Of the 88 patients screened at the Pain Clinic of a high-complexity teaching hospital in 2018, 16 met the inclusion criteria and were invited to participate in the intervention. Only eight agreed to participate, and six completed the intervention (Figure 1). Among the six patients who completed the intervention, three were women and three were men, with a mean age of 52.16 ± 5.63 years. All were in a stable relationship. The duration of the pain ranged from two to 17 years (11.5 ± 5.78).

Table 1 shows the pre- and postintervention results measured by the instruments used to evaluate pain, anxiety symptoms, depression symptoms, psychological inflexibility, self-efficacy, and social support. After the intervention, there was a statistically significant reduction in the perceived pain (p = 0.026), anxiety symptoms (p = 0.028), and depression symptoms (p = 0.028). The depression scores decreased categorically for four of the six participants. One went from mild to minimal, one went from moderate to mild, one went from severe to mild and one went from severe to moderate. Among those who did not experience a change, one remained in the minimal category and the other remained in the moderate category. The anxiety scores decreased in the category for five of the six participants. One went from severe to mild, two went from severe to moderate, one went from moderate to minimal, and one went from moderate to mild. The participants who did not change categorically remained in the minimal category.

The AAQ-II scores indicated that psychological inflexibility decreased from the pre- to the postintervention evaluation for all the participants, but this difference was not statistically significant. The mean participant score after the intervention (18.16), however, was below the mean score of nonclinical populations (mean 18.51 ± 7.05) (Bond et al., 2011), indicating that, although the difference was not statistically significant, there was a clinically significant difference after the intervention.

For self-efficacy, all the patients had increased scores after the intervention. The sum of the self-efficacy means, self-efficacy for pain control, functionality and coping with other symptoms underwent statistically significant improvements. However, these increases were not statistically significant for the total instrument score. Before the intervention, all the patients had a score below 185, which is considered the cutoff score for self-efficacy for chronic pain (Salvetti & Pimenta, 2005). After the intervention, only two of the six patients had a score below 185, and even these patients had increased scores in the postintervention evaluation.

The scores for social support in the material, affective, emotional, and informational dimensions increased after the intervention, but the pre- and postevaluations exhibited no significant difference.

Table 2 shows the comparative analysis of the quality of life before and after the intervention. After the intervention, functional capacity, pain, vitality, social aspect, emotional aspect, and mental health significantly improved. Although after the intervention, the scores improved for the physical aspects and general health status, the difference was not significant. These data improved in several of the quality-of-life domains because of the therapy.

Table 3 shows the correlations obtained through the application of the instruments that evaluated the quality-of-life domains and the anxiety symptoms, depression symptoms, and psychological inflexibility pre- and postintervention. The main correlations with the quality of life were found for depression symptoms and PF. This result is possibly related to the increase in the rate of behaviors displayed by the study participants, since pain took on a secondary role in their lives, which allowed greater social interactions, the display of more adaptive behaviors, and increased occurrence of reinforcers.

The patient reports during the intervention were recorded and may exemplify the acceptance of and commitment to living a value-driven life despite the pain. The data obtained through the instrument application signaled changes, and the statements help to understand how the values and changes in their life were perceived by each patient: 1) “Caring for my granddaughter is one of the reasons to get out of bed every day despite the pain”. 2) “My son called me to look at paintings. Before, I would not go. Now, I go. I laid on his bed and gave my opinion”. 3) “Before, I thought that pain controlled everything. Nowadays, I know that pain is just a small part of it. ... I can understand that pain is a part, but neither the greatest nor the most important part. I am more than pain. I am a father, I am a husband”. 4) “The worst is not when I isolate myself because of the pain but when it goes away and you realize you missed out on the whole day”. 5) “Before, I did nothing. I liked to play in the church, but I was in pain and therefore would not go. I understood that I could feel pain and still go. I liked the dynamics of the clay on the windshield” (refers to an experiential exercise performed in session, which focused on accepting adverse situations without attempting to change them, as such attempt worsens the situation).

The patients’ statements indicated that they considered changes to have occurred because of the therapeutic process: there is a possibility beyond pain. After values that made sense for each participant were identified (e.g., being a good father or being a good grandmother), a new perspective appeared, enabling not only the acceptance of pain but also engagement in reinforcing activities.

Psychological inflexibility, a key concept of ACT, seems to play an important role in emotional distress and pain (Gentili et al. 2019; Rickardsson et al., 2021). Although the AAQ-II scores pre- and postintervention exhibited no statistically significant difference, the increase in PF seems to have been sufficient to improve pain management, since the patients perceived a significantly lower intensity of pain. The patients’ psychological inflexibility clinically reduced; that is, most moved from the dysfunctional to the functional group according to the AAQ-II scores (Jacobson & Truax, 1991). Thus, the data obtained are compatible with other studies, which indicate that the reduction in psychological inflexibility plays an important role in the adaptation of patients to chronic pain (Gentili et al., 2019; Rickardsson et al., 2021).

The choice to live a value-driven life, one of the processes associated with the reduction in psychological inflexibility, was observed, as in another study (Casey et al., 2020), in the patient reports during the intervention. These data are consistent with the ACT premise that psychological inflexibility is associated with pain and suffering, preventing the person from adapting to their context and life situation. On the other hand, the increased flexibility allows the person to have contact with the consequences of their behavior in the present and to live according to their values (Casey et al., 2020; Hayes et al., 2012). This correlation was evidenced in the data of the present article, which showed changes in the correlations between the AAQ-II and the SF-36 pre- (no statistically significant correlation) and postintervention (statistically significant correlation between the AAQ-II and the SF-36 in the domains of physical aspects [p = 0.032], social aspects [p = 0.003], and mental health [p = 0.020]).

Yu et al. (2017) concluded that ACT-based treatment caused changes in the “self as context” and in comprehensive distancing, helping patients cope with chronic pain. The distancing from the “conceptualized self” and the search for the “self as context” enables a change in the perspective towards the event and helps the patient manage the current situation by allowing a type of cognitive defusion, that is, a change in the way the patient interacts with their thoughts, reducing their harmful effects on behavior (Hayes et al., 2006). Accepting pain and displaying responses that can produce positive reinforcers indicate that, despite the pain, living a worthwhile life is possible.

Although the objective of the intervention performed in this study was not to reduce pain directly, the participants’ pain scores decreased significantly, as indicated by the VAS. The acceptance of pain and the commitment to the resumption or introduction of reinforcing activities in their daily lives helped the patients gain control of contingencies (e.g., experiencing reinforcing situations, such as discussing paintings with a child despite the pain) than under the control of self-rules (e.g., “I cannot go out because I will feel a lot of pain”). In this sense, it is evident that value-oriented actions can help patients manage everyday situations and cope with potentially aversive situations (e.g., the possibility of pain). That is, although there is an aversive component (pain), there is also the possibility of the reinforcing event (e.g., caring for the granddaughter or relating to family members).

Given the impact of pain on overall functioning, studies have evaluated the quality of life of patients with chronic pain. The data obtained in this study are consistent with the literature, which associates pain with a worse quality of life and shows a relationship between pain reduction and an increased quality of life (Samani et al., 2019). The escape and avoidance of situations that require movement, avoided by patients with chronic pain, are also associated with a worse quality of life. In this study, the patients’ reports showed how much they avoided certain behaviors due to pain, leading to the loss of important reinforcers and causing a negative impact on the quality of life. On the other hand, the reports also showed the impact that the intervention had on the patient relationships and the quality of life.

The domains with the worst quality-of-life scores (SF-36) in the pre-intervention were the physical aspects and pain, and in the postintervention, they were the general health status and physical aspects. These data are consistent with the results of a study conducted in the same outpatient clinic (Martins et al., 2017). Therefore, this study’s patients may not have experienced a greater improvement in the physical domain because, despite the improvement observed in pain, pain continued to be present.

The literature has shown a relationship between quality of life, pain, anxiety symptoms, and depression symptoms. Björnsdóttir et al. (2017) concluded that a mindfulness-based interdisciplinary intervention with a pain specialist team was effective in managing long-term chronic musculoskeletal pain (six-month follow up). The present study also used mindfulness in part of the intervention, which specifically helped the participants come into contact with the present and break the link established between pain and other facets of life (e.g., being stuck in thoughts and self-rules). The analysis of the pre- and postintervention data for the correlations between the quality of life and the depression and anxiety symptoms measured by the SF-36, BDI, and BAI were also aligned with the data found in the literature.

Patients with chronic pain experience a consistent loss of reinforcers resulting from the limitation or reduction of activities. This loss occurs not only through pain but also through self-rules and verbal constraints (e.g., going out makes my pain worse), which can become a conditioned aversive stimulus, maintained through negative reinforcement (Luque-Suarez et al., 2018), which increases the probability of escape or avoidance responses. In this study, the relationship “social activities worsen pain intensity” was deconstructed during the intervention, which allowed the decrease in control by rules and the increase in control by contingencies. This is one of the ACT’s proposals, especially using cognitive defusion. The intervention also helps the patient to behave under the control of delayed reinforcement and not under the control of the elimination of the aversive stimulus.

The present study found a statistically significant clinical manifestation of depression symptoms. At some points, the groups discussed behavioral patterns aimed at developing repertoires as an alternative to escape and avoidance and related to obtaining positive reinforcers. The use of metaphors and mindfulness exercises at the end of each session also helped the participants to cope with aversive stimuli in the short term to obtain reinforcers in the medium and long terms (Report 5). This training, combined with behavioral therapies, has shown promising results in the treatment of depression in patients with chronic pain (De Jong et al., 2018; Vowles et al., 2020). Cheng et al. (2018) evaluated the relationship between depressive symptoms in adults and pain self-efficacy and concluded that self-efficacy is a protective factor for depressive symptoms. The reduction in depressive symptoms, in turn, can improve the quality of life of patients with chronic pain.

Social support can also contribute to an improved quality of life (Finlay et al., 2018). It involves relationships (person–person or person–person–environment) that can be explained by the selection-by-consequences model (Skinner, 1981). Although the study found no statistical correlation between these variables, several of the participant reports affirmed the importance of this relationship (Reports 1, 2 and 3). To better understand these relationships, it is necessary to look at the intertwining of contingencies, which indicates the importance of two or more people in a relationship (Glenn, 1991) and highlights the importance of the context in which “pain behavior” occurs.

The mediating value of reinforcement results in some noteworthy implications. Social reinforcement usually depends on the occurrence of a response. In addition, the condition of the reinforcing agent may vary, which leads to variation in the reinforcement. A third implication is the slow change in some contingency characteristics. Finally, the reinforcement scheme is rarely adjusted inorganically by the reinforcing agent (Skinner, 1953/2003). The following changes were observed during the sessions: the change in the participant’s behavior resulted in a change in the relationships around them and consequently a change in the reinforcement relationships.

The operant relationship in chronic pain was first evidenced by Fordyce (1976), which highlights the need to study social support for chronic pain. The chronic nature of pain means the subject experiencing the pain and the people around them must develop skills to manage the situation. The present study compared the social support available before and after the intervention. Although the instrument scores increased, the increase was not statistically significant. The group was expected to serve as an important source of both social support for the participants and skill development to manage pain. These were both supposed to develop based on the statements and strategies used by the other participants and on the repertoire developed through the participants’ contact with their peers, the participants’ access to the material, and their discussions with health professionals.

The lack of a significant increase in social support scores could be due to two possibilities. The first is that, unlike in Finlay et al. (2018), these participants did not know each other previously. The second is that they already had adequate social support before the intervention, and their group participation did not appreciably change that situation.

The present study concludes that the group treatment with ACT was effective for the participants, resulting in a statistically significant reduction in pain, anxiety and depression symptoms, and psychological inflexibility and a statistically significant improvement in the participants’ quality of life and self-efficacy scores. However, the small number of participants and the study design require further research. An additional important aspect to be included in future studies is a sleep evaluation, given that it is often altered in patients with chronic pain.