## 4 Discussion
This study has explored the possibility of advancing in this line of research, presenting preliminary results that allow for the planning of future studies that, through appropriate designs and sample sizes, aim to address this gap. All PPT values obtained by algometry in the sample evaluated in our study were lower than the standard values reported in previous literature [34; 64; 65]. This is consistent with evidence indicating that individuals with FM have lower PPT values compared to both healthy subjects [14] and subjects with other chronic pain conditions [35; 66]. PPT measurement is a highly reliable mechanical sensory quantitative test, validated for assessing MPS of the nociceptive pathway [34; 66]. [PERSON] et al. (2011) and [PERSON] et al. (2017) found that the generalized mechanical hyperalgesia observed in subjects with FM, as measured by PPTs at different anatomical sites, was not present in individuals with varying degrees of chronic low back pain, in whom hyperalgesia is localized to the lumbar spine [35; 66]. Our exploratory findings provide a foundation for future high-quality randomized controlled trials with larger sample sizes to address the gap in the literature and explore whether the response to iVRE is consistent across different chronic pain populations. The results observed in our sample preliminarily imply that there were no observable changes in the measured PPTs (95% CI include the null value), both after the first session and after six weeks of intervention. However, it is important to consider that evidence suggests the pain mechanisms involved in FM may not always align with changes measured through PPTs [67]. This initial finding suggests that our protocol may not have effectively activated the descending endogenous pain inhibitory mechanisms in the participants, both in terms of acute hypoalgesia induced by exercise (measured after the first session) and following the full protocol [34; 35]. These results could be influenced by factors such as the inherent limitations of the small sample size and single-arm design, the method used to measure the analgesic mechanism (more complex and comprehensive approaches exist) [68], the structure of the protocol, and the duration of the intervention [69]. In this regard, it seems that the frequency and the consistency of physical activity over time, rather than the specific type of exercise, primarily influence inflammatory modulation, cytokine regulation, and neuroimmune signaling, contributing to pain reduction in conditions, such as FM [69]. However, although it should be interpreted with extreme caution, our findings align with previous reports indicating that patients with FM may exhibit impairments in the exercise-induced hypoalgesia mechanism [70]. Considering this reasoning and the findings in the literature, it could be initially inferred that the iVRE program applied in this exploratory study with FM patients may have positively influenced perceived PI [25; 26; 71], which involves sensory, cognitive, and emotional processes but did not necessarily activate endogenous analgesic mechanisms efficiently, as measured by PPTs in both post-tests. Nevertheless, despite this reasoning being supported by evidence, it should be considered with extreme caution due to the methodological limitations of a small sample size in a pre-post, non-controlled exploratory study. Future high-quality research, including more extensive protocols and long-term follow-ups, is needed to confirm these preliminary findings and address the gap in the literature. Elucidating the therapeutic prognosis for FM patients is challenging due to the condition's unknown etiology, its profound impact on quality of life, and the variability in therapeutic options, which, while promising, exhibit differing levels of efficacy [72].