Self-reported physical activity predicts pain inhibitory and facilitatory function

Association between physical activity and pain processing in adults with chronic low back pain compared to pain-free controls

BACKGROUND

Pain sensitivity has been negatively associated with physical activity levels. Few studies have examined associations between experimentally induced pain sensitivity and physical activity in adults with chronic low back pain and pain-free controls.

OBJECTIVE

The objective of this study was to examine associations between physical activity levels and how an individual processes pain using experimentally induced pain stimuli.

METHODS

Seventy subjects (CLBP = 49; mean age = 46.8 ± 14.9; Pain-free = 21; mean age = 45.3 ± 18.2, n of females = 46) participated. A self-report questionnaire derived from the International Physical Activity Questionnaire (IPAQ) was used to calculate an activity level index. Pain sensitivity was assessed via quantitative sensory testing (QST) at the right lower extremity.

RESULTS

Moderate (U = 688, p< 0.05) and vigorous (U = 649, p< 0.05) physical activity levels were higher in pain-free vs. individuals with CLBP. Activity level was not associated with pain sensitivity (Pain-free: R2 = 0.02, p> 0.05; CLBP: R2 = 0.01, p> 0.05). Both moderate (R2 = 0.49, p< 0.05) and vigorous (R2 = 0.68, p< 0.01) physical activity were associated with pain modulation amongst pain-free individuals.

CONCLUSIONS

Findings suggest that physical activity influences pain modulation amongst pain-free individuals, however no relationship exists once CLBP is present. However, future investigation will elucidate the extent to which physical activity level either prevents CLBP or is effective in alleviating CLBP.

Predictors of multidimensional functional outcomes after total knee arthroplasty

Multiple assessments are used clinically after total knee arthroplasty (TKA) including self-report, performance tasks, and physical activity levels. It is unclear if these different functional assessments are interchangeable or if they measure different constructs. The objective of this study was to characterize different functional measures before and after TKA. We characterized function before and after TKA using perceived function (KOOS ADL), physical performance (gait speed), and daily activity (steps/day via accelerometry); compared function in people undergoing TKA to age-matched healthy controls; and examined characteristics of those undergoing TKA for potential predictors of postoperative function. Prior to TKA, all three functional assessments were significantly lower for participants than those of healthy controls and each measure remained lower for participants than for controls postoperatively. All three functional assessments developed differently over time postoperatively. Each functional outcome had a unique set of predictors. Perceived function was predicted primarily by anxiety and depression, physical performance was most strongly predicted by age, and daily activity was chiefly predicted by BMI. Pressure pain threshold was a common predictor across all models. Functional limitations exist preoperatively and persist postoperatively across different measures in people undergoing TKA when compared to those measures in healthy controls. Functional outcomes after TKA are different depending on the functional measure utilized, implying that different constructs underlie each measure. Multiple functional measures should be assessed to provide a more comprehensive assessment of function after TKA. Further work should assess the impact of interventions designed to treat modifiable predictors of postoperative TKA function. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2790-2798, 2017.

Physical Activity May Be Associated with Conditioned Pain Modulation in Women but Not Men among Healthy Individuals

Background

Conditioned pain modulation (CPM), a phenomenon also known as diffuse noxious inhibitory control, is thought to be affected by various factors, including sex and level of physical activity. However, the involvement of these factors in CPM remains unclear.

Methods

Eighty-six healthy young subjects (M/F, 43/43) participated in this study. Participants were assessed on the basis of their mechanical pressure pain threshold (PPT), CPM response, body mass index (BMI), basal metabolic rate (BMR), and duration of moderate-to-vigorous physical activity (MVPA) over a week, using a motion counter. Response to CPM was evaluated as PPT during painful cold stimulation relative to baseline PPT.

Results

Men showed significantly higher baseline PPT than women; however, this difference was no longer significant after controlling for confounders. Stepwise multiple linear regression analyses revealed BMR to be a significant contributor towards baseline PPT in the entire study population. In contrast, although there were no significant contributors to CPM response among men and in the overall study group, MVPA was positively associated with CPM response among women (β = 0.397).

Conclusions

These results suggest that, among healthy young individuals, CPM response may be associated with moderate-to-vigorous physical activity in women but not in men.

Psychosocial Influences on Exercise-Induced Hypoalgesia

Objective

The purpose of this study was to examine psychosocial influences on exercise-induced hypoalgesia (EIH).

Design

Randomized controlled trial.

Setting

Clinical research unit in a hospital.

Subjects

Fifty-eight healthy men and women (mean age = 21 ± 3 years) participated in this study.

Methods

Participants were first asked to complete a series of baseline demographic and psychological questionnaires including the Pain Catastrophizing Scale, the Fear of Pain Questionnaire, and the Family Environment Scale. Following this, they were familiarized with both temporal summation of heat pain and pressure pain testing protocols. During their next session, participants completed the Profile of Mood States, rated the intensity of heat pulses, and indicated their pressure pain thresholds and ratings before and after three minutes of submaximal, isometric exercise. Situational catastrophizing was assessed at the end of the experimental session.

Results

Results indicated that experimental pain sensitivity was significantly reduced after exercise ( P  < 0.05). Men and women did not differ on any of the measured psychosocial variables ( P  > 0.05). Positive family environments predicted attenuated pain sensitivity and greater EIH, whereas negative and chronic pain-present family environments predicted worse pain and EIH outcomes. Situational catastrophizing and negative mood state also predicted worse pain and EIH outcomes and were additionally associated with increased ratings of perceived exertion and muscle pain during exercise.

Conclusions

This study provides preliminary evidence that psychosocial variables, such as the family environment and mood states, can affect both pain sensitivity and the ability to modulate pain through exercise-induced hypoalgesia.

Conditioned pain modulation among young, healthy, and physically active African American and non-Hispanic White adults

OBJECTIVE

Research shows that African American (AA) adults experience more severe and frequent pain compared to non-Hispanic White (NHW) adults. Additionally, experimental studies demonstrate that AA adults exhibit less efficient central pain inhibition compared to NHW adults, which may partially explain the racial/ethnic disparities in pain. Evidence suggests that regular physical activity (PA) may help improve central pain inhibition, but research shows that AA adults engage in less PA, and are less likely to meet PA guidelines for health promotion compared to NHW adults. These observations suggest that PA levels may help better understand the racial/ethnic difference in central pain inhibition. Therefore, this study compared central pain inhibition and PA levels among AA and NHW adults.

METHODS

Young and healthy participants were recruited on campus, and 27 AA and 27 NHW adults completed this study. Central pain inhibitory processing was assessed using conditioned pain modulation (CPM), where changes in electrical pain ratings were quantified during and after exposure to pressure pain compared to baseline. PA levels were assessed using self-report questionnaires and accelerometer.

RESULTS

The participants were generally physically active, and most participants in both groups met the public recommendation of PA for health promotion. Electrical pain ratings were significantly reduced during and after exposure to pressure pain compared to baseline. There was no racial/ethnic difference in a magnitude of changes in electrical pain ratings.

CONCLUSION

Young, healthy, and physically active AA and NHW adults exhibit similar CPM responses. Regular PA may help attenuate the racial/ethnic difference in CPM responses.

Does exercise increase or decrease pain? Central mechanisms underlying these two phenomena

Exercise is an integral part of the rehabilitation of patients suffering a variety of chronic musculoskeletal conditions, such as fibromyalgia, chronic low back pain and myofascial pain. Regular physical activity is recommended for treatment of chronic pain and its effectiveness has been established in clinical trials for people with a variety of pain conditions. However, exercise can also increase pain making participation in rehabilitation challenging for the person with pain. Animal models of exercise-induced pain have been developed and point to central mechanisms underlying this phenomena, such as increased activation of NMDA receptors in pain-modulating areas. Meanwhile, a variety of basic science studies testing different exercise protocols, show exercise-induced analgesia involves activation of central inhibitory pathways. Opioid, serotonin and NMDA mechanisms acting in rostral ventromedial medulla promote analgesia associated with exercise. This review explores and discusses current evidence on central mechanisms underlying exercised-induced pain and analgesia.

Chronic pain in high school students is associated with physical activity and sleeping hours but not with screen time

Background Existing studies on the association between physical activity (PA), screen based time and sleeping show conflicting results. Objective This study investigates the association between chronic pain at different body regions and self-reported PA, screen based time and sleeping hours in high school students. Subjects A total of 969 students aged 13-19 years old. Methods Participants completed a questionnaire on chronic pain, time spent in moderate and vigorous PA, screen based time watching televivsion (TV)/digital versatile discs (DVD), playing, using mobile phones and computers and sleeping hours. Univariate and multivariate associations between pain and PA, screen based time and sleeping hours were investigated. Results In the univariate model time spent in moderate and vigorous PA, in screen based activities and sleeping were associated with pain in at least one body site. In the multivariate model, screen based activities were not associated with pain; sleeping 7 h or less and increased time in moderate PA were associated with pain at almost all body sites [odds ratio (OR) between 2.69-3.66 and 1.06-1.10, respectively]. Conclusion Time spent in PA and sleeping increased the risk of chronic pain in almost all body regions and might confound the association between screen based time and pain.

What to Build for Middle-Agers to Come? Attractive and Necessary Functions of Exercise-Promotion Mobile Phone Apps: A Cross-Sectional Study

BACKGROUND

Physical activity is important for middle-agers to maintain health both in middle age and in old age. Although thousands of exercise-promotion mobile phone apps are available for download, current literature offers little understanding regarding which design features can enhance middle-aged adults' quality perception toward exercise-promotion apps and which factor may influence such perception.

OBJECTIVES

The aims of this study were to understand (1) which design features of exercise-promotion apps can enhance quality perception of middle-agers, (2) whether their needs are matched by current functions offered in app stores, and (3) whether physical activity (PA) and mobile phone self-efficacy (MPSE) influence quality perception.

METHODS

A total of 105 middle-agers participated and filled out three scales: the International Physical Activity Questionnaire (IPAQ), the MPSE scale, and the need for design features questionnaire. The design features were developed based on the Coventry, Aberdeen, and London-Refined (CALO-RE) taxonomy. Following the Kano quality model, the need for design features questionnaire asked participants to classify design features into five categories: attractive, one-dimensional, must-be, indifferent, and reverse. The quality categorization was conducted based on a voting approach and the categorization results were compared with the findings of a prevalence study to realize whether needs match current availability. In total, 52 multinomial logistic regression models were analyzed to evaluate the effects of PA level and MPSE on quality perception of design features.

RESULTS

The Kano analysis on the total sample revealed that visual demonstration of exercise instructions is the only attractive design feature, whereas the other 51 design features were perceived with indifference. Although examining quality perception by PA level, 21 features are recommended to low level, 6 features to medium level, but none to high-level PA. In contrast, high-level MPSE is recommended with 14 design features, medium level with 6 features, whereas low-level participants are recommended with 1 feature. The analysis suggests that the implementation of demanded features could be low, as the average prevalence of demanded design features is 20% (4.3/21). Surprisingly, social comparison and social support, most implemented features in current apps, were categorized into the indifferent category. The magnitude of effect is larger for MPSE because it effects quality perception of more design features than PA. Delving into the 52 regression models revealed that high MPSE more likely induces attractive or one- dimensional categorization, suggesting the importance of technological self-efficacy on eHealth care promotion.

CONCLUSIONS

This study is the first to propose middle-agers' needs in relation to mobile phone exercise-promotion. In addition to the tailor-made recommendations, suggestions are offered to app designers to enhance the performance of persuasive features. An interesting finding on change of quality perception attributed to MPSE is proposed as future research.

The association between displacement of sedentary time and chronic musculoskeletal pain: an isotemporal substitution analysis

OBJECTIVES

Physical activity is an effective intervention for the prevention and management of chronic musculoskeletal pain (CMP). However, there is a lack of research to inform the intensity of physical activity that should be recommended. The aim of this study was to investigate the association between substituting 10minutes of sedentary time with either 10minutes of light physical activity (LPA) or moderate-to-vigorous physical activity (MVPA) and the CMP prevalence ratio.

DESIGN

Secondary Analysis (November 2015) of data from the Health Survey for England (2008).

PARTICIPANTS

2313 adults (≥16years).

MAIN OUTCOME MEASURES

Sedentary time, LPA and MVPA were measured using accelerometry. We used isotemporal models to quantify the prevalence ratio for CMP of replacing 10minutes of sedentary time with 10minutes of LPA or MVPA.

RESULTS

The prevalence of CMP in this sample was 17%. The unadjusted prevalence ratio was 0.99 (95% CI: 0.97 to 1.01) for LPA and 0.76 (0.70 to 0.84) for MVPA. The fully adjusted prevalence ratio was 1.01 (95% CI: 0.99 to 1.02) for LPA and 0.89 (0.82 to 0.96) for MVPA.

CONCLUSIONS

Substituting 10minutes of sedentary time with an equivalent period of LPA was not associated with a reduction in the prevalence ratio for CMP, whereas the equivalent replacement with MVPA showed a small protective relationship. Regarding CMP prevalence, physical activity intensity appears to be important, with MVPA rather than LPA showing a protective relationship. Prospective studies are needed to investigate causality.

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.

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.

Heightened cold pain and pressure pain sensitivity in young female adults with moderate-to-severe menstrual pain

This study investigated the association between menstrual pain severity and psychophysical measures of cold and pressure pain sensitivity. A cross-sectional design was used with young women (n = 432) from the Western Australian Pregnancy Cohort (Raine) Study. Menstrual pain severity and oral contraception use was obtained from questionnaires at 20 and 22-year follow-ups. A visual analog scale (VAS; range from 0 [none] to 10 [unbearable]) was used to measure menstrual pain severity at both 20 and 22 years over the 3-year period, with 3 groups created: (1) no pain or mild pain (VAS 0-3), (2) at least moderate pain at a minimum of 1 of the 2 time points (hereafter named "mixed)", and (3) severe pain (VAS 8-10). Cold pain sensitivity (dorsal wrist) and pressure pain sensitivity (lumbar spine, upper trapezius, dorsal wrist, and tibialis anterior) were assessed using standardised quantitative sensory testing protocols. Confounding variables included number of musculoskeletal pain sites, oral contraceptive use, smoking, physical activity, body mass index, psychological distress, and sleep. Severe menstrual pain and mixed menstrual pain were positively associated with heightened cold pain sensitivity (distant from menstrual pain referral site) and pressure pain sensitivity (local to menstrual pain referral site). These associations remained significant after adjusting for potential confounding variables including multisite musculoskeletal pain. Our findings suggest peripheral and central neurophysiological mechanisms contributing to heightened pain sensitivity in young women with moderate and severe menstrual pain. These data highlight the need for innovative management approaches to attenuate the negative impact of severe menstrual pain in young women.

Emerging Relationships between Exercise, Sensory Nerves, and Neuropathic Pain

The utilization of physical activity as a therapeutic tool is rapidly growing in the medical community and the role exercise may offer in the alleviation of painful disease states is an emerging research area. The development of neuropathic pain is a complex mechanism, which clinicians and researchers are continually working to better understand. The limited therapies available for alleviation of these pain states are still focused on pain abatement and as opposed to treating underlying mechanisms. The continued research into exercise and pain may address these underlying mechanisms, but the mechanisms which exercise acts through are still poorly understood. The objective of this review is to provide an overview of how the peripheral nervous system responds to exercise, the relationship of inflammation and exercise, and experimental and clinical use of exercise to treat pain. Although pain is associated with many conditions, this review highlights pain associated with diabetes as well as experimental studies on nerve damages-associated pain. Because of the global effects of exercise across multiple organ systems, exercise intervention can address multiple problems across the entire nervous system through a single intervention. This is a double-edged sword however, as the global interactions of exercise also require in depth investigations to include and identify the many changes that can occur after physical activity. A continued investment into research is necessary to advance the adoption of physical activity as a beneficial remedy for neuropathic pain. The following highlights our current understanding of how exercise alters pain, the varied pain models used to explore exercise intervention, and the molecular pathways leading to the physiological and pathological changes following exercise intervention.

Enhanced Pain Sensitivity Among Individuals With Symptomatic Knee Osteoarthritis: Potential Sex Differences in Central Sensitization

OBJECTIVE

Symptomatic knee osteoarthritis (OA) is a condition commonly associated with increased pain, disability, and functional limitations. Given the poor correspondence between radiographic evidence and clinical pain, central sensitization has been implicated as a potential mechanism underlying pain facilitation in knee OA. Sex may be a moderator of centrally mediated changes in knee OA pain; however, few studies have systematically assessed this. Therefore, the aim of this study was to examine differences in peripheral and central sensitization in men and women with symptomatic knee OA, as well as to determine whether these differences vary across age (middle age versus older age).

METHODS

Participants (n = 288) between the ages of 45 and 85 years completed a battery of quantitative sensory pain procedures assessing sensitivity to contact heat, cold pressor, mechanical pressure, and punctate stimuli. Differences in temporal summation (TS) were examined, as well as measures of clinical pain and functional performance.

RESULTS

When compared to men, women exhibited greater sensitivity to multiple pain modalities (i.e., lower heat, cold, pressure thresholds/tolerances, greater TS of pain); however, there were no sex differences in clinical pain, with the exception of greater widespread pain observed in women. Although there were select age-related differences in pain sensitivity, sex differences in pain varied minimally across the age cohort.

CONCLUSION

Overall, these findings provide evidence for greater overall sensitivity to experimental pain in women with symptomatic knee OA compared to men, suggesting that enhanced central sensitivity may be an important contributor to pain in this group.

Inventory of Personal Factors Influencing Conditioned Pain Modulation in Healthy People: A Systematic Literature Review

BACKGROUND

Conditioned pain modulation (CPM) is believed to play an important role in the development and exacerbation of chronic pain, because dysfunction of CPM is associated with a shift in balance between pain facilitation and pain inhibition. In many patients with central sensitization, CPM is less efficacious. Besides that, efficacy of CPM is highly variable in healthy people. Consequently, it seems that several individual variables may influence CPM. A systematic review examining personal factors influencing CPM was conducted.

METHODS

This systematic review follows the PRISMA guidelines. "Pubmed" and "Web of Science" were searched using different synonyms of CPM. Full-text clinical reports addressing the influence of personal factors on CPM in healthy adults were included. Checklists for RCTs and case-control studies provided by the Dutch Institute for Healthcare Improvement (CBO) and the Dutch Cochrane Centre were utilized to assess methodological quality. Levels of evidence and strength of conclusion were assigned using the CBO guidelines.

RESULTS

Forty-six articles were identified that reported the influence of personal factors on CPM. Quality assessment revealed 10 studies with a methodological quality less than 50% wherefore they were excluded (21.8%), resulting in a general total methodological quality score of 72.5%. Overall younger adult age, male gender, ovulatory phase, positive expectations, attention to the conditioning stimulus, and carrier of the 5-HTTLPR long allele result in better CPM.

CONCLUSION

It is advised for future studies to take these factors into account. Further research regarding the influence of oral contraceptives, catastrophizing, information about conditioning stimulation, distraction, physical activity, and genetics on CPM magnitude is required.

Endogenous inhibition of pain and spinal nociception in women with premenstrual dysphoric disorder

Purpose

Premenstrual dysphoric disorder (PMDD) is characterized by severe affective and physical symptoms, such as increased pain, during the late-luteal phase of the menstrual cycle. The mechanisms underlying hyperalgesia in women with PMDD have yet to be identified, and supraspinal pain modulation has yet to be examined in this population. The present study assessed endogenous pain inhibitory processing by examining conditioned pain modulation (CPM, a painful conditioning stimulus inhibiting pain evoked by a test stimulus at a distal body site) of pain and the nociceptive flexion reflex (NFR, a spinally-mediated withdrawal reflex) during the mid-follicular, ovulatory, and late-luteal phases of the menstrual cycle.

Methods

Participants were regularly-cycling women (14 without PMDD; 14 with PMDD). CPM was assessed by delivering electrocutaneous test stimuli to the sural nerve before, during, and after a painful conditioning ischemia task. Participants rated their pain to electrocutaneous stimuli, and NFR magnitudes were measured. A linear mixed model analysis was used to assess the influence of group and menstrual phase on CPM.

Results

Compared with controls, women with PMDD experienced greater pain during the late-luteal phase and enhanced spinal nociception during the ovulation phase, both of which were independent of CPM. Both groups showed CPM inhibition of pain that did not differ by menstrual phase. Only women with PMDD evidenced CPM inhibition of NFR.

Conclusion

Endogenous modulation of pain and spinal nociception is not disrupted in women with PMDD. Additionally, greater NFR magnitudes during ovulation in PMDD may be due to tonically-engaged descending mechanisms that facilitate spinal nociception, leading to enhanced pain during the premenstrual phase.

Lean mass predicts conditioned pain modulation in adolescents across weight status

BACKGROUND

There is a wide continuum of conditioned pain modulation (CPM) in adults with older adults experiencing an attenuated CPM response compared with younger adults. Less is known for adolescents and the role of anthropometrics.

METHODS

Fifty-six adolescents (15.1 ± 1.8 years; 32 normal weight and 24 overweight/obese; 27 boys) completed in a CPM session that included anthropometric testing. Pressure pain thresholds were measured at the nailbed and deltoid muscle (test stimuli) with the foot submerged in a cool or ice water bath (conditioning stimulus). Weight status, body composition (Dual-energy X-ray absorptiometry scan), physical activity levels and clinical pain were also evaluated.

RESULTS

The CPM response in adolescents was similar across sites (nailbed vs. deltoid), weight status (normal vs. overweight/obese) and sex. CPM measured at the deltoid muscle was positively associated with left arm lean mass but not fat mass; lean mass of the arm uniquely predicted 10% of the CPM magnitude. CPM measured at the nailbed was positively correlated with physical activity levels.

CONCLUSIONS

These results suggest that lean mass and physical activity levels may contribute to endogenous pain inhibition in adolescents across weight status.

Central sensitization and changes in conditioned pain modulation in people with chronic nonspecific low back pain: a case-control study

Quantitative sensory testing is widely used in human research to investigate the state of the peripheral and central nervous system contributions in pain processing. It is a valuable tool to help identify central sensitization and may be important in the treatment of low back pain. The aim of this study was to evaluate changes in local and segmental hypersensitivity and endogenous pain inhibition in people with chronic nonspecific low back pain. Thirty patients with chronic low back pain and thirty healthy subjects were studied. Pressure pain thresholds (PPTs) were measured from the lumbar region and over the tibialis anterior muscle (TA). A cold pressor test was used to assess the activation of conditioned pain modulation (CPM), and PPTs in the lumbar region were recorded 30 s after immersion of participant's foot in a bucket with cold water. People with chronic low back pain have significantly lower PPT than controls at both the lumbar region [89.5 kPa (mean difference) 95 % CI 40.9-131.1 kPa] and TA [59.45 kPa (mean difference) 95 % CI 13.49-105.42 kPa]. During CPM, people with chronic low back pain have significantly lower PPT than controls in lumbar region [118.6 kPa (mean difference) 95 % CI 77.9-159.2 kPa]. Women had significantly lower PPTs than men in both lumbar region [101.7 kPa (mean difference) 95 % CI 37.9-165.7 kPa] and over the TA [189.7 kPa (mean difference) 95 % CI 14.2-145.2 kPa]. There was no significant difference in PPTs in men between healthy controls and those with low back pain, suggesting the significant differences are mediated primarily by difference between women.

Exercise therapy for chronic pain

The benefit of exercise for pain control likely comes from the impact of exercise on the endogenous opioid system and on central pain modulatory systems. Patients with some chronic pain conditions seem to have a dysfunctional endogenous pain modulatory system, which should be considered when prescribing exercise. The prescription of exercise for chronic pain must address the biomechanical issues and the psychosocial factors that contribute to the patient's pain and disability. Patient education, coordination of care within the health care team, and selecting an exercise regimen that is meaningful to and achievable by the patient are all important components to promote a successful rehabilitation program.

Cerebral responses to innocuous somatic pressure stimulation following aerobic exercise rehabilitation in chronic pain patients: a functional magnetic resonance imaging study

OBJECTIVE

The purpose of this research was to assess the functional brain activity and perceptual rating of innocuous somatic pressure stimulation before and after exercise rehabilitation in patients with chronic pain.

MATERIALS AND METHODS

Eleven chronic pain patients and eight healthy pain-free controls completed 12 weeks of supervised aerobic exercise intervention. Perceptual rating of standardized somatic pressure stimulation (2 kg) on the right anterior mid-thigh and brain responses during functional magnetic resonance imaging (fMRI) were assessed at pre- and postexercise rehabilitation.

RESULTS

There was a significant difference in the perceptual rating of innocuous somatic pressure stimulation between the chronic pain and control groups (P=0.02) but no difference following exercise rehabilitation. Whole brain voxel-wise analysis with correction for multiple comparisons revealed trends for differences in fMRI responses between the chronic pain and control groups in the superior temporal gyrus (chronic pain > control, corrected P=0.30), thalamus, and caudate (control > chronic, corrected P=0.23). Repeated measures of the regions of interest (5 mm radius) for blood oxygen level-dependent signal response revealed trend differences for superior temporal gyrus (P=0.06), thalamus (P=0.04), and caudate (P=0.21). Group-by-time interactions revealed trend differences in the caudate (P=0.10) and superior temporal gyrus (P=0.29).

CONCLUSION

Augmented perceptual and brain responses to innocuous somatic pressure stimulation were shown in the chronic pain group compared to the control group; however, 12-weeks of exercise rehabilitation did not significantly attenuate these responses.

Cardiorespiratory effects of water ingestion during and after exercise

BACKGROUND

In prolonged exercise, the state of hypohydration due to sweating raises physiological stress and induces a drop in sports performance. However, the impact of water intake in cardiorespiratory parameters when administered during and after physical activity has not been well studied. This study aimed to analyze the effects of water intake in heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), partial oxygen saturation (SpO2) and respiratory rate during and after prolonged exercise.

METHODS

Thirty-one young males (21.55 ± 1.89 yr) performed three different protocols (48 h interval between each stage): I) maximal exercise test to determine the load for the protocols; II) Control protocol (CP) and; III) Experimental protocol (EP). The protocols consisted of 10 min at rest with the subject in the supine position, 90 min of treadmill exercise (60% of VO2 peak) and 60 min of rest placed in the dorsal decubitus position. No rehydration beverage consumption was allowed during CP. During EP, however, the subjects were given water (Vittalev, Spaipa, Brazil). The parameters HR, SBP, DBP, SpO2 and respiratory rate were measured at the end of the rest, in 30, 60 and 90 minutes of the activity, except the respiratory rate parameter, and at 1, 3, 5, 7, 10, 20, 30, 40, 50 and 60 minute post- exercise.

RESULTS

The hydration protocol provided minimal changes in SBP and DBP and a smaller increase in HR and did not significantly affect SpO2 during exercise and better HR recovery, faster return of SBP and DBP and a better performance for SpO2 and respiratory rate post-exercise.

CONCLUSION

Hydration with water influenced the behavior of cardiorespiratory parameters in healthy young subjects.