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.

Lifeworlds in pain: a principled method for investigation and intervention.

The experience of pain spans biological, psychological and sociocultural realms, both basic and complex, it is by turns necessary and devastating. Despite an extensive knowledge of the constituents of pain, the ability to translate this into effective intervention remains limited. It is suggested that current, multiscale, medical approaches, largely informed by the biopsychosocial (BPS) model, attempt to integrate knowledge but are undermined by an epistemological obligation, one that necessitates a prior isolation of the constituent parts. To overcome this impasse, we propose that an anthropological stance needs to be taken, underpinned by a Bayesian apparatus situated in computational psychiatry. Here, pain is presented within the context of lifeworlds, where attention is shifted away from the constituents of experience (e.g. nociception, reward processing and fear-avoidance), towards the dynamic affiliation that occurs between these processes over time. We argue that one can derive a principled method of investigation and intervention for pain from modelling approaches in computational psychiatry. We suggest that these modelling methods provide the necessary apparatus to navigate multiscale ontology and epistemology of pain. Finally, a unified approach to the experience of pain is presented, where the relational, inter-subjective phenomenology of pain is brought into contact with a principled method of translation; in so doing, revealing the conditions and possibilities of lifeworlds in pain.

Pain Unstuck: The Role of Action and Motivation.

BACKGROUND: What is it that motivates our actions? As human beings, existing as part of complex societies, the actions we take are subject to multiple, often competing motives. Spanning non-conscious reflexes, cognitively derived choice as well as long- and short-term goals, our actions allow us to make sense of our environment. Pain disrupts action and hijacks our intentions. Whilst considered adaptive when temporary, pain that persists continues to interrupt and can threaten our ability to actively investigate a changing world. OBJECTIVE: This work is a narrative review. RESULTS: Drawing upon three complementary theoretical approaches to pain: an embodied framework, a motivational approach and the avoidance-endurance model, this review places the relationship between pain, motivation and action at its core, unpicking a dynamic process that can become stuck. CONCLUSIONS: In taking a wide view of pain and action, we expose the nuances within drive to goal behaviour in the presence of pain. This has implications for the clinic, specifically in relation to assessing the multifactorial influences that shape action in pain. But it also seeks to go further, considering the broader environment in which we make decisions and the influence that other professionals, outside of typical healthcare roles, may play a part in the maintenance and resolution of pain.

Predicting the consequences of physical activity: An investigation into the relationship between anxiety sensitivity, interoceptive accuracy and action.

The ability to predict the consequences of our actions is imperative for the everyday success of our interactions. From negotiating an uneven surface, to mounting an immune response, we continually infer the limits of our body. The current investigation considered the impact that the inferred consequences of action has on the placement of limits. We hypothesised that the performance of individuals in a novel, sprint task would reflect both their ability to accurately detect changes in bodily arousal (Interoceptive Accuracy) and the inferred consequences associated with heightened arousal signals (Anxiety Sensitivity). We found that individuals who demonstrated accuracy associated with physiological arousal changes, and who showed a heightened fear of the consequences of arousal symptoms, modified their actions by decreasing their power output (mean Watts•kg-1) in a sprint task (ΔR2 = 0.19; F(1,34) = 19.87); p<0.001). These findings provide a basis for understanding the varying actions taken as we encounter bodily perturbation.

Pain: A Statistical Account.

Perception is seen as a process that utilises partial and noisy information to construct a coherent understanding of the world. Here we argue that the experience of pain is no different; it is based on incomplete, multimodal information, which is used to estimate potential bodily threat. We outline a Bayesian inference model, incorporating the key components of cue combination, causal inference, and temporal integration, which highlights the statistical problems in everyday perception. It is from this platform that we are able to review the pain literature, providing evidence from experimental, acute, and persistent phenomena to demonstrate the advantages of adopting a statistical account in pain. Our probabilistic conceptualisation suggests a principles-based view of pain, explaining a broad range of experimental and clinical findings and making testable predictions.

Psychological Approaches to Coping with Pain in Later Life.

A psychological model of coping with the demands of aging is outlined. Chronic pain is conceptualized as a challenge to normal aging, because it threatens identity, risks affective disorder (depression), and interferes with action. The sparse evidence for psychological interventions is reviewed, and a case is made for the types of interventions that should be developed to address the specific presentation of geriatric pain management.

Perceptual Inference in Chronic Pain: An Investigation Into the Economy of Action Hypothesis.

OBJECTIVE: The experience of chronic pain critically alters one's ability to interact with their environment. One fundamental issue that has received little attention, however, is whether chronic pain disrupts how one perceives their environment in the first place. The Economy of Action hypothesis purports that the environment is spatially scaled according to the ability of the observer. Under this hypothesis it has been proposed that the perception of the world is different between those with and without chronic pain. Such a possibility has profound implications for the investigation and treatment of pain. The present investigation tested the application of this hypothesis to a heterogenous chronic pain population. METHODS: Individuals with chronic pain (36; 27F) and matched pain-free controls were recruited. Each participant was required to judge the distance to a series of target cones, to which they were to subsequently walk. In addition, at each distance, participants used Numerical Rating Scales to indicate their perceived effort and perceived pain associated with the distance presented. RESULTS: Our findings do not support the Economy of Action hypothesis: there were no significant differences in distance estimates between the chronic pain and pain-free groups (F1,60=0.927; P=0.340). In addition, we found no predictive relationship in the chronic pain group between anticipated pain and estimated distance (F1,154=0.122, P=0.727), nor anticipated effort (1.171, P=0.281) and estimated distance (F1,154=1.171, P=0.281). DISCUSSION: The application of the Economy of Action hypothesis and the notion of spatial perceptual scaling as a means to assess and treat the experience of chronic pain are not supported by the results of this study.

The close proximity of threat: altered distance perception in the anticipation of pain.

Pain is an experience that powerfully influences the way we interact with our environment. What is less clear is the influence that pain has on the way we perceive our environment. We investigated the effect that the anticipation of experimental pain (THREAT) and its relief (RELIEF) has on the visual perception of space. Eighteen (11F) healthy volunteers estimated the distance to alternating THREAT and RELIEF stimuli that were placed within reachable space. The results determined that the estimated distance to the THREAT stimulus was significantly underestimated in comparison to the RELIEF stimulus. We conclude that pain-evoking stimuli are perceived as closer to the body than otherwise identical pain-relieving stimuli, an important consideration when applied to our decisions and behaviors in relation to the experience of pain.

Do people with chronic pain have impaired executive function? A meta-analytical review.

A widely held belief within the clinical community is that chronic pain is associated with cognitive impairment, despite the absence of a definitive systematic review or meta-analysis on the topic. The current systematic review and meta-analysis aimed to establish the current evidence concerning the difference in executive function between people with chronic pain and healthy controls. Six databases were searched for citations related to executive function and chronic pain from inception to June 24, 2013. Two reviewers independently assessed studies for eligibility and extracted relevant data according to the Cochrane Collaboration and Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Twenty five studies were included in the review and twenty two studies in the meta-analysis. A small to moderate impairment in executive function performance was found in people with chronic pain across cognitive components, although all studies had a high risk of bias. The current evidence suggests impairment of executive function in people with chronic pain, however, important caveats exist. First, executive function involves many cognitive components and there is no standard test for it. Second, moderators of executive function, such as medication and sleep, were seldom controlled for in studies of executive function performance.

Show me the skin! Does seeing the back enhance tactile acuity at the back?

A growing body of literature associates musculoskeletal disorders with cortical reorganisation. One condition in which reorganisation is established and treatments that 'train the brain' are being widely used is chronic back pain. Recent evidence suggests that treatments that involve tactile training are more effective if they incorporate multisensory mechanisms, most obviously vision. With regard to back pain however, we must first determine if tactile function is enhanced by incorporating other modalities. A series of three cross-over experiments were conducted in healthy pain-free subjects to determine whether tactile acuity is enhanced when participants can see the skin of their back during testing. An initial randomised cross-over experiment suggested tactile acuity was significantly enhanced when participants could see their backs (t(25) = -4.226, p < 0.001, r = 0.65). However, a second replication experiment was not corroborative. Both the second (F(3,66) = 1.00, p = 0.398) and third (t(9) = 0.969, p = 0.358) experiments suggested that seeing the back did not significantly affect tactile acuity, confirming that our initial results were likely due to chance. The principle that visual feedback improves tactile acuity at the hand does not apply to the back. These results strongly suggest that attempts to enhance tactile training by incorporating vision will not offer the benefit to treatment of back pain that has been observed for treatment of hand pain.

Perceptual bias in pain: a switch looks closer when it will relieve pain than when it won't.

Pain is fundamental to survival, as are our perceptions of the environment. It is often assumed that we see our world as a read-out of the sensory information that we receive; yet despite the same physical makeup of our surroundings, individuals perceive differently. What if we "see" our world differently when we experience pain? Until now, the causal effect of experimental pain on the perception of an external stimulus has not been investigated. Eighteen (11 female) healthy volunteers participated in this randomised repeated-measures experiment, in which participants estimated the distance to a switch placed on the table in front of them. We varied whether or not the switch would instantly stop a stimulus, set to the participant's pain threshold, being delivered to their hand, and whether or not they were required to reach for the switch. The critical result was a strong interaction between reaching and pain [F(1,181)=4.8, P=0.03], such that when participants experienced pain and were required to reach for a switch that would turn off the experimental stimulus, they judged the distance to that switch to be closer, as compared to the other 3 conditions (mean of the true distance 92.6%, 95% confidence interval 89.7%-95.6%). The judged distance was smaller than estimates in the other 3 conditions (mean±SD difference >5.7%±2.1%, t(181) >3.5, P<0.01 for all 3 comparisons). We conclude that the perception of distance to an object is modulated by the behavioural relevance of the object to ongoing pain.

Evidence for working memory deficits in chronic pain: a systematic review and meta-analysis.

People with chronic pain commonly report impaired cognitive function. However, to date, there has been no systematic evaluation of the body of literature concerning cognitive impairment and pain. Nor have modern meta-analytical methods been used to verify and clarify the extent to which cognition may be impaired. The objective of this study was to systematically evaluate and critically appraise the literature concerning working memory function in people with chronic pain. The study was conducted along Cochrane collaboration and Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement guidelines. A sensitive search strategy was designed and conducted with the help of an expert librarian using 6 databases. Twenty-four observational studies evaluating behavioural and/or physiological outcomes in a chronic pain group and a control group met the inclusion criteria. All studies had a high risk of bias, owing primarily to lack of assessor blinding to outcome. High heterogeneity within the field was found with the inclusion of 24 papers using 21 different working memory tests encompassing 9 different working memory constructs and 9 different chronic pain populations. Notwithstanding high heterogeneity, pooled results from behavioural outcomes reflected a consistent, significant moderate effect in favour of better performance by healthy controls and, with the exception of one study, pooled results from physiological outcomes reflected no evidence for an effect. Future research would benefit from the use of clearly defined constructs of working memory, as well as standardised methods of testing.

Assessing tactile acuity in rheumatology and musculoskeletal medicine--how reliable are two-point discrimination tests at the neck, hand, back and foot?

OBJECTIVE: Chronic pain from rheumatic and musculoskeletal conditions is associated with cortical changes and altered tactile acuity. Tactile acuity is considered a clinical signature of primary somatosensory representation. The two-point discrimination (TPD) threshold is increasingly used both clinically and in research. Remarkably, the reliability and precision of the measure at commonly used sites has not been determined. This study aimed to determine the utility, intra- and inter-rater reliability, bias and variability of TPD threshold assessment at the neck, back, hand and foot using mechanical callipers. METHODS: Intra- and inter-rater reliability of TPD was assessed at the back, neck, hand and foot of 28 healthy young adults by 28 clinicians. Each clinician received training in the assessment of TPD using mechanical callipers and following a standardized protocol. Intraclass correlation coefficients (ICCs) and Bland-Altman plots were used to assess reliability, bias and variability. RESULTS: Intra-rater assessments in all four regions and inter-rater assessments at the neck and foot were reliable (ICC range 0.79-0.86), but large variability was seen in all assessments. Inter-rater assessment of the back (ICC = 0.66) and hand (ICC = 0.62) was deemed unreliable. Negligible systematic bias suggested learning did not affect reliability. CONCLUSION: Individual clinicians are able to reliably assess TPD threshold at the neck, back, hand and foot using mechanical callipers. Measures obtained by different clinicians were only reliable for the neck and foot. Large variability was observed in all assessments, which suggests clinicians should be cautious when interpreting changes in tactile acuity in individual patients.

Chronic tension-type headache is associated with impaired motor learning.

BACKGROUND: Supraspinal activity-dependent neuroplasticity may be important in the transition from acute to chronic pain. We examined neuroplasticity in a cortical region not considered to be a primary component of the central pain matrix in chronic tension-type headache (CTTH) patients. We hypothesised that neuroplasticity would be exaggerated in CTTH patients compared to healthy controls, which might explain (in part) the development of chronic pain in these individuals. METHODS: Neuroplasticity was examined following a ballistic motor training task in CTTH patients and control subjects (CS). Changes in peak acceleration (motor learning) and motor-evoked potential (MEP) amplitude evoked by single-pulse transcranial magnetic stimulation were compared. RESULTS: CTTH patients showed significantly less motor learning on the training task than CS (mean acceleration increase 87% CTTH, 204% CS, P < .05), and CS but not CTTH patients showed a significant increased MEP amplitude following training (CS: F = 2.9, P < .05; CTTH: F = 1.6, P > .05). CONCLUSIONS: These findings suggest a deficit in use-dependent neuroplasticity within networks responsible for task performance in CTTH patients which might reflect reciprocal influences between primary motor cortex and interconnected pain processing networks. These findings may help explain the positive effects of facilitatory non-invasive brain stimulation targeting motor areas on chronic pain and help elucidate the mechanisms mediating chronic pain.

The effects of graded motor imagery and its components on chronic pain: a systematic review and meta-analysis.

UNLABELLED: Graded motor imagery (GMI) is becoming increasingly used in the treatment of chronic pain conditions. The objective of this systematic review was to synthesize all evidence concerning the effects of GMI and its constituent components on chronic pain. Systematic searches were conducted in 10 electronic databases. All randomized controlled trials (RCTs) of GMI, left/right judgment training, motor imagery, and mirror therapy used as a treatment for chronic pain were included. Methodological quality was assessed using the Cochrane risk of bias tool. Six RCTs met our inclusion criteria, and the methodological quality was generally low. No effect was seen for left/right judgment training, and conflicting results were found for motor imagery used as stand-alone techniques, but positive effects were observed for both mirror therapy and GMI. A meta-analysis of GMI versus usual physiotherapy care favored GMI in reducing pain (2 studies, n = 63; effect size, 1.06 [95% confidence interval, .41, 1.71]; heterogeneity, I(2) = 15%). Our results suggest that GMI and mirror therapy alone may be effective, although this conclusion is based on limited evidence. Further rigorous studies are needed to investigate the effects of GMI and its components on a wider chronic pain population. PERSPECTIVE: This systematic review synthesizes the evidence for GMI and its constituent components on chronic pain. This review may assist clinicians in making evidence-based decisions on managing patients with chronic pain conditions.