A Standardized Assessment of Movement-Evoked Pain Ratings is Associated with Functional Outcomes in Older Adults with Chronic Low Back Pain

Abstract

Objective:

Despite high prevalence estimates, chronic low back pain (CLBP) remains poorly understood among older adults. Movement-evoked pain (MeP) is an understudied factor in this patient population that may importantly contribute to disability. This study investigated whether a novel MeP paradigm contributed to self-reported and performance-based function in older adults with CLBP.

Methods:

This secondary analysis includes baseline data from 230 older adults with CLBP in the context of a prospective cohort study. The Repeated Chair Rise Test, Six Minute Walk Test, and Stair Climbing Test were used to elicit pain in this population; post-test LBP ratings were aggregated to yield the MeP variable. Self-reported and performance-based function were measured by the Late Life Function and Disability Index (LLFDI) scaled function score and Timed Up-and-Go Test (TUG), respectively. Robust regression with HC3 standard errors was used to model adjusted associations between MeP and both functional outcomes; age, sex, body mass index, and pain characteristics (i.e., intensity, quality and duration) were utilized as covariates.

Results:

MeP was present in 81.3% of participants, with an average rating of 5.09 (SD=5.4). Greater aggregated post-test MeP was associated with decreased LLFDI scores (b=−0.30, t=−2.81, p=0.005) and poorer TUG performance (b=0.081, t=2.35, p=0.020), independent of covariates. LBP intensity, quality and duration were not associated with the LLFDI or TUG (all p>0.05).

Discussion:

Aggregated post-test MeP independently contributed to worse self-reported and performance-based function among older adults with CLBP. To understand long-term consequences of MeP, future studies should examine longitudinal associations between MeP and function in this population.

INTRODUCTION

Chronic low back pain (CLBP) affects an estimated 13.1% of adults in the United States every year, and is associated with increased socioeconomic and comorbidity burdens.^1,2 CLBP prevalence is on the rise, particularly among older adults,^1,3 who are prone to accelerated functional decline ^4-6 and poor health outcomes.^7-10 To halt or reverse trends of poor health outcomes in this population, it is imperative to better understand which aspects of pain contribute to disability in older adults; one way to advance knowledge in this manner is to develop discriminative pain outcome measures.

Self-reported recall and spontaneous pain outcome assessments ineffectively account for underlying peripheral or central sensitization processes that may influence prognosis for individuals with CLBP.^11-15 Prior literature has advocated for investigation of movement-evoked pain (MeP), or pain exacerbation as a product of movement, as a means to more accurately assess the multidimensional nature of chronic pain.^12,13,16 However, studies to date have incompletely detailed procedures for the quantifying MeP.^13,16 The lack of development of MeP assessments restricts the ability to understand how pain with movement influences physical function, thereby hindering attempts to intervene upon chronic pain that affects daily life (or high-impact chronic pain).^17,18

A recent review concluded that MeP outcomes should be specific to the condition (i.e., LBP).¹⁶ Prior evidence has established that older adults with LBP perform worse on tests of physical function compared to pain-free counterparts.^4,6,19,20 Physical function tests often require lumbopelvic movement, and the lumbopelvic complex is an origin of pain for older adults with CLBP; thus, standardized tests of physical function may simultaneously evoke pain and provide valuable prognostic information about disability. In this capacity, MeP methodology that includes standardized functional testing may uncover an aspect of the chronic pain experience that uniquely contributes to disability in older adults with CLBP. MeP may be a crucial modifiable impairment in older adults with CLBP, but its relationship with self-reported and performance-based physical function is unknown.

Here, we propose to calculate MeP as an aggregate of post-test LBP ratings following standardized measures that include transitional mobility (the Repeated Chair Rise Test [RCR] and Stair Climbing Test [SCT]) and walking endurance (the Six-Minute Walk Test [6MWT]).²¹ These measures each require repetitive movements of the lumbopelvic complex in distinct contexts. Given the variable nature of CLBP presentations in older adults,^22,23 aggregating post-test LBP ratings may increase the likelihood of successfully eliciting MeP in this population. Further, the above mentioned measures account for different components of physical function and are predictive of downstream health outcomes in older adults,^24-27 thus providing complementary prognostic information.

In this investigation, we sought to assess the extent to which aggregated post-test MeP is associated with both self-reported and performance-based function in older adults with CLBP. Our intent was to expand upon prior MeP investigations by administering a general measure of self-reported function, and utilizing a performance-based functional task separate from the measures that yielded our aggregate MeP variable. Therefore, the purpose of this study was to assess cross-sectional associations between aggregated post-test MeP and both the Late Life Function and Disability Instrument (LLFDI) and Timed Up-and-Go Test (TUG). We hypothesized that greater MeP would be associated with worse self-reported and physical performance outcomes, independent of pain duration, pain quality, and pain intensity.

MATERIALS AND METHODS

Participants

Participants were recruited for a prospective cohort study, conducted from March 2013 to December 2016; details regarding study procedures and recruitment strategies have been previously published.²⁸ Participants were eligible for participation if they were between the ages of 60-85 years, cognitively intact and had non-specific CLBP (i.e., pain intensity≥3/10, pain frequency≥4 days/week, pain duration≥3 months). Exclusion criteria were non-mechanical LBP symptomatology, lower extremity pain intensity greater than LBP intensity, current spinal or hip fractures, severely impaired ambulatory capacity requiring the use of a walker, diagnosis of a progressive neurological disorder, and terminal illness. Of 432 community-dwelling older adults who were screened, 250 participants were enrolled (Figure 1). All study participants read and signed a written informed consent document.

Figure 1:

Flow diagram of participant enrollment

Evaluations for this secondary analysis were conducted in the clinical research laboratory at the University of Delaware. Licensed physical therapists collected standardized lumbar spine, hip, and physical performance measurements. The study protocol was approved by the University of Delaware Institutional Review Board, and conformed to the principles of the Declaration of Helsinki from the World Medical Association.

Composite LBP Intensity

LBP intensity was measured with the Pain Thermometer Scale (0=no pain; 10=worst pain imaginable).^29,30 Participants were asked to rate their current LBP intensity, as well as their best and worst LBP intensity in the 24 hours preceding the baseline evaluation. LBP intensity ratings were averaged to form a composite score, given that composite pain intensity scores tend to yield better psychometric properties than individual pain ratings.^31,32

Pain Quality

The McGill Pain Questionnaire (MPQ) was administered prior to all performance testing to capture pain quality (78 words, total score from 0-78).³³ Participants were instructed to mark adjectives describing their present pain experience; only one adjective could be marked per category, and participants could leave a category unmarked if it did not aptly characterize their pain. The sum of all marked adjectives was calculated to represent the Pain Rating Index (MPQ-PRI), which is a reliable and valid assessment of chronic pain.^34-36

Post-Performance Movement-Evoked Pain Aggregate

The RCR, SCT and 6MWT were included in aggregate post-test MeP calculations given their discriminative ability to exacerbate lower quarter pain in older adults.^37-39 The RCR was completed as described in the Short Physical Performance Battery; participants were asked to stand from a chair with armrests 5 times as quickly and safely as possible without upper extremity assistance.⁹ The RCR has been found to be reliable and valid among individuals with LBP ^40,41 and older adults.^42-44 For the SCT, participants were asked to ascend and descend 12 steps at a comfortable pace;⁴⁵ the SCT has been found to be reliable and valid among older adults.⁴⁶ For the 6MWT, participants were instructed to cover as much distance as possible in 6 minutes along a rectangular pathway.⁴⁷ The 6MWT has previously established reliability and validity among older adults.²⁶ To aggregate post-test MeP ratings, participants were queried about their LBP intensity rating (0=no pain; 10=worst pain imaginable) after completing each respective test. The post-test LBP intensity ratings were then summed together, creating a possible MeP range from 0-30. This MeP aggregate rating was then used in subsequent analyses.

Participant Demographics, Pain Duration, and Anthropometrics

At baseline, participant demographics (age and sex) and LBP duration (expressed in years) were collected. Height and weight were measured and converted to body mass index (BMI).

Self-Reported Function: Late Life Function and Disability Instrument (LLFDI)

The LLFDI, a generic measure of self-reported function, was administered before all performance testing to evaluate function irrespective of pain. The functional component of this outcome assesses perceived difficulty across 32 physical tasks; scaled overall function scores range from 0-100, with higher values indicating greater levels of functioning.⁴⁸ The reliability and validity of the LLFDI has been established in a recent systematic review of geriatric literature.⁴⁸

Physical Performance: Timed Up-and-Go Test

The TUG was completed using a standard height armchair, positioned along a 3-meter walkway.⁴⁹ Participants were instructed to stand from the chair, walk at their usual comfortable pace past a demarcation 3-meters away, and return to a sitting position in the chair. The duration (in seconds) required to complete the test was recorded as the output variable. Three trials were averaged for subsequent analyses, with lower values indicating better mobility performance. Prior evidence has established that the TUG has excellent reliability and validity,⁴⁹ and is predictive of falls among older adults.⁵⁰

We used the TUG as a measure of physical performance because the test combines a transitional mobility task with ambulation; these functional tasks mirror components of the RCR and 6MWT tests. Thus, we are maintaining specificity between our aggregated post-test MeP variable and our performance-based outcome. The TUG was not included in our aggregate post-test MeP ratings, allowing us to examine whether discretely measured MeP is associated with performance in a separate functional context. The TUG was completed after the RCR, but before the SCT and 6MWT. Participants self-selected rest times between functional tests, allowing episodic increases in LBP to subside prior to initiating the subsequent test, which minimized possible interactions between the tests included in aggregated MeP calculations and TUG performance.

Statistical Analysis

All statistical analyses were completed with SPSS 26 (SPSS, Inc. Armonk, NY). Statistical significance was set at p<0.050. For descriptive analysis, means and standard deviations were computed for continuous variables while frequencies were examined for categorical variables. A bivariate correlation matrix was created to assess the strengths of relationships between respective pain variables and both functional outcomes. Variance inflation factors (VIF) were examined to detect instances of multicollinearity.

Two multiple linear regression models were initially used to examine adjusted associations between MeP and both the LLFDI and TUG. These regression models included 7 independent variables: age, sex, BMI, LBP duration, MPQ-PRI, composite LBP intensity, and MeP. The normality assumption was examined by the Shapiro-Wilk and Kolmogorov–Smirnov tests, while the homoscedasticity assumption was evaluated with White’s test. The LLFDI and TUG models both violated the normality assumption. To address normality violations, robust regression with HC3 standard errors⁵¹ was used to test associations between aggregated post-test MeP and both the LLFDI and TUG, while adjusting for covariates. Adjusted R² values were examined to determine model fit.

RESULTS

Descriptive statistics of baseline participant characteristics are presented in Table 1. Our cohort was 69.7±6.8 years old on average with slightly more females (51.2%) than males. Participants’ reported having LBP for an average 5.7 years (SD=7.7), with mild-to-moderate composite LBP intensities on average (M=3.1, SD=1.5). After completing RCR, SCT and 6MWT tests, participants’ MeP ratings ranged from 0-25 with a mean of 5.09 (SD=5.4; see distribution in Figure 2). MeP data was unavailable for 20 participants from the original cohort for several reasons: inability to finish the test, safety concerns, or refusal to complete the test. Of the available data (n=230), 187 participants endorsed MeP ratings ≥1. Average LLFDI overall function (M=58.0, SD=8.9) and TUG (M=10.5, SD=2.9) scores in this cohort are comparable to prior investigations in older adults.^52-54

Table 1:

Baseline participant characteristics

Variable	n	Mean±SD or n(%)
Age (y)	250	69.7±6.8
Sex (female)	250	128 (51.2%)
Race (Caucasian)	249	213 (85.2%)
Education (graduated college or more)	250	146 (58.4%)
Occupation Status (retired)	249	161 (64.7%)
BMI (kg/m2)	248	29.4±5.7
LBP onset (years)	250	5.7±7.7
MPQ-PRI (0-78)	248	16.7±11.2
Composite LBP Intensity (0-10)	250	3.1±1.5
Aggregated Post-Test MeP (0-30)	230	5.9±5.4
LLFDI: Overall Function (0-100)	245	58.0±8.9
TUG (s)	250	10.5±2.9

Abbreviations: BMI = body mass index; LBP = low back pain; LLFDI = Late Life Function and Disability Index; MeP = Movement-Evoked Pain; MPQ-PRI = McGill Pain Questionnaire Pain Rating Index; TUG = Timed Up-and-Go Test

Figure 2:

Frequency distribution of movement-evoked pain ratings

Table 2 displays bivariate correlations. MeP was positively correlated with composite LBP intensity (r=0.550, p<0.01) and pain quality (r=0.354, p<0.01), but not LBP duration (p>0.05). Pain quality, composite LBP intensity and MeP were negatively correlated with the LLFDI overall function score (all p<0.01); of these variables, MeP had the strongest negative correlation with the LLFDI (r=−0.337). Composite LBP intensity (r=0.20) and MeP (r=0.20) were positively correlated with performance on the TUG (both p<0.01). Age, sex and BMI also had negative correlations with the LLFDI (r between −0.144 and −0.319, all p<0.01) and positive correlations with the TUG (r between 0.106 and 2.40, all p<0.05). LBP duration was not correlated with either of the primary outcome measures (p>0.05).

Table 2:

Pearson correlations (r) between movement-evoked pain, pain characteristics, demographics, and self-perceived and performance-based function

	Age	Sex	BMI	LBP Duration	MPQ- PRI	Composite LBP Intensity	MeP	LLFDI	TUG
Age	1
Sex	−0.091	1
BMI	−0.023	−0.096	1
LBP Duration	−0.060	−0.056	0.144*	1
MPQ-PRI	−0.151*	0.098	0.195**	−0.081	1
Composite LBP	−0.082	0.101	0.111	0.003	0.368**	1
MeP	−0.073	0.165**	0.029	−0.087	0.354**	0.550**	1
LLFDI	−0.144*	−0.216**	−0.319**	0.034	−0.276**	−0.306**	−0.337**	1
TUG	0.240**	0.106*	0.182**	0.017	0.081	0.200**	0.203**	−0.471**	1

Abbreviations: BMI = body mass index; LBP = low back pain; LLFDI = Late Life Function and Disability Index; MeP = Movement-Evoked Pain; MPQ-PRI = McGill Pain Questionnaire Pain Rating Index; TUG = Timed Up-and-Go Test

^*p<0.050

^**p<0.010

Note: sex correlation coefficients from Kendall’s tau

Multicollinearity was not present among regression model inputs (all VIFs between 1.037 and 1.531). Table 3 contains robust regression model output for adjusted associations between the MeP and the LLFDI. The model accounted for 37.1% of the variance in LLFDI score (F(7,214)=18.01, p<0.001, _adjR²=0.350). Greater MeP was independently associated with reduced LLFDI scores (b=−0.30, t=−2.81, p=0.005). Neither pain quality nor composite LBP intensity were associated with the LLFDI (p=0.072 and p=0.073, respectively). Increased age (b=−0.24, t=−3.14, p=0.002), BMI (b=−0.56, t=−7.12, p<0.001), and being female (b=4.75, t=4.88, p<0.001), were associated with worse LLFDI scores.

Table 3:

Robust regression output for associations with the Late Life Function and Disability Index Scaled Overall Function Score

Variable	b	Standard Error	t-statistic	p-value
Age	−0.239	0.076	−3.138	0.002**
Sex	4.754	0.975	4.875	<0.001**
BMI	−0.557	0.078	−7.115	<0.001**
LBP Duration	0.049	0.072	0.679	0.498
MPQ-PRI	−0.098	0.054	−1.808	0.072
Composite LBP Intensity	−0.713	0.395	−1.803	0.073
Aggregated Post-Test MeP	−0.300	0.107	−2.811	0.005**

Abbreviations: BMI = body mass index; LBP = low back pain; LLFDI = Late Life Function and Disability Index; MeP = Movement-Evoked Pain; MPQ-PRI = McGill Pain Questionnaire Pain Rating Index; TUG = Timed Up-and-Go Test

^*p<0.050

^**p<0.010

Robust regression model output for adjusted associations between MeP and performance on the TUG is presented in Table 4. The model accounted for 18.8% of the variance in TUG performance (F(7,219)=7.26, p<0.001, _adjR²=0.162). Greater MeP was independently associated with worse performance on the TUG (b=0.081, t=2.35, p=0.020). Pain quality and composite LBP intensity were not significantly associated with TUG performance (p=0.488 and p=0.596, respectively). Similar to the LLFDI, increased age (b=0.11, t=4.35, p<0.001), higher BMI (b=0.063, t=2.15, p=0.033) and being female (b=−0.673, t=−2.33, p=0.021) were associated with poorer performance on the TUG.

Table 4:

Robust regression output for associations with the Timed Up-and-Go Test

Variable	b	Standard Error	t-statistic	p-value
Age	0.114	0.026	4.347	<0.001**
Sex	−0.673	0.289	−2.326	0.021*
BMI	0.063	0.029	2.150	0.033*
LBP Duration	−0.008	0.018	−0.452	0.651
MPQ-PRI	0.011	0.015	0.695	0.488
Composite LBP Intensity	−0.064	0.122	−0.530	0.596
Aggregated Post-Test MeP	0.081	0.034	2.346	0.020*

Abbreviations: BMI = body mass index; LBP = low back pain; LLFDI = Late Life Function and Disability Index; MeP = Movement-Evoked Pain; MPQ-PRI = McGill Pain Questionnaire Pain Rating Index; TUG = Timed Up-and-Go Test

^*p<0.050

^**p<0.010

DISCUSSION

This study is the first to operationally define MeP as an aggregate of post-test pain evoked across several different standardized physical performance tasks in a cohort of older adults with CLBP. Further, this investigation is novel because we evaluated how aggregated MeP contributed to a general measure of self-reported function as well as a performance-based task that was not included in MeP calculations. Greater MeP was associated with poorer self-reported and performance-based function, independent of covariates including composite LBP intensity and pain quality. Notably, composite LBP intensity and pain quality were not associated with either primary outcome measure. This evidence establishes that MeP uniquely affects perceived functional level and discrete functional tasks outside of the context in which pain was elicited. Therefore, MeP is a distinct component of the chronic pain experience that is associated with disability in this patient population. These results provide several points of insight regarding aggregated post-test MeP in older adults with CLBP.

Novel MeP Paradigm

The heterogeneity of MeP assessments has hindered efforts to standardize this outcome measure.^13,16 MeP methodology can be expanded by using standardized tests of physical function to elicit pain; this approach allows for the measurement of dynamic pain behavior while simultaneously providing prognostic information.^13,16 We utilized reliable and valid measures of transitional mobility (RCR and SCT) and walking endurance (6MWT) given their potential to characterize the compound nature of pain in our cohort; 81.3% of participants (n=230) endorsed post-test LBP intensity ratings ≥1, suggesting that our approach successfully elicited MeP. Compared to the use of a composite score for MeP (i.e., average post-test LBP across tasks), our approach has several practical advantages. The use of an aggregate score simplifies the interpretation of beta coefficients; the results can be interpreted based on 1-unit increases in post-test LBP as opposed to 1-unit increases in average post-test LBP. Further, our aggregate measure captures cumulative load of post-test LBP; the wider range of possible ratings increases the likelihood that our aggregate measure of MeP will have a greater sensitivity to change than a mean of post-test LBP ratings that is constrained between 0-10. Our methodology could serve as a blueprint for the evaluation of MeP in other persistent musculoskeletal conditions that may experience pain exacerbations during multifaceted tests of physical function, such as hip and knee osteoarthritis.

Traditional MeP calculation methods often employ delta scores that are derived from a unimodal functional task. In the context of MeP, delta scores rely on the assumption that pain will consistently summate or diminish throughout a particular task. Given that pain behavior is variable in older adults,^55,56 and underlying contributors to CLBP symptoms vary across older adults,^22,23 delta scores may mischaracterize nuanced pain behavior; thus, traditional MeP calculations may lack construct validity and generalizability among older adults with CLBP. In turn, our operationalization of MeP with post-test pain ratings demonstrated construct validity by discriminating varying degrees of MeP in our cohort. Further, our MeP paradigm is externally and ecologically valid since it was derived from performance-based tests that resemble everyday functional tasks. Thus, the aggregation of post-test pain ratings may be a feasible and useful method to evaluate MeP in other geriatric chronic pain syndromes. Future studies should seek to establish condition-specific test-retest reliability of aggregated post-test pain ratings.

MeP and Measures of Function

MeP was negatively associated with overall self-reported function and transitional mobility in older adults with CLBP independent of covariates that have previously been shown to affect physical function: spontaneous pain intensity, pain quality, sex, BMI and age.^57-61 This finding suggests that MeP is related to downstream health outcomes given that poorer LLFDI ratings and worse performance on the TUG are predictive of future disability and adverse health outcomes in older adults.^50,62,63 Further, the impact of MeP can be contextualized relative to minimal clinically important difference (MCID) values for the LLFDI and TUG. Increases in MeP of 7 and 17 would yield small (MCID = 2 points) and substantial (MCID = 5 points) declines in self-reported function, respectively.⁶⁴ Similarly, increases in MeP of 10 would yield clinically worse transitional mobility performance on the TUG (MCID = 0.8 seconds).⁶⁵ Given that MeP ratings ranged from 0-25 in our participants, it is entirely possible for MeP to exert clinically relevant negative effects on self-reported and performance-based function in older adults with CLBP. Finally, MeP was more strongly associated with perception-based function compared to performance-based function; as such, future studies should evaluate the ability of psychological interventions (e.g., cognitive-behavioral therapy) to reframe perceptions of pain and disability surrounding movement in this patient population. ^66,67

To date, it is unclear how MeP translates into worse physical function. Literature has established that CLBP is associated with reduced trunk muscle integrity due to fat infiltration,^68,69 altered spine and lower extremity kinematics during functional movements,^70,71 and neuromuscular activation deficits.^72-77 Poorer performance on functional tasks may then be due to long-standing consequences of pain (i.e., poor muscle composition) or real-time fluctuations in pain that could alter movement patterns or hinder neuromuscular activation. In addition to neuromuscular impairments, acute-on-chronic pain exacerbation has been shown to decrease energetic efficiency during ambulation in older adults with CLBP and radiculopathy.⁷⁸ Therefore, the effect of MeP on physical function may stem from impairments in multiple body systems in older adults with CLBP; further evidence is required to elucidate the relative contribution of these mechanisms.

Pain Theories

Further experimental investigation is required to determine how peripheral and central pain mechanisms contribute to MeP exacerbations. In the absence of experimental evidence, however, we will explore the theoretical implications of possible peripheral and central pain mechanisms below.

In the context of CLBP, heightened pain during lower extremity functional tasks may originate from a myriad of peripheral mechanisms. The RCR, SCT and 6MWT each involve lumbopelvic motion as well as varying levels of muscular effort and spinal loading^79-83; thus, pain could plausibly arise from muscular, arthrogenic, discogenic, or neurogenic origins. Muscular, arthrogenic, and discogenic pain exacerbations may be the result of increases in proinflammatory mediators and neuropeptides.^84-86 Neurogenic pain may worsen as a result of repetitive lumbar extension during transitional mobility or ambulatory tasks, which reduces space in the spinal canal and/or intervertebral foramina.⁸⁷ Further experimental investigation is required to disentangle the influence of peripheral pain mechanisms on MeP.

Pain-related fear and central sensitization are two centrally-mediated pathways that could influence MeP. Though pain-related fear was not included in this investigation, prior literature in middle-aged adults with CLBP suggests that fear of movement may impact measures of MeP derived from a graded lifting task.⁸⁸ Given that our paradigm utilized salient tasks to elicit MeP, and older adults tend to have lower levels of kinesiophobia and pain catastrophizing than middle-aged adults,^89,90 the association between pain-related fear and MeP may have been attenuated in our cohort. Nevertheless, further investigation is required in older adults to assess how fear of movement (and other pain-related fear constructs) may influence MeP. Regarding central sensitization, prior evidence has correlated MeP with temporal summation of mechanical pain in adults with CLBP⁹¹ as well as temporal summation and aftersensations of heat pain in adults with persistent LBP.⁹² Given that 43 participants in our cohort did not experience MeP during functional testing, MeP may be indicative of group differences in pain processing. To better elucidate centrally-mediated mechanisms of MeP, experimental pain testing should be collected in parallel with MeP measurements in this patient population.

Strengths and Limitations

Our results should be viewed in the context of study limitations. The study was cross-sectional and observational in nature, so causal claims cannot be made about the association between MeP and decreased self-reported and performance-based physical function. Further, investigation of MeP was not a primary aim of the parent study, thereby constraining the experimental design of this secondary analysis. The TUG was administered after the RCR but before the SCT and 6MWT; this sequencing may have detracted from TUG performance and inflated subsequent post-test LBP measurements. Thus, our findings should be cautiously interpreted, such that participants who demonstrate a higher propensity for MeP across different functional contexts may be prone to decreased physical function. In order to more directly evaluate if aggregated post-test LBP ratings affect physical function, future research in this area should measure the functional outcome of interest after MeP has been elicited with chair rise, stair climbing, and walking tasks. Other potential limitations of our design were the lack of measuring durations of individualized rest periods and situational pain catastrophizing, which is a salient measure of psychological distress specific to physical performance tasks. Variations in rest times and situational pain catastrophizing may have differentially influenced the magnitude of MeP or physical performance across participants; thus, we recommend that future studies treat rest periods and situational pain catastrophizing as a priori covariates. Finally, our cohort had relatively mild pain and moderate functional characteristics, which may lessen the generalizability of our findings to more pain-stricken or disabled CLBP populations. This limitation may bias our findings towards the null, though, since individuals with more severe CLBP may be more susceptible to the pathway between MeP and poorer physical function. Despite the limitations, our study represents a first step towards standardizing a methodology to elicit MeP with validated physical function tests in older adults with CLBP.

Our study also has substantial strengths that should be considered. First, our study has a large sample size relative to other MeP literature.¹⁶ In addition, our measure of MeP was derived from three complementary tests of physical function; the use of standardized tests enhances the generalizability, reproducibility, and prognostic capability of this MeP methodology. Our study also addressed a knowledge gap by establishing that the influence of MeP is not restricted to specific contexts; rather, MeP during one activity may detract from performance on a discrete activity. Therefore, our aggregate post-test MeP paradigm warrants future study to investigate its relationship with other pain, physical function, and psychological correlates.

CONCLUSION

Aggregated post-test MeP was independently associated with worse overall self-reported and performance-based function. MeP appears to be distinct from both pain quality and composite LBP intensity, suggesting that MeP may be a unique dimension of the chronic pain experience that is more strongly associated with disability. Further investigation is required to uncover peripheral and central pain mechanisms that underlie MeP in this patient population. Regarding our paradigm, multifaceted tests of physical function elicited MeP in the majority of our cohort of older adults with CLBP; as such, this MeP methodology may be applicable across other axial or lower extremity geriatric pain syndromes. Altogether, development and standardization of a functionally relevant MeP paradigm has the potential to improve assessment and treatment of the highly-vulnerable population of older adults with CLBP.