Fibromyalgia (FM) is a rheumatic condition, characterized by chronic and widespread spontaneous skeletal muscle pain, as well as chronic headaches, sore throats, visceral pain, sensory hyper-responsiveness, and a wide variety of symptoms with no obvious tissue pathology (Wolfe et al., 2011). FM is a common pain disorder that primarily affects women, and it is highly comorbid with other functional somatic disorders, stress, and depression (Wolfe et al., 1995). Unfortunately, there is currently no curative treatment for this condition (Thieme et al., 2017). In addition to pain, which is the most prominent feature of FM, patients often experience higher levels of fatigue, sleep disturbances, memory deficits, and mood difficulties (Clauw, 2014).

Mindfulness involves “paying attention in a particular way: on purpose, in the present moment, and nonjudgmentally” (Kabat-Zinn, 1994, p.4). It refers to the cultivation of conscious awareness and attention on a moment-to-moment basis. The most well-known variant of mindfulness-based interventions (MBI) is mindfulness-based stress reduction (MBSR), a group therapy program that provides systematic training in mindfulness meditation as a self-regulation approach to stress reduction (Bishop, 2002).

In its original version, MBSR is an eight-week program in mindfulness training. The standard program includes weekly group sessions of 2–2.5 hours and one full-day session after six to seven weeks. The program’s core elements consist of various mental and physical mindfulness exercises: (1) body scan exercises (paying close attention to all body parts, from head to toe), (2) mental exercises focusing one’s attention on breathing, (3) physical exercises (e.g., walking meditation) focusing on being aware of bodily sensations and one’s own limits during exercises, and (4) practicing being fully aware during everyday activities. Essential to all parts of the program is developing an accepting and non-reactive attitude to what one experiences in the present moment. In each session, time is allocated for group members to reflect together on what they experience when they practice mindfulness. Between sessions, participants are instructed to listen to 30–45 minutes of guided exercises in body-scan, sitting meditation, focusing on breathing and yoga stretching (Kabat-Zinn, 1990).

According to a growing body of evidence, MBSR may improve FM patients’ well-being. Overall, studies that have examined MBSR on FM patients pointed to its effectiveness in improving various psychological and physiological aspects, such as physical symptoms, depression, pain, and fatigue (e.g., Schmidt et al., 2011; Sephton et al., 2007). However, according to a meta-analysis that was conducted by Lauche and colleagues (2013), the results of the above-mentioned studies were inconclusive concerning the reported measures. For example, three studies reported significant changes in pain intensity (Astin et al., 2003; Goldenberg et al., 1994; Grossmann et al.,2007), while others did not find a significant effect for pain. Another issue that should be addressed is the importance of properly defining a control group in MBSR research. The most common control group in MBSR research is wait-list control group, in which participants are being measured while they are waiting for the intervention, receiving no active treatment (e.g., He et al., 2021). According to the critical analysis by Leça and Tavares (2022), the complexity rises when the waiting list participants spontaneously changed their activities during their participation in the study. Additionally, not all RCTs reported adequate randomization and allocation (Lauche et al., 2013). Few studies include only an intervention group, using a design that limit the ability to make meaningful comparisons (e.g., Kaplan, Goldenberg & Goldenberg, 1993). Finally, there are significant gaps in the research field of MBSR for FM concerning the timing of conducting the measurements. First, most of the studies examined the short-term effectiveness of MBSR and not the effectiveness over time, which is an important factor in a chronic disease such as FM. Second, studies in the field concentrated only on outcome variables and mainly, focusing on the change from pre- to post-intervention, and not how the intervention works. In the current study we will try to bridge these gaps.

In the last decade, there is an increased interest in mechanisms of change underlying MBSR interventions, i.e., identifying the therapeutic components that are responsible for the effectiveness of MBSR. Mindfulness practice involves changes in cognitive and mental capacities, such as increased awareness and reduced ruminations (e.g., Labelle et al., 2015) that were examined in previous studies as mechanisms of change (Alsubaie et al., 2017). Surprisingly, only one study to date examined the possible mechanisms of change of MBSR among FM patients (Pérez-Aranda et al., 2019). Therefore, there is clearly a need to expand our understanding on factors that may play a role in MBSR’s effectiveness among this patient population.

In this study, we aim to examine the role of pain cognitions in the effectiveness of MBSR. Specifically, we aim to expand the examination of mechanisms of change in MBSR by examining two pain-related cognitions: psychological inflexibility in pain and pain catastrophizing. Both factors have been studied in the context of psychological interventions aiming to improve symptoms and general well-being of individuals with chronic pain.

Psychological flexibility in pain is the capacity to address pain from a free and independent point of view, with the ability to recognize and accept pain (as opposed to avoid it) and, on the other hand, without being caught up in it (Sullivan et al., 1995). PIPS is very common among individuals suffering from chronic pain or physical discomfort (Rodero et al., 2013). It is comprised of two dimensions: pain avoidance (i.e., the tendency to withdraw from planned activities in response to pain) and cognitive fusion (the inability to separate oneself from thoughts about pain). It is often difficult for patients to manage obstacles and strive towards life goals while pain is present. Consequently, chronic pain patients tend to develop a variety of psychologically inflexible coping approaches, such as believing their personal goals are unattainable due to their pain, or the avoidance they often develop from pain-related experiences.

Only a handful of studies have examined the role of PIPS as a potential mechanism of change in psychological interventions for patients suffering from chronic pain (e.g., Hedman-Lagerlöf et al., 2019). For example, Wicksell and colleagues (2010), examined the mediating role of PIPS in Acceptance and Commitment Therapy (ACT) for patients with chronic pain following whiplash. They found that PIPS mediated the effect of pain-related disability and life satisfaction.

The second component that will be examined as a mechanism of change is Pain catastrophizing (PCS). PCS is defined as "a cognitive and emotional state where patients magnify the threat value of a pain stimulus in the context of pain" and are unable to inhibit intrusive pain-related thoughts (Sullivan & Bishop, 1995). It is comprised of three components: Rumination, Magnification, and Helplessness. A growing body of literature links catastrophizing and depression to the experience of pain across several rheumatic diseases (Edwards et al., 2011), and the maladaptive coping strategy of PCS is believed to play a key role in FM (Baastrup et al., 2016). Thus, the PCS is believed to play a key role in FM (Baastrup et al., 2016) and is positively associated with pain intensity among FM patients (e.g., Paschali et al., 2021). Several studies have examined the role of PCS as a potential mechanism of change in psychotherapy for general chronic pain conditions, such as CBT (Smeets et al., 2006) and ACT (Trompetter et al., 2015). However, as mentioned above, no study has examined PCS as a mechanism of change in psychological interventions For FM.

In the current study we aim to bridge these gaps, by conducting a thorough examination of a variety of physical and psychological aspects, covering FM symptoms, depression and PSS. Additionally, we will explore PIPS and PCS as potential mechanisms of change in MBSR for FM.

Furthermore, due to FM patients’ physical limitations, administering the generic MBSR intervention may prove as both challenging and ineffective, as individuals may feel too limited or distressed to participate. Others might experience difficulties with prolonged sitting/meditating, which may, in turn, may result in high dropout rates (Nam & Toneatto, 2016). Thus, an adapted protocol is called for. In this study we will apply a newly adapted MBSR protocol, that was designed to meet the unique characteristics and needs of FM patients. Our attempt to adapt the generic protocol goes hand in hand with the growing attempt to adapt psychotherapy protocols in general (Hamburg & Collins, 2010), and MBSR protocols specifically, to the needs and characteristics of unique patient populations (e.g., Moss et al., 2015).

The current study presents three major research questions: 1. Is MBSR effective for treating FM patients? 2. What are the long-term effects of MBSR? 3. What are the mechanisms of change that are associated with MBSR? Based on these questions we hypothesis that FM patients receiving MBSR will show greater improvements from pre- to post-intervention in FM, Depression and PSS, compared to waitlist (WL) control group. Additionally, all expected changes of MBSR between pre- and post-intervention will remain stable over a 6-month follow-up period. Finally, the effect of MBSR on FM symptoms, Depression, and PSS, will be mediated by the change in level of PIPS and PCS.