Hidden risk factors and the mediating role of sleep in work-related musculoskeletal discomforts

Musculoskeletal discomforts (MSDs) are prevalent occupational health issues affecting individuals in contemporary societies and among working populations [1, 2]. MSDs encompass a wide range of painful injuries and disorders that affect several anatomical tissues, including muscles, tendons, peripheral nerves, joints, vascular support structures, and the spinal column, in both the lower and upper limbs [3]. MSDs can affect workers in all sectors and occupations and can lead to high costs for enterprises and society. Based on the report from the European Agency for Safety and Health at Work, MSDs are the most prevalent work-related health issue in the European Union, accounting for over 50% of serious work-related diseases [4]. In Iran, MSDs have been reported as the main cause of disability and complaints in the workplace [5]. Moreover, many studies have shown that low back pain is the primary contributor to disability within the realm of non-communicable diseases, including in both industrialized and developing nations. In the year 2020, the global prevalence of low back pain exceeded 500 million cases [6]. According to projections, the prevalence of low back pain is expected to exceed 800 million individuals worldwide by the year 2050 [7].

MSDs have a progressive and multifaceted etiology, which is marked by a high level of diagnostic complexity [8]. There is widespread recognition that MSDs are strongly influenced by work-related factors. However, prior research has identified many risk factors, including personal, physical (biomechanical), and psycho-organizational aspects, associated with the development of MSDs [9]. Age, gender, body mass index, sleeping habits, systemic diseases and personality traits are the most important individual factors [3, 10‐14]. There is no doubt that biodynamic risk factors such as poor posture at work, force exertion, repetition movement, prolonged sitting, vibration, and high workload play the main roles, and the influence exerted by these elements on the development of MSDs is well-recognized [15, 16]. The present emphasis on methods, policies, and programs to prevent MSDs mostly centers on physical variables, whereas psycho-organizational elements are often overlooked [17, 18]. Therefore, there are some hidden work-related risk factors such as shift work, job stress, and sleep problems that few studies have attempted to focus on. Shift workers may be at higher risk for developing MSDs compared to those who work regular daytime hours. Moreover, stress at work is a condition that can arise from various sources such as heavy workloads, long working hours, lack of control over tasks, inadequate job resources or support, poor relationships with colleagues or supervisors, and conflicts between work and personal life. Prolonged exposure to job stress can have adverse effects on human health [5].

Healthcare and hospital workers (HCWs) have a higher prevalence of MSDs, mainly affecting the back, neck, shoulder, and knee regions, three to four times higher than other occupational categories [19]. The high prevalence of MSDs in HCWs is often linked to physically demanding aspects of their job, such as lifting patients, prolonged periods of standing, and repetitive motions [20, 21]. Approximately one-third of sick days taken by HCWs are attributed to MSDs [22]. Sleep problems in HCWs are a recognized manifestation of job stress and shift work, a phenomenon that has been extensively reported among HCWs due to patient care 24 h a day [23]. Marvaldi et al. [24] reported that the prevalence of sleep disorders among nurses was 44.0% (95% CI, 24.6–64.5). Shift work can indeed have a significant impact on sleep, and many studies have reported high prevalence rates of sleep disorders among shift workers. The nature of shift work, with irregular or overnight hours, can disrupt the body’s natural sleep-wake cycle and lead to difficulties in getting adequate and restful sleep [5]. Moreover, job stress can be a significant factor contributing to sleep disorders. The demands and pressures of work can lead to increased levels of stress, anxiety, and worry, which in turn can disrupt sleep patterns. Common sleep disorders associated with job stress include insomnia, restless leg syndrome, and sleep apnea [25]. One study by Hamming found a weak association between sleep disorders and the development of MSDs [26]. Their findings report that general and occupational stress were reported to be significantly related to sleep disorders. However, another study found that in emergency HCWs, sleep disturbances are significantly associated with MSDs and occupational stress [27]. Moreover, according to studies, there is a bidirectional relationship between sleep problems and MSDs [28, 29], whereby sleep disturbances have been found to exacerbate symptoms of MSDs, while MSDs hinder the ability to achieve restful sleep. Some research has presented conflicting findings in this regard. Evaluation of the association between sleep problems and MSDs is a crucial matter for enhancing management strategies, preventing MSDs, reducing workforce impairment, increasing job satisfaction, increasing efficiency, and ultimately enhancing the quality of service provided to patients. Although it has been proven that awkward posture, force exertion, repetitive movements, manual material handling, and tasks are the main occupational risk factors in creating MSDs however, some other occupational risk factors such as shift work, job-related stress, and sleep issues may also indirectly contribute to the development of musculoskeletal disorders that have not been profoundly studied. Therefore, this study aimed to hypothesize that shift work and job stress are two hidden risk factors for MSDs, and in this relationship sleep problems are mediators. Moreover, the relationship between sleep problems, job stress, shift work, and musculoskeletal discomforts, and the bi-directional relationship between MSDs and sleep problems was investigated among healthcare workers.

The results showed that 46.4% of participants were women and 53.6% were men. The mean ± SD of age and work experience of participants were 30.33 ± 6.99 and 6.24 ± 4.90 years respectively. The mean ± SD of the body mass index of workers was 25.36 ± 3.48 kg/m². Table 1 presents the prevalence rate of MSDs in the participants. As indicated, the highest level of discomfort has been reported in the neck, back, knees, and legs respectively.

Moreover, the mean ± SD of the total score of job stress in participants was estimated at 111.17 ± 16.68. Figure 3 illustrates the average score of the seven sub-scales of job stress in the participants.

The results of descriptive and analytical statistics of sleep variables based on Musculoskeletal discomforts have been provided in Table 2. The subscales of sleep latency and sleep duration have the highest rates. Table 2 shows that there is a significant relationship between indexes of sleep quality and insomnia severity with musculoskeletal discomforts.

Table 3 provides the descriptive and analytical statistics of sleep variables and Musculoskeletal discomforts based on shift work. As can be seen, there is a significant difference between the two sub-scales of sleep latency and sleep duration and also the total indexes of sleep quality and insomnia severity in two shifts of fixed and rotating.

Figure 4 illustrates the assumed model explaining the path analysis of job stress and shift work on musculoskeletal discomforts directly and indirectly by mediating sleep indices.

The results of the pathway analysis model and direct and indirect path coefficients of job stress and shift work on MSDs and the significance level of each path have been shown in Table 4. As shown, the path coefficients of job stress on indexes of quality sleep and insomnia severity were significant. Also, the path coefficient of shift work on quality sleep index was significant. In return, the path coefficients of shift work on the insomnia severity index were not significant. Additionally, Table 4 indicates a mutually significant association between indexes of quality sleep and severity of insomnia and musculoskeletal discomfort.

Table 5 reveals the fit indices of the developed pathway analysis model. As Table 5 shows, all the values were nearly acceptable.

Previous research has highlighted that healthcare and hospital workers, particularly nurses, experience a relatively high incidence of work-related musculoskeletal discomforts (MSDs), sleep disturbances, and stress [26]. These issues are often attributed to factors such as awkward postures, repetitive movements, manual material handling, physically demanding work environments, and mental workloads. Given the demanding nature of their jobs, it is crucial to explore additional risk factors. Therefore, few studies have specifically examined the combined impact of shift work, work-related stress, and sleep disorders on MSDs among healthcare professionals. Shift work disrupts natural sleep patterns, leading to misalignment between work hours and the body’s internal clock. This misalignment can contribute to health issues. Additionally, stress—both on and off the job—plays a significant role in the well-being of healthcare workers. Therefore, understanding the interplay between these factors is essential for developing effective preventive strategies. In the present study, the relationship between sleep problems, job stress, shift work, and MSDs with the moderating effect of sleep problems, and the bi-directional relationship between MSDs and sleep problems was investigated among healthcare workers. Finally, the causal paths were assumed for shift work and job stress as potential and hidden risk factors and sleep indexes as mediating variables in the creation of MSDs. We found that sleep quality (and its 6 subscales) and insomnia were significantly associated with MSDs. A meta-analysis study [36], based on 17 cross-sectional and cohort studies, found that chronic low back pain is linked to various sleep-related issues. These include heightened sleep disorders, decreased sleep duration and quality, prolonged time to fall asleep, impaired daytime functioning, and increased dissatisfaction and distress related to sleep. Also, a cross-sectional study among 450 patients reported that insomnia is associated with musculoskeletal pain [37]. The precise mechanism underlying the relationship between sleep and musculoskeletal discomforts remains unclear. Research conducted on adult populations has demonstrated that sleep deprivation decreases pain tolerance and results in increased pain sensitivity [38]. In a previous review, Finan et al. investigated the main central pathways that are involved in the regulation of pain and sleep [39]. The authors highlighted changes in the opioidergic and monoaminergic pathways linked to chronic pain disorders, which could explain disruptions in wakefulness and sleep cycles.

The findings of this study also indicated a significant difference in indexes of sleep quality and insomnia severity in two shift working groups. However, there is extensive evidence of sleep disturbance caused by shift work in workers who work unusual hours [40]. But even though there is no significant difference in MSDs in the two shift working groups, it was considered that the prevalence rate of MSDs was higher in rotating shift working groups.

As assumed, the results based on the path model indicated that job stress has a weak direct effect on MSDs, whereas it has a potential effect on MSDs through the mediating role of sleep quality and insomnia. A study among HCWs found that job stress is strongly associated with MSDs [26]. Li et al. [41], Constructed a Bayesian model demonstrating the direct effect of job stress on MSDs. Evidence shows that job stress is a hidden risk factor for developing MSDs [42]. Furthermore, psychological stress can lead to the ongoing release of catechol amines and cortisol, potentially impeding the process of musculoskeletal healing [43]. Experiencing job stress can have psychological, physiological, and behavioral effects on a person. This can cause changes in body chemistry that increase the chances of developing MSDs [44, 45].

The pathway analysis model also depicted that shift work does not affect MSDs directly and sleep indexes play a mediating role in this relationship. Even though shift work has been associated with an increased risk of developing MSDs due to factors such as prolonged standing or sitting, repetitive tasks, and constant physical exertion, however, research suggests the disruption of circadian rhythms caused by irregular sleep patterns and reduced time for rest and recovery can also contribute to musculoskeletal issues [40].

Based on the path model, MSDs have a bi-directional association with insomnia that is stronger than sleep quality. Consistent with this finding, there was a prospective and bi-directional association between poor sleep quality and chronic low back pain in school teachers [46]. Conversely, a previous study showed that previous lower back pain was a factor in causing sleep disruption [47]. Our developed conceptual model demonstrated that insomnia, sleep quality, and job stress were all predictive factors for MSDs. Therefore, based on the results, strategies and interventions should be developed to address these risk factors and mitigate the occurrence of MSDs in the healthcare setting. Job stress reduction programs, such as stress management techniques and workload management, can be implemented to minimize the impact of stress on healthcare workers’ musculoskeletal health. Shift work schedules should be designed to minimize the disruption of circadian rhythms and ensure adequate rest and recovery periods for healthcare workers.

The findings of this study strongly support this postulate that occupational stress and rotating work shifts can be potential and hidden risk factors for MSDs that have been identified as predictors or correlates of poor sleep and only secondarily can determine and equally cause MSDs. Therefore, sleep problems can cause MSDs, which MSDs also in turn produce sleep disorders. In other words, MSDs can be indirectly developed by work stress and shift work, whereas sleep disorders are only or mainly directly caused by shift work and stress and also can result directly from MSDs. These findings have implications for improving the overall health, safety, and well-being of healthcare workers.