Extended Abstract
Introduction
In the workplace, human beings are affected by various harmful factors such as ergonomic, physical, chemical, etc. All of these factors cause fatigue, early weakness, and, in economic terms, a waste of time and money [1]. The term “musculoskeletal disorders” refers to a large group of inflammatory and destructive diseases that affect the muscles, ligaments, tendons, joints, intervertebral disks, nerves, and blood vessels [2, 3]. Work-related musculoskeletal disorders (WRMDs) are associated with risk factors in the workplace and are known by various names such as cumulative trauma disorders and repetitive traction injuries [4]. In today’s world, the issue of prevention and control of WRMDs is extremely important because a large part of the compensation paid to the injured workforce belonged to these disorders. Studies have shown that more than half of the absences in the workplace are caused by musculoskeletal disorders [5]. 
Work-related injuries can lead to problems such as job loss, job restrictions, fatigue, burnout, or eventually change of job [6]. WRMDs are among the most important causes of occupational injury and disability in industrialized and developing countries [7, 8]. Improper body posture and lack of knowledge about the correct principles of work are among the most important causes of WRMDs. These disorders are the main occupational problems among health care providers [9-12].
Physiotherapy is one of the occupations in the field of rehabilitation that is prone to WRMDs for various reasons, such as direct contact with patients, different activities, and physical conditions during work [13]. The rate of these injuries among physiotherapists in the UK has been reported 68% [14]; in Australia, 55% [15]; in Turkey, 85% [16]; in Nigeria, 91.3% [17]; and in Greece, 89% [18]. In Iran, Sharhaninezhad et al. (2014) conducted a study in Ahvaz City and their findings indicated a high prevalence of musculoskeletal problems among physical therapists [19]. Nazari et al. (2016) conducted a study in the cities of Hamedan, Nahavand, and Malayer. They reported a prevalence rate of 58.3% among physical therapists [20]. Several studies have suggested that WRMDs have been frequently experienced by physiotherapists [21]. Recent evidence suggests that the prevalence of work-related injuries in therapists is increasing every year [6]. Overall, it is estimated that the direct and indirect costs of musculoskeletal disorders may account for about 1% of the gross domestic product of industrialized countries [22].
Information about work-related injuries among physiotherapists is limited [6, 15, 18]. Considering that there is no study on work-related musculoskeletal problems among physiotherapists in Iran, we aimed to investigate the relationship between WRMDs with various types of treatment used by physiotherapists in Iran.
Materials and Methods
This is a descriptive-analytical epidemiological study with a cross-sectional design. The study population consists of all physiotherapists working in Iran in 2016. According to the Iranian Physiotherapy Association, the study population was 3600. Of these, 1200 physiotherapists participating in the 27th Iranian Physiotherapy Congress were selected. The inclusion criteria were having academic education in physiotherapy with at least a bachelor’s degree, at least 1 year of work experience, and without musculoskeletal disorders before engaging in physiotherapy. The exclusion criteria were unwillingness to continue participation and having a disease in other systems of the body, including neurological and rheumatic diseases, malignancies, and joint replacement. After distributing 1200 questionnaires, only 686 were returned. Of these, 16 were excluded due to missing some inclusion criteria; 4 due to having work experience less than 1 year; and 12 due to having other diseases. Finally, 670 physiotherapists participated in the study.
Data collection tools were a demographic form as well as the common therapeutic techniques used by participants (the method used for more than 60% of their patients), and general Nordic questionnaire for measuring the prevalence of WRMDs. It is a self-report tool that assesses WRMDs in 9 areas of the body (neck, shoulders, upper back, lower back, elbows, wrists/hands, hips/thighs, knees, and ankles/feet) over 1 year. This questionnaire is one of the most widely-used questionnaires in the field of musculoskeletal disorders, designed in 1987 by Kuorinka et al. [23]. It lacks an overall score and determines the frequency of injury. For the Persian version of this questionnaire, the internal consistency was found 0.8 and repeatability as a Kappa> 0.7 at P<0.001 [24]. 
Before data collection, informed consent was obtained from the participants. They were assured of the confidentiality of their information and were free to leave the study at any time. After collecting data, they were analyzed using the Chi-square and Fisher exact tests in SPSS V. 23. The significance level was set at 0.05.
Results
The mean±SD age of the participants was 37.09±9.91 years ranged 22-69 years (53.9% females and 46.1% males). Also, 91.8% of them were right-handed; 70.3% had a colleague or assistant in their work environment, and 69.6% had more than 5 years of experience. Table 1 presents the demographic information of the participants. WRMDs were significantly higher in women compared to men in the neck, shoulders, wrists/hands, upper back, and knees (P<0.001). There was a significant relationship between age and WRMDs in the elbow (P=0.021) and upper back (P=0.02) of the participants. Those with ages between 30 and 40 years had the highest rate of WRMDs in the upper back area. 
There was no significant association between the prevalence of WRMDs and work experience, having an assistant or colleague, being a right-handed or left-handed, and smoking. The common therapeutic techniques used by the participants were exercise therapy (89.6%), electrotherapy (88.8%), patient training (82.2%), mobilization (59.4%), stretching (58.3%), manual massage (46.7%), dry needling (40%), myofascial release (34.3%), muscle energy technique (34%), taping (33.4%), massage by a device (27.2%), respiratory physiotherapy (26.1%), manipulation (18.8%), water therapy (3.8%), and other methods (12.8%) (Table 2, Figure 1). 
To measure the relationship between these methods provided by physiotherapists and WRMDs, we used the Chi-square and Fisher exact tests. The results showed a significant correlation of WRMDs with treatment methods in 7 out of 9 areas. In particular, WRMDs were associated with manual massage (P=0.001), myofascial release (P=0.011), mobilization (P=0.007), muscle energy technique (P=0.007), and dry needling (P=0.032) in the neck area; with mobilization (P=0.005) and taping (P=0.014) in the shoulder area. Also, WRMDS are associated with respiratory physiotherapy (P=0.007) in elbows. 
WRMDS are correlated with manual massage (P=0.027), myofascial release (P=0.001), mobilization (P=0.046), muscle energy technique (P=0.004), and taping (P=0.016) in wrists/hands.  In the upper back, WRMDs are associated with manual massage (P=0.007), mobilization (P=0.014), and taping (P=0.004). In the lower back, WRMDs are seen with myofascial release (P=0.036), mobilization (P=0.015), taping (P=0.035), and muscle energy technique (P=0.044). Finally, WRDMs are observed with water therapy (P=0.037) in knees.
 (Table 3).
4. Discussion
The main purpose of this study was to investigate the relationship between work-related musculoskeletal problems and the common therapeutic methods used by the Iranian physiotherapists. There was a significant relationship between gender and incidence of WRMDs, which is consistent with the study of Adegoke et al. They identified female gender as a factor in the development of musculoskeletal disorders [17]. However, it was against the results of Salik and Özcan, Sharhaninezhad et al., and Nazari et al. [16, 19, 20]. Adegoke et al. and Glover et al. reported that in the first 5 years of employment, musculoskeletal injuries are more common [14, 17]. In our study, there was no relationship between work experience and the higher musculoskeletal disorders which is in agreement with the results of Darragh et al. [6] and Sharhaninezhad et al. [19] studies. In the study of Borke et al. [25], performing manual therapy such as mobilization and working on soft tissue, lifting and transferring patients were among the tasks associated with developing WRMDs. The present study also reported these findings. Joint mobilization (43%) and manual massage (41%) are two factors that can cause musculoskeletal disorders in the wrists and fingers [27]. In our study, mobilization (37%) and manual massage (38%) were also responsible factors for musculoskeletal disorders in the wrist area. Manual techniques performed by physiotherapists put stress on the hands and fingers [28]. In Wajon et al. study [29], a significant relationship was found between the use of force and thumb pain during manual therapy [29]. Physiotherapists who use manual techniques are about 3.5 times more likely to hurt their wrists/hands than other therapists [25]. In our study, a significant statistical relationship was found between WRMDs in the wrist area and performing a manual massage, myofascial release, mobilization, muscle energy technique, and taping.  This finding agrees with other studies that have linked the use of manual therapy techniques such as massage to wrists and hands symptoms [20, 25, 30]. Alrowayeh et al. [31], however, found no significant association between job factors and increased work-related musculoskeletal injuries.
Kuehnel et al. [32] in a study compared the prevalence of work-related injuries among college students during manual therapy class in five different continents and found different rates. They indicated that these different rates may be due to cultural differences. For example, the definitions of pain, health, and injury vary in different cultural communities [32]. The point to consider in this study is that the prevalence of work-related musculoskeletal problems among Iranian physiotherapists had a significant relationship with some techniques that they used for treatment such as dry needling and taping. This result indicates that physiotherapists may use incorrect postures to perform these techniques, which can put high pressure on the joints. Amini et al. introduced improper handling as the most common cause of injuries in therapists [33]. Rahimi Moghadam et al. stated that with an increase in ergonomics knowledge, the incidence of musculoskeletal disorders in individuals decreases [9].
One of the strengths of this study was its implementation at the national level with a high number of samples (686 physiotherapists). It is also the first study in Iran to examine the relationship between therapeutic methods used by physiotherapists and WRMDs. The limitations of this study were as follows:  not including all physiotherapists in the country, using a simple sampling method, and lacking the cooperation of some participants. It is suggested that other studies be conducted in this field using a cluster sampling method at the national level.
5. Conclusion
There is a significant relationship between WRMDs and gender, as these disorders are more common in women. This may be due to differences in muscle structure and volume, sex hormones, and biomechanical differences between men and women. There is also a significant relationship between the incidence of these disorders and treatment methods used by physiotherapists. Appropriate decisions need to be made to improve and teach physiotherapists how to manipulate the patients. Teaching physiotherapists to perform the methods correctly, have rest and pause in performing methods that may take a long time, and use existing equipment to prevent occupational injuries can play an important role in reducing their injuries. Increased awareness in the field of ergonomics reduces WRMDs. Training programs can also have a significant impact on increasing the knowledge of correct physical postures while working.
Ethical Considerations
Compliance with ethical guidelines
Ethical considerations were observed in the study and ethical approval was obtained from the Research Ethics Committee of the University of Welfare and Rehabilitation Sciences (Code: IR.USWR.REC.1395.66). 
Funding
The present paper was extracted from the MA. thesis of Mahdi Rahmati-Yami approved by department of Physiotherapy, University of Social Welfare and Rehabilitation Sciences. 

Authors' contributions
Conceptualization: Noureddin Karimi, Leyla Rahnema, and Mehdi Rahmati Yami; Methodology: Noureddin Karimi, Samaneh Hosseinzadeh, Mehdi Rahmati Yami, and Elham Azarmi; Validation and supervision: Noureddin Karimi, Leyla Rahnema,and Samaneh Hosseinzadeh; data analysis: Leyla Rahnema,and Samaneh Hosseinzadeh, and Mehdi Rahmati Yami; investigation: Leyla Rahnema,and Samaneh Hosseinzadeh, Noureddin Karimi, Mehdi Rahmati Yami, and Elham Azarmi; resources: Mehdi Rahmati Yami, Elham Azarmi, Noreddin Karimi, and Leyla Rahnema; initial draft preparation, editing & review, visulaization: Mehdi Rahmati Yami and Elham Azarmi; project administration: Noureddin Karimi.
Conflicts of interest
The authors declared no conflict of interest.
Acknowledgements
The authors would like to thank physiotherapists Dr Bandpey, Dr Abdollahi, Mr Moazzenzadeh, Mr Najafi Sani, Mr Shahrakinasab, Mr Alasti, Dr Ravanbakhsh, Ms Monjazi, Ms Khodadadi, Mr Nourollahzadeh, Ms Naghdi, Ms Abdolalizadeh, Ms Mirshahi, and all participants for their valuable cooperation.