Fibromyalgia (FM) is a chronic syndrome characterised by widespread musculoskeletal pain, frequently accompanied by fatigue, sleep disturbances, cognitive impairment, and memory deficits (1). In Spain, FM affects approximately 2–4% of the population and constitutes the leading cause of chronic widespread musculoskeletal pain, with women disproportionately affected (2). Despite advances in research and refinement of diagnostic criteria, its incidence continues to rise, underscoring the magnitude of the condition as a persistent health challenge (3). Given its high prevalence and the substantial work absenteeism it generates, FM represents a pressing public health concern (4).

The aetiology of FM remains largely unknown, which poses significant challenges for both accurate diagnosis and the development of effective therapeutic strategies (5). Current management typically involves a combination of pharmacological and non-pharmacological interventions, with the latter gaining increasing importance due to their potential to improve quality of life and alleviate pain while avoiding the adverse effects commonly associated with pharmacotherapy (6).

Mounting evidence suggests that FM is underpinned by alterations in central pain processing. Functional neuroimaging studies have demonstrated abnormal connectivity patterns, including increased coupling between somatosensory regions and pain-related cortical areas, alongside reduced functional integration within descending inhibitory networks. These disruptions contribute to augmented pain sensitivity and a diminished capacity to modulate nociceptive input, thereby perpetuating chronic pain (7, 8).

In addition to central mechanisms, peripheral factors such as body mass index (BMI) and body fat distribution have been increasingly recognised as relevant modulators of symptom severity in FM (9). Another peripheral mechanism related to the development of FM is small fibre pathology, which affects approximately 50% of people with FM (10). Recent evidence indicates that obesity can act as a peripheral disruptor of cortical inhibitory mechanisms, thereby exacerbating clinical manifestations including pain, fatigue and depressive symptoms (11). Moreover, the prevalence of overweight and obesity among people with FM is substantially higher than in the general population, and these conditions are associated with greater tender-point sensitivity, heightened pain perception and poorer physical function (12). Central adiposity and reduced skeletal muscle mass may further compromise mobility and attenuate treatment response. In addition, obesity and higher BMI have been linked to impaired cognitive performance, which may further increase the disease burden in FM patient (13). Taken together, these findings underscore the importance of assessing BMI and body composition in FM patients to better characterise their contribution to disease severity and to inform more personalised management strategies.

The assessment of FM remains challenging due to its heterogeneous clinical presentation, reliance on subjective symptoms, and the absence of specific biomarkers (14). Furthermore, frequent psychiatric comorbidities, particularly anxiety and depression, exert a significant influence on pain perception and functional outcomes (15). As most assessment tools rely heavily on self-report measures, integrating both subjective and objective parameters is essential for achieving a more accurate and personalised evaluation, thereby facilitating improved diagnostic precision and more effective therapeutic planning (6).

The primary objective of the present study is to investigate the relationship between pain, physical capacity and body composition in patients with FM. A secondary objective is to explore the impact of FM on psychological wellbeing, with particular emphasis on anxiety and depression.

The mean age of participants was 54.06 ± 9.66 years. Sociodemographic characteristics of the study sample are summarised in Table 1.

Descriptive results regarding functionality, pain sensitivity, and body composition are presented in Table 2.

The mean age of participants was 54.06 ± 9.66 years, with the majority being women (96.3%). The mean BMI was 27.47 ± 5.66 kg/m². Most participants were married (56.3%), while 22.5% were separated, 20.0% single, and 1.3% widowed. In terms of employment status, 49.4% were unemployed or on sick leave, and 31.7% were employed. Regarding menstrual status, 53.8% were menopausal, 22.5% menstruating, 20.0% non-menstruating women, and 3.8% men. One in five participants were smokers, while most reported no alcohol intake.

Functional performance was impaired across all tests: mean handgrip strength was 21.17 ± 8.49 kg, 5-STST averaged 12.83 ± 5.70 s, TUG 9.72 ± 7.10 s, and gait speed 1.01 ± 0.56 s. The FIQ score (65.27 ± 16.07) reflected a high disease burden, while PSQI scores (14.88 ± 4.29) indicated poor sleep quality. Anxiety and depression levels were elevated (HADS-A: 12.65 ± 4.56; HADS-D: 9.93 ± 4.56).

Pain intensity was high (VAS: 7.03 ± 1.94), with pressure pain thresholds below 2.0 kg/cm² at all tender points. Body composition analysis showed increased adiposity (PBF: 37.02 ± 8.34%; VFL: 13.02 ± 5.07) and reduced lean mass (SMM: 24.08 ± 3.96 kg).

Moderate positive correlations were observed between pain and psychological symptoms: FIQ scores correlated with both depression (r = 0.430, p < 0.05) and anxiety (r = 0.477, p < 0.01), emphasising the strong association between pain and psychological distress in FM.

With respect to the relationship between functional capacity and psychological or clinical outcomes, moderate correlations were observed between performance on physical tests and levels of depression, as well as the overall impact of FM. Specifically, poorer performance on the 5-STST was associated with higher depression scores and greater disease impact. Similarly, TUG performance correlated with depressive symptoms (Table 3).

No significant correlations were identified between FM impact or pain and the body composition variables assessed (Table 4).

A multiple linear regression model was performed with the Fibromyalgia Impact Questionnaire (FIQ) score as the dependent variable of interest. In the final model, the predictors explained a substantial proportion of the variance, with an adjusted R² of 0.595, indicating that approximately 60% of the variability in FIQ scores was accounted for by the included variables. The model accounted for 59.5% of the variance in FIQ (R² = 0.595; adjusted R² = 0.570; standard error of the estimate = 11.040). The overall fit was significant, F(4, 63) = 23.169, p < 0.001. Pain (VAS) and depressive symptoms (HADS-depression) contributed independently to higher FIQ, whereas handgrip strength and total body water showed marginal/non-significant effects (Table 5).

The present study sought to examine interrelationships among FM impact, pain intensity, functional capacity, and psychological symptoms (anxiety and depression) according HADS questionnaire, as well as associations with body composition. Consistent with prior work, our participants displayed elevated pain levels (VAS 7.03 ± 1.94) and a high perceived disease burden (FIQ 65.27 ± 16.07).

In comparative populations, such as people with rheumatoid arthritis, individuals with FM often show worse pain experience, catastrophising, and central sensitisation (27). That study, along with ours, emphasises the importance of addressing pain, functional impairment, and psychosocial factors in tandem. Other authors have demonstrated that pain catastrophising and depressive symptoms are key mediators of disability in FM (28).

The literature indicates that high scores in HADS and kinesiophobia are negatively associated with physical functioning and quality of life in FM, fostering avoidance behaviours that exacerbate chronic pain (29). In our sample, the HADS-A and HADS-D questionnaire scores were 12.65 ± 4.56 and 9.93 ± 4.56, respectively. These data suggested that the patients exhibited a moderate level of anxiety and a mild level of depression. We found moderate correlations between depression and performance on the 5-STST (r = 0.325) and TUG (r = 0.346). Additionally, FIQ correlated moderately with performance in all physical tests. These findings reinforce the idea that multidimensional treatment combining supervised physical exercise and psychological interventions it’s necessary to improve the outcomes for patients with FM (30).

In relation to body composition parameters, a study conducted on Spanish women with FM showed that 31.5% were obese and 38.5% were overweight (31). This trend also occurs in our study, as the mean BMI value is 27.47 ± 5.66, indicating overweight. This indicates that there is a prevalence of excess adiposity in women with FM, which is related to an increase in inflammatory hormones that can cause increased sensitivity to pain (9). A study conducted with women with FM found an association between waist circumference, BMI, and low levels of physical activity, especially with light physical activity (32).

According to the results of our study, we can observe that pain appeared as the main determinant of functional capacity. This reinforces the role of chronic pain as a limitation of functional capacity in subjects with FM. Similarly, total body water and handgrip strength were related to functional capacity. According to the data obtained, these variables follow a trend suggesting that the functional capacity of people with FM depends mainly on muscle quality and neuromuscular efficiency. Other studies have shown that grip strength is an indicator of functional capacity in women with FM (33). Furthermore, women with FM have a higher percentage of fat mass and greater grip strength than healthy women (34). It has also been observed that people with FM present high levels of depression, which has a negative impact on functional capacity and activities of daily living (35).

Low physical activity is a frequent characteristic in FM populations. Sedentarism may exacerbate metabolic dysfunction and foster central adiposity, thus creating a vicious cycle of pain-inactivity. In line with this, we observed moderate correlations between FIQ and physical test performance, reinforcing the notion that physical deconditioning is intertwined with symptom severity. Meta-analyses and systematic reviews show that both endurance and resistance training can ameliorate FM impact, reduce pain, and improve psychological outcomes (36-39). In particular, resistance exercise has recently shown promising effects on depression and fatigue in women with FM, with clinically meaningful improvements (41). Another trial comparing resistance training of different intensities found that low-intensity regimens yielded greater reductions in depressive symptoms at 4 weeks among FM patients (40). Taken together, these results support the adoption of a multidisciplinary treatment approach targeting body composition, motor function, pain modulation, and mental health (13).

These findings highlight the necessity of adopting a multidisciplinary management strategy that integrates therapeutic exercise, tailored pain management, psychological support, and interventions targeting body composition and overall health. Such an approach may optimise functionality, reduce symptom burden, and improve quality of life in this population.

Some of the limitations of this study are that, as it is a cross-sectional design, it prevents causal inferences between the variables examined. Furthermore, although the inclusion criteria were neutral, our sample is exclusively female. This is due to the etiopathogenesis of the pathology and is consistent with the existing literature, but it limits the generalization of the findings to male patients. The sample size is small, which restricts statistical power and external validity. Finally, the absence of a healthy control group prevents direct comparison of functional and psychological outcomes with normative populations.

In subsequent research phases, efforts will be directed towards recruiting a sex-balanced cohort including healthy controls, which would enable normative benchmarking and more accurate modelling of predictive pathways. Moreover, longitudinal and interventional study designs will be essential to elucidate causal mechanisms and guide the development of optimised, personalised therapeutic protocols for individuals with FM.

Patients in this study reported severe pain and increased sensitivity to pain, especially in the epicondyles. Strong correlations emerged between higher pain levels, greater disease impact and higher scores in anxiety and depression symptoms. Although skeletal muscle mass appeared preserved, it was not associated with physical performance. Pain intensity and depressive symptoms were the strongest predictors of fibromyalgia impact, while grip strength and total body water showed a lesser contribution.