Analgesia following exercise: a review

Afferent thermosensory function in relapsing-remitting multiple sclerosis following exercise-induced increases in body temperature

NEW FINDINGS

What is the central question of this study? Between 60 and 80% of multiple sclerosis (MS) patients experience transient worsening of symptoms with increased body temperature (heat sensitivity). As sensory abnormalities are common in MS, we asked whether afferent thermosensory function is altered in MS following exercise-induced increases in body temperature. What is the main finding and its importance? Increases in body temperature of as little as ∼0.4°C were sufficient to decrease cold, but not warm, skin thermosensitivity (∼10%) in MS, across a wider temperature range than in age-matched healthy individuals. These findings provide new evidence on the impact of heat sensitivity on afferent function in MS, which could be useful for clinical evaluation of this neurological disease. In multiple sclerosis (MS), increases in body temperature result in transient worsening of clinical symptoms (heat sensitivity or Uhthoff's phenomenon). Although the impact of heat sensitivity on efferent physiological function has been investigated, the effects of heat stress on afferent sensory function in MS are unknown. Hence, we quantified afferent thermosensory function in MS following exercise-induced increases in body temperature with a new quantitative sensory test. Eight relapsing-remitting MS patients (three men and five women; 51.4 ± 9.1 years of age; Expanded Disability Status Scale score 2.8 ± 1.1) and eight age-matched control (CTR) subjects (five men and three women; 47.4 ± 9.1 years of age) rated the perceived magnitude of two cold (26 and 22°C) and two warm stimuli (34 and 38°C) applied to the dorsum of the hand before and after 30 min cycling in the heat (30°C air; 30% relative humidity). Exercise produced similar increases in mean body temperature in MS [+0.39°C (95% CI: +0.21, +0.53) P = 0.001] and CTR subjects [+0.41°C (95% CI: +0.25, +0.58) P = 0.001]. These changes were sufficient to decrease thermosensitivity significantly to all cold [26°C stimulus, -9.1% (95% CI: -17.0, -1.5), P = 0.006; 22°C stimulus, -10.6% (95% CI: -17.3, -3.7), P = 0.027], but not warm, stimuli in MS. Contrariwise, CTR subjects showed sensitivity reductions to colder stimuli only [22°C stimulus, -9.7% (95% CI: -16.4, -3.1), P = 0.011]. The observation that reductions in thermal sensitivity in MS were confined to the myelinated cold-sensitive pathway and extended across a wider (including milder and colder) temperature range than what is observed in CTR subjects provides new evidence on the impact of rising body temperature on afferent neural function in MS. Also, our findings support the use of our new approach to investigate afferent sensory function in MS during heat stress.

Occlusion of blood flow attenuates exercise-induced hypoalgesia in the occluded limb of healthy adults

Animal studies have demonstrated an important role of peripheral mechanisms as contributors to exercise-induced hypoalgesia (EIH). Whether these same mechanisms contribute to EIH in humans is not known. In the current study, pain thresholds were assessed in healthy volunteers ( n = 36) before and after 5 min of high-intensity leg cycling exercise and an equivalent period of quiet rest. Pressure pain thresholds (PPTs) were assessed over the rectus femoris muscle of one leg and first dorsal interosseous muscles (FDIs) of both arms. Blood flow to one arm was occluded by a cuff throughout the 5-min period of exercise (or rest) and postexercise (or rest) assessments. Ratings of pain intensity and pain unpleasantness during occlusion were also measured. Pain ratings during occlusion increased over time (range, 1.5 to 3.5/10, all d > 0.63, P < 0.001) similarly in the rest and exercise conditions ( d < 0.35, P > 0.4). PPTs at all sites were unchanged following rest (range, −1.3% to +0.9%, all d < 0.05, P > 0.51). Consistent with EIH, exercise significantly increased PPT at the leg (+29%, d = 0.69, P < 0.001) and the nonoccluded (+23%, d = 0.56, P < 0.001) and occluded (+8%, d = 0.19, P = 0.003) unexercised arms. However, the increase in the occluded arm was significantly smaller ( d = −1.03, P < 0.001). These findings show that blocking blood flow to a limb during exercise attenuates EIH, suggesting that peripheral factors contribute to EIH in healthy adults.

NEW & NOTEWORTHY This is the first demonstration in humans that a factor carried by the circulation and acting at the periphery is important for exercise-induced hypoalgesia. Further understanding of this mechanism may provide new insight to pain relief with exercise as well as potential interactions between analgesic medications and exercise.

Pain perception and cardiovascular system response among athletes playing contact sports

The aim of this study was to determine whether the contact sports change the perception of pain as assessed by the cold pressor test (CPT), and if the test induces the same reaction of the cardiovascular system in contact athletes and non-athletes. The study involved 321 healthy men; 140 contact athletes and 181 students of the University of Szczecin (control). Pain threshold and pain tolerance were evaluated using CPT. Cardiovascular measurements were made during CPT. The contact athletes showed a much higher tolerance to pain than the control group (median time 120 vs. 94 s, respectively, p = 0.0002). The thresholds of pain in both groups did not differ significantly between the groups. Systolic blood pressure measured before and during the test in all three measurements was statistically significantly higher in athletes compared with the control group. Heart rate and diastolic blood pressure did not differ significantly between the studied groups.

Examining the relationship between endogenous pain modulation capacity and endurance exercise performance

The aim of the current study was to examine the relationship between pain modulatory capacity and endurance exercise performance. Twenty-seven recreationally active males between 18 and 35 years of age participated in the study. Pain modulation was assessed by examining the inhibitory effect of a noxious conditioning stimulus (cuff occlusion) on the perceived intensity of a second noxious stimulus (pressure pain threshold). Participants completed two, maximal voluntary contractions followed by a submaximal endurance time task. Both performance tasks involved an isometric contraction of the non-dominant leg. The main analysis uncovered a correlation between pain modulatory capacity and performance on the endurance time task (r = -.425, p = .027), such that those with elevated pain modulation produced longer endurance times. These findings are the first to demonstrate the relationship between pain modulation responses and endurance exercise performance.

Exercise induced hypoalgesia is elicited by isometric, but not aerobic exercise in individuals with chronic whiplash associated disorders

Background and aims

Reduced pain sensitivity following exercise is termed exercise induced hypoalgesia (EIH). Preliminary evidence suggests that impairment of EIH is evident in individuals with whiplash associated disorders (WAD) following submaximal aerobic exercise. This study aimed to compare EIH responses to isometric and aerobic exercise in patients with chronic WAD and healthy controls and investigate relationships between EIH, conditioned pain modulation (CPM) and psychological factors in patients with chronic WAD.

Methods

A cross sectional pre-post study investigated the effect of a single session of submaximal aerobic cycling exercise and a single session of isometric timed wall squat exercise on EIH in a group of participants with chronic WAD (n = 21) and a group of asymptomatic control participants (n = 19). Bivariate analyses between EIH and baseline measures of CPM and psychological features (fear of movement, pain catastrophization and posttraumatic stress symptoms) were also investigated.

Results

The isometric wall squat exercise but not the aerobic cycling exercise resulted in EIH in both groups (P < .023) with no between-group differences (P > .55) demonstrated for either exercise. There were no significant associations measured between EIH (for either exercise performed), and CPM, or any of the psychological variables.

Conclusions

This study showed that individuals with chronic WAD and mild to moderate pain and disability, and no evidence of dysfunctional CPM, demonstrated reduced pain sensitivity, both in the cervical spine and over the tibialis anterior following an isometric, timed wall squat exercise. Cycling exercise did not increase pain sensitivity.

Implications

Individuals with chronic WAD and mild to moderate levels of neck pain and disability may experience less pain sensitivity both locally and remotely following an exercise program directed at nonpainful muscles performing isometric exercises. Individuals cycling for 30 min at 75% of age-predicted heart rate maximum do not experience increased pain sensitivity.

The effects of elevated pain inhibition on endurance exercise performance

BACKGROUND

The ergogenic effects of analgesic substances suggest that pain perception is an important regulator of work-rate during fatiguing exercise. Recent research has shown that endogenous inhibitory responses, which act to attenuate nociceptive input and reduce perceived pain, can be increased following transcranial direct current stimulation of the hand motor cortex. Using high-definition transcranial direct current stimulation (HD-tDCS; 2 mA, 20 min), the current study aimed to examine the effects of elevated pain inhibitory capacity on endurance exercise performance. It was hypothesised that HD-tDCS would enhance the efficiency of the endogenous pain inhibitory response and improve endurance exercise performance.

METHODS

Twelve healthy males between 18 and 40 years of age (M = 24.42 ± 3.85) were recruited for participation. Endogenous pain inhibitory capacity and exercise performance were assessed before and after both active and sham (placebo) stimulation. The conditioned pain modulation protocol was used for the measurement of pain inhibition. Exercise performance assessment consisted of both maximal voluntary contraction (MVC) and submaximal muscular endurance performance trials using isometric contractions of the non-dominant leg extensors.

RESULTS

Active HD-tDCS (pre-tDCS, -.32 ± 1.33 kg; post-tDCS, -1.23 ± 1.21 kg) significantly increased pain inhibitory responses relative to the effects of sham HD-tDCS (pre-tDCS, -.91 ± .92 kg; post-tDCS, -.26 ± .92 kg; p = .046). Irrespective of condition, peak MVC force and muscular endurance was reduced from pre- to post-stimulation. HD-tDCS did not significantly influence this reduction in maximal force (active: pre-tDCS, 264.89 ± 66.87 Nm; post-tDCS, 236.33 ± 66.51 Nm; sham: pre-tDCS, 249.25 ± 88.56 Nm; post-tDCS, 239.63 ± 67.53 Nm) or muscular endurance (active: pre-tDCS, 104.65 ± 42.36 s; post-tDCS, 93.07 ± 33.73 s; sham: pre-tDCS, 123.42 ± 72.48 s; post-tDCS, 100.27 ± 44.25 s).

DISCUSSION

Despite increasing pain inhibitory capacity relative to sham stimulation, active HD-tDCS did not significantly elevate maximal force production or muscular endurance. These findings question the role of endogenous pain inhibitory networks in the regulation of exercise performance.

The Ottawa panel clinical practice guidelines for the management of knee osteoarthritis. Part one: introduction, and mind-body exercise programs

OBJECTIVE

To identify effective mind-body exercise programs and provide clinicians and patients with updated, high-quality recommendations concerning non-traditional land-based exercises for knee osteoarthritis.

METHODS

A systematic search and adapted selection criteria included comparative controlled trials with mind-body exercise programs for patients with knee osteoarthritis. A panel of experts reached consensus on the recommendations using a Delphi survey. A hierarchical alphabetical grading system (A, B, C+, C, D, D+, D-) was used, based on statistical significance ( P < 0.5) and clinical importance (⩾15% improvement).

RESULTS

The four high-quality studies identified demonstrated that various mind-body exercise programs are promising for improving the management of knee osteoarthritis. Hatha Yoga demonstrated significant improvement for pain relief (Grade B) and physical function (Grade C+). Tai Chi Qigong demonstrated significant improvement for quality of life (Grade B), pain relief (Grade C+) and physical function (Grade C+). Sun style Tai Chi gave significant improvement for pain relief (Grade B) and physical function (Grade B).

CONCLUSION

Mind-body exercises are promising approaches to reduce pain, as well as to improve physical function and quality of life for individuals with knee osteoarthritis.

Modest Amounts of Voluntary Exercise Reduce Pain- and Stress-Related Outcomes in a Rat Model of Persistent Hind Limb Inflammation

Aerobic exercise improves outcomes in a variety of chronic health conditions, yet the support for exercise-induced effects on chronic pain in humans is mixed. Although many rodent studies have examined the effects of exercise on persistent hypersensitivity, the most used forced exercise paradigms that are known to be highly stressful. Because stress can also produce analgesic effects, we studied how voluntary exercise, known to reduce stress in healthy subjects, alters hypersensitivity, stress, and swelling in a rat model of persistent hind paw inflammation. Our data indicate that voluntary exercise rapidly and effectively reduces hypersensitivity as well as stress-related outcomes without altering swelling. Moreover, the level of exercise is unrelated to the analgesic and stress-reducing effects, suggesting that even modest amounts of exercise may impart significant benefit in persistent inflammatory pain states.

PERSPECTIVE

Modest levels of voluntary exercise reduce pain- and stress-related outcomes in a rat model of persistent inflammatory pain, independently of the amount of exercise. As such, consistent, self-regulated activity levels may be more relevant to health improvement in persistent pain states than standardized exercise goals.

The Ottawa panel clinical practice guidelines for the management of knee osteoarthritis. Part two: strengthening exercise programs

OBJECTIVE

To identify effective strengthening exercise programs and provide rehabilitation teams and patients with updated, high-quality recommendations concerning traditional land-based exercises for knee osteoarthritis.

METHODS

A systematic search and adapted selection criteria included comparative controlled trials with strengthening exercise programs for patients with knee osteoarthritis. A panel of experts reached consensus on the recommendations using a Delphi survey. A hierarchical alphabetical grading system (A, B, C+, C, D, D+ or D-) was based on statistical significance ( p < 0.5) and clinical importance (⩾15% improvement).

RESULTS

The 26 high-quality studies identified demonstrated that various strengthening exercise programs with/without other types of therapeutic exercises are generally effective for improving knee osteoarthritis management within a six-month period. Strengthening exercise programs demonstrated a significant improvement for pain relief (four Grade A, ten Grade B, two Grade C+), physical function (four Grade A, eight Grade B) and quality of life (three Grade B). Strengthening in combination with other types of exercises (coordination, balance, functional) showed a significant improvement in pain relief (three Grade A, 11 Grade B, eight Grade C+), physical function (two Grade A, four Grade B, three Grade C+) and quality of life (one Grade A, one Grade C+).

CONCLUSION

There are a variety of choices for strengthening exercise programs with positive recommendations for healthcare professionals and knee osteoarthritis patients. There is a need to develop combined behavioral and muscle-strengthening strategies to improve long-term maintenance of regular strengthening exercise programs.

Promoting Gait Recovery and Limiting Neuropathic Pain After Spinal Cord Injury

Most persons living with a spinal cord injury experience neuropathic pain in the months following their lesion, at the moment where they receive intensive gait rehabilitation. Based on studies using animal models, it has been proposed that central sensitization in nociceptive pathways (maladaptive plasticity) and plasticity related to motor learning (adaptive plasticity) share common neural mechanisms and compete with each other. This article aims to address the discrepancy between the growing body of basic science literature supporting this hypothesis and the general belief in rehabilitation research that pain and gait rehabilitation represent two independent problems. First, the main findings from basic research showing interactions between nociception and learning in the spinal cord will be summarized, focusing both on evidence demonstrating the impact of nociception on motor learning and of motor learning on central sensitization. Then, the generalizability of these findings in animal models to humans will be discussed. Finally, the way potential interactions between nociception and motor learning are currently taken into account in clinical research in patients with spinal cord injury will be presented. To conclude, recommendations will be proposed to better integrate findings from basic research into future clinical research in persons with spinal cord injury.

Physical Activity to Reduce Systemic Inflammation Associated With Chronic Pain and Obesity: A Narrative Review

INTRODUCTION

The increasing prevalence of chronic pain and obesity has significant health and cost implications for economies in the developed and developing world. Evidence suggests that there is a positive correlation between obesity and chronic pain and the link between them is thought to be systemic inflammation.

OBJECTIVES

The aim of this narrative review was to explore the physiological links between chronic musculoskeletal pain and obesity and to consider the potential role of regular physical activity in providing a means of managing obesity-related chronic pain.

DISCUSSION

Systemic inflammation, mechanical overload, and autonomic dysfunction are associated with increased prevalence and severity of chronic pain in individuals with obesity. It has been proposed, therefore, that interventions that target systemic inflammation could help to reduce chronic pain in obese individuals. Reduction in abdominal fat has been shown to alleviate pain and reduce the systemic markers of inflammation that contribute to chronic pain. Interventions that include exercise prescription have been shown to reduce both abdominal fat and systemic inflammation. Furthermore, exercise is also known to reduce pain perception and improve mental health and quality of life that also improves pain outcomes. However, adherence to formal exercise prescription is poor and therefore exercise programmes should be tailored to the interests, needs, and abilities of individuals to reduce attrition.

Thermal sensation during mild hyperthermia is modulated by acute postural change in humans

Thermal sensation represents the primary stimulus for behavioral and autonomic thermoregulation. We assessed whether the sensation of skin and core temperatures for the driving force of behavioral thermoregulation was modified by postural change from the supine (Sup) to sitting (Sit) during mild hyperthermia. Seventeen healthy young men underwent measurements of noticeable increase and decrease (±0.1 °C/s) of skin temperature (thresholds of warm and cold sensation on the skin, 6.25 cm² of area) at the forearm and chest and of the whole-body warm sensation in the Sup and Sit during normothermia (NT; esophageal temperature (T_es), ∼36.6 °C) and mild hyperthermia (HT; T_es, ∼37.2 °C; lower legs immersion in 42 °C of water). The threshold for cold sensation on the skin at chest was lower during HT than NT in the Sit (P < 0.05) but not in Sup, and at the forearm was lower during HT than NT in the Sup and further in Sit (both, P < 0.05), with interactive effects of temperature (NT vs. HT) × posture (Sup vs. Sit) (chest, P = 0.08; forearm, P < 0.05). The threshold for warm sensation on the skin at both sites remained unchanged with changes in body posture or temperature. The whole-body warm sensation was higher during HT than NT in both postures and higher in the Sit than Sup during both NT and HT (all, P < 0.05). Thus, thermal sensation during mild hyperthermia is modulated by postural change from supine to sitting to sense lesser cold on the skin and more whole-body warmth.

Exploring the Mechanisms of Exercise-Induced Hypoalgesia Using Somatosensory and Laser Evoked Potentials

Exercise-induced hypoalgesia is well described, but the underlying mechanisms are unclear. The aim of this study was to examine the effect of exercise on somatosensory evoked potentials, laser evoked potentials, pressure pain thresholds and heat pain thresholds. These were recorded before and after 3-min of isometric elbow flexion exercise at 40% of the participant's maximal voluntary force, or an equivalent period of rest. Exercise-induced hypoalgesia was confirmed in two experiments (Experiment 1–SEPs; Experiment 2–LEPs) by increased pressure pain thresholds at biceps brachii (24.3 and 20.6% increase in Experiment 1 and 2, respectively; both d > 0.84 and p < 0.001) and first dorsal interosseous (18.8 and 21.5% increase in Experiment 1 and 2, respectively; both d > 0.57 and p < 0.001). In contrast, heat pain thresholds were not significantly different after exercise (forearm: 10.8% increase, d = 0.35, p = 0.10; hand: 3.6% increase, d = 0.06, p = 0.74). Contrasting effects of exercise on the amplitude of laser evoked potentials (14.6% decrease, d = −0.42, p = 0.004) and somatosensory evoked potentials (10.9% increase, d = −0.02, p = 1) were also observed, while an equivalent period of rest showed similar habituation (laser evoked potential: 7.3% decrease, d = −0.25, p = 0.14; somatosensory evoked potential: 20.7% decrease, d = −0.32, p = 0.006). The differential response of pressure pain thresholds and heat pain thresholds to exercise is consistent with relative insensitivity of thermal nociception to the acute hypoalgesic effects of exercise. Conflicting effects of exercise on somatosensory evoked potentials and laser evoked potentials were observed. This may reflect non-nociceptive contributions to the somatosensory evoked potential, but could also indicate that peripheral nociceptors contribute to exercise-induced hypoalgesia.

A Standardized "Rescue" Exercise Program for Symptomatic Flare-up of Knee Osteoarthritis: Description and Safety Considerations

Study Design Secondary analysis of clinical trial data. Background Knee osteoarthritis (OA) management has changed significantly over recent decades toward nonpharmacological treatments, particularly exercise. However, the optimal exercise program remains to be established. Objective To describe the implementation of standardized rescue exercises for patients with pain exacerbations and to assess whether performing these benefit or further worsen symptoms in patients with exacerbated symptoms of knee OA. Methods The data from 2 randomized controlled studies of exercise in patients with knee OA were used. A supervised, standard exercise program that included standardized "rescue" exercises to be performed in the event of symptomatic exacerbation, defined as knee pain of greater than 5 on a 0-to-10 numeric pain-rating scale, was conducted for 12 weeks at 3 sessions per week. Pain ratings were obtained before and after each exercise session. Results Of 131 participants included, 2 never commenced the exercise program, leaving 129 to be included in the analysis. The analysis was observational and thus had no comparison group. During the program, 36 participants (28%) were referred to the rescue exercises. In 63% of the rescue sessions, the participants experienced decreased pain intensity (average ± SD, -2.6 ± 2.3), 27% reported no change in pain, and 10% reported increased pain intensity (average ± SD, 1.3 ± 0.5). Conclusion Having a predefined and standardized rescue exercise option appears beneficial, and did not result in further worsening of exacerbated knee OA symptoms. The intervention may be particularly relevant for patients with knee OA who have more severe symptoms. Level of Evidence Therapy, level 2b. Registered at www.clinicaltrials.gov (NCT01545258 and NCT01945749). J Orthop Sports Phys Ther 2016;46(11):942-946. Epub 28 Sep 2016. doi:10.2519/jospt.2016.6908.

Prevalence and factors associated with disturbed sleep in patients with ankylosing spondylitis and non-radiographic axial spondyloarthritis: a systematic review

This review explores the prevalence and factors associated with disturbed sleep for patients with ankylosing spondylitis and non-radiographic axial spondyloarthritis in order to clarify consistent findings in this otherwise disparate research field. The association of physical, demographic and psychological factors correlating with poor sleep was explored, and the effectiveness of interventions assessed. Ten electronic databases were searched: AMED, CINAHL, Embase, Medline, PsycINFO, PubMed, Scopus, Web of Science, OpenGrey and BASE. Following application of inclusion and exclusion criteria, 29 articles were critically assessed on the basis of methodology, experimental design, ethics and quality of sleep data, leading to the selection of 15 studies for final review. Poor sleep was reported in 35-90% of patients with axial spondyloarthritis and is more prevalent within this clinical population compared to healthy control subjects. Disturbed sleep is an important aspect of disease for patients and reflects the severity of disease activity, pain, fatigue and functional disability. However, the direction of this relationship is undetermined. Associations with age, gender, years spent in education, quality of life and depression have also been demonstrated. Anti-TNF medication is effective in reducing poor sleep, and exercise has also produced beneficial results. Future research into poor sleep should take account of its multifactorial nature. There is also a current lack of research investigating non-pharmacological interventions or combination therapies. A standardised, validated measurement of poor sleep, appropriate for regular patient screening, would be a useful first step for future research.

Exercise-induced hypoalgesia: Pain tolerance, preference and tolerance for exercise intensity, and physiological correlates following dynamic circuit resistance exercise

Previous research has demonstrated significant decreases in pain perception in healthy individuals following both aerobic and upper body resistance exercise, but research on circuit training has been limited. The purpose of the study was to determine the effects of a strenuous bout of dynamic circuit resistance exercise on pain threshold and pain tolerance in conjunction with changes in blood lactate levels, heart rate (HR), and perceived exertion. A sample of 24 college-age students participated in 2 sessions: (1) a maximal strength testing session and (2) a circuit training bout of exercise that consisted of 3 sets of 12 repetitions with a 1:1 work to rest ratio at 60% one-repetition maximum (1-RM) predicted from a three-repetition maximum (3-RM) for 9 exercises. Participants exhibited increases in pain tolerance, blood lactate levels, HR and perceived exertion following resistance exercise. Preference for exercise intensity was positively correlated with lactate post exercise and tolerance for exercise intensity was positively correlated with pain tolerance and lactate post exercise. In conclusion, this is the first study to demonstrate increases in pain tolerance following a dynamic circuit resistance exercise protocol and disposition for exercise intensity may influence lactate and pain responses to circuit resistance exercise.

Pressure and cold pain threshold reference values in a large, young adult, pain-free population

Background and aims

Currently there is a lack of large population studies that have investigated pain sensitivity distributions in healthy pain free people. The aims of this study were: (1) to provide sex-specific reference values of pressure and cold pain thresholds in young pain-free adults; (2) to examine the association of potential correlates of pain sensitivity with pain threshold values.

Methods

This study investigated sex specific pressure and cold pain threshold estimates for young pain free adults aged 21–24 years. A cross-sectional design was utilised using participants (n =617) from the Western Australian Pregnancy Cohort (Raine) Study at the 22-year follow-up. The association of site, sex, height, weight, smoking, health related quality oflife, psychological measures and activity with pain threshold values was examined. Pressure pain threshold (lumbar spine, tibialis anterior, neck and dorsal wrist) and cold pain threshold (dorsal wrist) were assessed using standardised quantitative sensory testing protocols.

Results

Reference values for pressure pain threshold (four body sites) stratified by sex and site, and cold pain threshold (dorsal wrist) stratified by sex are provided. Statistically significant, independent correlates of increased pressure pain sensitivity measures were site (neck, dorsal wrist), sex (female), higher waist-hip ratio and poorer mental health. Statistically significant, independent correlates of increased cold pain sensitivity measures were, sex (female), poorer mental health and smoking.

Conclusions

These data provide the most comprehensive and robust sex specific reference values for pressure pain threshold specific to four body sites and cold pain threshold at the dorsal wrist for young adults aged 21–24 years. Establishing normative values in this young age group is important given that the transition from adolescence to adulthood is a critical temporal period during which trajectories for persistent pain can be established.

Implications

These data will provide an important research resource to enable more accurate profiling and interpretation of pain sensitivity in clinical pain disorders in young adults. The robust and comprehensive data can assist interpretation of future clinical pain studies and provide further insight into the complex associations of pain sensitivity that can be used in future research.

Is tailored treatment superior to non-tailored treatment for pain and disability in women with non-specific neck pain? A randomized controlled trial

BACKGROUND

The evidence for the effect of treatments of neck pain is modest. In the absence of causal treatments, a possibility is to tailor the treatment to the individuals' functional limitations and symptoms. The aim was to evaluate treatment effects of a tailored treatment versus a non-tailored treatment. Our hypothesis was that tailored treatment (TT) would have better effect on pain intensity and disability than either non-tailored treatment (NTT) (same treatment components but applied quasi-randomly) or treatment-as-usual (TAU) (no treatment from the study, no restrictions). We further hypothesized that TT and NTT would both have better effect than TAU.

METHOD

One hundred twenty working women with subacute and chronic non-specific neck pain were allocated to 11 weeks of either TT, NTT or TAU in a randomized controlled trial with follow-ups at 3, 9 and 15 months. The TT was designed from a decision model based on assessment of function and symptoms with defined cut-off levels for the following categories: reduced cervical mobility, impaired neck-shoulder strength and motor control, impaired eye-head-neck control, trapezius myalgia and cervicogenic headache. Primary outcomes were pain and disability. Secondary outcomes were symptoms, general improvement, work productivity, and pressure pain threshold of m. trapezius.

RESULTS

Linear mixed models analysis showed no differences between TT and NTT besides work productivity favoring TT at 9- and 15-months follow-ups. TT and NTT improved significantly more than TAU on pain, disability and symptoms at 3-month follow-up. General improvement also favored TT and NTT over TAU at all follow-ups.

CONCLUSION

Tailored treatment according to our proposed decision model was not more effective than non-tailored treatment in women with subacute and chronic neck pain. Both tailored and non-tailored treatments had better short-term effects than treatment-as-usual, supporting active and specific exercise therapy, although therapist-patient interaction was not controlled for. Better understanding of the importance of functional impairments for pain and disability, in combination with a more precise tailoring of specific treatment components, is needed to progress.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN 49348025. Registered 2 August 2011.

The Rationale for Exercise in the Management of Pain in Parkinson's Disease

Pain is a distressing non-motor symptom experienced by up to 85% of people with Parkinson’s disease (PD), yet it is often untreated. This pain is likely to be influenced by many factors, including the disease process, PD impairments as well as co-existing musculoskeletal and/or neuropathic pain conditions. Expert opinion recommends that exercise is included as one component of pain management programs; however, the effect of exercise on pain in this population is unclear. This review presents evidence describing the potential influence of exercise on the pain-related pathophysiological processes present in PD. Emerging evidence from both animal and human studies suggests that exercise might contribute to neuroplasticity and neuro-restoration by increasing brain neurotrophic factors, synaptic strength and angiogenesis, as well as stimulating neurogenesis and improving metabolism and the immune response. These changes may be beneficial in improving the central processing of pain. There is also evidence that exercise can activate both the dopaminergic and non-dopaminergic pain inhibitory pathways, suggesting that exercise may help to modulate the experience of pain in PD. Whilst clinical data on the effects of exercise for pain relief in people with PD are scarce, and are urgently needed, preliminary guidelines are presented for exercise prescription for the management of central neuropathic, peripheral neuropathic and musculoskeletal pain in PD.

Which Non-Pharmacological Treatment is More Effective on Clinical Parameters in Patients With Fibromyalgia: Balneotherapy or Aerobic Exercise?

OBJECTIVES

This study aims to determine the effects of non-pharmacological therapies, namely balneotherapy, exercise, and the combined use of balneotherapy and exercise, on total myalgic score (TMS), sleep quality, health status, and signs of depression in patients with fibromyalgia syndrome, and to compare the efficacies of these treatment programs with respect to the above parameters.

PATIENTS AND METHODS

A total of 120 female subjects (mean age 37.21±12.45 years; range 18 to 63 years) diagnosed with fibromyalgia were enrolled. The patients were randomized into three groups with 40 patients in each (group 1: balneotherapy group, group 2: balneotherapy + exercise group, and group 3: exercise group). The patients underwent the treatment program for five days a week for a total of three weeks. Clinical parameters, Fibromyalgia Impact Questionnaire, Pittsburgh Sleep Quality Index, TMS, and Beck Depression Scale were evaluated at pre-treatment and post- treatment periods, and at the third-month control visit.

RESULTS

There were no differences between the groups with respect to Fibromyalgia Impact Questionnaire, Pittsburgh Sleep Quality Index, TMS and Beck Depression Scale scores on pre-treatment evaluation, while the combined use of balneotherapy + aerobic exercise was more effective on TMS (p<0.001), health status (p=0.009), and level of depression (p<0.001) in post-treatment evaluation. A better state of well-being with respect to sleep quality was achieved by balneotherapy and balneotherapy + exercise groups. The third-month comparisons, on the other hand, demonstrated that the balneotherapy + exercise group had a greater state of well-being with respect to TMS (p<0.001) and general health status (p<0.001). Balneotherapy + exercise and exercise therapy benefited signs of depression to a better degree (p<0.001). Balneotherapy and combined balneotherapy + exercise therapy produced more effective results in terms of sleep quality (p<0.001). TMS regressed to near baseline levels (p=0.397), while Fibromyalgia Impact Questionnaire levels rose to near baseline levels at the third-month control in the exercise therapy group (p=0.070).

CONCLUSION

The combined application of balneotherapy + exercise therapy, which are two of the recommended non-pharmacological treatments, may have superior and more sustained effects than administering either therapy alone.

Transcranial Direct Current Stimulation Combined with Aerobic Exercise to Optimize Analgesic Responses in Fibromyalgia: A Randomized Placebo-Controlled Clinical Trial

Fibromyalgia is a chronic pain syndrome that is associated with maladaptive plasticity in neural central circuits. One of the neural circuits that are involved in pain in fibromyalgia is the primary motor cortex. We tested a combination intervention that aimed to modulate the motor system: transcranial direct current stimulation (tDCS) of the primary motor cortex (M1) and aerobic exercise (AE). In this phase II, sham-controlled randomized clinical trial, 45 subjects were assigned to 1 of 3 groups: tDCS + AE, AE only, and tDCS only. The following outcomes were assessed: intensity of pain, level of anxiety, quality of life, mood, pressure pain threshold, and cortical plasticity, as indexed by transcranial magnetic stimulation. There was a significant effect for the group-time interaction for intensity of pain, demonstrating that tDCS/AE was superior to AE [F (13, 364) = 2.25, p = 0.007] and tDCS [F (13, 364) = 2.33, p = 0.0056] alone. Post-hoc adjusted analysis showed a difference between tDCS/AE and tDCS group after the first week of stimulation and after 1 month intervention period (p = 0.02 and p = 0.03, respectively). Further, after treatment there was a significant difference between groups in anxiety and mood levels. The combination treatment effected the greatest response. The three groups had no differences regarding responses in motor cortex plasticity, as assessed by TMS. The combination of tDCS with aerobic exercise is superior compared with each individual intervention (cohen's d effect sizes > 0.55). The combination intervention had a significant effect on pain, anxiety and mood. Based on the similar effects on cortical plasticity outcomes, the combination intervention might have affected other neural circuits, such as those that control the affective-emotional aspects of pain.

TRIAL REGISTRATION

(www.ClinicalTrials.gov), identifier NTC02358902.

Exercise Strengthens Central Nervous System Modulation of Pain in Fibromyalgia

To begin to elucidate the mechanisms underlying the benefits of exercise for chronic pain, we assessed the influence of exercise on brain responses to pain in fibromyalgia (FM). Complete data were collected for nine female FM patients and nine pain-free controls (CO) who underwent two functional neuroimaging scans, following exercise (EX) and following quiet rest (QR). Brain responses and pain ratings to noxious heat stimuli were compared within and between groups. For pain ratings, there was a significant (p < 0.05) Condition by Run interaction characterized by moderately lower pain ratings post EX compared to QR (d = 0.39–0.41) for FM but similar to ratings in CO (d = 0.10–0.26), thereby demonstrating that exercise decreased pain sensitivity in FM patients to a level that was analogous to pain-free controls. Brain responses demonstrated a significant within-group difference in FM patients, characterized by less brain activity bilaterally in the anterior insula following QR as compared to EX. There was also a significant Group by Condition interaction with FM patients showing less activity in the left dorsolateral prefrontal cortex following QR as compared to post-EX and CO following both conditions. These results suggest that exercise appeared to stimulate brain regions involved in descending pain inhibition in FM patients, decreasing their sensitivity to pain. Thus, exercise may benefit patients with FM via improving the functional capacity of the pain modulatory system.

Effect of forced treadmill exercise and blocking of opioid receptors with naloxone on memory in male rats

Background:

The forced treadmill running can influence the opioid contents of the brain, through both effects of exercise and the effects of stress caused by coercion. Since opioids can cause negative effects on brain functions, this study aimed to evaluate the effect of forced treadmill exercise and blocking of opioid receptors with naloxone on memory in male rats.

Materials and Methods:

Experimental groups were the control, the exercise, the naloxone, and the naloxone exercise. The exercise program was treadmill running at 22 m/min at 0° inclination for 50 min/day, 6 days/week, for 4 weeks. Naloxone (1 mg/kg) was injected 5 min before the treadmill running. Morris water maze and passive avoidance learning tests were used for evaluation of memory. Acquisition phase of both tests was performed before interventions, and memory was evaluated 1-day and 1-week after the last session of exercise and treatments.

Results:

Our data showed that forced exercise impaired performance in passive avoidance learning test (P < 0.05 and P <0.01, 1-day, and 1-week after the last session of exercise and treatments, respectively). Spatial memory was only impaired after 1-week in the exercise group. Naloxone had no significant effect on memory in the control group. However, it improved memory in the exercise group, as there was no significant difference between the control and the naloxone exercise in both tests.

Conclusion:

The data correspond to the possibility that opioidergic system may have mediatory roles in exercise-induced responses in forced exercise. These roles are likely harmful for memory.

Effect of physical activity level on orthodontic pain perception and analgesic consumption in adolescents

INTRODUCTION

The objective of this study was to assess the effect of baseline physical activity level on orthodontic pain perception and analgesic consumption after orthodontic separator placement in adolescents.

METHODS

One hundred fifty participants (mean age, 14.5 years; SD, 1.7 years; 73 girls, 77 boys) were included in this longitudinal study. The physical activity questionnaire was used to assess their baseline physical activity levels. Once participants completed the questionnaire, orthodontic separators were placed at the mesial and distal contact points of the maxillary and mandibular first molars. A 100-mm visual analog scale was used for pain assessment. Analgesic consumption was recorded as a binary response (yes/no). Both outcomes were assessed at 1 baseline time point and 7 follow-up time points (bedtime on days 1 to 7). A multilevel mixed-effect model analysis approach was used to analyze the longitudinal data.

RESULTS

Of the 150 participants in the study, data from 137 were included in the analysis (mean age, 14.4 years; SD, 1.7 years; 65 girls, 72 boys). Compared with the low-activity group (84 participants; 61.3%), the high-activity group (53 participants; 38.7%) experienced significantly less pain (mean estimate, -8.958; P = 0.0114; 95% confidence interval, -15.868 to -2.049) and consumed fewer analgesics (odds ratio, 0.443; P <0.0318; 95% confidence interval, 0.199 to 0.786) during the study period.

CONCLUSIONS

Physical activity has a significant influence on orthodontic pain perception and analgesic consumption in adolescents undergoing orthodontic treatment. Further research is needed on this topic to elucidate the association between physical activity and orthodontic pain.

Pain thresholds following maximal endurance exercise

PURPOSE

Physical exercise causes alterations in pain sensitivity. Many studies verified so-called exercise-induced analgesia caused by submaximal aerobic intensity. This study aimed to determine the effect of an endurance exercise to exhaustion on pain sensitivity of healthy young men.

METHOD

Pressure pain thresholds (PPTs) [in Newton, (N)] of 50 healthy males (mean age 26 ± 4 years) were applied to knee, ankle and elbow joints as well as to the sternum and forehead. This was followed by a bout of cycling ergometer exercise to exhaustion. The whole process was repeated after 20 and 60 min respectively.

RESULTS

Endurance exercise to exhaustion decreased PPTs at sternum and forehead significantly, while thresholds at the joints were not affected. Pain thresholds at forehead and sternum declined 20 min after exercise with the forehead's threshold being more reduced. PPTs remain decreased until 60 min after exercise (forehead: from 43.6 ± 15.2 N to 36.6 ± 19.8 N to 37.2 ± 13.4 N; sternum: from 46.8 ± 21.0 N to 42.5 ± 17.1 N to 44.8 ± 18.2 N). Modulation of pain sensitivity showed large effect sizes over time for both landmarks (forehead w = 0.65; sternum w = 0.50).

CONCLUSION

Exhaustive endurance exercise is followed by a hyperalgetic condition at forehead and sternum. This may be due to either a reduction in pain inhibiting or an activation in pain stimulating pathways.

Mechanisms of exercise-induced hypoalgesia

The purpose of this study was to examine opioid and endocannabinoid mechanisms of exercise-induced hypoalgesia (EIH). Fifty-eight men and women (mean age = 21 years) completed 3 sessions. During the first session, participants were familiarized with the temporal summation of heat pain and pressure pain protocols. In the exercise sessions, following double-blind administration of either an opioid antagonist (50 mg naltrexone) or placebo, participants rated the intensity of heat pulses and indicated their pressure pain thresholds and pressure pain ratings before and after 3 minutes of submaximal isometric exercise. Blood was drawn before and after exercise. Results indicated that circulating concentrations of 2 endocannabinoids, N-arachidonylethanolamine and 2-arachidonoylglycerol, as well as related lipids oleoylethanolamide, palmitoylethanolamide, N-docosahexaenoylethanolamine, and 2-oleoylglycerol, increased significantly (P < .05) following exercise. Pressure pain thresholds increased significantly (P < .05), whereas pressure pain ratings decreased significantly (P < .05) following exercise. Also, temporal summation ratings were significantly lower (P < .05) following exercise. These changes in pain responses did not differ between the placebo and naltrexone conditions (P > .05). A significant association was found between EIH and docosahexaenoylethanolamine. These results suggest involvement of a nonopioid mechanism in EIH following isometric exercise.

PERSPECTIVE

Currently, the mechanisms responsible for EIH are unknown. This study provides support for a potential endocannabinoid mechanism of EIH following isometric exercise.

Voluntary Exercise Training: Analysis of Mice in Uninjured, Inflammatory, and Nerve-Injured Pain States

Both clinical and animal studies suggest that exercise may be an effective way to manage inflammatory and neuropathic pain conditions. However, existing animal studies commonly use forced exercise paradigms that incorporate varying degrees of stress, which itself can elicit analgesia, and thus may complicate the interpretation of the effects of exercise on pain. We investigated the analgesic potential of voluntary wheel running in the formalin model of acute inflammatory pain and the spared nerve injury model of neuropathic pain in mice. In uninjured, adult C57BL/6J mice, 1 to 4 weeks of exercise training did not alter nociceptive thresholds, lumbar dorsal root ganglia neuronal excitability, or hindpaw intraepidermal innervation. Further, exercise training failed to attenuate formalin-induced spontaneous pain. Lastly, 2 weeks of exercise training was ineffective in reversing spared nerve injury-induced mechanical hypersensitivity or in improving muscle wasting or hindpaw denervation. These findings indicate that in contrast to rodent forced exercise paradigms, short durations of voluntary wheel running do not improve pain-like symptoms in mouse models of acute inflammation and peripheral nerve injury.

Effect of Exercise on µ-Opioid Receptor Expression in the Rostral Ventromedial Medulla in Neuropathic Pain Rat Model

OBJECTIVE

To investigate the effects of aerobic exercise on neuropathic pain and verify whether regular treadmill exercise alters opioid receptor expression in the rostral ventral medulla (RVM) in a neuropathic pain rat model.

METHODS

Thirty-two male Sprague-Dawley rats were used in the study. All rats were divided into 3 groups, i.e., group A, sham group (n=10); group B, chronic constriction injury (CCI) group (n=11); and group C, CCI+exercise group (n=11). Regular treadmill exercise was performed for 30 minutes a day, 5 days a week, for 4 weeks at the speed of 8 m/min for 5 minutes, 11 m/min for 5 minutes, and 22 m/min for 20 minutes. Withdrawal threshold and withdrawal latency were measured before and after the regular exercise program. Immunohistochemistry and Western blots analyses were performed using antibodies against µ-opioid receptor (MOR).

RESULTS

Body weight of group C was the lowest among all groups. Withdrawal thresholds and withdrawal latencies were increased with time in groups B and C. There were significant differences of withdrawal thresholds between group B and group C at 1st, 2nd, 3rd, and 4th weeks after exercise. There were significant differences of withdrawal latencies between group B and group C at 3rd and 4th weeks after exercise. MOR expression of group C was significantly decreased, as compared to that of group B in the RVM and spinal cord.

CONCLUSION

In neuropathic pain, exercise induced analgesia could be mediated by desensitization of central MOR by endogenous opioids, leading to the shift of RVM circuitry balance to pain inhibition.

Moderate exercise training attenuates inflammatory mediators in DRG of Type 1 diabetic rats

Painful neuropathy is a long-term and difficult to treat complication of diabetes that affects 25% of diabetic patients and interferes with their quality of life. Unfortunately, available medical treatments are relatively ineffective due to dependency and addiction. Emerging research indicates that moderate-to-vigorous physical activity provides health-related benefits. However, adequate data is not available to determine whether regular exercise would prevent or delay the development of painful neuropathy in subjects with Type 1 diabetes. This study demonstrates the significance of moderate exercise in the amelioration of pain in animals with Type 1 diabetes after 6weeks of exercise paradigm. After initial acclimatization, streptozotocin-diabetic animals were placed in motorized running wheels for 60minperday, for five days a week for 6weeks starting at one week after diabetes. A growing body of evidence suggests that the release of proinflammatory cytokines plays an important role in the development and persistence of pain. This study demonstrates that moderate exercise increases the expression of inhibitory neurotransmitter enkephalin and also reduces the presence of a number of proinflammatory cytokines in the dorsal root ganglia (DRG), subsequently impeding the development of neuropathy along with a decrease in the voltage gated ion channels in the DRG. Overall, the study suggests that exercise may provide an alternate route of treatment of painful neuropathy in Type 1 diabetic subjects by decreasing the use of pain medications, thereby providing a more useful and efficient way for pain management.

A Critical Analysis of the British Horseracing Authority's Review of the Use of the Whip in Horseracing

Simple Summary

This is a critique of the British Horseracing Authority’s 2011 report, A Review of the Use of the Whip in Horseracing. It analyses the way the report uses science and public opinion research to reach conclusions on the animal welfare impact of whip use. Our analysis suggests that some of the report’s findings are insufficiently defended by the report and that further independent scientific review is needed to reach definitive conclusions about whip use on racehorse welfare.

Abstract

There is increasing controversy about the use of the whip as a performance aid in Thoroughbred horseracing and its impact on horse welfare. This paper offers a critical analysis of the British Horseracing Authority’s (BHA) 2011 Report Responsible Regulation: A Review of the Use of the Whip in Horseracing. It examines the BHA’s process of consultation and use of science and public opinion research through the application of current scientific literature and legal analysis. This analysis suggests that the BHA’s findings on the welfare impact and justification for whip use are insufficiently defended by the report. These findings indicate that the report is an inadequate basis from which to draw any definitive conclusions on the impact of whips on racehorse welfare. Further review is needed, undertaken by an independent scientific body, to advance this debate.

Prevalence of chronic pain and its association with the sociodemographic situation and physical activity in leisure of elderly in Florianópolis, Santa Catarina: population-based study

OBJECTIVE

To estimate the prevalence of chronic pain and its association with socioeconomic and demographic status, and leisure physical activity in the elderly population.

METHODS

This study is part of an epidemiological cross-sectional population-based household survey called EpiFloripa Elderly 2009-2010, which was conducted with 1,705 elderly individuals (≥ 60 years) residents of Florianópolis, Santa Catarina. From the positive response to chronic pain, the associations with the variables were investigated through a structured interview. Descriptive statistics were conducted, including ratio calculation and 95% confidence intervals. In crude and adjusted analysis, Poisson regression was utilized, estimating prevalence ratios, with 95% confidence intervals and ≤ 0.05 p-values.

RESULTS

Among the subjects, 29.3% (IC95% 26.5 - 32.2) reported chronic pain. Adjusted analysis showed that being female, having less years of schooling, and being in worse economic situation were significantly associated with a higher prevalence of chronic pain. Being physically active during leisure time was significantly associated with lower prevalence of the outcome.

CONCLUSIONS

Therefore, it is clear that chronic pain affects a considerable amount of elderly individuals. Social inequalities are a harmful influence in these individuals' quality of life, inasmuch as those inequalities increase the frequency with which chronic pain afflicts them. At the same time, physical activity during leisure time decreases chronic pain frequency. It is fundamental that public health policies subsidize multidisciplinary pain management programs, which should include health targeted physical activity for the elderly, thus preventing the decrease in quality of life that chronic pain brings to this population.