Pain intensity and physical performance among individuals with fibromyalgia in mid-to-late life: The influence of depressive symptoms

Abstract

This study investigated the mediating role of depressive symptoms among 147 middle-aged and older adults with FM in the relationship between pain intensity and 4 objective measures of physical performance: Fullerton Advanced Balance scale (FAB), 6-Minute Walk Test (6MWT), 30-Second Chair Stand (30SCS), and 8-Foot Up and Go Test (8FUPGT). Asymptotic mediation analyses revealed that depressive symptoms fully mediated the relationship between pain intensity and FAB (95% CI [−0.40, −0.10]) and 8FUPGT (CI [0.02, 0.11]) and partially mediated the relationship to 6MWT (CI [−9.15, −2.20]) and 30SCS (CI [−0.29, −0.06]). Findings support the evaluation of co-morbid depression in FM.

Keywords

chronic pain depressive symptoms fibromyalgia pain intensity physical performance

Fibromyalgia (FM) is a chronic pain condition characterized by widespread pain that affects approximately 2%–5% of the general population (Jones et al., 2015a; Wolfe et al., 2010), and is more common among women (Wolfe et al., 2018). FM is frequently associated with a variety of comorbid conditions including but not limited to fatigue, sleep difficulties, emotional function difficulties, cognitive difficulties, and depression (Andrade et al., 2018; Luque-Reca et al., 2019). Limitations brought on by symptoms of FM are frequently reported (Hadlandsmyth et al., 2017; Lukkahatai et al., 2016), and associated with poorer physical function, quality of life, and subsequently psychiatric conditions such as depression (Dailey et al., 2016; Galvez-Sánchez et al., 2020).

Pain and physical performance

Research documents reduced physical function and ability among persons with FM that is partly attributed to pain intensity (Umeda et al., 2015). Additional research has documented a unique association between pain and physical functioning among FM patients (Dailey et al., 2016). For instance, Torma et al. (2013) examined correlates of physical functioning among persons with FM and found that pain intensity was associated with reduced self-reported physical function after controlling for sociodemographic characteristics and psychosocial factors. Another study found altered functional performance among persons with FM compared to pain-free controls wherein a negative association between pain severity and objectively measured gait and balance performance was found among FM participants (Costa et al., 2017).

While research supports a unique relationship between chronic pain and physical function, pain severity is not associated with functional limitation in isolation, given that functional ability differs across FM patients reporting similar pain intensity (Pérez-Aranda et al., 2019). Moreover, pharmacological and non-pharmacological pain reduction interventions designed to augment physical function have reported inconsistent reductions in pain, with small effect sizes (Nüesch et al., 2013). These observations suggest that other factors, in addition to pain intensity, may contribute to reduced physical function, such as psychological factors. In support of this conjecture, research supports a bidirectional relationship between pain and physical performance wherein depression is implicated as a mediator in this relationship (Scott et al., 2016). Indeed, past research indicates a positive and unique association between pain severity and depressive symptoms when controlling for other psychological factors (Lami et al., 2018). Taken together, depression may function as a mechanism through which pain intensity contributes to reduced functional outcomes among FM patients.

Depression and FM

Depression is among the most common comorbidities within the FM population, and recent systematic review evidence reports a lifetime prevalence of approximately 63% (Kleykamp et al., 2021). Further, the prevalence of mood disorders including depression is estimated to be approximately three times higher among the FM population compared to the general population (Løge-Hagen et al., 2019), and FM patients report higher rates of depression compared to individuals with other chronic pain conditions (Gracely et al., 2012). Depression is an established risk factor for serious illness and research suggests that chronic pain increases the risk of cardiovascular disease-related mortality, with greater pain intensity strengthening this relationship (Fayaz et al., 2016). Given the high prevalence of depression among the FM population, it is reasonable to hypothesize that depression may play a role in the relationship between pain and physical function among FM patients. Importantly, a bidirectional relationship exists between FM and depression (Chang et al., 2015). Much like chronic pain, depression is associated with reduced physical activity, physical function (McLoughlin et al., 2011), and greater pain intensity within the FM population (Hadlandsmyth et al., 2017). Also, Ang et al. (2011) found that FM patients with depressive symptoms had higher pain sensitivity, whereas the converse was found among participants without depressive symptoms.

Objective physical performance measures are frequently used in empirical research to assess the presence of physical limitation or impairment across various functional areas. Popular physical performance instruments and their area of assessment include the Fullerton Advanced Balance Scale for balance (FAB; Rose et al., 2006), the 6-Minute Walk Test for cardiorespiratory fitness (6MWT; Rikli & Jones, 1999, 2013a), the 30-Second Chair Stand for lower-body strength (30SCS; Rikli & Jones, 1999, 2013a), and the 8-Foot Up and Go Test for muscle strength, coordination, and agility (8FUPGT; Rikli & Jones, 1999, 2013a).

To this end, evidence also supports a relationship between chronic pain and depressive symptoms and their association with physical performance among the FM population. Notably, research indicates that persons with FM generally score below criterion fitness standards among objective physical performance measures including the FAB, 6MWT, 30SCS, and 8FUPGT, and depression and pain severity are inversely associated with performance (Jones et al., 2015b). For example, one study found that, after controlling for depressive symptoms, pain intensity was associated with reduced self-reported physical function among FM participants (Torma et al., 2013). Moreover, Costa et al. (2017) compared FM and non-FM participants on several physical performance measures including the 6MWT and found that FM participants generally scored lower across all indicators and performance was related to both pain intensity and depressive symptoms among FM participants. Additionally, Breda et al. (2013) found that while Brazilian FM and non-FM participants reported comparable physical activity levels, FM participants had lower 6MWT performance, attributable to FM symptoms. In a similar study, Del Pozo-Cruz et al. (2017) examined depression severity, FM symptoms (including pain intensity), and functional capacity (i.e. lower body strength) among Spanish women with FM. Findings indicated that depressive symptoms were associated with more FM symptoms (e.g. greater pain) and reduced lower body strength demonstrated by poorer 30SCS performance (Del Pozo-Cruz et al., 2017). Further, Dailey et al. (2016) found that both depressive symptoms and FM symptoms (e.g. pain intensity) were associated with reduced 6MWT performance among women with FM. Notably, more variance was accounted for in physical performance when both FM symptoms (e.g. pain intensity) and depressive symptoms were considered (Dailey et al., 2016). In addition, Soriano-Maldonado et al. (2016) found a negative association between depressive symptoms and both the 8FUPGT and 6MWT performance among women with FM. Taken together, this evidence supports the conjecture that both pain and depression are related to poorer physical performance among middle-aged and older adults with FM.

While a bidirectional relationship between FM and depression is noted (Chang et al., 2015), chronic pain as a risk factor for depression in the general population (Hooten, 2016; Ohayon & Schatzberg, 2003), and within the general chronic pain population, most individuals develop depressive symptoms following the onset of chronic pain (Ohayon & Schatzberg, 2010), suggesting a possible sequential relationship. In support of this conjecture, Okifuji et al. (2011) examined daily depressive symptoms using ecological momentary assessment in FM patients and found that pain was experienced prior to depressive symptoms and magnified emotional distress. Interestingly, in other chronic pain conditions (i.e. upper extremity musculoskeletal illness), evidence has indicated a bidirectional mediation effect of depression and pain intensity on physical performance, supporting a reinforcement mechanism between these two factors (Talaei-Khoei et al., 2018). Despite this, research examining the joint relationships between pain intensity and depressive symptoms, and the subsequent impact on physical performance among the FM population, is limited. It is important to note that while these relationships are established among other chronic pain disorders, such as chronic low back pain (e.g. Marshall et al., 2017), to our knowledge only one previous study has examined these relationships by proposing depressive symptoms as a mediator in the association between pain intensity and physical functioning among FM patients. Steiner et al. (2017) examined a large sample of FM patients and found that depressive symptoms partially mediated the relationship between pain severity and self-reported physical functioning across time. While other studies have examined potential mediators in the relationship between pain and physical function (e.g. sleep; Miró et al., 2011), these variables are also correlated with depression. Taken together, depression is implicated to partially explain the relationship between pain and physical function among persons with FM, although this supposition warrants further investigation. Acquiring a better understanding of depression as a mechanism through which chronic pain intensity contributes to poor functional outcomes in FM patients will clarify the need for depression-targeted treatment interventions, which may serve as viable modalities to subsequently improve functional capacity.

Current study

While research on mechanisms of chronic pain that contribute to reduced physical function among the FM population is limited, depression is supported as one potential mechanism. However, depression has yet to be examined in this relationship using objective indicators of physical performance. Thus, this study proposed depressive symptoms as a mediator in the relationship between pain intensity and several indicators of objective physical performance among middle-aged and older adults with FM. It was hypothesized that (1) pain intensity would be associated with poorer physical performance across all indicators (i.e. FAB, 6MWT, 30SCS, and 8FUPGT) and that (2) depressive symptoms would partially mediate the relationship between pain intensity and all indicators of physical performance (i.e. FAB, 6MWT, 30SCS, and 8FUPGT). Partial mediation effects of depressive symptoms, instead of full mediations, were hypothesized given the wealth of evidence supporting a unique association between pain and physical function.

Method

Participants

Participants included in this cross-sectional analysis were first time participants enrolled across several waves of a larger longitudinal study in which data collection occurred once every 2 years from 2008 to 2018, as described elsewhere (e.g. Jones et al., 2010). The study sample (n = 147) included 137 women (93.2%) and 10 men (6.8%) diagnosed with FM whose ages ranged from 50 to 85 (M = 61.18, SD = 7.80). The sample was largely White (79.7%), retired (33.6%), married (56.8%), and received some college education (62%). Complete sample demographics are provided in Table 1.

Table 1.

Demographic information and clinical characteristics (n = 147).

	M (SD)	Frequency	%
Age	61.18 (7.80)
Pain intensity	5.96 (2.66)
BDI-II	16.37 (9.94)
FAB	30.99 (5.31)
6MWT	530.48 (112.97)
30SCS	10.60 (3.96)
8FUPGT	6.12 (3.96)
Gender
Female		137	93.2
Race/ethnicity
White/European American		114	79.7
Hispanic		4	2.7
African American		2	1.4
Asian American		2	1.4
Multiracial		22	15.3
Other		3	2
Income
<$9999		4	2.8
$10,000–29,999		20	14.2
$30,000–59,999		41	29.1
$60,000–89,999		30	21.3
$90,000–199,999		34	24.1
$200,000+		5	3.5
Employment status
Retired		49	33.6
Working		41	28.1
Unemployed/not working		21	14.3
Permanently disabled		29	19.9
Other		6	4.1
Marital status
Never married		9	6.2
Married		83	56.8
Divorced/separated		40	27.4
Widowed		14	9.6
Highest completed education
High school or less		11	7.5
Some college/trade school		55	37.4
College degree		36	24.5
Professional/graduate degree		45	30.6
Fall in past 12 months
Yes		62	42.25

BDI-II: beck depression inventory-II; FAB: Fullerton advanced balance; 6MWT: 6-minute walk test; 30SCS: 30-second chair stand; 8FUPGT: 8-foot up and go test.

Procedure

Participants were recruited from local FM support groups, senior centers, and housing facilities in the Southern California region. Prospective participants were invited to contact research personnel for eligibility screening. Participants met the following inclusion criteria: (1) at least 50 years old, (2) community-residing, (3) functionally independent, and (4) received a formal FM diagnosis from a medical professional. Prospective participants were not enrolled if they (1) could not walk for 6 minutes without assistance or (2) had a preexisting medical condition considered unsafe to engage in submaximal exercise, which included serious heart/lung disease(s) or bone/muscular/neurological conditions that could be exacerbated by exercise (American College of Sports Medicine guidelines; Dwyer & Davis, 2007). Participants were not enrolled if there was any perceivable health or safety risk in engaging in physical performance assessments. Lastly, given a unique association between depression and cognitive function (Bell et al., 2018), participants were screened for cognitive impairment using the Mini-mental Status Examination (MMSE; Folstein et al., 1975) which measures orientation, attention, memory, language, and visual-spatial skills. MMSE scores below 25 suggest possible cognitive impairment (Folstein et al., 1975).

Participants meeting inclusion criteria were mailed a packet that included a paper study informed consent document, and sociodemographic and health history questionnaires to complete prior to in-person assessment. Informed consent provided approval of the use of data for research and publication purposes while maintaining anonymity and confidentiality. Thereafter, subjects were scheduled for a data collection appointment with a phone call reminder provided 1 day before the appointment day. During data collection, study consent forms and initial questionnaires were reviewed by appropriate research personnel and participants’ questions about the study were answered. Afterward, participants gathered in a shared space where they completed self-report instruments and were then sent to private rooms to complete all physical performance assessments. Participants completed all physical performance assessments in the same order as listed below. All study protocols and procedures were approved by the California State University, Fullerton institutional review board prior to data acquisition (HSR-17-18-547).

Measures

Sociodemographic characteristics

Participants provided information on age, gender, race/ethnicity, income, education level, marital status, and the presence of falls in the past 12 months using questions drawn from the National Fibromyalgia Association Questionnaire (NFAQ; Bennett et al., 2007).

Pain intensity

Pain intensity was self-reported with the following question: “What was your average daily pain level in the past week?” anchored on an 11-point numeric rating scale with response options ranging from 0 (No pain) to 10 (Worst pain), drawn from the NFAQ (Bennett et al., 2007). The numeric rating scale has demonstrated adequate psychometric properties in comparison to similar measures of pain intensity such as the visual analog scale (Hawker et al., 2011).

Beck Depression Inventory-II

The Beck Depression Inventory-II (BDI-II; Beck et al., 1996) is a 21-item instrument used to assess depressive symptoms over the past 2 weeks. The BDI-II items are rated on a 4-point Likert scale with response options ranging from 0 to 3, with higher scores indicating more severity. Summed scores were calculated with higher scores indicating greater depressive symptomology. Scores ⩾29 indicate severe depressive symptoms (Beck et al., 1996). The BDI-II has demonstrated strong psychometric properties among older adults with and without FM (Follick et al., 2016).

Physical performance measures

Objective physical performance measures were used to assess the prevalence of physical limitation and impairment. This measurement strategy was selected based on its feasibility in community-based settings along with standard protocols for administration containing adequate reliability and validity for each assessment. Three of the four assessments described below were drawn from the Senior Fitness Test (Rikli & Jones, 2013a): the 6MWT, 30SCS, and 8FUPGT.

Fullerton Advanced Balance Scale

The Fullerton Advanced Balance Scale (FAB; Rose et al., 2006) was used to objectively assess balance. The FAB contains 10 items designed to measure balance skills requiring static and dynamic postural control (e.g. stand on a firm surface with feet together/eyes closed; turn 360° in both directions). FAB items were rated on a 5-point ordinal scale with response options ranging from 0 (unable) to 4 (independent task completion), with higher scores indicating better balance (Rose et al., 2006). Scores were summed with possible scores ranging from 0 to 40. The FAB has demonstrated strong test-retest and interrater reliability and convergent validity with other balance assessments such as the Berg Balance Scale (Klein et al., 2011; Rose et al., 2006). Past research supports the FAB as a comprehensive measure of balance among middle-aged and older adults with FM (Follick et al., 2016).

The 6-Minute Walk Test

The 6-Minute Walk Test (6MWT; Rikli & Jones, 1999, 2013a) was used to measure functional exercise capacity through cardiorespiratory fitness. Participants were instructed to walk safely and comfortably as quickly as possible during a 6-minute interval along a 50-yard, flat rectangular space. The maximum distance (yards) walked was recorded, where higher scores reflect better performance (Rikli & Jones, 2013b). Research documents satisfactory psychometric properties of the 6MWT among samples of middle-aged and older adults with FM (Follick et al., 2016).

The 30-Second Chair Stand

The 30-Second Chair Stand (30SCS; Rikli & Jones, 1999, 2013a) was used to assess lower-body strength through the number of times a person can stand then sit in a chair in 30 seconds, where more stands within the allotted time reflect better performance (Rikli & Jones, 2013b). The 30SCS has demonstrated adequate psychometric properties among samples of middle-aged and older adults with FM (Cherry et al., 2012).

The 8-foot Up and Go Test

The 8-foot Up and Go Test (8FUPGT; Rikli & Jones, 1999, 2013a) is a well-established test for middle-aged and older adults designed to measure overall functional mobility including muscle strength, coordination, and agility. Participants were seated in a chair with a cone placed 8 feet away from the front edge of the chair. Participants walked as quickly and safely as possible around the cone, returning to the chair to sit. The fastest time (seconds) to complete the task out of two test trials was recorded. Longer periods of time to complete the task reflect poorer performance (Rikli & Jones, 2013b). Previous studies have reported strong psychometric properties of the 8FUPGT among samples of middle-aged and older adults with FM (Follick et al., 2016).

Data analysis

Participant characteristics were examined using frequencies and proportions or means and standard deviations, as appropriate. Univariate and multivariate normality assumptions were examined using skewness and kurtosis, and outliers were screened using z scores for pain intensity, BDI-II, FAB, 6MWT, 30SCS, and 8FUPGT, as well as Mahalanobis distance using SPSS version 27. Cases were considered univariate outliers if z’s > 3.29, p < 0.001 and multivariate outliers if Mahalanobis distance >22.46, p < 0.001 (Ullman, 2019). Bivariate correlations were used to assess multicollinearity and independent-sample t-tests were used to assess mean differences across key demographic variables to assess for the inclusion of potential covariates.

To identify the relationships among pain intensity, depressive symptoms, and several indicators of objective physical performance among participants with FM, mediation analyses using an asymptotic percentile bootstrapping approach were performed (Preacher & Hayes, 2008). Percentile bootstrapping was selected for its strength with smaller samples compared to other methods (Creedon & Hayes, 2015; Fritz and Mackinnon, 2007; Preacher & Hayes, 2008). Specifically, mediation models with 5000 resamples were conducted using PROCESS macro version 3.5 for SPSS version 27 (Model 4; Hayes, 2017). Four mediation models included pain intensity as the predictor, with depressive symptoms proposed as the mediator, and with the FAB, 6MWT, 30SCS, or 8FUPGT as the outcome variables, while controlling for age. Age was included as an a priori covariate for all functional outcome variables, given its association with physical performance (Jones et al., 2015b; Torma et al., 2013). The relevance of this procedure was confirmed upon inspection of bivariate correlations. To assess the indirect mediation effects, confidence intervals that do not cross zero are considered statistically significant (Preacher & Hayes, 2008). Unstandardized coefficients are reported for all mediation analyses.

Data sharing statement

Are de-identified individual participant data available (including data dictionaries)? Yes.

What data in particular are shared? All participant data presented in this study after de-identification.

What other documents are available? Explanatory memo, Syntax file, and Data output.

Results

Preliminary analyses

Bivariate associations (Table 2) indicated that age was associated with all primary outcome variables (r’s: −0.283, −0.432, p’s < 0.05) except 30SCS and 8FUPGT (p’s > 0.05), and thus was included as a covariate for all mediation models. Pain intensity was associated with BDI-II, 6MWT, and 30SCS (r’s: −0.305, −0.361, p’s < 0.05), but not FAB or 8FUPGT (p’s > 0.05). BDI-II was associated with all primary outcome variables (r’s: −0.376, −0.208, p’s < 0.05). All physical performance measures were correlated (r’s: −0.599, −0.521, p’s < 0.05). Means and standard deviations of all primary study variables are provided in Table 1. Despite an unequal distribution of males (n = 10) and females (n = 137) in the sample, independent-sample t-tests revealed no mean differences across pain intensity, BDI-II, FAB, 6MWT, 30SCS, or 8FUPGT (p’s > 0.05). Moreover, the year/wave in which data collection occurred was also not associated with any primary outcome variables (p’s > 0.05). Two multivariate outliers were detected (Mahalanobis distance >22.56, p < 0.001), and analyses were conducted with and without these outliers. Results did not change with these outliers excluded and thus, to conserve power, these cases were kept in the final sample (n = 147). Lastly, two participants scored 22 and 24 on the MMSE, suggesting possible mild dementia (Folstein et al., 1975). Analyses were conducted without these cases (n = 145) and because results did not change, all cases were retained in the reported analyses (n = 147) to conserve power. There were no missing data.

Table 2.

Bivariate correlations among primary study variables.

	1	2	3	4	5	6	7
1. Age	–	−0.204*	−0.220**	0.432***	−0.283**	−0.021	0.157
2. Pain intensity		–	0.361***	−0.139	−0.305***	−0.329***	0.151
3. BDI-II			–	−0.272**	−0.352***	−0.376***	0.208**
4. FAB				–	−0.599***	−0.411**	−0.493***
5. 6MWT					_	0.521***	−0.510***
6. 30SCS						–	−0.615***
7. 8FUPGT							–

n = 147. BDI-II: beck depression inventory-II; FAB: Fullerton advanced balance; 6MWT: 6-minute walk test; 30SCS: 30-second chair stand; 8FUPGT: 8-foot up and go test.

p < 0.05. **p < 0.01. ***p < 0.001.

Mediations

A causal step approach was used to evaluate mediation as partial or full. When direct effects (path c′) and indirect paths (a × b) were both significant, partial mediation was designated. If the indirect path (a × b) was significant while the direct effect (path c′) was not, full mediation was designated. If only path a or path b was significant, mediation would be designated only if the indirect path was statistically significant (Hayes, 2017).

FAB

In the mediation model with FAB as the outcome variable, the unmediated model indicated that pain intensity was associated with FAB (path c; b = −0.52, p = 0.003), after controlling for age (b = −0.33, p < 0.001). In the mediated model, pain intensity was positively associated with BDI-II (path a; b = 1.29, p < 0.001), after controlling for age (b = −0.19, p = 0.049) and BDI-II was negatively associated with FAB (path b; b = −0.19, p < 0.001), after controlling for age (b = −0.36, p < 0.001). The indirect association between pain intensity and FAB via BDI-II was significant (path ab; indirect effect = −0.24, SE = 0.08, 95% CI [−0.40, −0.10]). In the mediated model, pain intensity was not associated with FAB (path c′; b = −0.28, p = 0.102), suggesting full mediation. Thus, higher pain intensity was associated with increased depressive symptoms, which in turn was associated with reduced FAB performance. Calculation of the effect size (ab/c) indicated that approximately 46% of the variance in the relationship between pain intensity and FAB was explained by depressive symptoms.

6MWT

In the mediation model with 6MWT as the outcome variable, the unmediated model indicated that pain intensity was inversely associated with 6MWT (path c; b = −18.37, p < 0.001), after controlling for age (b = −5.19, p < 0.001). In the mediated model, pain intensity was positively associated with BDI-II (path a; b = 1.29, p < 0.001), after controlling for age (b = −0.19, p = 0.049) and BDI-II was negatively associated with 6MWT (path b; b = −4.05, p < 0.001), after controlling for age (b = −5.96, p < 0.001). The indirect association between pain intensity and 6MWT via BDI-II was significant (path ab; indirect effect = −5.21, SE = 1.78, 95% CI [−9.15, −2.20]). In the mediated model, pain intensity remained associated with 6MWT (path c′; b = −13.15, p < 0.001), suggesting partial mediation. Thus, pain intensity was associated with increased depressive symptoms which in turn, was associated with reduced 6MWT performance. Calculation of the effect size (ab/c) indicated that approximately 28% of the variance in the relationship between pain intensity and 6MWT was explained by depressive symptoms.

30SCS

In the mediation model with 30SCS as the outcome variable, the unmediated model indicated that pain intensity was associated with 30SCS (path c; b = −0.58, p < 0.001), after controlling for age (b = −0.045, p = 0.271). In the mediated model, pain intensity was positively associated with BDI-II (path a; b = 1.29, p < 0.001), after controlling for age (b = −0.19, p = 0.049) and BDI-II was negatively associated with 30SCS (path b; b = −0.13, p < 0.001), after controlling for age (b = −0.07, p = 0.082). The indirect association between pain intensity and 30SCS via BDI-II was significant (path ab; indirect effect = −0.16, SE = 0.06, 95% CI [−0.29, −0.06]). In the mediated model, pain intensity remained associated with 30SCS (path c′; b = −0.42, p = 0.004), suggesting partial mediation. Thus, pain intensity was associated with increased depressive symptoms, which in turn was associated with reduced 30SCS performance. Calculation of the effect size (ab/c) indicated that approximately 29% of the variance in the relationship between pain intensity and 30SCS was explained by depressive symptoms.

8FUPGT

In the final mediation model with 8FUPGT as the outcome variable, the unmediated model indicated that pain intensity was associated with 8FUPGT (path c; b = 0.16, p = 0.038), after controlling for age (b = 0.05, p = 0.022). In the mediated model, pain intensity was positively associated with BDI-II (path a; b = 1.29, p < 0.001), after controlling for age (b = −0.19, p = 0.049) and BDI-II was positively associated with 8FUPGT (path b; b = 0.04, p = 0.026), after controlling for age (b = 0.06, p = 0.008). The indirect association between pain intensity and 8FUPGT via BDI-II was significant (path ab; indirect effect = 0.06, SE = 0.02, 95% CI [0.02, 0.11]). In the mediated model, pain intensity was not associated with 8FUPGT (path c′; b = 0.11, p = 0.188), suggesting full mediation. Thus, greater pain intensity was associated with more depressive symptoms, which in turn was associated with higher 8FUPGT scores (reflecting poorer performance). Calculation of the effect size (ab/c) indicated that approximately 38% of the variance in the relationship between pain intensity and 8FUPGT was explained by depressive symptoms.

Results of mediation analyses are provided in Figure 1.

Discussion

This study examined the mediating role of depressive symptoms in the relationship between pain intensity and four domains of objective physical performance. The prevalence of depressive symptoms found in this study was within previously reported ranges (Kleykamp et al., 2021). Pain, a central component to FM, is associated with reduced physical function among the FM population (Dailey et al., 2016; Torma et al., 2013). Results from the current study reflect these findings; pain intensity was associated with physical performance across all indicators, before considering depressive symptoms. Past research supports a unique association between pain intensity and physical function among persons with FM (Costa et al., 2017; Dailey et al., 2016; Umeda et al., 2015). Moreover, prior research indicates that depressive symptoms are related to pain (Lami et al., 2018) and magnify the relationship between pain and both physical function (Torma et al., 2013) and performance (Breda et al., 2013; Costa et al., 2017; Dailey et al., 2016; Del Pozo-Cruz., 2017; Jones et al., 2010, 2015b) among the FM population, consistent with the present study’s findings.

It was hypothesized that depressive symptoms would partially mediate the relationship between pain intensity and FAB, 6MWT, 30SCS, and 8FUPGT. While studies using mediation are limited, research documents unique associations between pain and depressive symptoms with physical performance, in line with current findings. For instance, research indicates that FM participants perform lower on FAB, 6MWT, and 30SCS compared to criterion fitness standards (Jones et al., 2015b), with pain severity and depressive symptoms amplifying this relationship, consistent with present findings. In support of the current study, past research has found lower objective physical performance (e.g. 6MWT) among FM participants compared to non-FM counterparts, a difference associated with pain intensity and depressive symptoms (Breda et al., 2013; Costa et al., 2017). Another study found that depressive symptoms and pain intensity were associated with reduced 30SCS performance among FM participants (Del Pozo-Cruz et al., 2017), consistent with the current study. Moreover, Dailey et al. (2016) found a unique association between depressive symptoms and FM symptoms (including pain intensity) with reduced 6MWT performance. This finding is echoed in the current study where depressive symptoms partially mediated the relationship between pain intensity and 6MWT. Further, present findings on the 8FUPGT support prior research (Soriano-Maldonado et al., 2016) by noting a significant relationship between depressive symptoms and reduced performance. While research has examined mediation effects of the relationships under study among other chronic pain disorders (e.g. Marshall et al., 2017), Steiner et al. (2017) did so among FM patients. While the current study used objective measures of physical performance, the results of Steiner et al. (2017) are partially supported in that mediation effects of depressive symptoms were observed. However, in their original study, Steiner et al. (2017) observed exclusively partial mediation effects and this analysis was conducted over time using subjective physical function measures. Present results extend this finding by highlighting partial and full mediation effects of depressive symptoms in the relationship between pain intensity and measures of objective physical performance.

Taken together, depressive symptoms mediated the relationship between pain intensity and all physical performance measures either partially or fully. While partial mediation effects were hypothesized, it was revealed that depressive symptoms fully mediated the relationship between FAB and 8FUPGT. This observation highlights the importance of depressive symptoms in the relationship between pain intensity and these two domains of physical performance. It is possible that the nature of FAB and 8FUPGT assessments more accurately capture areas of functional ability associated with depressive symptoms. Specifically, together they assess balance, coordination, and overall body control through dynamic movement, an area that may be particularly impacted by depressive symptoms among the FM population. Further, it is not unreasonable to have detected full mediation given that meta-analytic evidence documents that psychological interventions targeting psychological distress enhance daily functioning among the FM population (Bernardy et al., 2013).

Findings illustrate the association between pain intensity and physical performance among individuals with FM. Moreover, they also highlight the key contribution of depressive symptoms in this relationship. Specifically, current findings indicated that depressive symptoms demonstrated partial or full mediation, accounting for a sizeable percentage of the variability across all physical performance indicators. Given the high incidence of depression among the FM population, it is important to explore this factor and its relationship to the risk of disability and impairment.

Study findings provide clinically-relevant implications for depression-targeted interventions to subsequently improve physical functioning among middle-aged and older adults with FM. That is, depressive symptoms represent a modifiable factor for treatment interventions for FM. In support of this, meta-analytic evidence indicates that targeted psychological treatment interventions aimed at reducing depressive symptoms can subsequently improve physical function and ability (Bernardy et al., 2013). For instance, various treatments modified for FM (i.e. treatments targeting both the physical and psychological impact of FM) have demonstrated significant reductions in FM symptoms and co-morbid depressive symptoms with the use of cognitive-behavioral interventions (De La Vega et al., 2018; Zareen, & Jahangir, 2019), mindfulness practices (Amutio et al., 2015; Pleman et al., 2019; Verkaik et al., 2014), motivational interviewing (Steiner et al., 2013), and acceptance and commitment therapies delivered in-person (Wicksell et al., 2013) and online (Simister et al., 2018).

Limitations and future directions

This study is not without limitations. First, the sample was comprised of community-dwelling middle-aged and older adults living in southern California, limiting generalizability. Moreover, only participants able to maintain independent physical and functional capacity were enrolled in this study, and thus persons with FM who are functionally impaired were not represented in this study. Future research is needed to assess the association of depressive symptoms with pain intensity and physical performance among low-functioning aging adults with FM who represent a relatively understudied FM subpopulation. Also, the sample was majority White and female, further limiting generalizability to racial/ethnic minorities and males. In addition, only one dimension of pain (pain intensity) was examined in this study. Future studies should evaluate additional dimensions of pain (e.g. pain catastrophizing, pain interference) to evaluate the multidimensional impact of pain on depressive symptoms and physical performance. Notably, pain intensity and depressive symptoms were measured using self-report and are thus, vulnerable to response bias. Future research should use objective measures of pain intensity to potentially yield more precise results. Additionally, this study considered only one psychological factor (depressive symptoms), whereas examining additional mental health factors or multiple factors simultaneously may provide a more comprehensive representation. Therefore, further research is needed to assess additional mediators in the relationship between chronic pain and physical performance among the FM population. Additionally, the study sample reported elevated rates of depressive symptoms. While this is consistent with prevalence estimates of depression among the FM population, it hinders the generalizability to less depressed samples.

Conclusion

This study highlights the influential role of depressive symptoms in the relationship between pain intensity and physical performance in FM. Study findings also illustrate the importance of the assessment and management of co-morbid depression to prevent the risk of physical impairment and disability in community-dwelling adults with FM.

Research Data

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Research Data, sj-docx-1-hpq-10.1177_13591053211009286 for Pain intensity and physical performance among individuals with fibromyalgia in mid-to-late life: The influence of depressive symptoms by Dylan G Serpas, Laura Zettel-Watson and Barbara J Cherry in Journal of Health Psychology

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Research Data, sj-sav-2-hpq-10.1177_13591053211009286 for Pain intensity and physical performance among individuals with fibromyalgia in mid-to-late life: The influence of depressive symptoms by Dylan G Serpas, Laura Zettel-Watson and Barbara J Cherry in Journal of Health Psychology

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Research Data, sj-sps-3-hpq-10.1177_13591053211009286 for Pain intensity and physical performance among individuals with fibromyalgia in mid-to-late life: The influence of depressive symptoms by Dylan G Serpas, Laura Zettel-Watson and Barbara J Cherry in Journal of Health Psychology

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Research Data, sj-spv-4-hpq-10.1177_13591053211009286 for Pain intensity and physical performance among individuals with fibromyalgia in mid-to-late life: The influence of depressive symptoms by Dylan G Serpas, Laura Zettel-Watson and Barbara J Cherry in Journal of Health Psychology

Footnotes

Data availability statement

Data for this article is available online.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship and/or publication of this article: This study was funded by intramural grants awarded by California State University, Fullerton.

ORCID iD

Dylan G Serpas

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