The main finding of the present study was that a 6-month Pilates NME intervention decreased severe multisite pain in health care workers with recurrent non-specific LBP.
Multisite pain is common among individuals with LBP and it responds less favorably to treatment [4,8]. The definition of multisite pain varies, and a clear standard to define the disorder is lacking. In this study, the prevalence of multisite pain (i.e., 3 or more musculoskeletal pain sites) at baseline was high (72%), which is higher than the prevalence in the general population [10].Therefore, we used a new classification for severe multisite pain which takes into account the intensity, frequency, and number of pain sites (i.e., intensity of pain NRS 4 or more, frequency of pain daily or nearly daily, at least 3 pain sites). The prevalence of severe multisite pain was 23% at baseline, 27% among the exercise group, and 19% among the controls.
According to a recent meta-analysis, there is low quality evidence that Pilates, stabilization/motor control, resistance training, and aerobic exercise training are the most effective treatments for adults with non-specific LBP [23]. In the present study, exercise intervention comprised Pilates-type NME for a 6-month period focused on controlling neutral spine posture. The mean exercise attendance was 1.1 sessions (60 minutes per session). In the analysis, exercisers were compared to non-exercisers (controls). After the 6-month NME intervention, severe multisite pain decreased in the exercise group from 27% to 9%. However, the effects of the intervention diluted thereafter.
An understanding of the underlying factors behind multisite pain can help develop rehabilitation strategies for individuals with multisite pain [13]. According to recent studies, advanced age, female sex, living alone, unemployment, smoking, overweight, depressive and/or anxiety symptoms, and low self-rated health are independent predictors for multisite pain [13-14]. Furthermore, the presence of multisite pain increases the risk for poor quality of life [20]. A recent cross-sectional study of patients with chronic musculoskeletal pain reported significantly lower health-related quality of life than patients without pain [31]. In the present study, we found that low self-rated health, although not age, was significantly associated with increased severe multisite pain. The lack of age association may have been because all participants in the study were approximately the same age (aged between 30 and 55 years). According to previous studies, multisite pain is constant due to exposure to several risk factors, rather than the result of a specific risk factor [10].
Multisite pain can represent a much higher impact on the daily life of workers than musculoskeletal pain at one body site [16]. Perceived multisite pain increases the risk for poor future work ability, and it can cause productivity loss at work [10,16,18]. Workability is a multidimensional concept, as it describes the physical and mental ability of workers to cope with the demands of their work and achieving a balance between a person`s resources and work demands [32]. Furthermore, work ability cannot be separated from life outside work. For example, the family and close community of a person can also affect work ability [33]. Therefore, the promotion of work ability may need a more multidisciplinary approach than exercise intervention alone. Physical ability is one part of workability, so it would be interesting to study how exercise intervention could improve work ability among health care workers. According to recent randomized controlled trials, only a few studies have evaluated relevant interventions for nurses with LBP, and there is no strong evidence of the efficacy of any one intervention in preventing or treating LBP in nurses [34]. In the present study, NME intervention reduced severe multisite pain among health care workers with recurrent LBP. Interestingly, NME targeted for LBP also reduced multisite pain, even though the mean exercise attendance was 1.1 sessions per week instead of the targeted 2 sessions per week. One explanation for this finding might be an increase in muscle strength from training. Further, although the exercise program was primarily focused on controlling the neutral spine posture, secondary training objectives were to increase strength in the lower limbs and to achieve normal range of motion [28].
Exercise-induced hypoalgesia (EIH) might be a second explanation why NME reduced multisite pain in this study. EIH refers to a reduction in pain that occurs during or following exercise. In healthy, pain-free populations, a single bout of aerobic or resistance exercise leads to EIH, a generalized reduction in pain and pain sensitivity that occurs during exercise and for some time afterwards [35-36]. In contrast, EIH is more variable in chronic pain populations. According to Rice et al., exercise does not reduce pain in people with chronic pain. The mechanisms underlying EIH are not fully understood. Biological mechanisms that may contribute to EIH are the opioid system, the endocannabinoid system, the serotonergic system, the immune system, and the autonomic nervous system (Rice). A recent study reported that cycling also produced EIH in young nurses. Indeed, a maximal graded cycling exercise test led to EIH at the local, regional, and global body regions in pain-free female nurses [37]. In the present study, most participants (over 60%) had non-chronic LBP, which supports the explanation that EIH played a role in the decrease in multisite pain seen in this study.
The strengths of the study include the unique study population in terms of non-chronic LBP (i.e., recurrent LBP) who undertake physically strenuous work and who are still able to work, and a 24-month follow-up period. Furthermore, the current study was based on the NURSE randomized controlled trial. We used a new classification of severe multisite pain which takes into consideration the number of pain sites, the intensity of the pain, and the frequency of the pain. The limitations of this study include a relatively small study sample, a quite narrow age range, and only female participants. In future, it would be important to also study the effects of NME on multisite pain among a larger age group and among males.