Exercise-induced Hypoalgesia in People With Knee Osteoarthritis With Normal and Abnormal Conditioned Pain Modulation

Validity of central pain processing biomarkers for predicting the occurrence of oncological chronic pain: a study protocol

BACKGROUND

Despite recent improvements in cancer detection and survival rates, managing cancer-related pain remains a significant challenge. Compared to neuropathic and inflammatory pain conditions, cancer pain mechanisms are poorly understood, despite pain being one of the most feared symptoms by cancer patients and significantly impairing their quality of life, daily activities, and social interactions. The objective of this work was to select a panel of biomarkers of central pain processing and modulation and assess their ability to predict chronic pain in patients with cancer using predictive artificial intelligence (AI) algorithms.

METHODS

We will perform a prospective longitudinal cohort, multicentric study involving 450 patients with a recent cancer diagnosis. These patients will undergo an in-person assessment at three different time points: pretreatment, 6 months, and 12 months after the first visit. All patients will be assessed through demographic and clinical questionnaires and self-report measures, quantitative sensory testing (QST), and electroencephalography (EEG) evaluations. We will select the variables that best predict the future occurrence of pain using a comprehensive approach that includes clinical, psychosocial, and neurophysiological variables.

DISCUSSION

This study aimed to provide evidence regarding the links between poor pain modulation mechanisms at precancer treatment in patients who will later develop chronic pain and to clarify the role of treatment modality (modulated by age, sex and type of cancer) on pain. As a final output, we expect to develop a predictive tool based on AI that can contribute to the anticipation of the future occurrence of pain and help in therapeutic decision making.

Exercise-induced hypoalgesia in chronic neck pain: A narrative review

Chronic neck pain (CNP) is a worldwide health problem with several risk factors. One of the most widely used treatments for managing this condition is therapeutic exercise, which could generate a response called exercise-induced hypoalgesia (EIH). There is no consensus on the best exercise modality to induce hypoalgesia. Therefore, this review aims to analyze and synthesize the state-of-the-art about the hypoalgesic effect of exercise in subjects with CNP. We included articles on EIH and CNP in patients older than 18 years, with pain for more than three months, where the EIH response was measured. Articles that studied CNP associated with comorbidities or measured the response to treatments other than exercise were excluded. The studies reviewed reported variable results. Exercise in healthy subjects has been shown to reduce indicators of pain sensitivity; however, in people with chronic pain, the response is variable. Some investigations reported adverse effects with increased pain intensity and decreased pain sensitivity, others found no clinical response, and some even reported EIH with decreased pain and increased sensitivity. EIH is an identifiable, stimulable, and helpful therapeutic response in people with pain. More research is still needed on subjects with CNP to clarify the protocols and therapeutic variables that facilitate the EIH phenomenon. In addition, it is necessary to deepen the knowledge of the intrinsic and extrinsic factors that influence EIH in people with CNP.

Subgrouping of facilitatory or inhibitory conditioned pain modulation responses in patients with chronic knee pain. Explorative analysis from a multicentre trial

BACKGROUND

Facilitatory and inhibitory conditioned pain modulation (CPM) responses are observed in healthy volunteers and chronic pain patients, but the clinical implications for phenotyping are unknown. This study aimed to subgroup and compare chronic knee pain patients according to their CPM responses.

METHODS

This explorative, cross-sectional study included 127 patients with chronic knee pain (osteoarthritis or following total knee arthroplasty). Individual CPM responses were categorized as facilitatory (test stimuli pain intensity increased when conditioning stimuli were applied), as inhibitory (test stimuli pain intensity decreased) or as no change (defined as less than 5.3% change in pain intensity). Outcomes were clinical pain intensities, temporal summation, widespread pain, self-reported physical function, PainDETECT questionnaire and Pain Quality Assessment Scale. Data were analysed as comparisons between the inhibitory and the facilitatory groups and using multivariate linear regression models.

RESULTS

Fifty-four patients had facilitatory CPM responses, 49 had inhibitory CPM responses, and 24 showed no change in CPM response. A between-group difference was observed for self-reported physical function, with the facilitatory CPM group reporting better function (54.4 vs. 46.0, p = 0.028) and the facilitatory CPM group reported more deep pain sensations (3.2 vs. 2.0, p = 0.021). The remaining outcomes showed no between-group differences. Higher clinical pain intensity and facilitated temporal summation were associated in the facilitated CPM group but not in the inhibitory CPM group.

CONCLUSION

These explorative findings indicated that quantitative clinical and experimental differences exist between facilitatory or inhibitory CPM responses in a chronic knee pain patient population. Differences in patients' CPM responses should be further investigated to unravel possible clinical importance.

SIGNIFICANCE

Our findings confirm that conditioned pain modulation consist of inhibitory and facilitatory responders among a patient population with chronic knee pain. This explorative study indicates that patients with either facilitatory or inhibitory conditioned pain modulation could exhibit differences in pain outcomes. Subgrouping of chronic pain patients depending on individual conditioned pain modulation responses could be considered in phenotyping patients prior to inclusion in clinical trials or used for personalizing the management regime.

Exercise-Induced Hypoalgesia in Patients with Chronic Whiplash-Associated Disorders: Differences between Subgroups Based on the Central Sensitization Inventory

BACKGROUND

Physical exercise is an important element in the rehabilitation of chronic whiplash-associated disorders, with the physiological process underlying pain reduction called exercise-induced hypoalgesia. In chronic whiplash-associated disorders, exercise-induced hypoalgesia appears impaired, and the research suggests a relationship with symptoms of dysfunctional nociceptive processing, such as central sensitization. This study improves our understanding of exercise-induced hypoalgesia in chronic whiplash-associated disorders by examining the differences between the extent of exercise-induced hypoalgesia in subgroups based on scores on the central sensitization inventory (CSI).

METHODS

Data were collected from 135 participants with chronic whiplash-associated disorders who completed a set of questionnaires. Pain pressure thresholds and temporal summations were assessed before and after a submaximal aerobic bicycle exercise test.

RESULTS

We observed no interaction effect between exercise-induced hypoalgesia and the CSI scores for both pain pressure threshold and temporal summation. No overall statistical effect was measured in the analysis of the effect of time. The pain pressure threshold significantly related to the CSI. The temporal summation showed no correlation.

CONCLUSIONS

During this study, we did not find evidence for a difference in the presence of exercise-induced hypoalgesia when the subgroups were created based on the central sensitization cluster calculator. Limited evidence was found for the influence of CSI scores on the delta pain pressure threshold.

Exercise therapy for knee osteoarthritis pain: how does it work? A study protocol for a randomised controlled trial

INTRODUCTION

Muscle strengthening training (MST) and behavioural graded activity (BGA) show comparable effects on knee osteoarthritic (KOA) pain, but the mechanisms of action remain unclear. Both exercise-induced anti-inflammation and central sensitisation are promising pathways for pain relief in response to exercise therapy in patients with KOA: MST has the potential to decrease inflammation and BGA has the potential to decrease central sensitisation. Hence, this study aims to examine inflammation and central sensitisation as mediators for the effect of MST and/or BGA on pain in patients with KOA.

METHODS AND ANALYSIS

The Knee OsteoArthritis PAIN trial started on 10 January 2020 (anticipated end: April 2024). The three-arm clinical trial aims to recruit 90 KOA patients who will be randomly allocated to 12 weeks of (1) MST, (2) BGA or (3) care as usual. Assessments will be performed at baseline, 13 and 52 weeks after finishing the intervention. Outcomes, including pain (Knee injury and Osteoarthritis Outcome Score), were chosen in line with the OARSI recommendations for clinical trials of rehabilitation interventions for OA and the IMMPACT/OMERACT recommendations for the assessment of physical function in chronic pain clinical trials. Inflammation as well as features of central sensitisation (including conditioned pain modulation, offset analgesia, temporal summation of pain and event-related potentials following electrical stimulation), will be considered as treatment mediators. A multiple mediators model will be estimated with a path-analysis using structural equation models. In July 2023, all 90 KOA patients have been included and 42 participants already finished the study.

ETHICS AND DISSEMINATION

This study obtained ethics approval (B.U.N. 143201941843). Unravelling the mechanisms of action of exercise therapy in KOA will not only be extremely valuable for researchers, but also for exercise immunology and pain scientists and clinicians.

TRIAL REGISTRATION NUMBER

NCT04362618.

Reliability and measurement error of exercise-induced hypoalgesia in pain-free adults and adults with musculoskeletal pain: A systematic review

OBJECTIVES

We systematically reviewed the reliability and measurement error of exercise-induced hypoalgesia (EIH) in pain-free adults and in adults with musculoskeletal (MSK) pain.

METHODS

We searched EMBASE, PUBMED, SCOPUS, CINAHL, and PSYCINFO from inception to November 2021 (updated in February 2024). In addition, manual searches of the grey literature were conducted in March 2022, September 2023, and February 2024. The inclusion criteria were as follows: adults - pain-free and with MSK pain - a single bout of exercise (any type) combined with experimental pre-post pain tests, and assessment of the reliability and/or measurement error of EIH. Two independent reviewers selected the studies, assessed their Risk of Bias (RoB) with the COnsensus-based Standards for the selection of health Measurement INstruments (COSMIN) RoB tool, and graded the individual results (COSMIN modified Grading of Recommendations Assessment, Development, and Evaluation).

RESULTS

We included five studies involving pain-free individuals (n = 168), which were deemed to have an overall "doubtful" RoB. No study including adults with MSK pain was found. The following ranges of parameters of reliability and measurement error of EIH were reported: intraclass correlation coefficients: 0-0.61; kappa: 0.01-0.46; standard error of measurement: 30.1-105 kPa and 10.4-21%; smallest detectable changes: 83.54-291.1 kPa and 28.83-58.21%.

CONCLUSIONS

We concluded, with a very low level of certainty, that the reliability and measurement error of EIH is, in pain-free adults, respectively, "insufficient" and "indeterminate." Future studies should focus on people with MSK pain and could consider using tailored exercises, other test modalities than pressure pain threshold, rater/assessor blinding, and strict control of the sources of variations (e.g., participants' expectations).

Are biomarkers associated with sensitivity to physical activity?

BACKGROUND

Activity-based treatments play an integral role in managing musculoskeletal conditions including low back pain. However, while therapeutic exercise has been shown to reduce pain in such conditions, certain individuals experience a paradoxical pain increase in response to exercise. The physiological processes underlying this sensitivity to physical activity (SPA) are not fully understood, however stress and inflammation have been shown to contribute to SPA. The present cross-sectional study investigated whether physiological indicators of stress (cortisol) and inflammation (IL-6) help explain SPA.

METHODS

Twenty-seven patients with chronic low back pain and 21 healthy controls completed a 1-h exercise session of standardized physical tasks. SPA was calculated from the difference between post- and pre-exercise pain levels. Participant's saliva was collected at several timepoints for cortisol and IL-6 levels quantification. Their waking cortisol response was calculated to reflect their cortisol regulation. Reactivity of IL-6 and cortisol was calculated to reflect changes in these measures during exercise.

RESULTS

IL-6 reactivity was significantly and positively correlated with SPA among participants with low back pain. In contrast, neither cortisol waking response nor cortisol reactivity was significantly correlated within the low back pain group. No significant differences in IL-6 reactivity, cortisol reactivity or cortisol waking response were observed.

CONCLUSION

These findings are the first to link SPA to an objective biomarker among people with low back pain. These findings help describe the physiological mechanisms of SPA and can support new clinical research that targets the inflammatory response of patients with chronic low-back pain and elevated SPA.

SIGNIFICANCE

This study reveals a correlation between SPA and an objective salivary biomarker of IL-6 in people with low back pain, improving our understanding of this clinically relevant subjective experience.

The effects of upper- vs. lower-body aerobic exercise on perceived pain in individuals with chronic knee pain: a randomised crossover trial

Background and objectives

Some patients with chronic knee pain experience an increase in knee pain following a single bout of exercise involving their knee joint, which can negatively affect exercise adherence and thus result in reduced overall health and lack of disease management. We want to determine whether a single bout of upper-body (UB) aerobic arm-ergometry exercise is effective in reducing the experience of pain in those with chronic knee pain compared with lower-body (LB) aerobic leg ergometry exercise.

Methods

A total of 19 individuals (women = 11, men = 8; age = 63 ± 8 years; body mass index = 24 ± 3 kg/m2) who suffered from chronic knee pain for ≥3 months took part in this study. Arm-ergometry and cycle-ergometry exercises were performed for 30 min at a moderate intensity, separated by 7 days. Pain intensity was assessed by means of a visual analogue scale (VAS) pre- and post-exercise and for 7 days post-exercise. Pressure pain threshold (PPT) and mechanical detection threshold (MDT) were measured pre- and post-exercise at both local and distal anatomical sites. Data are presented as mean ± SD.

Results

VAS pain was significantly reduced (p = 0.035) at 1 day post-exercise following the UB exercise trial (-1.4 ± 0.8) when compared with the LB exercise trial (+0.1 ± 2.1). Both UB and LB exercises were effective in reducing local and distal PPT. MDT responses were heterogeneous, and no differences between the UB and LB exercise conditions were noted.

Conclusion

An acute bout of upper-body aerobic arm-ergometry exercise evoked a significant decrease in the affected knee joint pain in individuals with chronic knee pain of up to 24 h/1 day post-exercise compared with lower-body aerobic exercise. While the exact mechanisms remain unclear, upper-body exercise may offer a viable, novel therapeutic treatment for patients with chronic knee pain.

Exercise-induced hypoalgesia with end-stage knee osteoarthritis during different blood flow restriction levels: Sham-controlled crossover study

BACKGROUND

Blood flow restriction (BFR) training could be a valuable treatment to induce exercise-induced hypoalgesia (EIH) in patients with end-stage knee osteoarthritis. However, the use of BFR in these patients is poorly explored and there is no evidence about the training dosage needed.

OBJECTIVE

To evaluate the effect of resistance training protocols with different occlusion levels of blood flow restriction (BFR) on EIH in patients with end-stage knee osteoarthritis.

DESIGN

Crossover study.

SETTING

University physical exercise laboratory.

PARTICIPANTS

26 adults with end-stage knee osteoarthritis.

INTERVENTIONS

Patients performed four sets (30, 15, 15, and 15 repetitions) separated by 1-minute rests of three protocols/sessions of low-load (30% one-repetition-maximum) seated knee extensions with elastic bands and BFR: placebo (sham BFR), BFR at 40% arterial occlusion pressure (AOP) and BFR at 80% AOP.

MAIN OUTCOME MEASURES

Pressure Pain Thresholds (PPT) and Visual Analog Scale (VAS) collected before, immediately after session, and after 10 minutes.

RESULTS

No differences in EIH were found between the different levels of BFR. However, 80% AOP protocol worsened VAS scores immediately (mean difference [MD]: -21.2 (95% confidence interval [CI] -33.9 to -8.5) while improving PPT immediately (MD affected limb: -.6 [95% CI -1.1 to -.2]); contralateral: -.6 (95% CI -1.0 to -.2]) and at 10 minutes (MD affected limb: -.6 [95% CI) -1.2 to -.1]; contralateral: -.7 [95% CI -1.1 to -.2]; and forearm: -.5 [95% CI -.9 to -.05]) post-exercise compared to baseline.

CONCLUSIONS

There is no EIH difference after using different occlusion levels. EIH is modulated by pain-related psychological constructs and self-perceived health status.

Effect of Voluntary Exercise on Endogenous Pain Control Systems and Post-traumatic Headache in Mice

Traumatic brain injury (TBI) can cause acute and chronic pain along with motor, cognitive, and emotional problems. Although the mechanisms are poorly understood, previous studies suggest disruptions in endogenous pain modulation may be involved. Voluntary exercise after a TBI has been shown to reduce some consequences of injury including cognitive impairment. We hypothesized, therefore, that voluntary exercise could augment endogenous pain control systems in a rodent model of TBI. For these studies, we used a closed-head impact procedure in male mice modeling mild TBI. We investigated the effect of voluntary exercise on TBI-induced hindpaw nociceptive sensitization, diffuse noxious inhibitory control failure, and periorbital sensitization after bright light stress, a model of post-traumatic headache. Furthermore, we investigated the effects of exercise on memory, circulating markers of brain injury, neuroinflammation, and spinal cord gene expression. We observed that exercise significantly reduced TBI-induced hindpaw allodynia and periorbital allodynia in the first week following TBI. We also showed that exercise improved the deficits associated with diffuse noxious inhibitory control and reduced bright light stress-induced allodynia up to 2 months after TBI. In addition, exercise preserved memory and reduced TBI-induced increases in spinal BDNF, CXCL1, CXCL2, and prodynorphin expression, all genes previously linked to TBI-induced nociceptive sensitization. Taken together, our observations suggest that voluntary exercise may reduce pain after TBI by reducing TBI-induced changes in nociceptive signaling and preserving endogenous pain control systems. PERSPECTIVE: This article evaluates the effects of exercise on pain-related behaviors in a preclinical model of traumatic brain injury (TBI). The findings show that exercise reduces nociceptive sensitization, loss of diffuse noxious inhibitory control, memory deficits, and spinal nociception-related gene expression after TBI. Exercise may reduce or prevent pain after TBI.

Psychophysical assessment of pain in adults with moderate and severe haemophilia: A cross-sectional study

BACKGROUND

Joint pain is the hallmark of haemophilia; therefore it seems clinically rather a musculoskeletal than a bleeding disorder. Although joint pain in people with haemophilia (PwH) is a complex and multidimensional problem, pain assessment remains primarily focused on the structural evaluation of their joints. Whereas, only few data are available on the potential implication of psychophysical and psychological factors.

OBJECTIVE

This study aimed to perform a psychophysical pain assessment including quantitative sensory testing (QST) and an evaluation of psychological factors in a large sample of PwH, to get insight into the individuals' pain system.

METHODS

Ninety-nine adults (36.9 ± 13.5 years) with moderate/severe haemophilia A/B and 46 healthy controls filled in self-reported pain and psychological questionnaires and underwent a QST evaluation including static and dynamic tests. Static tests focused on the determination of thermal detection and pain thresholds and mechanical pressure pain thresholds. Dynamic tests evaluated pain facilitation and the efficacy of endogenous pain inhibition. Besides comparing PwH and healthy controls, between-subgroup differences were studied in PwH based on their pain distribution.

RESULTS

The study revealed increased thermal and mechanical pain sensitivity and the presence of unhelpful psychological factors such as anxiety/depression in PwH. Among the subgroups, especially PwH with widespread pain showed altered somatosensory functioning. Enhanced pain facilitation and impaired efficacy of endogenous pain inhibition in PwH could not be observed.

CONCLUSION

Altered somatosensory functioning and unhelpful psychological factors, appear to play an important role in the pathophysiology of pain in PwH, especially in PwH with widespread pain.

Modulation of pain perceptions following treadmill running with different intensities in females

We aimed to compare the effects of three intensities of treadmill running on exercise-induced hypoalgesia (EIH) in healthy individuals. We anticipated that the primary and secondary changes in pain perception and modulation may differ between running intensities. Sixty-six women were randomly assigned to one of three treadmill running intensities for 35 min: 40% reserved heart rate (HRR), 55% HRR, or 70% HRR. The effects of EIH were assessed using pressure pain thresholds (PPT) and tolerance thresholds (PPTol). We measured conditional pain modulation (CPM). Compared with baseline, PPT and PPTol significantly increased in all groups during running and at the 5-10-min follow-up. The PPT and PPTol changes in the moderate- and low-intensity groups were significantly higher than those in the high-intensity group during running and 24 h after running, while the CPM responses of the high-intensity group were significantly reduced at the 24-h follow-up. Moderate- and low-intensity running may elicit significant primary and secondary (persisting over 24 h) EIH effects and increase CPM responses in females. However, high-intensity running induced only limited analgesic effects and reduced CPM responses, which may be attributed to the activation of endogenous pain modulation.

Central sensitization in adolescents with hypermobility spectrum disorder or hypermobile Ehlers-Danlos syndrome-a feasibility study

BACKGROUND

Pain is a major symptom in adolescents with hypermobility spectrum disorder or hypermobile Ehlers-Danlos syndrome. Although the underlying mechanism causing generalized pain in children with hypermobility spectrum disorder or hypermobile Ehlers-Danlos syndrome is unclear, central sensitization has been suggested as a possible explanation. The aim of this study was to explore the feasibility of a study protocol for a future case-control study, investigating features of central sensitization in adolescents with hypermobility spectrum disorder or hypermobile Ehlers-Danlos syndrome.

METHODS

Central sensitization features were measured in ten patients and nine healthy controls aged 13-17 years via experimental pain measurement quantifying primary and secondary hyperalgesia, endogenous pain modulation, and exercise-induced hyperalgesia. Descriptive statistics were used. Frequency, median, and range values were calculated.

RESULTS

Eleven out of 57 patients chose to participate. No control could be recruited through public schools. Therefore, a convenience sampling strategy was used for the recruitment of the control group. The process of assessing primary and secondary hyperalgesia, endogenous pain modulation, and exercise-induced hyperalgesia was well tolerated by all participants (patients and controls). When assessing endogenous pain modulation via conditioned pain modulation, two participants in the patient group and three in the control group did not achieve a pain experience ≥ 3 on the numerical rating scale when immersing their hands in cold water.

CONCLUSION

This study investigated the feasibility, safety, and toleration of experimental pain measurements in adolescents with hypermobility spectrum disorder or hypermobile Ehlers-Danlos syndrome. Although the test protocol proved to be sufficiently feasible for use with the participant group, it will need to be adapted in the main study in order to obtain more reliable data. Recruitment, especially of participants for the control group, can be a major obstacle for future studies and requires careful planning.

TRIAL REGISTRATION

Researchweb.org, 270,501. Registered on 9 May 2019.

Additive beneficial effects of aerobic training and royal jelly on hippocampal inflammation and function in experimental autoimmune encephalomyelitis rats

BACKGROUND

Although the beneficial role of training and the use of some antioxidants in physiological and psychological disorders in autoimmune diseases has been reported, the simultaneous effect of aerobic training (AT) and royal jelly (RJ) with different doses is not well understood. The present study aimed to investigate the impact of AT and RJ on inflammatory factors in the hippocampus, as well as depression and anxiety in the experimental autoimmune encephalomyelitis (EAE).

METHODS

Sprague-Dawley rats with EAE were assigned to seven groups: (1) EAE without any other intervention (EAE); (2) sham, receiving normal saline (Sh); (3) 50 mg/kg RJ (RJ50); (4) 100 mg/kg RJ (RJ100); (5) AT; (6) AT + RJ50; and (7) AT + RJ100. In addition, a healthy control group was assessed.

RESULTS

EAE significantly increased interleukin 17 (IL-17), transforming growth factor-β (TGF-β) gene expression and immobilization time as well as anxiety and depression indices, and significantly decreased interleukin 10 (IL-10), compared to the control group. AT decreased significantly IL-17, TGF-β gene expression and immobilization time as well as anxiety and depression indices, while it significantly increased IL-10, compared to the EAE group. RJ50 and RJ100 decreased significantly IL-17, IL-23 gene expression, anxiety and depression indices, and significantly increased IL-10 compared to the EAE group. AT + RJ50 and AT + RJ100 significantly decreased IL-17, IL-23, and TGF-β and as well as anxiety and depression indices while significantly increasing IL-10 compared to the EAE group. The effects of AT + RJ100 on significant decreasing IL-17, IL-23, anxiety and depression and increasing TGF-β, IL-10 were more favorable than RJ50.

CONCLUSION

AT and RJ improved inflammatory and regulatory factors of autoimmunity and reduced anxiety and depression. The RJ combined with AT induced additive effects while using RJ100 was more favorable than RJ50.

The autonomic and nociceptive response to acute exercise is impaired in people with knee osteoarthritis

Objectives

An acute bout of exercise typically leads to short term exercise induced hypoalgesia (EIH), but this response is more variable in many chronic pain populations, including knee osteoarthritis (OA) and fibromyalgia (FM). There is evidence of autonomic nervous system (ANS) dysfunction in some chronic pain populations that may contribute to impaired EIH, but this has not been investigated in people with knee OA. The aim of this study was to assess the acute effects of isometric exercise on the nociceptive and autonomic nervous systems in people with knee OA and FM, compared to pain-free controls.

Methods

A cross-sectional study was undertaken with 14 people with knee OA, 13 people with FM, and 15 pain free controls. Across two experimental sessions, baseline recordings and the response of the nociceptive and autonomic nervous systems to a 5-min submaximal isometric contraction of the quadriceps muscle was assessed. The nociceptive system was assessed using pressure pain thresholds at the knee and forearm. The ANS was assessed using high frequency heart rate variability, cardiac pre-ejection period, and electrodermal activity. Outcome measures were obtained before and during (ANS) or immediately after (nociceptive) the acute bout of exercise.

Results

Submaximal isometric exercise led to EIH in the control group. EIH was absent in both chronic pain groups. Both chronic pain groups showed lower vagal activity at rest. Furthermore, people with knee OA demonstrated reduced vagal withdrawal in response to acute isometric exercise compared to controls. Sympathetic reactivity was similar across groups.

Discussion

The findings of reduced tonic vagal activity and reduced autonomic modulation in response to isometric exercise raise the potential of a blunted ability to adapt to acute exercise stress and modulate nociception in people with knee OA. The impairment of EIH in knee OA may, in part, be due to ANS dysfunction.

Activity-related pain predicts pain and functional outcomes in people with knee osteoarthritis: A longitudinal study

Knee Osteoarthritis (OA) is a prevalent musculoskeletal condition, commonly resulting in pain and disability. However, pain and disability in this population are poorly related with the degree of structural joint damage. Underlying pain mechanisms, including activity-related pain and sensitization assessed via Quantitative Sensory Testing (QST), may better predict pain and functional outcomes of those with knee OA. Therefore, the aim of this study was to explore whether activity-related pain and sensitization assessed via QST predict future pain, function, fatigue, physical performance and quality of life outcomes in those living in the community with knee OA. Eighty-six participants with knee OA were recruited in Dunedin, New Zealand. Those eligible to participate underwent baseline testing including QST as well as measures of activity-related pain including Movement-evoked Pain (MEP) and Sensitivity to Physical Activity (SPA). Outcome measures exploring pain, function, fatigue and quality of life outcomes were collected at baseline, and two follow-up periods (two and nine weeks). Univariable linear regression models were developed followed by multivariable linear regression models for each prognostic marker adjusting for age, gender, BMI, OA duration, baseline pain intensity and socioeconomic status. Activity-related measures of pain, including MEP and SPA, demonstrated predictive associations with pain and functional outcomes prospectively in those with knee OA. Therefore, those demonstrating activity-related pain are at future risk of greater pain, disability and reduced quality of life. Larger, externally validated longitudinal studies are required which include individuals with more severe knee OA.

Protein Changes After 6 weeks of Walking and the Relationship to Pain in Adults with Knee Osteoarthritis

Background: Knee osteoarthritis (KOA) affects 22.9% of individuals over the age of 40 and causes significant pain and disability. Pain is the most prevalent and troublesome symptom of KOA leading patients to seek medical interventions for relief. Knee osteoarthritis pain has both peripheral and central mechanisms that vary by individual. Non-pharmacological pain management strategies such as walking is the first step in reducing KOA pain. However, initiation of a walking regime can induce knee pain for some and the mechanism by which habitual walking reduces KOA pain is unclear. Purpose: The purpose of this study was to use a discovery proteomics approach and quantitative sensory testing (QST) to determine the molecular changes that occur after habitual walking and their relationship to pain sensitivity. Research Design and Study Sample: We conducted a pre-test/post-test study using QST to measure neurophysiological parameters at the knee and contralateral forearm and examined platelet protein signatures before and after 6 weeks of walking 3 days per week for 30 minutes among six adults with KOA and six healthy controls. Results: Knee pain sensitivity did not change significantly after 6 weeks of walking among either KOA or healthy participants. However, forearm pressure pain sensitivity decreased for both groups after walking, indicating reduction in central pain pathways. Protein signatures showed downregulation of immune and inflammatory, pathways among KOA participants after walking which were upregulated in healthy controls. Conclusion: These differences may contribute differences in centralized pain thresholds seen between KOA and healthy participants.

Exercise-Induced Hypoalgesia Following Proprioceptive Neuromuscular Facilitation and Resistance Training Among Individuals With Shoulder Myofascial Pain: Randomized Controlled Trial

BACKGROUND

Various exercises can attenuate pain perception in healthy individuals and may interact with the descending pain modulation in the central nervous system. However, the analgesic effects of exercise in patients with myofascial pain can be disrupted by the pathological changes during chronic pain conditions. Thus, the exercises targeted on the facilitation of the sensory-motor interaction may have a positive impact on the restoration of the descending pain modulation and the analgesia effects.

OBJECTIVE

This paper estimates the effect of proprioceptive neuromuscular facilitation (PNF) and resistance training on exercise-induced hypoalgesia (EIH) and conditioned pain modulation (CPM) among patients with myofascial pain syndrome.

METHODS

A total of 76 female patients with myofascial pain syndrome (aged 18-30 years), with the pain in the upper trapezius and a visual analog scale score of greater than 30/100 mm, were enrolled in the study. Participants were randomly assigned into 3 intervention groups, including isometric (n=18, 24%), isotonic (n=19, 25%), and PNF (n=20, 26%) exercises, as well as 1 control group (n=19, 25%) with no intervention. Pressure pain threshold and the CPM responses at the myofascial trigger point, arm, and leg sites were assessed before and after the exercise session. The effective EIH response was reflected in the improvement of pressure pain thresholds.

RESULTS

There was an increase in pressure pain thresholds and CPM responses at trigger point (P<.001 and P<.001), arm (P<.001 and P<.001), and leg sites (P<.001 and P=.03) in participants who performed PNF and isotonic exercise, while the isometric exercise only increased pressure pain thresholds at leg sites (P=.03). Compared with the control group, both the isotonic (P=.02) and PNF (P<.001) groups showed greater EIH responses at the trigger points. In comparison to the control group, only the PNF exercise (P=.01) significantly improved pressure pain thresholds and CPM responses at arm and leg sites compared to the control group.

CONCLUSIONS

PNF, isotonic, and isometric exercises could lead to local and global EIH effects. The improvement in CPM response following PNF and isotonic exercises suggested that the EIH mechanisms of different resistance exercises may be attributed to the enhancement of the endogenous pain modulation via the motor-sensory interaction from the additional eccentric and dynamic muscle contraction.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCtr202111090819166165; https://tinyurl.com/2ab93p7n.

Is low intensity exercise sufficient to induce exercise-induced pain threshold modulation in people with persistent pain?

OBJECTIVES

We investigated whether a 12-min walk test (12MWT) yielded exercise-induced pain threshold modulation (EIPM) within people with persistent pain and whether baseline self-report and pain sensitivity measures differed according to these responses.

DESIGN

Cross-sectional study.

METHODS

Two cohorts (tertiary/community) (n = 88) with persistent pain underwent pressure pain threshold (PPT) testing before and after a 12MWT to determine exercise-induced pain threshold modulation responses. Baseline self-report (pain severity, pain distribution, psychological distress, sleep) and baseline widespread pain sensitivity (WPS) (high/low) were recorded. Within and between-group differences were analysed using paired t-tests and repeated measure analyses of covariance. Individual EIPM responses were categorised as hyperalgesic, no change and hypoalgesic responses. Differences in baseline self-report and pain sensitivity measures between EIPM categories were investigated.

RESULTS

No significant within- or between-group differences in PPT following the 12MWT were detected (p > 0.05). Individual responses showed that up to 30% of the community and 44% of the tertiary cohort demonstrated >20% change in PPT (in either direction). Significant differences were shown in pain distribution (p = 0.002) and baseline WPS (p = 0.001) between people with hyperalgesic, no change, hypoalgesic responses. People with 4-5 pain regions were more likely hyperalgesic (χ2 = 9.0, p = 0.003); people with low baseline WPS were more likely to demonstrate no change (p = 0.002).

CONCLUSION

Low or self-selected intensity exercise was insufficient to induce exercise-induced pain modulation at group level. Individual responses were variable with pain distribution and baseline WPS differing between responses. Future research could evaluate responses and associated factors in larger samples with high baseline pain sensitivity specifically.

Hypoalgesia after exercises with painful vs. non-painful muscles in healthy subjects - a randomized cross-over study

OBJECTIVES

Exercise-induced hypoalgesia (EIH) is a decrease in the pain sensitivity after exercise. Individuals with chronic pain show less EIH after one exercise session compared with pain-free individuals possibly due to pain in exercising muscles. The primary aim of this randomized controlled cross-over study was to compare the EIH response at the exercising thigh muscle following exercises performed with painful vs. non-painful muscles. Secondary aims were to explore if a reduced EIH response was confined to the painful muscle, and whether the muscle pain intensity and the EIH responses were negatively associated.

METHODS

In two sessions, 34 pain-free participants received a painful (hypertonic saline, 5.8%) injection and a control (isotonic saline, 0.9%) injection in the right thigh muscle before performing a 3 min isometric wall squat exercise. Pressure pain thresholds (PPTs) were assessed at both thighs and the left neck/shoulder at baseline, after injections and after exercise. Pain intensities in the thighs were rated on numerical rating scales (NRS: 0-10).

RESULTS

Hypertonic saline induced moderate thigh pain at rest (NRS: 4.6 ± 2.1) compared to the control injection (NRS: 0.3 ± 0.4; p<0.001). EIH at the thighs and neck/shoulder were not different between sessions (Injected thigh: 0 kPa; 95% CI: -51 to 52; Contralateral thigh: -6 kPa; 95% CI: -42 to 30; neck/shoulder: 19 kPa; 95% CI: -6 to 44). No significant associations between pain intensity ratings immediately after the Painful injection and EIH responses at any assessment sites were found (right thigh: β=0.08, 95% CI: -12.95 to 20.64, p=0.64, left thigh: β=-0.33, 95% CI: -27.86 to 0.44, p=0.06; neck/shoulder: β=-0.18, 95% CI: -15.11 to 4.96, p=0.31).

CONCLUSIONS

Pain in the area of an exercising muscle did not reduce local or systemic EIH responses.

TRIAL REGISTRATION NUMBER

NCT04354948.

Inflammatory and Immune Protein Pathways Possible Mechanisms for Pain Following Walking in Knee Osteoarthritis

BACKGROUND

Knee osteoarthritis affects nearly 30% of adults aged 60 years or older and causes significant pain and disability. Walking is considered a "gold standard" treatment option for reducing knee osteoarthritis pain and maintaining joint mobility but does not reduce pain for all adults with knee osteoarthritis pain and may induce pain-particularly when starting a walking routine. The mechanism by which walking is helpful for knee osteoarthritis pain is unclear. Quantitative sensory testing has revealed that knee osteoarthritis pain has both peripheral and central components, which vary by individual.

OBJECTIVE

The purpose of this study was to better understand the mechanisms underlying the value of walking for knee pain.

METHODS

We conducted a pretest/posttest study using quantitative sensory testing to measure neurophysiological parameters and examined systemic protein signatures. Adults with knee osteoarthritis and healthy controls underwent quantitative sensory testing and blood draw for platelet proteomics before and after a 30-minute walk at 100 steps per minute.

RESULTS

A single 30-minute walk moderately increased pressure pain sensitivity at the affected knee among persons with knee osteoarthritis. Healthy adults showed no difference in pain sensitivity. Protein signatures among participants with knee osteoarthritis indicated changes in inflammatory and immune pathways, including the complement system and SAA1 protein that coincided with changes in pain with walking and differed from healthy participants.

DISCUSSION

One goal of developing individualized interventions for knee osteoarthritis pain is to elucidate the mechanisms by which self-management interventions affect pain. The addition of therapies that target the complement system or SAA1 expression may improve the pain sensitivity after a moderate walk for adults with knee osteoarthritis.

Differences in Quantitative Sensory Testing Outcomes Between Patients With Low Back Pain in Primary Care and Pain-free Controls

OBJECTIVES

Quantitative Sensory Testing (QST) is used to test somatosensory functioning in on people with chronic LBP in secondary/tertiary health care facilities. Studies using QST-testing on LBP populations in primary care are scarce. Central Sensitization Inventory (CSI) measures central sensitization (CS)-related symptoms and studies investigating the differences between QST-testing and participants with LBP with a positive and negative score on the CSI questionnaire are also rare. This case-control study investigates differences of an extensive QST-measurement between patients with acute, chronic LBP, and pain-free controls (PFCs) in primary care. Secondary aim is to investigate differences of an extensive QST-measurement between "CS" and "no-CS" group.

MATERIALS AND METHODS

Participants with LBP were recruited from November 2016 to October 2019. Demographic and clinical information was collected and a standardized QST protocol was taken. Data analysis involved determining differences between groups.

RESULTS

Data of 100 participants with LBP and 50 PFCs were analyzed. Heat pain thresholds, pressure pain threshold, and conditioned pain modulation local and remote were significantly moderately to relatively strongly affected by acute, chronic LBP and PFCs (P<0.001 to 0.001). Lumbar temporal summation was significantly moderately affected by acute, chronic LBP, and PFCs (P=0.001). Only pressure pain threshold showed significant difference between "CS" and "no-CS" group (P=0.001 to 0.002).

DISCUSSION

Signs of enhanced nociceptive processing and disturbed top-down nociceptive modulation are apparent in people with acute and chronic LBP in primary care. Results indicate existence of central mechanisms in LBP in primary care.

Comparison between exercise therapy and non-hydrolyzed collagen (UC-II) in functionality and quality of life in women with knee osteoarthritis : A randomized controlled clinical trial

BACKGROUND

Knee osteoarthritis (OA) is characterized by a progressive degeneration of cartilage and menisci, leading to pain and locomotor disability. Here, we aimed to assess the effect of an exercise protocol and the oral use of non-hydrolyzed collagen (UC-II) on the functionality and quality of life of women with knee OA.

MATERIAL AND METHODS

Individuals were divided into three groups (CG [control group]; MG [medication group]; EG [exercise group]). In the CG there was no intervention, while MG received an oral dose (1 capsule/day) of UC-II and the EG held 12 sessions of an exercise protocol.

RESULTS

In the functionality tests (6-min walk test, 6MWT and timed up and go test [TUG]) the EG (p < 0.001/p = 0.020) and MG (p = 0.010/p = 0.010) revealed a significant improvement when compared to the CG. In the analysis of quality of life by WOMAC, a significant improvement was found only in the EG (p = 0.030) when compared to the CG; the same happened in the stiffness domain (EG, p = 0.010), despite in the pain domain, both the EG (p < 0.001) and the MG (p = 0.060) were better than the CG.

CONCLUSION

Data obtained here reveal that an exercise protocol and UC-II have similar effects for functionality, despite exercise being superior in promoting the quality of life score.

High Prevalence of Pain Sensitization in Knee Osteoarthritis: A Meta-Analysis with Meta-Regression

OBJECTIVE

The aim of this meta-analysis was to study the evidence on pain sensitization in knee osteoarthritis (OA), providing a quantitative synthesis of its prevalence and impact. Factors associated with pain sensitization were also investigated.

METHODS

Meta-analysis; PubMed (MEDLINE), Cochrane Central Register (CENTRAL), and Web of Science were searched on February 2021. Level I to level IV studies evaluating the presence of pain sensitization in patients with symptomatic knee OA, documented through a validated method (questionnaires or quantitative sensory testing), were included. The primary outcome was the prevalence of pain sensitization. Factors influencing the prevalence were also evaluated, as well as differences in terms of pain thresholds between knee OA patients and healthy controls.

RESULTS

Fifty-three articles including 7,117 patients were included. The meta-analysis of proportion documented a prevalence of pain sensitization of 20% (95% confidence interval [CI] = 16%-26%) with a significant heterogeneity of results (I² = 89%, P < 0.001). The diagnostic tool used was the main factor influencing the documented prevalence of pain sensitization (P = 0.01). Knee OA patients presented higher pain sensitivity compared with healthy controls, both in terms of local pressure pain threshold (standardized mean difference [SMD] = -1.00, 95% CI = -1.67 to -0.32, P = 0.007) and distant pressure pain threshold (SMD = -0.54, 95% CI = -0.76 to -0.31, P < 0.001).

CONCLUSIONS

Knee OA pain presents features that are consistent with a significant degree of pain sensitization. There is a high heterogeneity in the reported results, mainly based on the diagnostic tool used. The identification of the best methods to detect pain sensitization is warranted to correctly evaluate and manage symptoms of patients affected by knee OA.

REGISTRATION

PROSPERO CRD42019123347.

Effect of Neuromuscular Electrical Stimulation During Walking on Pain Sensitivity in Women With Obesity With Knee Pain: A Randomized Controlled Trial

OBJECTIVE

To assess the extent to which pain sensitivity is altered in women with obesity with frequent knee symptoms who walk with either a hybrid training system (HTS) that provides antagonist muscle electrical stimulation vs sensory transcutaneous electrical nerve stimulation (TENS).

DESIGN

Randomized, double-blinded, controlled trial.

SETTING

University-based fitness center.

PARTICIPANTS

Twenty-eight women (N=28) with obesity, aged 40-70 years, with daily knee symptoms.

INTERVENTIONS

Participants were randomized to 12 weeks of biweekly 30-minute walking exercise with either HTS (HTSW group) or sensory TENS (control group).

MAIN OUTCOME MEASURES

Pressure pain thresholds (PPTs) at the more symptomatic knee (local PPT) and PPT at the ipsilateral pain-free wrist (remote PPT).

RESULTS

After adjustment for preintervention values and body mass index (BMI), there was a statistically significant improvement in local PPT in the HTSW group compared with the control group (P=.039). After adjustment for pretraining value, age, and BMI, changes in remote PPT when comparing groups did not reach statistical significance, although the HTS group tended to demonstrate increased remote PPT (P=.052) compared with the control group. Moreover, after adjustment for pretraining value, knee pain, and quality of life, comparing groups did not reach statistical significance, although the HTS group tended to demonstrate decreased knee pain (P=.069) compared with the control group.

CONCLUSIONS

Augmentation of walking exercise with HTS was more effective than application of sensory TENS in improving local pain sensitivity at the knee but not at the wrist in women with obesity with frequent knee symptoms.

The effect of prolonged experimental neck pain on exercise-induced hypoalgesia

ABSTRACT

Neck pain is a common musculoskeletal problem often accompanied by reduced exercise-induced hypoalgesia (EIH) or hyperalgesia compared to an asymptomatic population. This study investigated EIH in a healthy population during experimental neck pain. Forty participants were randomized into this double-blinded parallel-group study. On four separate test days (Day0, Day2, Day4, Day15), participants completed the Neck Disability Index (NDI) and scored neck pain intensity during head movements on a numerical rating scale (NRS). At the end of Day0 and Day2, Nerve Growth Factor (NGF) or isotonic saline (control) was injected into the right splenius capitis muscle. Pressure pain thresholds (PPTs) were recorded bilaterally over splenius capitis (neck), temporalis (head) and tibialis anterior (leg) muscles on all days. On Day0, Day4 and Day15, PPTs were recorded before and after a hand-bike exercise. EIH was defined as the PPT increase caused by the exercise. Compared with the control-group, the NGF-group demonstrated higher NDI scores at Day2 and Day4 (P<0.001,η2>0.557) and higher NRS scores (P<0.03,η2>0.09) along with reduced neck PPTs (P<0.01,d>0.44) at Day2(Right:95%CI[26.0,54.0];Left:95%CI[6.8,26.9]), Day4(Right:95%CI[40.5, 67.9];Left:95%CI[6.9,28.2]) and Day15(Right:95%CI[5.6,37.2];Left:95%CI[6.9,34.8]). Across days, the EIH-effect was reduced at the neck site in the NGF-group compared to the control-group (P<0.001,η2P=0.367,95%CI[-34.5,-13.7]). At the head and leg sites, the NGF-group showed reduced EIH-effect compared to the control-group (P<0.05,d>0.43) on Day4(Head:95%CI[-61.4,-22.9];Leg:95%CI[-154.7,-72.4]) and Day15(Head:95%CI[-54.3,-7.6];Leg:95%CI[-122.7,-34.4]). These results indicate that a few days of clinically comparable neck pain and hyperalgesia might have a negative impact on EIH-responses and may help explain why some neck pain patients do not experience immediate positive effects of exercise.

Does aerobic exercise effect pain sensitisation in individuals with musculoskeletal pain? A systematic review

Background

Pain sensitisation plays a major role in musculoskeletal pain. However, effective treatments are limited, and although there is growing evidence that exercise may improve pain sensitisation, the amount and type of exercise remains unclear. This systematic review examines the evidence for an effect of aerobic exercise on pain sensitisation in musculoskeletal conditions.

Methods

Systematic searches of six electronic databases were conducted. Studies were included if they examined the relationship between aerobic physical activity and pain sensitisation in individuals with chronic musculoskeletal pain, but excluding specific patient subgroups such as fibromyalgia. Risk of bias was assessed using Cochrane methods and a qualitative analysis was conducted.

Results

Eleven studies (seven repeated measures studies and four clinical trials) of 590 participants were included. Eight studies had low to moderate risk of bias. All 11 studies found that aerobic exercise increased pressure pain thresholds or decreased pain ratings in those with musculoskeletal pain [median (minimum, maximum) improvement in pain sensitisation: 10.6% (2.2%, 24.1%)]. In these studies, the aerobic exercise involved walking or cycling, performed at a submaximal intensity but with incremental increases, for a 4-60 min duration. Improvement in pain sensitisation occurred after one session in the observational studies and after 2-12 weeks in the clinical trials.

Conclusions

These findings provide evidence that aerobic exercise reduces pain sensitisation in individuals with musculoskeletal pain. Further work is needed to determine whether this translates to improved patient outcomes, including reduced disability and greater quality of life.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05047-9.

Quantitative Sensory Testing Protocols to Evaluate Central and Peripheral Sensitization in Knee OA: A Scoping Review

OBJECTIVE

This scoping review analyzed various quantitative sensory testing methodologies used in the assessment of sensitization and how sensitization is defined in people with knee osteoarthritis.

DESIGN

A scoping review.

SETTING

All clinical and research settings.

SUBJECTS

Non-surgical adults with knee osteoarthritis.

METHODS

This scoping review was guided by existing scoping review methodologies. Relevant studies were extracted from the following electronic databases: Medical Literature Analysis and Retrieval System Online, Excerpta Medica Database, Allied and Complementary Medicine Database and the Cumulative Index to Nursing Allied Health Literature. Abstract and full article screening and data extraction were performed in pairs. Information on quantitative sensory testing techniques and parameters was extracted and summarized in tables. General and technique specific definitions of sensitization were extracted from included texts.

RESULTS

Our search yielded 4199 articles, of which 50 were included in our review. The most common quantitative sensory test was pressure pain threshold. In total 28 unique testing sites were found speaking to the high degree of variability between studies. Sensitization was poorly defined with only 8 studies fully operationalizing it, 22 partially, and the remainder did not provide sufficient information to meet our criteria.

CONCLUSION

This scoping review has provided an overview of the most common methods of quantitative sensory testing being implemented in the assessment of nervous system sensitization to nociceptive signaling in people with knee osteoarthritis. This study provides a foundation for future development of quantitative sensory testing methodology for research and clinical practice in the osteoarthritis population.

Endogenous Modulation of Pain: The Role of Exercise, Stress, and Cognitions in Humans

BACKGROUND

Pain is a complex and highly subjective phenomenon that can be modulated by several factors. On the basis of results from experimental and clinical studies, the existence of endogenous pain modulatory mechanisms that can increase or diminish the experience of pain is now accepted.

METHODS

In this narrative review, the pain modulatory effects of exercise, stress, and cognitions in humans are assessed.

RESULTS

Experimental studies on the effect of exercise have revealed that pain-free participants show a hypoalgesic response after exercise. However, in some patients with chronic pain, this response is reduced or even hyperalgesic in nature. These findings will be discussed from a mechanistic point of view. Stress is another modulator of the pain experience. Although acute stress may induce hypoalgesia, ongoing clinical stress has detrimental effects on pain in many patients with chronic pain conditions, which have implications for the understanding, assessment, and treatment of stress in patients with pain. Finally, cognitive strategies play differing roles in pain inhibition. Two intuitive strategies, thought suppression and focused distraction, will be reviewed as regards experimental, acute, and chronic pain.

CONCLUSION

On the basis of current knowledge on the role of exercise, stress, and cognitive pain control strategies on the modulation of pain, implications for treatment will be discussed.

The predictive value of quantitative sensory testing: a systematic review on chronic postoperative pain and the analgesic effect of pharmacological therapies in patients with chronic pain

Studies have suggested that quantitative sensory testing (QST) might hold a predictive value for the development of chronic postoperative pain and the response to pharmacological interventions. This review systematically summarizes the current evidence on the predictive value of QST for chronic postoperative pain and the effect of pharmacological interventions. The main outcome measures were posttreatment pain intensity, pain relief, presence of moderate-to-severe postoperative pain, responders of 30% and 50% pain relief, or validated questionnaires on pain and disability. A systematic search of MEDLINE and EMBASE yielded 25 studies on surgical interventions and 11 on pharmacological interventions. Seventeen surgical and 11 pharmacological studies reported an association between preoperative or pretreatment QST and chronic postoperative pain or analgesic effect. The most commonly assessed QST modalities were pressure stimuli (17 studies), temporal summation of pain (TSP, 14 studies), and conditioned pain modulation (CPM, 16 studies). Of those, the dynamic QST parameters TSP (50%) and CPM (44%) were most frequently associated with chronic postoperative pain and analgesic effects. A large heterogeneity in methods for assessing TSP (n = 4) and CPM (n = 7) was found. Overall, most studies demonstrated low-to-moderate levels of risk of bias in study design, attrition, prognostic factors, outcome, and statistical analyses. This systematic review demonstrates that TSP and CPM show the most consistent predictive values for chronic postoperative pain and analgesic effect, but the heterogeneous methodologies reduce the generalizability and hence call for methodological guidelines.

Exercise-induced hypoalgesia and pain reduction following blood flow restriction: A brief review

OBJECTIVE

To review past literature regarding exercise-induced hypoalgesia and pain reduction following blood flow restriction interventions, and to discuss potential mechanisms as well as future considerations towards the efficacy of blood flow restriction in pain reduction following exercise.

METHODS

To be eligible for inclusion, studies had to include acute exercise, or long-term training interventions, with blood flow restriction, along with including pre and post intervention pain measurements.

RESULTS

A total of 13 studies met the inclusion criteria. Among these 13 studies, 3 studies examined exercise-induced hypoalgesia after an acute bout of resistance exercise with blood flow restriction, and 10 studies investigated pain reduction following long-term blood flow restriction training.

CONCLUSIONS

Existing literature suggests that low load resistance exercise with blood flow restriction may serve as an effective pain management method for those who are unable or unwilling to train with high loads. Several potential mechanisms have been suggested, however, the roles of these mechanisms are still unclear and require further clarification. Future research should consider implementing different methods of blood flow restriction application, and research study design to clarify the utility and efficacy of blood flow restriction as a pain management tool, by itself or in combination with exercise.

Should Exercises be Painful or not? Effects on Clinical and Experimental Pain in Individuals with Shoulder Pain

Exercise can reduce pain, however the effect of painful versus non-painful exercises is uncertain. The primary aim of this randomized crossover study was to compare the effect of painful versus nonpainful isometric shoulder exercises on pain intensity after exercise in individuals with rotator cuff-related shoulder pain. Secondary exploratory aims were to describe the effects on pressure pain thresholds (PPTs), conditioned pain modulation (CPM) and muscle strength. On separate days, 35 individuals performed painful isometric shoulder exercises (external rotation; 20% above pain threshold), nonpainful isometric shoulder exercises (external rotation; 20% below pain threshold), and a rest condition, in randomised order. Shoulder pain intensity, PPTs, CPM, and external rotation strength were assessed before, immediately after and 45 minutes after conditions. No significant differences were observed between painful and nonpainful exercises. Visual analogue scale scores increased immediately after both painful and non-painful exercises compared with rest (P = .047, partial ƞ² = .07), but were similar to preexercise levels after 45 minutes. No changes in PPTs, CPM, or muscle strength after exercises compared with rest were observed. Painful and non-painful isometric exercises caused a moderate but short-lasting increase in shoulder pain in individuals with RCRSP. Isometric exercises had no effect on pain sensitivity and shoulder muscle strength or CPM. Perspective: This study evaluated for the first time in individuals with rotator cuff-related shoulder pain the effects of painful versus non-painful isometric exercises on different pain-related outcome measures. Both painful and non-painful isometric exercises caused a moderate but relatively short-lasting increase in shoulder pain in individuals with rotator cuff-related shoulder pain. Trial registration number: (ClinicalTrials.gov) NCT03675399.

Does isometric exercise result in exercise induced hypoalgesia in people with local musculoskeletal pain? A systematic review

OBJECTIVE

The aim of this review was to investigate if exercise induced hypoalgesia (EIH) occurs following isometric muscle contraction in people with local musculoskeletal symptoms.

DESIGN

Systematic review.

DATA SOURCES

MEDLINE, EMBASE, CINAHL & SportDiscus electronic databases were searched (inception to April 2020).

ELIGIBILITY CRITERIA

Two authors independently evaluated eligibility. Randomised controlled and crossover (repeated measures) trials that measured the effects of isometric exercise in participants with localised musculoskeletal pain during, and up to 2 hours after isometric exercise were included. Other inclusion criteria included comparison to another intervention, or comparison to healthy controls. Primary outcomes were experimentally induced pain thresholds and secondary outcomes included measures of pain sensitivity from clinical testing.

RESULTS

13 studies with data from 346 participants were included for narrative synthesis. EIH was reported in some upper and lower limb studies but there were no consistent data to show isometric exercises were superior to comparison interventions.

CONCLUSION

There was no consistent evidence for EIH following isometric exercise in people with musculoskeletal pain. These findings are different to those reported in asymptomatic populations (where EIH is consistently demonstrated) as well as conditions associated with widespread symptoms such as fibromyalgia (where isometric exercise may induce hyperalgesia). Although well tolerated when prescribed, isometric exercise did not induce EIH consistently for people seeking care for local musculoskeletal symptoms. The variance in the dose, location of contraction and intensity of protocols included in this review may explain the inconsistent findings. Further work is required to better understand endogenous analgesia in musculoskeletal pain conditions.

Masterclass: A pragmatic approach to pain sensitivity in people with musculoskeletal disorders and implications for clinical management for musculoskeletal clinicians

INTRODUCTION

Research on musculoskeletal disorders indicates that pain sensitivity can be an important consideration for musculoskeletal clinicians in the holistic view of a patient presentation. However, diversity in research findings in this field can make this a difficult concept for clinicians to navigate. Limited integration of the concept of pain sensitivity into clinical practice for musculoskeletal clinicians has been noted.

PURPOSE

The purpose of this masterclass is to provide a framework for the consideration of pain sensitivity as a contributing factor in the presentation of people with musculoskeletal pain. It provides pragmatic synthesis of the literature related to pain sensitivity through a lens of how this information can inform clinical practice for musculoskeletal clinicians. Guidance is provided in a 'how to' format for integration of this knowledge into the clinical encounter to facilitate personalised care.

IMPLICATIONS

The relationship of pain sensitivity with pain and disability is not clear or linear. The real importance of pain sensitivity in a clinical presentation may be: (1) the potential for pain sensitivity to modify the effect of common treatments utilised by musculoskeletal clinicians, or (2) the effect of pain sensitivity on the prognosis/course of a disorder. Screening tools and subjective features have been highlighted to indicate when physical assessment of pain sensitivity should be prioritised in the physical examination. A pragmatic blueprint for specific assessment related to pain sensitivity has been outlined. A framework for integrating assessment findings into clinical reasoning to formulate management plans for the pain sensitive patient is provided.

Within-session test-retest reliability of pressure pain threshold and mechanical temporal summation in healthy subjects

Objective

To determine the absolute and relative intra-rater within-session test-retest reliability of pressure pain threshold (PPT) and mechanical temporal summation of pain (TSP) at the low back and the forearm in healthy participants and to test the influence of the number and sequence of measurements on reliability metrics.

Methods

In 24 participants, three PPT and TSP measures were assessed at four sites (2 at the low back, 2 at the forearm) in two blocks of measurements separated by 20 minutes. The standard error of measurement, the minimal detectable change (MDC) and the intraclass correlation coefficient (ICC) were investigated for five different sequences of measurements (e.g. measurement 1, 1–2, 1-2-3).

Results

The MDC for the group (MDC_gr) for PPT ranged from 28.71 to 50.56 kPa across the sites tested, whereas MDC_gr for TSP varied from 0.33 to 0.57 out of 10 (numeric scale). Almost all ICC showed an excellent relative reliability (between 0.80 and 0.97), except when only the first measurement was considered (moderate). Although minimal differences in absolute PPT reliability were present between the different sequences, in general, using only the first measurement increase measurement error. Three TSP measures reduced the measurement error.

Discussion

We established that two measurements of PPT and three of TSP reduced the measurement error and demonstrated an excellent relative reliability. Our results could be used in future pain research to confirm the presence of true hypo/hyperalgesia for paradigms such as conditioned pain modulation or exercise-induced hypoalgesia, indicated by a change exceeding the measurement variability.

Modulation of Exercise-Induced Hypoalgesia Following an Exercise Intervention in Healthy Subjects

BACKGROUND

Exercise is recommended to promote and maintain health and as treatment for more than 25 diseases and pain conditions. Exercise-induced hypoalgesia (EIH), a measure of descending pain inhibitory control, has been found to be impaired in some chronic pain conditions, but it is currently unclear if EIH is modifiable. This study investigated whether a long-term exercise intervention could modulate EIH in healthy subjects.

METHODS

In 38 healthy subjects, EIH was assessed as change in pressure pain threshold (PPT) after a three-minute isometric wall squat within the first week and after approximately seven weeks of military training (MT). Further, temporal summation of pain (TSP) and Knee injury and Osteoarthritis Outcome Score (KOOS) were assessed. Physical performance capacity was assessed using the Endurance 20-m shuttle run fitness test (20MSR). Hypoalgesic (EIH > 0.0 kPa) and hyperalgesic (EIH ≤ 0.0 kPa) subgroups were defined based on baseline EIH. Change in EIH following MT was used as the primary outcome.

RESULTS

Increased EIH (P = 0.008), PPT (P < 0.003), and 20MSR (P < 0.001) were found following MT, with no changes in TSP and KOOS (P > 0.05). Subjects with a hyperalgesic EIH response at baseline (26% of the participants) presented significantly improved EIH following MT (P = 0.010). Finally, an association between 20MRS change and EIH change was found (r = 0.369, P = 0.023).

CONCLUSIONS

MT increased EIH, especially in subjects who demonstrated a hyperalgesic response at baseline. Improvement in physical performance capacity was associated with an improvement in EIH, indicating that improvement in physical performance capacity may improve central pain mechanisms.

Effect of exercise on pain processing and motor output in people with knee osteoarthritis: a systematic review and meta-analysis

OBJECTIVE

Guidelines recommend exercise as a core treatment for knee osteoarthritis. However, it is unclear how exercise affects measures of pain processing and motor function. The aim was to evaluate the effect of exercise on measures of pain processing and motor function in people with knee osteoarthritis.

METHODS

We searched five electronic databases (MEDLINE, EMBASE, CINAHL, SCOPUS and Cochrane Central Register of Controlled Trials) for studies on knee osteoarthritis, of any design, evaluating pain processing and motor function before and after exercise. Data were pooled with random-effects meta-analysis. Study quality was assessed using the Downs and Black and quality of evidence was assessed using the GRADE.

RESULTS

Eighteen studies were eligible and 16 were included. Following acute exercise, pressure pain threshold increased local to the study limb (standardised mean difference [95% confidence interval (CI)] 0.26, [0.02, 0.51], n = 159 from 5 studies), but there was no statistically significant change remote from the study limb (0.09, [-0.11, 0.29], n = 90 from 4 studies). Following an exercise program (range 5-12 weeks) there were no statistically significant changes in pressure pain threshold (local 0.23, [-0.01, 0.47], n = 218 from 8 studies; remote 0.33 [-0.13, 0.79], n = 76 from 4 studies), temporal pain summation (0.38 [-0.08, 0.85], n = 122 from 3 studies) or voluntary quadriceps muscle activation (4.23% [-1.84 to 10.30], n = 139 from 4 studies).

CONCLUSION

Very-low quality evidence suggests that pressure pain threshold increases following acute exercise. Very-low quality evidence suggests that pressure pain threshold, temporal pain summation or voluntary quadriceps activation do not change statistically significantly following exercise programs.

The Interplay between Oxidative Stress, Exercise, and Pain in Health and Disease: Potential Role of Autonomic Regulation and Epigenetic Mechanisms

Oxidative stress can be induced by various stimuli and altered in certain conditions, including exercise and pain. Although many studies have investigated oxidative stress in relation to either exercise or pain, the literature presents conflicting results. Therefore, this review critically discusses existing literature about this topic, aiming to provide a clear overview of known interactions between oxidative stress, exercise, and pain in healthy people as well as in people with chronic pain, and to highlight possible confounding factors to keep in mind when reflecting on these interactions. In addition, autonomic regulation and epigenetic mechanisms are proposed as potential mechanisms of action underlying the interplay between oxidative stress, exercise, and pain. This review highlights that the relation between oxidative stress, exercise, and pain is poorly understood and not straightforward, as it is dependent on the characteristics of exercise, but also on which population is investigated. To be able to compare studies on this topic, strict guidelines should be developed to limit the effect of several confounding factors. This way, the true interplay between oxidative stress, exercise, and pain, and the underlying mechanisms of action can be revealed and validated via independent studies.

Efficacy of Physical Therapy on Nociceptive Pain Processing Alterations in Patients with Chronic Musculoskeletal Pain: A Systematic Review and Meta-analysis

INTRODUCTION

Chronic musculoskeletal pain is a major health, social, and economic problem. Most of the subjects who suffer from chronic musculoskeletal pain present processes of central sensitization. Temporal summation and conditioned pain modulation are the two most commonly used clinical measures of this. The objective of this review is to evaluate the effects of physical therapy on temporal summation (TS) and conditioned pain modulation (CPM) in patients with chronic musculoskeletal pain.

METHODS

This is a systematic review and meta-analysis. We searched the MEDLINE, EMBASE, CINAHL, EBSCO, PubMed, PEDro, Cochrane Collaboration Trials Register, Cochrane Database of Systematic Reviews, and SCOPUS databases. Different mesh terms and key words were combined for the search strategy, with the aim of encompassing all studies that have used any type of physical therapy treatment in patients with chronic musculoskeletal pain and have measured both TS and CPM.

RESULTS

Eighteen studies remained for qualitative analysis and 16 for quantitative analysis. Statistically significant differences with a 95% confidence interval (CI) were obtained for TS (-0.21, 95% CI = -0.39 to -0.03, Z = 2.50, P = 0.02, N = 721) and CPM (0.34, 95% CI = 0.12 to 0.56, Z = 2.99, P = 0.003, N = 680) in favor of physical therapy as compared with control. Manual therapy produces a slight improvement in TS, and physical therapy modalities in general improve CPM. No significant differences between the subgroups of the meta-analysis were found. The methodological quality of the studies was high.

CONCLUSIONS

Physical therapy produces a slight improvement in central sensitization (CS)-related variables, with TS decreased and CPM increased when compared with a control group in patients with CMP. Only significant differences in TS were identified in the manual therapy subgroup.

Exercise-induced hypoalgesia after acute and regular exercise: experimental and clinical manifestations and possible mechanisms in individuals with and without pain

This review describes methodology used in the assessment of the manifestations of exercise-induced hypoalgesia in humans and previous findings in individuals with and without pain. Possible mechanisms and future directions are discussed.

Exercise and physical activity is recommended treatment for a wide range of chronic pain conditions. In addition to several well-documented effects on physical and mental health, 8 to 12 weeks of exercise therapy can induce clinically relevant reductions in pain. However, exercise can also induce hypoalgesia after as little as 1 session, which is commonly referred to as exercise-induced hypoalgesia (EIH). In this review, we give a brief introduction to the methodology used in the assessment of EIH in humans followed by an overview of the findings from previous experimental studies investigating the pain response after acute and regular exercise in pain-free individuals and in individuals with different chronic pain conditions. Finally, we discuss potential mechanisms underlying the change in pain after exercise in pain-free individuals and in individuals with different chronic pain conditions, and how this may have implications for clinical exercise prescription as well as for future studies on EIH.

Exercise-induced pain threshold modulation in healthy subjects: a systematic review and meta-analysis

Background

The use of exercise is a potential treatment option to modulate pain (exercise-induced hypoalgesia). The pain threshold (PT) response is a measure of pain sensitivity that may be a useful marker to assess the effect of physical exercise on pain modulation.

Aim

The aim of this systematic review and meta-analysis is to evaluate the PT response to exercise in healthy subjects.

Methods

We searched in MEDLINE, EMBASE, Web of Science, Lilacs, and Scopus using a search strategy with the following search terms: "exercise" OR "physical activity" AND "Pain Threshold" from inception to December 2nd, 2019. As criteria for inclusion of appropriate studies: randomized controlled trials or quasi-experimental studies that enrolled healthy subjects; performed an exercise intervention; assessed PT. Hedge's effect sizes of PT response and their 95% confidence intervals were calculated, and random-effects meta-analyses were performed.

Results

For the final analysis, thirty-six studies were included (n=1326). From this we found a significant and homogenous increase in PT in healthy subjects (ES=0.19, 95% CI= 0.11 to 0.27, I2=7.5%). According to subgroup analysis the effect was higher in studies: with women (ES=0.36); performing strength exercise (ES=0.34), and with moderate intensity (ES=0.27), and no differences by age were found. Confirmed by the meta-regression analysis.

Conclusion

This meta-analysis provides evidence of small to moderate effects of exercise on PT in healthy subjects, being even higher for moderate strength exercise and in women. These results support the idea of modulation of the endogenous pain system due to exercise and highlight the need of clinical translation to chronic pain population.

Central sensitization inventory scores correlate with pain at rest in patients with hip osteoarthritis: a retrospective study

Background

Patients with persistent pain due to osteoarthritis (OA) complain of multiple symptoms that cannot be explained solely by structural changes. A poor correlation exists between structural and inflammatory changes in OA and pain levels. Central sensitization (CS) has been identified as a factor that induces chronic pain in patients with OA. Although it is important to identify osteoarthritis patients with CS components, the prevalence and characteristics of CS, especially those in patients with hip OA, are not well understood. Thus, we aimed to determine the prevalence and characteristics of CS in patients with hip OA, in this study.

Methods

The CS Inventory (CSI), used as a non-invasive routine clinical tool to evaluate the presence of CS 1 month before surgery in 100 patients with hip OA, was measured at our outpatient clinic, and the data were retrospectively reviewed. We determined the number of patients with a CSI score of 40 points or higher and assessed the relationships between the CSI score and clinical factors (including age, duration of hip pain, degree pain at rest and on activity, by using the visual analogue scale [VAS] and the Harris Hip Score) using the Spearman’s correlation coefficient.

Results

The mean age of participants was 63.9 ± 11.6 years, and there were 15 men and 85 women. All patients had hip OA, categorised as advanced and terminal stage (Tönnis grade 2–3) on preoperative plain radiography. The mean duration of hip pain was 4.2 ± 4.4 years. The mean CSI score was 19.5 ± 11.3 and 5 (5.0%) of the patients had a score of 40 or more points. CSI scores correlated significantly only with VAS pain at rest (r = 0.348, P < 0.001).

Conclusion

In this study, 1 out of every 20 hip OA patients had CS components. CSI scores were significantly correlated with pain at rest in hip OApatients. CS approaches to hip OA may be one of the treatment options for pain at rest.

The Relationship Between Daily Physical Activity and Pain in Individuals with Knee Osteoarthritis

Objective

Investigate the association between physical activity and pain severity in individuals with knee osteoarthritis.

Design

Cross-sectional; systematic review with meta-analyses.

Methods

Thirty-one participants with knee osteoarthritis underwent assessment of symptoms via self-report questionnaires and quantitative sensory testing. Following testing, physical activity and symptoms were monitored for seven days using accelerometers and logbooks. Cross-correlation analyses were performed on fluctuations in symptoms and physical activity across the week to detect the relative timing of the strongest association between pain and activity. These data were complemented by meta-analyses of studies that examined correlations between pain from knee osteoarthritis and physical activity or fitness.

Results

Pain severity at baseline correlated with moderate to vigorous physical activity (r2 = 0.161–0.212, P &lt; 0.05), whereby participants who were more physically active had less pain. Conversely, the peak of the cross-correlation analyses was most often positive and lagging, which indicated that pain was increased subsequent to periods of increased activity. These superficially discrepant findings were supported by the results of a meta-analysis of 13 studies and 9,363 participants, which identified significant heterogeneity for associations between physical activity and pain (I2 = 91%). Stronger inverse associations were found between fitness and pain.

Conclusions

Associations between physical activity and pain in people with knee osteoarthritis are variable and dynamic. These results reflect the beneficial impact of an active lifestyle and accompanying higher fitness. Yet, the side effect of acute periods of physical activity to transiently exacerbate pain may influence the behavior of some people to avoid activity because of pain.

Pain intensity and pressure pain thresholds after a light dynamic physical load in patients with chronic neck-shoulder pain

Background

To investigate the development of pain intensity and pressure pain thresholds during and 24 h after a light dynamic physical load among patients with chronic neck-shoulder pain.

Methods

Twenty-six patients with chronic neck-shoulder pain and 12 healthy controls were included. The participants arm-cycled on an ergometer. Effort was rated with the Borg Rating of Perceived Exertion scale (RPE), and pain intensity with an numeric rating scale (NRS). Pressure pain thresholds were measured by an algometer. Participants started a pain diary 1 week before the physical exercise and continued until 1 week after. Pain intensity was assessed before, during and the following two evenings after arm-cycling. Pressure pain thresholds were assessed before, 15 min after, 105 min after and 24 h after.

Results

The chronic pain group showed increased pain intensity during, and the following two evenings after the arm cycling, and decreased pain thresholds immediately after the arm cycling involving painful regions. In the patient group there were no impact on pain thresholds in the neck the following day.

Conclusions

Patients with chronic neck-shoulder pain reported increased pain intensity during and in the evenings after a light dynamic load involving painful regions. In addition, they showed decreased pain thresholds close to the exercise, indicating mechanical hyperalgesia.

The addition of blood flow restriction to resistance exercise in individuals with knee pain: a systematic review and meta-analysis

BACKGROUND

Blood flow restriction (BFR) is an effective clinical intervention used to increase strength in healthy individuals. However, its effects on pain and function in individuals with knee pain are unknown.

OBJECTIVE

To determine the effectiveness of adding BFR to resistance exercise for pain relief and improvement of function in patients with knee pain.

METHODS

Systematic review with meta-analysis of randomized clinical trials. Medline, Central, Embase, PEDro, Lilacs, CINAHL, SPORTDiscus, and Web of Science databases were searched from inception to May 2019. Randomized clinical trials that compared resistance exercise with or without BFR to treat knee pain and function in individuals older than 18 years of age with knee pain were included.

RESULTS

Eight randomized clinical trials met the eligibility criteria and for the quantitative synthesis, five studies were included. The pooled standardized mean difference (SMD) estimate showed that resistance exercises with BFR was not more effective than resistance exercises for reducing pain (SMD: -0.37cm, 95% CI=-0.93, 0.19) and improving knee function (SMD=-0.23 points, 95% CI=-0.71, 0.26) in patients with knee pain.

CONCLUSION

In the short term, there is low quality of evidence that resistance exercise with BFR does not provide significant differences in pain relief and knee function compared to resistance exercises in patients with knee pain. PROSPERO registration number: CRD42018102839.

Impact of Therapeutic Interventions on Pain Intensity and Endogenous Pain Modulation in Knee Osteoarthritis: A Systematic Review and Meta-analysis

OBJECTIVE

To study the impact of therapeutic interventions on pain analgesia and endogenous pain modulation in knee osteoarthritis (KOA).

DESIGN

Systematic review and meta-analysis.

METHODS

We searched for KOA randomized clinical trials and observational studies with data on therapeutic interventions comparing pain intensity, temporal summation (TS), and conditioned pain modulation (CPM) scores relative to control. These data were pooled as Hedge's g. To study the relationship between pain intensity and TS/CPM, we performed metaregression with 10,000 Monte-Carlo permutations.

RESULTS

We reviewed 11 studies (559 participants). On studying all the interventions together, we found no significant changes in pain modulation, TS, or CPM. Our findings show that this lack of difference is likely because surgical and nonsurgical interventions resulted in contrary effects. Metaregression significantly correlated pain reduction with normalization of TS and CPM.

CONCLUSIONS

We demonstrate an association between pain reduction and TS/CPM normalization. Though we cannot directly compare these interventions, the results allow us to draw hypotheses on potential practice schemas. Recovering defective endogenous pain modulation mechanisms may help establish long-term analgesia. However, to validate these paradigms as robust clinical biomarkers, further investigation into their mechanisms would be necessary. The registration number for this review is CRD42017072066.

Angiotensin receptor blockade mimics the effect of exercise on recovery after orthopaedic trauma by decreasing pain and improving muscle regeneration

KEY POINTS

Our tibial fracture orthopaedic injury model in mice recapitulates the major manifestations of complex trauma, including nociceptive sensitization, bone fracture, muscle fibrosis and muscle fibre loss. Delayed exercise after complex orthopaedic trauma results in decreased muscle fibrosis and improved pain Losartan, an angiotensin-receptor blocker with anti-fibrotic abilities, recapitulates the effect of exercise on post-injury recovery and may provide an enhanced recovery option for those who are unable to exercise after injury ABSTRACT: Chronic pain and disability after limb injury are major public health problems. Early mobilization after injury improves functional outcomes for patients, although when and how to implement rehabilitation strategies remains a clinical challenge. Additionally, whether the beneficial effects of exercise can be reproduced using pharmacological tools remains unknown and may benefit patients who are unable to exercise as a result of immobilization. We developed a murine model of orthopaedic trauma combining tibia fracture and pin fixation with muscle damage. Behavioural measures included mechanical nociceptive thresholds and distances run on exercise wheels. Bone healing was quantified using microcomputed tomagraphic scanning, and muscle fibre size distribution and fibrosis were followed using immunohistochemistry. We found that the model provided robust mechanical allodynia, fibrosis and a shift to smaller average muscle fibre size lasting up to 5 weeks from injury. We also observed that allowing 'late' (weeks 1-2) rather than 'early' (weeks 0-1) exercise after injury resulted in greater overall running activity and greater reversal of allodynia. In parallel, the late running paradigm was associated with reduced muscle fibrosis, earlier increase in muscle fibre diameter and a short-term benefit in reducing callus volume. Providing the anti-fibrotic angiotensin receptor blocker losartan to mice in drinking water reduced both allodynia and muscle fibrosis. Combining losartan and late exercise provided no additional benefit. We conclude that early healing after orthopaedic trauma must be allowed prior to the initiation of exercise to achieve optimal pain, functional and physiological outcomes and that losartan is a viable candidate for translational studies.

Best Evidence Rehabilitation for Chronic Pain Part 5: Osteoarthritis

Osteoarthritis (OA) is a leading cause of chronic pain and disability in older adults, which most commonly affects the joints of the knee, hip, and hand. To date, there are no established disease modifying interventions that can halt or reverse OA progression. Therefore, treatment is focused on alleviating pain and maintaining or improving physical and psychological function. Rehabilitation is widely recommended as first-line treatment for OA as, in many cases, it is safer and more effective than the best-established pharmacological interventions. In this article, we describe the presentation of OA pain and give an overview of its peripheral and central mechanisms. We then provide a state-of-the-art review of rehabilitation for OA pain—including self-management programs, exercise, weight loss, cognitive behavioral therapy, adjunct therapies, and the use of aids and devices. Next, we explore several promising directions for clinical practice, including novel education strategies to target unhelpful illness and treatment beliefs, methods to enhance the efficacy of exercise interventions, and innovative, brain-directed treatments. Finally, we discuss potential future research in areas, such as treatment adherence and personalized rehabilitation for OA pain.