |
| Yes | 20 (24.1) | 13 (24.5) | ||
| Hip | No | 70 (84.43) | 45 (84.43) | 0.565 |
| Yes | 13 (15.7) | 8 (15.1) | ||
| Back | No | 54 (65.1) | 29 (54.7) | 0.152 |
| Yes | 29 (34.9) | 24 (45.3) | ||
| Low back | No | 42 (50.6) | 22 (41.5) | 0.195 |
| Yes | 42 (49.4) | 22 (58.5) | ||
| Knee | No | 50 (60.2) | 33 (62.3) | 0.479 |
| Yes | 33 (39.8) | 20 (37.7) | ||
| Ankle | No | 62 (74.7) | 43 (81.1) | 0.256 |
| Yes | 21 (25.3) | 10 (18.9) | ||
aValue are expressed as number percent.
Significant difference was observed between the prevalence of disorder in shoulder (P - value = 0.001) at 2 companies. There was no significant relationship amongst the prevalence of disorder in other parts of body in 2 companies (Neck; P - value = 0.209, Elbow; P - value = 0.167, Wrist; P - value = 0.556, Back; P - value = 0.152, Low back; P - value =0.195, Knee; P - value =0.479, Ankle; P - value =0.256).
4.4. Personality Trait and Musculoskeletal Disorder
The effects of the results were obtained from the multiple regression logistic model has been represented in Table 3 for determining the personality trait that affects the musculoskeletal disorder in different parts of the body in the studied individuals. The results indicated that the individuals with a lower extraversion score had a higher chance to musculoskeletal disorder prevalence in wrist (OR = 0.920, CI95% = 0.840 - 937, P - value = 0.013) and hip (OR = 0.932, CI95% = 0.866 - 992, P - value = 0.044) comparing to those with high extraversion score. Individual with low emotional stability had a high chance to musculoskeletal disorder prevalence in shoulder (OR = 0.907, CI95% = 0.841 - 983, P - value = 0.012), wrist (OR = 0.919, CI95% =0.847 - 997, P - value = 0.043), back (OR = 0.922, CI95% = 0.856 - 994, P - value = 0.034), low back (OR = 0.923, CI95% =0.859 - 992, P - value = 0.029), and ankle (OR = 0.895, CI95% =0.819 - 978, P - value = 0.014) than an individual with high emotional stability score. Individuals with low conscientiousness score also had a high chance to musculoskeletal disorder prevalence in hip (OR = 0.879, CI95% = 0.798 - 968, P - value = 0.009) than individual with high conscientiousness score. Individuals with a low agreeableness score had a high chance to musculoskeletal disorder prevalence in the shoulder (OR = 0.880, CI95% = 0.808 - 960, P - value = 0.004), back (OR = 0.855, CI95% =0.783 - 934, P - value = 0.001), Hip (OR = 0.866, CI95% = 0.804 - 917, P - value = 0.006) and ankle (OR = 0.821, CI95% =0.803 - 927, P - value = 0.019).
Table 3. Multiple Regression Logistic Model for Determining the Personality Trait That Affect the Musculoskeletal Disorder in Different Part of Body in the Studied People
| Limb | Musculoskeletal Prevalence | Personality Trait | P Value | OR | CI 95% | |
|---|---|---|---|---|---|---|
| Lower | Upper | |||||
| Extraversion | ||||||
| Wrist | No | 33.36 | 0.013 | 0.920 | 0.840 | 0.937 |
| Yes | 30 | |||||
| Hip | No | 33 | 0.044 | 0.932 | 0.866 | 0.992 |
| Yes | 31 | |||||
| Emotional stability | ||||||
| Shoulder | No | 33.7 | 0.012 | 0.907 | 0.841 | 0.983 |
| Yes | 31 | |||||
| Wrist | No | 33.54 | 0.043 | 0.919 | 0.847 | 0.997 |
| Yes | 31 | |||||
| Back | No | 33.7 | 0.034 | 0.922 | 0.856 | 0.994 |
| Yes | 31.7 | |||||
| Low back | No | 34 | 0.029 | 0.923 | 0.859 | 0.992 |
| Yes | 32 | |||||
| Ankle | No | 33.4 | 0.014 | 0.895 | 0.819 | 0.978 |
| Yes | 30 | |||||
| Conscientiousness | ||||||
| Hip | No | 40.36 | 0.009 | 0.879 | 0.798 | 0.968 |
| Yes | 39 | |||||
| Agreeableness | ||||||
| Shoulder | No | 43.4 | 0.004 | 0.880 | 0.808 | 0.960 |
| Yes | 40.3 | |||||
| Back | No | 41 | 0.000 | 0.855 | 0.783 | 0.934 |
| Yes | 38 | |||||
| Hip | No | 40 | 0.006 | 0.866 | .804 | 0.917 |
| Yes | 35 | |||||
| Ankle | No | 40 | 0.019 | 0.821 | .803 | 0.927 |
| Yes | 37 | |||||
5. Discussion
The results of the present study revealed that the distribution of musculoskeletal disorders in the lower back were high in both companies. The second part of body that had a high prevalence of disorder in the dairy company was the shoulder, which had a significant difference with prevalence of a shoulder disorder in the petrochemical company.
5.1. Extraversion
There was a negative significant relationship between extraversion traits of individual and musculoskeletal disorders prevalence in the wrist, which is in agreement with the Malchaire et al. study that was conducted on 133 women from 7 different companies working at constraining workplace with very repetitive work (27). In the Vasseljen et al. case - control study, which investigated the psychological and psychosocial risk factors for shoulder and neck pain at the workplace, no associations was observed between pain in neck and shoulders and extraversion traits (28). Furthermore, Edvin Bru et al. observed no associations between the extraversion traits and musculoskeletal disorders in a study that was conducted on the female hospital staff (29). Extravert people were active, energetic, and assertive whereas individuals with lower extraversion were quiet, reserved, and shy (14). Some other studies have also indicated the positive association between extraversion and muscle strength (13, 22). In agreement with the present study, however, muscles of the extrovert people were strong; they were low prone to the musculoskeletal disorders than introvert individuals. Oron et al. conducted the similar study on soldiers and observed that extrovert individuals suffered from musculoskeletal disorders (30).
5.2. Emotional Stability
In the present study, negative significant association was observed between emotional stability and prevalence of musculoskeletal disorder in the shoulder, wrist, back, low back, and ankle. Emotional stability was in opposite of neuroticism. In agreement of the present study results, evidence of a positive association was mentioned between neuroticism and physical function in some previous studies. In these studies, individuals with higher scores on neuroticism had mobility limitations and disability than those with lower scores (9, 31, 32). Rogaland et al. studied 86 female hospital staff for observation of any association between the personality traits and musculoskeletal pain of the neck, shoulders and lower back. The results showed a positive significant association between the neuroticism, shoulder, and low back pain (29). Astrand studied 391 male employees in a Swedish pulp and paper industry. The results showed an association between back pain and neuroticism trait of individual (33). In other studies, higher risks of unhealthy behaviors were observed amongst the individuals with high neuroticism scores (34, 35).
5.3. Conscientiousness
In the present study, negative significant association was observed between conscientiousness and prevalence of musculoskeletal disorder in the Hip. In agreement with the present study, Conscientiousness has been reported as a determinant factor in healthy behavior (12). Conscientiousness as the personality trait may be described such that the society accepts it as a favorite mode and facilitate it as task and goal-oriented behavior. So, individuals with this trait are rule based capable of doing their work based on the correct way. So, they are not prone to musculoskeletal disorders than individuals with low score of conscientiousness.
5.4. Agreeableness
The negative significant association was observed between agreeableness and prevalence of musculoskeletal disorder in shoulder, back, hip, and ankle. Individuals with high scores of agreeableness had a lower chance for musculoskeletal disorder than individuals with high scores. In agreement of the present study, in a recent meta-analysis, agreeableness correlates with physical activity (11), A positive association of agreeableness with other healthy behaviors has been reported in other studies (34, 36). Individuals with agreeableness trait, social and prosocial orientation in front of others, showed characteristics such as altruism, kindness, trust, and humility. Therefore, observance laws and labor standards were more likely to be agreed by these people. Therefore, this trait can prevent them from getting musculoskeletal disorders.
Mental factors are one of the most important parameters in prevalence of musculoskeletal disorders. Individual differences are very important in determining how people behave in the workplace. The human factors directly affect the human behavior. Usually, people respond to stress depending on their personality. People that have personality trait of conscientiousness perform their tasks on time and with calm and less prone to the musculoskeletal complications. Also, someone who has a high level neuroticism trait may perform poorly in response to environmental stresses. These people are more prone to get musculoskeletal complications.
Personality traits, including emotional stability, conscientiousness, and neuroticism can be involved in prevalence of musculoskeletal complications. Therefore, notice of personality traits can be used to predict the probability of musculoskeletal disorder in people. Then, the necessary tailored training proportional to the individual's personality traits seems to be helpful for the prevention of musculoskeletal disorders.
As a further study, more uniform population should be chosen to reveal the personality traits of people in developing musculoskeletal disorders, efficiently.
