Through the Lens of Movement-Evoked Pain: A Theoretical Framework of the "Pain-Movement Interface" to Guide Research and Clinical Care for Musculoskeletal Pain Conditions

Over 120 million Americans report experiencing pain in the past 3 months. Among these individuals, 50 million report chronic pain and 17 million report pain that limits daily life or work activities on most days (ie, high-impact chronic pain). Musculoskeletal pain conditions in particular are a major contributor to global disability, health care costs, and poor quality of life. Movement-evoked pain (MEP) is an important and distinct component of the musculoskeletal pain experience and represents an emerging area of study in pain and rehabilitation fields. This focus article proposes the "Pain-Movement Interface" as a theoretical framework of MEP that highlights the interface between MEP, pain interference, and activity engagement. The goal of the framework is to expand knowledge about MEP by guiding scientific inquiry into MEP-specific pathways to disability, high-risk clinical phenotypes, and underlying individual influences that may serve as treatment targets. This framework reinforces the dynamic nature of MEP within the context of activity engagement, participation in life and social roles, and the broader pain experience. Recommendations for MEP evaluation, encompassing the spectrum from high standardization to high patient specificity, and MEP-targeted treatments are provided. Overall, the proposed framework and recommendations reflect the current state of science in this emerging area of study and are intended to support future efforts to optimize musculoskeletal pain management and enhance patient outcomes. PERSPECTIVE: Movement-evoked pain (MEP) is a distinct component of the musculoskeletal pain experience and emerging research area. This article introduces the "Pain-Movement Interface" as a theoretical framework of MEP, highlighting the interface between MEP, pain interference, and activity engagement. Evaluating and treating MEP could improve rehabilitation approaches and enhance patient outcomes.

Admission Cognition and Function Predict Change in Physical Function Following Skilled Nursing Rehabilitation

OBJECTIVES

Many older adults are discharged from skilled nursing facilities (SNFs) at functional levels below those needed for safe, independent home and community mobility. There is limited evidence explaining this insufficient recovery. The purpose of this secondary analysis was to determine predictors of physical function change following SNF rehabilitation.

DESIGN

Secondary analysis of a prospective observational cohort study.

SETTING AND PARTICIPANTS

Across 4 SNFs, data were collected from 698 adults admitted for physical rehabilitation following an acute hospitalization.

METHODS

Physical function recovery was evaluated as change from admission to discharge in Short Physical Performance Battery (SPPB) scores (N = 698) and gait speed (n = 444). Demographic and clinical characteristics collected at admission served as potential predictors of physical function change. Following imputation, a standardized model selection estimator was calculated for predictors per physical function outcome. Predictor estimates and 95% CIs were calculated for each outcome model.

RESULTS

Higher cognitive scores [standardized β (βSTD) = 0.11, 95% CI: 0.0004, 0.20] and higher activities of daily living (ADL) independence at admission (βSTD = 0.22, 95% CI: 0.05, 0.34) predicted greater SPPB change; higher SPPB scores at admission (βSTD = -0.26, 95% CI: -0.35, -0.14) predicted smaller SPPB change. Higher ADL independence at admission (βSTD = 0.17, 95% CI: 0.01, 0.37) predicted greater gait speed change; faster gait speed at admission (βSTD = -0.30, 95% CI: -0.44, -0.15) predicted smaller gait speed change.

CONCLUSIONS AND IMPLICATIONS

Admission cognition, ADL independence, and physical function predicted physical function change following post-hospitalization rehabilitation. Inverse findings for admission physical function and ADL independence predictors suggest independence with ADL is not necessarily aligned with mobility-related function. Findings highlight that functional recovery is multifactorial and requires comprehensive assessment throughout SNF rehabilitation.

High-intensity home health physical therapy among older adult Veterans: A randomized controlled trial

BACKGROUND

Older adult Veterans are at high risk for adverse health outcomes following hospitalization. Since physical function is one of the largest potentially modifiable risk factors for adverse health outcomes, our purpose was to determine if progressive, high-intensity resistance training in home health physical therapy (PT) improves physical function in Veterans more than standardized home health PT and to determine if the high-intensity program was comparably safe, defined as having a similar number of adverse events.

METHODS

We enrolled Veterans and their spouses during an acute hospitalization who were recommended to receive home health care on discharge because of physical deconditioning. We excluded individuals who had contraindications to high-intensity resistance training. A total of 150 participants were randomized 1:1 to either (1) a progressive, high-intensity (PHIT) PT intervention or (2) a standardized PT intervention (comparison group). All participants in both groups were assigned to receive 12 visits (3 visits/week over 30 days) in their home. The primary outcome was gait speed at 60 days. Secondary outcomes included adverse events (rehospitalizations, emergency department visits, falls and deaths after 30 and 60-days), gait speed, Modified Physical Performance Test, Timed Up-and-Go, Short Physical Performance Battery, muscle strength, Life-Space Mobility assessment, Veterans RAND 12-item Health Survey, Saint Louis University Mental Status exam, and step counts at 30, 60, 90, 180 days post-randomization.

RESULTS

There were no differences between groups in gait speed at 60 days, and no significant differences in adverse events between groups at either time point. Similarly, physical performance measures and patient reported outcomes were not different at any time point. Notably, participants in both groups experienced increases in gait speed that met or exceeded established clinically important thresholds.

CONCLUSIONS

Among older adult Veterans with hospital-associated deconditioning and multimorbidity, high-intensity home health PT was safe and effective in improving physical function, but not found to be more effective than a standardized PT program.

Advancing Rehabilitation Paradigms for Older Adults in Skilled Nursing Facilities: An Effectiveness-Implementation Hybrid Type 1 Clinical Trial Protocol

OBJECTIVE

Skilled nursing facility rehabilitation is commonly required to address hospital-associated deconditioning among older adults with medical complexity. In skilled nursing facilities, standard-of-care rehabilitation focuses on low-intensity interventions, which are not designed to sufficiently challenge skeletal muscle and impart functional improvements. In contrast, a high-intensity resistance training approach (IntenSive Therapeutic Rehabilitation for Older NursinG homE Residents; i-STRONGER) in a single-site pilot study resulted in better physical function among patients in skilled nursing facilities. To extend this work, an effectiveness-implementation hybrid type 1 design, cluster-randomized trial will be conducted to compare patient outcomes between 16 skilled nursing facilities utilizing i-STRONGER principles and 16 Usual Care sites.

METHODS

Clinicians at i-STRONGER sites will be trained to deliver i-STRONGER as a standard of care using an implementation package that includes a clinician training program. Clinicians at Usual Care sites will continue to provide usual care. Posttraining, changes in physical performance (eg, gait speed, Short Physical Performance Battery scores) from patients' admission to discharge will be collected over a period of 12 months. The Reach, Effectiveness, Adoption, Implementation, and Maintenance framework will be used to evaluate i-STRONGER effectiveness and factors underlying successful i-STRONGER implementation. Effectiveness will be evaluated by comparing changes in physical function between study arms. Reach (proportion of patients treated with i-STRONGER), adoption (proportion of clinicians utilizing i-STRONGER), implementation (i-STRONGER fidelity), and maintenance (i-STRONGER sustainment) will be concurrently quantified and informed by clinician surveys and focus groups.

IMPACT

This effectiveness-implementation hybrid type 1 cluster-randomized trial has the potential to shift rehabilitation care paradigms in a nationwide network of skilled nursing facilities, resulting in improved patient outcomes and functional independence. Furthermore, evaluation of the facilitators of, and barriers to, implementation of i-STRONGER in real-world clinical settings will critically inform future work evaluating and implementing best rehabilitation practices in skilled nursing facilities.

Low Risk for Persistent Back Pain Disability Is Characterized by Lower Pain Sensitivity and Higher Physical Performance

OBJECTIVE

The STarT Back Tool (SBT) predicts risk for persistent low back pain (LBP)-related disability based on psychological distress levels. Other non-psychological factors associated with LBP, such as pain sensitivity and physical performance, may further characterize SBT-risk subgroups. The purpose of this study was to determine whether a low-risk SBT subgroup demonstrated lower pain sensitivity and/or higher physical performance compared with a medium-/high-risk SBT subgroup.

METHODS

In this cross-sectional, secondary analysis, adults with LBP (N = 76) completed SBT and demographics (age, sex, race, chronicity) questionnaires. Participants underwent pain sensitivity (local and remote pressure pain thresholds, temporal summation, conditioned pain modulation) and physical performance (Back Performance Scale, walking speed, obstacle negotiation, Timed "Up & Go" [TUG], TUG Cognitive) testing. Independent samples t tests determined low- versus medium-/high-risk SBT subgroup differences. A follow-up discriminant function analysis was also conducted.

RESULTS

The medium-/high-risk subgroup demonstrated a lower proportion of participants with acute pain. The low-risk subgroup demonstrated lower pain sensitivity (higher local pressure pain thresholds and higher conditioned pain modulation) and higher physical performance (superior Back Performance Scale scores, faster walking speeds, faster obstacle approach and crossing speeds, and faster TUG completion). Discriminant function analysis results supported the 2-subgroup classification and indicated strong to moderate relationships with obstacle crossing speed, chronicity, and conditioned pain modulation.

CONCLUSION

Lower pain sensitivity and higher physical performance characterized the low-risk SBT subgroup and may represent additional LBP prognostic factors associated with persistent disability. Longitudinal studies are needed to confirm whether these factors can enhance SBT prediction accuracy and further direct treatment priorities.

IMPACT

Sensory and physical factors contribute to SBT risk classification, suggesting additional, non-psychological factors are indicative of favorable LBP outcomes. Findings highlight the need for assessment of multiple factors to improve LBP clinical prediction.

LAY SUMMARY

People at low risk for back pain disability have less sensitivity to pain and better physical performance. By measuring these factors, physical therapists could guide treatment and improve outcomes for people with back pain.

Rehabilitation with accurate adaptability walking tasks or steady state walking: A randomized clinical trial in adults post-stroke

OBJECTIVE

To assess changes in walking function and walking-related prefrontal cortical activity following two post-stroke rehabilitation interventions: an accurate adaptability (ACC) walking intervention and a steady state (SS) walking intervention.

DESIGN

Randomized, single blind, parallel group clinical trial.

SETTING

Hospital research setting.

SUBJECTS

Adults with chronic post-stroke hemiparesis and walking deficits.

INTERVENTIONS

ACC emphasized stepping accuracy and walking adaptability, while SS emphasized steady state, symmetrical stepping. Both included 36 sessions led by a licensed physical therapist. ACC walking tasks recruit cortical regions that increase corticospinal tract activation, while SS walking activates the corticospinal tract less intensely.

MAIN MEASURES

The primary functional outcome measure was preferred steady state walking speed. Prefrontal brain activity during walking was measured with functional near infrared spectroscopy to assess executive control demands. Assessments were conducted at baseline, post-intervention (three months), and follow-up (six months).

RESULTS

Thirty-eight participants were randomized to the study interventions (mean age 59.6 ± 9.1 years; mean months post-stroke 18.0 ± 10.5). Preferred walking speed increased from baseline to post-intervention by 0.13 ± 0.11 m/s in the ACC group and by 0.14 ± 0.13 m/s in the SS group. The Time × Group interaction was not statistically significant (P = 0.86). Prefrontal fNIRS during walking decreased from baseline to post-intervention, with a marginally larger effect in the ACC group (P = 0.05).

CONCLUSIONS

The ACC and SS interventions produced similar changes in walking function. fNIRS suggested a potential benefit of ACC training for reducing demand on prefrontal (executive) resources during walking.

Empirically derived back pain subgroups differentiated walking performance, pain, and disability

ABSTRACT

Low back pain (LBP) is a leading cause of disability. However, the processes contributing to disability are not well understood. Therefore, this study (1) empirically derived LBP subgroups and (2) validated these subgroups using walking performance, pain, and disability measures. Seventy adults with LBP underwent testing for a priori determined sensory (temporal summation; conditioned pain modulation), psychological (positive affect/coping; negative coping), and motor (trunk extensor muscle activation during forward bending and walking) measures. A hierarchical cluster analysis determined subgroups that were then validated using walking (walking speed; Timed Up and Go [TUG]; TUG-Cognitive [TUG-Cog]; obstacle negotiation) and clinical (Brief Pain Inventory; Oswestry Disability Index; low back pressure pain threshold) measures. Two subgroups were derived: (1) a "Maladaptive" subgroup (n = 21) characterized by low positive affect/coping, high negative coping, low pain modulation, and atypical trunk extensor activation and (2) an "Adaptive" subgroup (n = 49) characterized by high positive affect/coping, low negative coping, high pain modulation, and typical trunk extensor activation. There were subgroup differences on 7 of 12 validation measures. The Maladaptive subgroup had reduced walking performance (slower self-selected walking speed, TUG completion, and obstacle approach and crossing speed) and worse clinical presentation (higher pain intensity, pain interference, and disability) (moderate to large effect sizes; P's < 0.05). Findings support the construct validity of this multidimensional subgrouping approach. Longitudinal studies are needed to determine whether the Maladaptive subgroup is predictive of poor outcomes, such as pain chronicity or persistent disability.

Sensory and Psychological Factors Predict Exercise-Induced Shoulder Injury Responses in a High-Risk Phenotype Cohort

Our prior studies identified a high-risk phenotype (ie, high pain sensitivity variant of the catechol-O-methyltransferase gene (Single Nucleotide Polymorphism [SNP] rs6269) and pain catastrophizing scores) for shoulder pain. The current study identified sensory and psychological predictors of heightened pain responses following exercise-induced shoulder injury. Healthy participants (N = 131) with the SNP rs6269 catechol-O-methyltransferase gene and Pain Catastrophizing Scale scores ≥5 underwent baseline sensory and psychological testing followed by an established shoulder fatigue protocol, to induce muscle injury. Movement-evoked pain, pain intensity, disability, and strength were assessed 24 hours postinjury. Demographic, sensory, and psychological variables were included as predictors in full and parsimonious models for each outcome. The highest variance explained was for the shoulder disability outcome (full model R2 = .20, parsimonious R2 = .13). In parsimonious models, the individual predictors identified were: 1) 1st pulse heat pain sensitivity for isometric shoulder movement-evoked pain and pain intensity; 2) pressure pain threshold for shoulder disability; 3) fear of pain for active shoulder movement-evoked pain and shoulder disability; and 4) depressive symptoms for shoulder strength. Findings indicate specific pain sensitivity and psychological measures may have additional prognostic value for self-reported disability within a high-risk phenotype. These findings should be tested in a clinical cohort for validation. PERSPECTIVE: The current study extends previous work by providing insight regarding how poor shoulder outcomes may develop within a high-risk phenotype. Specifically, 1st pulse heat pain sensitivity and pressure pain threshold were sensory measures, and fear of pain and depressive symptoms were psychological measures, that improved prediction of different shoulder outcomes.

Psychometric Evaluation of the Optimal Screening for Prediction of Referral and Outcome Yellow Flag (OSPRO-YF) Tool: Factor Structure, Reliability, and Validity

Psychological characteristics consistently predict clinical outcomes for musculoskeletal pain conditions. The Optimal Screening for Prediction of Referral and Outcome Yellow Flag (OSPRO-YF) tool assesses negative mood, fear-avoidance, and positive affect/coping. Psychometric testing of the tool is needed to guide clinical use. The purpose of this secondary analysis was to determine the OSPRO-YF factor structure (17- and 10-item versions) and test factor reliability and concurrent validity. Data from 2 musculoskeletal pain cohorts (n1 = 428; n2 = 440) were used. An exploratory factor analysis (EFA) identified the factor structure in the first cohort; a confirmatory factor analysis (CFA) validated the factor structure in the second cohort. EFA yielded 4 factors for the 17-item version (catastrophizing, positive coping, negative mood, fear-avoidance) and 3 factors for the 10-item version (negative coping, negative mood positive affect/coping). CFA indicated good fit for the10-item and 17-item models. Factors from both versions demonstrated moderate to good test-retest reliability. Regression results revealed that factors from both versions contributed significantly to variance in pain intensity, disability, and quality of life. Results indicate the OSPRO-YF is a reliable and valid multidimensional psychological assessment tool for individuals with musculoskeletal pain. Future studies are needed to establish the OSPRO-YF as a prognostic and treatment monitoring tool. PERSPECTIVE: This article presents the psychometric properties of the OSPRO-YF tool. Findings indicate the OSPRO-YF is a reliable and valid multidimensional psychological assessment tool for individuals with musculoskeletal pain. Implementation of the OSPRO-YF tool may better guide clinical decision making and may lead to improved musculoskeletal pain management strategies.

Interpreting Prefrontal Recruitment During Walking After Stroke: Influence of Individual Differences in Mobility and Cognitive Function

Background: Functional near-infrared spectroscopy (fNIRS) is a valuable neuroimaging approach for studying cortical contributions to walking function. Recruitment of prefrontal cortex during walking has been a particular area of focus in the literature. The present study investigated whether task-related change in prefrontal recruitment measured by fNIRS is affected by individual differences in people post-stroke. The primary hypotheses were that poor mobility function would contribute to prefrontal over-recruitment during typical walking, and that poor cognitive function would contribute to a ceiling in prefrontal recruitment during dual-task walking (i.e., walking with a cognitive task). Methods: Thirty-three adults with chronic post-stroke hemiparesis performed three tasks: typical walking at preferred speed (Walk), serial-7 subtraction (Serial7), and walking combined with serial-7 subtraction (Dual-Task). Prefrontal recruitment was measured with fNIRS and quantified as the change in oxygenated hemoglobin concentration (ΔO2Hb) between resting and active periods for each task. Spatiotemporal gait parameters were measured on an electronic walkway. Stepwise regression was used to assess how prefrontal recruitment was affected by individual differences including age, sex, stroke region, injured hemisphere, stroke chronicity, 10-meter walking speed, balance confidence measured by Activities-specific Balance Confidence (ABC) Scale, sensorimotor impairment measured by Fugl-Meyer Assessment, and cognitive function measured by Mini-Mental State Examination (MMSE). Results: For Walk, poor balance confidence (ABC Scale score) significantly predicted greater prefrontal recruitment (ΔO2Hb; R 2 = 0.25, p = 0.003). For Dual-Task, poor cognitive function (MMSE score) significantly predicted lower prefrontal recruitment (ΔO2Hb; R 2 = 0.25, p = 0.002). Conclusions: Poor mobility function predicted higher prefrontal recruitment during typical walking, consistent with compensatory over-recruitment. Poor cognitive function predicted lower prefrontal recruitment during dual-task walking, consistent with a recruitment ceiling effect. These findings indicate that interpretation of prefrontal recruitment should carefully consider the characteristics of the person and demands of the task.

The impact of multisite pain on functional outcomes in older adults: biopsychosocial considerations

Multisite pain, or pain that occurs simultaneously at >1 anatomical site, is more prevalent than single-site pain. While multisite pain affects over half of older adults, it remains an understudied pain entity that may have important functional implications in an aging population. Greater understanding of this complex pain entity from a biopsychosocial perspective is critical for optimizing clinical and functional outcomes in older adults with pain. Therefore, the primary purpose of this review is to summarize the relationship between multisite pain and functional outcomes in older adults to further elucidate the impact of multisite pain as a distinct entity within this population. A comprehensive literature search revealed 17 peer-reviewed articles. Multisite pain in older individuals is associated with reductions in several physical function domains: 1) lower-extremity mobility; 2) upper-extremity impairments; 3) balance and increased fall risk; and 4) general disability and poor physical function. Further, multisite pain in older individuals is associated with psychological dysfunction (eg, anxiety and depressive symptoms) and social factors (eg, income and education). Overall, this review highlights the scant literature investigating the functional implications of multisite pain in an aging population. Further, while multisite pain appears to have functional consequences, the neurobiological mechanisms contributing to this relationship are unknown. Thus, how this pain characteristic may contribute to the variability in pain-related functional outcomes among older adults is not clear. Future investigations are strongly warranted to advance the understanding of multisite pain and its broad impact on physical and psychosocial function in older adults.

Prolonged Reduction in Shoulder Strength after Transcutaneous Electrical Nerve Stimulation Treatment of Exercise-Induced Acute Muscle Pain

OBJECTIVES

Transcutaneous electrical nerve stimulation (TENS) is commonly used for reducing musculoskeletal pain to improve function. However, peripheral nerve stimulation using TENS can alter muscle motor output. Few studies examine motor outcomes following TENS in a human pain model. Therefore, this study investigated the influence of TENS sensory stimulation primarily on motor output (strength) and secondarily on pain and disability following exercise-induced delayed-onset muscle soreness (DOMS).

METHODS

Thirty-six participants were randomized to a TENS treatment, TENS placebo, or control group after completing a standardized DOMS protocol. Measures included shoulder strength, pain, mechanical pain sensitivity, and disability. TENS treatment and TENS placebo groups received 90 minutes of active or sham treatment 24, 48, and 72 hours post-DOMS. All participants were assessed daily.

RESULTS

A repeated measures analysis of variance and post-hoc analysis indicated that, compared to the control group, strength remained reduced in the TENS treatment group (48 hours post-DOMS, P < 0.05) and TENS placebo group (48 hours post-DOMS, P < 0.05; 72 hours post-DOMS, P < 0.05). A mixed-linear modeling analysis was conducted to examine the strength (motor) change. Randomization group explained 5.6% of between-subject strength variance (P < 0.05). Independent of randomization group, pain explained 8.9% of within-subject strength variance and disability explained 3.3% of between-subject strength variance (both P < 0.05).

DISCUSSION

While active and placebo TENS resulted in prolonged strength inhibition, the results were nonsignificant for pain. Results indicated that higher pain and higher disability were independently related to decreased strength. Regardless of the impact on pain, TENS, or even the perception of TENS, may act as a nocebo for motor output.

Prefrontal over-activation during walking in people with mobility deficits: Interpretation and functional implications

BACKGROUND

Control of walking by the central nervous system includes contributions from executive control mechanisms, such as attention and motor planning resources. Executive control of walking can be estimated objectively by recording prefrontal cortical activity using functional near infrared spectroscopy (fNIRS).

OBJECTIVE

The primary objective of this study was to investigate group differences in prefrontal/executive control of walking among young adults, older adults, and adults post-stroke. Also assessed was the extent to which walking-related prefrontal activity fits existing cognitive frameworks of prefrontal over-activation.

METHODS

Participants included 24 adults post-stroke with moderate to severe walking deficits, 15 older adults with mild gait deficits, and 9 young healthy adults. Executive control of walking was quantified as oxygenated hemoglobin concentration in the prefrontal cortex measured by fNIRS. Three walking tasks were assessed: typical walking, walking over obstacles, and walking while performing a verbal fluency task. Walking performance was assessed by walking speed.

RESULTS

There was a significant effect of group for prefrontal activity (p < 0.001) during typical and obstacles walking tasks, with young adults exhibiting the lowest level of prefrontal activity, followed by older adults, and then adults post-stroke. In young adults the prefrontal activity during typical walking was much lower than for the verbal fluency dual-task, suggesting substantial remaining prefrontal resources during typical walking. However, in older and post-stroke adults these remaining resources were significantly less (p < 0.01). Cumulatively, these results are consistent with prefrontal over-activation in the older and stroke groups, which was accompanied by a steeper drop in walking speed as task complexity increased to include obstacles (p < 0.05).

CONCLUSIONS

There is a heightened use of prefrontal/executive control resources in older adults and post-stroke adults during walking. The level of prefrontal resource utilization, particularly during complex walking tasks like obstacle crossing, may approach the ceiling of available resources for people who have walking deficits. Prior cognitive research has revealed that prefrontal over-activation combined with limited prefrontal resources can lead to poor cognitive performance. The present study suggests a similar situation influences walking performance. Future research should further investigate the extent to which prefrontal over-activation during walking is linked to adverse mobility outcomes.