CLBP was responsible for the creation of 60.1 million disability-adjusted life-years (DALY) in 2015. Since 1990, with a 54% increase, it has the highest prevalence in low- and middle-income countries . Examination of patients' demographic parameters demonstrated that there was a significant relationship between age, BMI, job, work experience, working hours per day, type of work shift, education level, monthly income, type of occupational task, previous LBP, history of underlying diseases and type of LBP in the subjects (Table 1). Previous studies have shown that these parameters are among the influencing factors in the chronicity of LBP [2, 35]. It has been found that patients with older ages, higher BMI, higher working hours, and jobs with higher workload are at higher risk of CLBP [36, 37]. Previous studies have shown that income levels are also an important factor in preventing CLBP, and people with higher incomes are likely to be in better lifestyle status and have a lower risk of CLBP , which is consistent with the findings of the present study. A history of previous LBP is also a crucial factor in the chronicity of LBP. So that if the patient has not been appropriately treated in the past, the pain has entered into the chronic phase, and in the case of recurrence of LBP, the person is entirely prone to CLBP. It was also found that a history of underlying diseases can affect the patient psychologically and physiologically dimensions and facilitate the chronicity of LBP . Shift work schedule was also an important factor in the LBP chronicity. Perhaps the reason can be found in the decrease in sleep quality. A higher percentage of patients with CLBP were working at night and shift work, compared to patients with acute and sub-acute LBP.
Among patients with CLBP the mean score of fear-avoidance beliefs about work activities (FABQ-W) and fear-avoidance beliefs about physical activity (FABQ-PA) was significantly higher than patients with acute/subacute LBP (Table 2). The study by Woby et al. showed that as people's self-efficacy decreases due to LBP, fear of movement and avoidant behaviors increase, which can lead to CLBP. Also, reducing fear-avoidance beliefs concerning work activities and physical activity leads to increased self-control against pain and disability. It can be a useful step in preventing the CLBP . Chung et al. Also showed that fear-avoidance beliefs are an important factor in the chronicity of LBP and related disability that is in line with the findings of the present study .
The rate of depression among patients with CLBP was significantly higher than patients with acute and subacute LBP (Table 2). The study conducted by Cougot et al. revealed that depression is an important factor in CLBP and long absences from work . The study by Shmagel et al. also demonstrated that a high percentage of patients with CLBP were in severe and very severe depression levels, which is consistent with the findings of the present study . Depression, stress, and anxiety are risk factors and a consequence for the chronicity of LBP and lead to a decrease in the treatment process's efficiency . Depression severely affects a patient's life quality, reduces physical activity, increases the risk of a variety of mental illnesses, and in some patients can lead to refusal to continue treatment [2, 10].
The catastrophic rate of pain in patients with CLBP was significantly higher compared to the control group. Individuals with acute and sub-acute LBP, due to their pain's destructive nature, imagine it more intensely, exert more physical and psychological pressure on themselves, and thus pave the way for chronicity of LBP. It is quite probable that patients engage in pain avoidance behaviors and are always waiting for the occurrence of pain in response to the fear of catastrophic pain and in an attempt to control the painful event that may occur in the future. Many empirical studies have shown that catastrophic pain is directly associated with CLBP, which is consistent with the present study [2, 41]. The mean value of kinesiophobia among patients with CLBP is much higher than other patients. Previous studies have shown a direct and significant relationship between psychological factors such as kinesiophobia and catastrophic pain, and chronicity of acute and sub-acute LBP, which is in line with the present study findings [2, 13]. Some studies have explicated that in many cases, fear of movement and pain can be more debilitating than pain and accelerates LBP chronicity . In general, it can be claimed that all three parameters of kinesiophobia, catastrophic pain, and fear-avoidance beliefs are closely related to each other, and each parameter can accelerate the process of LBP chronicity.
The sleeping hours of patients with CLBP were shorter than control group, which was rooted in their pain. The results explained that the mean score of all sleep quality components except subjective sleep quality among patients with CLBP was higher (Table 3). The mean total score of sleep quality among patients with CLBP was higher than control group, which indicates poor sleep quality among them and can lead to more psychological and physical stress and as a result, the chronicity process of LBP can be facilitated . It can be explained that patients with CLBP have more delayed sleep, shorter sleep duration, more sleep disturbances, and higher use of sedative medication compared to other patients. Previous studies have shown that the quality of sleep among patients with CLBP was significantly lower than patients with acute LBP, and sleep is one of the effective parameters in the chronicity of LBP, which was compatible with the present research .
The score of some lifestyle components like spiritual growth, interpersonal relationships, physical activity, and nutrition in patients with CLBP was lower than other patients (Table 4). The obtained results indicate that patients with acute and sub-acute LBP are more sensitive to their health status due to the shorter LBP duration (less than three months) and have more social interactions and interpersonal relationships. Despite the presence of pain, they had more physical activity and better nutritional status than patients with CLBP. Furthermore, patients with CLBP have experienced more pain tolerance because they have struggled with pain for a more extended time and have generally been more successful in managing the stress caused by their pain. Finally, it was noticed that patients with acute and sub-acute LBP had a better lifestyle, which is consistent with previous studies' results [28, 42]. Previous studies have revealed that increasing muscle strength through light exercise can help support the spine. Improving the flexibility of the muscles, tendons, and ligaments of the back increases the range of motion and help improve patient function. Aerobic exercise also increases blood flow and nutrients to the back's soft tissues and accelerates the healing process . There is a significant relationship between the degree of disability, depression, anxiety, and lifestyle levels of patients, and lifestyle is a strong predictor for LBP chronicity .
Brox et al. also revealed that the rate of disability in patients with CLBP was significantly higher than acute and sub-acute cases. The degree of disability is an important predictor for LBP chronicity, which is consistent with the present study results . The disability and severity of pain are both a risk factor and a consequence of LBP, which can be subjective or objective. In both cases, it can lead to a variety of physical and psychosocial problems and eventually CLBP.
The regression model explicated that weight, BMI, job, type of occupational task, previous LBP, work shifts, underlying diseases, income, fear-avoidance beliefs, Kinesiophobia, pain catastrophizing, depression, health responsibility, physical activity, interpersonal relationships, sleep duration, sleep disturbances, sleep quality, and patients' disability are among the most important risk factors in the chronicity of LBP. These findings indicate that LBP is a complex and multifactorial phenomenon that different pathologic, anatomic, neurophysiologic, physical, and psychologic factors are influential in its development and chronicity.
The path analysis model revealed that lifestyle indirectly predicts CLBP and avoids large effects on the parameters of disability, pain intensity, sleep quality, depression, and fear-avoidance beliefs, and other parameters can directly affect and predict the chronicity of LBP. Depression was the most important predictor of CLBP with a standardized path coefficient of 0.68 (Figure 1).
Among the strengths of the present study we can point out the evaluation and modeling the wide range of individual, psychological, psychosocial, and physical parameters in the development of CLBP for the first time in Iran. Our findings can create a novel insight into various risk factors affecting the chronicity of acute and sub-acute LBP. The present study can be a practical step towards establishing a targeted treatment plan and also preventing the chronicity of LBP. The cost of treatment and healthcare systems differ considerably from country to country and are influenced by local health, treatment, and social systems. CLBP and its associated costs are projected to increase in the coming decades, especially in low- and middle-income countries such as Iran, where health care systems are often somewhat hard to access in case of critical situations (like coronavirus pandemic) and have fewer financial resources. Therefore, global research efforts and initiatives are needed to reduce LBP and prevent the chronicity of LBP as an important and crucial public health problem.
Among the limitations of the present study it can be noted as: the impossibility of conducting a prospective cohort study and examining the trend of changes in various physical, psychological, and psychosocial parameters during the therapeutic interventions, and evaluating the effectiveness of intervention measures. Also, during the present study, temporal relationships or causal inferences between different risk factors were not investigated. Therefore, it is suggested that in the future, researchers will conduct prospective studies with appropriate physical and psychological clinical interventions and also report the effectiveness of each intervention.