Alterations in endogenous pain modulation in endurance athletes: an experimental study using quantitative sensory testing and the cold-pressor task

Physical activity is predictive of conditioned pain modulation in healthy individuals: a cross-sectional study

Even in healthy populations, conditioned pain modulation (CPM) magnitude varies. This may be accounted for by (non-)modifiable factors, including physical activity. Yet, little research has thoroughly examined physical activity and its relation with CPM magnitude in a representative sample. Therefore, the present study investigated the predictive effect of physical activity on CPM magnitude in 105 healthy adults. Physical activity was assessed during seven consecutive days by self-report using the International Physical Activity Questionnaire and by monitored-based accelerometry. CPM was examined using a heterotopic noxious conditioning stimulation protocol during which the effect of a hot water conditioning stimulus on pressure pain thresholds was evaluated. Comparative, correlation, and hierarchical linear regression analyses were performed. Report-based walking predicts 4.8% of variance in pain modulatory capacity, moderate physical activity predicts 10.2% of variance in pain modulatory capacity, and report-based time spent on total physical activity predicts 7.0% of variance in pain modulatory capacity. More MET-minutes/week spent on total physical activity, including walking and moderate physical activity is associated with greater pain modulatory capacity. The findings of this study add to the limited evidence on the predictive effect of physical activity on CPM. It urges to consider physical activity a confounding factor when examining CPM. The current study provides evidence that a physically active lifestyle benefits endogenous pain modulation in healthy adults. Given its potential, walking and moderate-intensity physical activity might be achievable treatment strategies for pain patients known to have impaired CPM. PERSPECTIVE: The results of this article show that a physically active lifestyle including larger amounts of walking and moderate activity predict greater pain modulatory capacity. TRIAL REGISTRATION: This study has not been preregistered.

Athletes and Experimental Pain: A Systematic Review and Meta-Analysis

The evidence that athletes respond to and report indices of experimental pain differently to non-athlete populations was analysed. Databases screened were SPORTDiscus, PubMED, PsycArticles, the Cochrane Library (Cochrane Database of Systematic Reviews), Web of Science, Scopus, and CINAHL. Studies that compared experimentally induced pain responses (threshold, tolerance, intensity, unpleasantness, bothersomeness, and effect on performance) in athletes and controls were included. Meta-analyses were performed where appropriate and effects were described as standardised mean differences, pooled using random effects models. Thirty-six studies (2,492 participants) met the inclusion criteria comprising 19 pain tolerance, 17 pain threshold, 21 pain intensity, 5 pain unpleasantness, 2 performance in pain and 1 bothersomeness study. Athletes demonstrated greater pain tolerance (g = .88 [95% confidence interval [CI] .65, .13]) and reported less pain intensity (g = -.80, [95% CI -1.13, -.47]) compared to controls; they also had higher pain threshold but with smaller effects (g = .41, [95% CI .08, .75]). Differences for unpleasantness did not reach statistical significance but the effects were large (g = -1.23 [95% CI -2.29, .18]). Two studies reported that performance in pain was better in contact athletes than non-athletes, and one concluded that athletes find pain less bothersome than controls. There were considerable inconsistencies in the methods employed that were reflected in the meta-analyses' findings. Sub-group analyses of tolerance and intensity were conducted between endurance, contact, and other athlete groups, but were not significant. The data suggest that athletic participation is associated with altered pain responses, but mechanisms remain unclear and more transparent methods are recommended.This study was registered on the PROSPERO site in January 2019 (ref ID: CRD42019119611). PERSPECTIVE: This review examined differences in pain outcomes (threshold, tolerance, intensity, unpleasantness, bothersomeness) and the effect of pain on performance, in athletes versus controls. Meta-analyses revealed athletes had higher threshold and tolerance and found pain less intense than controls; there was some evidence of differences in bothersomeness and performance.

Nociceptive Processing of Elite Athletes Varies between Sport-Specific Loads: An EEG-Based Study Approach

INTRODUCTION

For the downstream nociceptive processing of elite athletes, recent studies indicate that athletes probably tolerate more pain as compared with a normally active population. Phenotyping the nociceptive processing of athletes in different types of endurance sports can provide insight into training-specific effects, which may help in understanding the long-term effects of specific exercise.

METHODS

Twenty-six elite endurance athletes from the disciplines of rowing, triathlon, and running and 26 age- and sex-matched, recreationally active control subjects who participated in the subjective pain perception and processing of standardized noxious stimuli were investigated by EEG. This included standardized heat pain thresholds (HPT) and contact heat-evoked potentials from heat stimulation, measured with EEG as well as pinprick-evoked potentials from mechanical stimulation.

RESULTS

After noxious stimulation, athletes showed a higher activation of the event-related spectral perturbation (ERSP) patterns in the N2P2 EEG response at the Cz Electrode compared with the controls. After noxious contact heat stimulation, triathletes had a higher ERSP activation compared with the controls, whereas the rowers had a higher ERSP activation after noxious mechanical stimulation. Also, HPT in triathletes were increased despite their increased central activation after thermal stimulation. We found a correlation between increased HPT and training hours and years, although athletes did not differ within these variables.

CONCLUSIONS

Although we were able to identify differences between athletes of different endurance sports, the reasons and implications of these differences remain unclear. The study of sport-specific somatosensory profiles may help to understand the mechanisms of exercise-related long-term effects on pain processing and perception. Furthermore, sport-specific somatosensory effects may support the personalization of exercise interventions and identify risk factors for chronic pain in elite athletes.

Vagal tone, pain sensitivity and exercise-induced hypoalgesia: The effect of physical activity level

BACKGROUND

Vagal activity has analgesic effects that are attributed to exercise-induced hypoalgesia (EIH). High vagal tone and low pain sensitivity are reported in individuals who routinely exercise yet, their association is unclear. Furthermore, it is unknown if the heightened vagal tone following high physical activity predicts and intensifies EIH.

METHODS

Fifty-one healthy participants (27 low-moderately physically active; 27 females) underwent a resting-state electrocardiogram followed by heart rate variability analysis. Pain measurements, including pressure (PPT) and heat (HPT) pain thresholds, ratings of tonic heat pain (THP) and conditioned pain modulation (CPM) paradigm, were conducted pre- and post-exercise on a cycle ergometer.

RESULTS

The highly active group demonstrated higher vagal tone compared to the low-moderately active (root mean square of successive differences between R-R intervals: 63.96.92 vs. 34.78 ms, p = 0.018; percentage of successive R-R intervals that exceed 50 ms: 24.41 vs. 11.52%, p = 0.012). Based on repeated-measure ANOVA, the highly active group showed higher PPT at pre-exercise, compared to the low-moderately active group (382 kPa vs. 327 kPa; p = 0.007). Post-exercise, both groups demonstrated EIH, increased HPT (p = 0.013) and decreased THP ratings (p < 0.001). Linear regression revealed that only in the low-moderately active group, higher vagal tone was associated with more efficient pre-exercise CPM and a greater reduction in THP ratings post-exercise (p ≤ 0.01).

CONCLUSIONS

Highly active individuals demonstrate greater vagal tone and lower pain sensitivity but no greater EIH. Vagal tone moderates pain inhibition efficiency and EIH only in low-moderately active individuals. These findings suggest that physical activity level moderates the vagal-pain association via the endogenous analgesia system.

SIGNIFICANCE

Highly physically active individuals exhibit greater vagal tone and reduced sensitivity to experimental pain, yet they do not benefit more from exercise-induced hypoalgesia (EIH) compared to low-moderately active individuals. Moreover, low-moderately active individuals with greater vagal tone exhibited more efficient endogenous pain inhibition and greater EIH, suggestive of the moderation effect of physical activity level on vagal-pain associations.

Reduced somatosensory evoked potentials and paired-pulse inhibition in the primary somatosensory cortex of athletes with chronic pain

PURPOSE

Chronic pain impedes athletic training and performance. However, it is challenging to identify the precise causes of chronic pain for effective treatment. To examine possible neuroplastic changes in sensory transmission and cortical processing, we compared somatosensory evoked potentials (SEPs) and paired-pulse inhibition (PPI) in primary sensory cortex (S1) between athletes with chronic pain and control athletes.

METHODS

Sixty-six intercollegiate athletes (39 males and 27 females) were recruited for this study, 45 control athletes and 21 reporting persistent pain for > 3 months. Sensory-evoked potentials were induced in S1 by constant-current square-wave pulses (0.2-ms duration) delivered to the right median nerve, while PPI was induced by paired stimulation at interstimulus intervals of 30 and 100 ms (PPI-30 and PPI-100 ms, respectively). All participants were randomly presented with total 1,500 (each 500 stimuli) single stimuli and stimulus pairs at 2 Hz.

RESULTS

Both N20 amplitude and PPI-30 ms were significantly lower in athletes with chronic pain compared to control athletes, while P25 amplitude and PPI-100 ms did not differ significantly between groups.

CONCLUSION

Chronic pain in athletes is associated with substantially altered excitatory-inhibitory balance within the primary somatosensory cortex, possibly due to reduced thalamocortical excitatory transmission and suppressed cortical inhibitory transmission.

Efficiency of pain inhibition and facilitation of fibromyalgia patients is not different from healthy controls: Relevance of sensitivity-adjusted test stimuli

Background

Pain is a dynamic phenomenon dependent on the balance of endogenous excitatory and inhibitory systems, which can be characterized by quantitative sensory testing. Many previous studies of pain modulatory capacity of patients with fibromyalgia syndrome (FM) have reported decreased pain inhibition or increased pain facilitation. This is the first study to assess pain modulation, including conditioned pain modulation (CPM) and temporal pain summation, in the same healthy control (HC) and FM participants.

Methods

Only sensitivity-adjusted stimuli were utilized for testing of conditioned pain modulation (CPM) and temporal pain summation in 23 FM patients and 28 HC. All subjects received sensitivity-adjusted ramp-hold (sRH) during testing of pain facilitation (temporal summation) and pain inhibition (CPM). CPM efficacy was evaluated with test stimuli applied either concurrently or after application of the conditioning stimulus. Finally, the effects of CPM on pressure pain thresholds were tested.

Results

FM subjects required significantly less intense test and conditioning stimuli than HC participants to achieve standardized pain ratings of 50 ± 10 numerical rating scale (NRS) (p = 0.03). Using such stimuli, FM subjects' temporal pain summation and CPM efficacy was not significantly different from HC (all p > 0.05), suggesting similar pain facilitation and inhibition. Furthermore, the CPM efficacy of FM and HC participants was similar regardless of whether the test stimuli were applied during or after the conditioning stimulus (p > 0.05).

Conclusion

Similar to previous studies, FM participants demonstrated hyperalgesia to heat, cold, and mechanical stimuli. However, using only sensitivity-adjusted stimuli during CPM and temporal summation testing, FM patients demonstrated similarly effective pain inhibition and facilitation than HC, suggesting that their pain modulation is not abnormal.

EEG-based sensory testing reveals altered nociceptive processing in elite endurance athletes

Increased exercise loads, as observed in elite athletes, seem to modulate the subjective pain perception in healthy subjects. The combination of electroencephalography (EEG) and standardized noxious stimulation can contribute to an objective assessment of the somatosensory stimulus processing. We assessed the subjective pain ratings and the electroencephalogram (EEG)-based response after standardized noxious mechanical and thermal stimuli as well as during conditioned pain modulation (CPM) in 26 elite endurance athletes and compared them to 26 recreationally active controls. Elite endurance athletes had consistently stronger somatosensory responses in the EEG to both mechanical and thermal noxious stimuli than the control group. We observed no significant group differences in the subjective pain ratings, which may have been influenced by our statistics and choice of stimuli. The CPM testing revealed that our conditioning stimulus modulated the subjective pain perception only in the control group, whereas the EEG indicated a modulatory effect of the conditioning stimulus on the spectral response only in the athletes group. We conclude that a higher activation in the cortical regions that process nociceptive information may either be an indicator for central sensitization or an altered stimulus salience in the elite endurance athletes' group. Our findings from our CPM testing were limited by our methodology. Further longitudinal studies are needed to examine if exercise-induced changes in the somatosensory system might have a critical impact on the long-term health of athletes.

Caffeine Attenuates Electroacupuncture Effect on Pressure Pain Threshold and Tolerance in Healthy Individuals: A Randomized Controlled Trial

Introduction

The effect of caffeine on acupuncture analgesia in humans is unclear. This study aimed to investigate whether caffeine-containing beverage intake influences the effect of electroacupuncture (EA) on static quantitative sensory testing (QST) and dynamic QST in healthy subjects.

Methods

A total of 40 healthy subjects were enrolled and randomly assigned to receive coffee containing moderate doses of caffeine (coffee group) or non-caffeinated juice (juice group) for 4 weeks. The primary outcome measures were the pressure pain threshold (PPT), pressure pain tolerance (PPTo), and heat pain threshold (HPT) as static QST parameters. Numerical rating scales (NRS) of heat stimulus and nociceptive flexor reflex (RIII reflex), as parameters of dynamic QST, were also examined. EA stimulation with tolerance intensity was performed at ST36 (Zusanli)-GB34 (Yanglingquan) points at weeks 0, 2, and 4. PPT, PPTo, and HPT were detected pre- and post- EA. The NRS scores were examined pre-, during, and post-EA, and 1 min after EA was completed. The RIII reflex was examined pre- and 1–5 min post-EA.

Results

At week 0, both groups showed increased PPT and PPTo and decreased NRS scores of heat stimuli and RIII reflex after EA, but HPT was not affected. After 4 weeks, the effects of EA on PPT and PPTo were attenuated in the coffee group compared to the juice group, whereas the effect of EA on the NRS scores and RIII reflex were not influenced. There was no significant difference found at week 2 for these indications. EA also did not affect the HPT in both groups at week 4.

Conclusion

Moderate caffeine intake reduced the effects of EA on PPT and PPTo in healthy subjects.

Quantitative Sensory Changes Related to Physical Activity in Adult Populations: A Scoping Review

ABSTRACT

Exercise-induced hypoalgesia related to physical activity produces sensory adaptations, but its mechanism remains unclear. Quantitative sensory testing is an effective measurement tool to identify sensory changes, but the extent of evidence linking quantitative sensory testing and physical activity has not been explored. The purpose of this scoping review is to synthesize the evidence on using quantitative sensory testing to evaluate psychophysical changes related to physical activity in adult populations. The researchers developed a comprehensive search strategy with a Health Sciences Librarian using the Arksey and O'Malley Methodological framework. Four databases (Medline [PubMed], CINAHL, Web of Science, and Embase) were searched for peer-reviewed primary research. After 2790 articles were evaluated, 196 studies were included for final review. More than half of studies used randomized controlled trial design (50.5%), followed by quasi-experimental (24.0%) and observational (25.5%) strategies. Healthy adults (42.9%) and individuals with chronic health conditions (20.9%) were examined most frequently. Aerobic (27.6%) and strength (21.4%) physical activity types were most commonly studied. Static quantitative sensory testing measures of pressure pain threshold (84%) were used most frequently. The findings of this scoping review demonstrate available evidence for quantitative sensory testing as a measurement tool of neuromodulation related to physical activity in adult populations. A systematic review is warranted to examine outcomes and recommendations.

Body image dissatisfaction and experimental pressure pain sensitivity in a cohort of 13-year-old adolescents

OBJECTIVE

We aimed to quantify the associations between body image (dis)satisfaction and pressure pain thresholds in adolescents, using data from Generation XXI, a population-based cohort study in Portugal.

METHODS

We assessed 1785 13-year old adolescents cross-sectionally. Body image satisfaction was measured using the Children's Figure Rating Scale. Pain detection and tolerance thresholds were assessed using cuff pressure algometry. We quantified the associations between body image categories (satisfied, prefers slightly thinner, prefers much thinner, and prefers heavier) and pain detection and tolerance thresholds using linear and logistic regression for continuous and binary (odds of achieving the highest distribution quarter) outcomes, respectively. Models were adjusted to pubertal stage and body mass index.

RESULTS

Adolescents who desired a heavier silhouette had lower pressure pain tolerance thresholds when compared to those who were satisfied (linear regression coefficient: -3.95; 95% confidence interval: -6.68, -1.21), which was more precise in boys (-3.51; -7.17, -0.08). Those adolescents also had lower odds of achieving the highest quarter of pressure pain tolerance threshold (odds ratio: 0.66; 0.48, 0.90), especially girls (0.58; 0.35, 0.98). Adolescents who desired much thinner silhouettes had lower odds of achieving the highest quarter of pressure pain tolerance (0.68; 0.46, 1.00), and this was clearer in girls (0.66; 0.48, 0.90). Pain detection thresholds did not show robust associations with body image dissatisfaction.

CONCLUSION

Our study suggests an association between satisfaction with one's silhouette and pain tolerance in adolescents from the general population, arguing for an integrated approach to the assessment of body image and pain sensitivity.

Both Gender and Agonistic Experience Affect Perceived Pain during the Cold Pressor Test

Background. Differences in pain perception in athletes have recently been highlighted in the literature. Objectives. To compare gender ratings of perceived pain in athletes with low and high agonistic experiences (N = 200) using the Cold Pressor Test (CPT). Methods. A three-way repeated measures ANOVA to assess both the effects of the athletes’ gender and lower vs. higher agonistic experiences in the intensity of perceived pain at the beginning of the cold box hand immersion (L₀) and after a 90 s interval (L₁). Results. There was a statistically significant interaction effect between the level of the agonistic experience and gender in the two moments: p < 0.001; η_p² = 0.266; F(1,49) = 9.771. Simple main effects analysis showed a significative difference for females at L₀: F(1,99) = 93.567, p < 0.025, partial η² = 0.302) and for males at L₁: F(1,99) = 173.420, p < 0.025, partial η² = 0.666. At the initial moment of CPT, the female athletes showed significantly higher perceived intensity than males, regardless of their experience level. After a 90 s interval, a significantly lower pain perception effect associated with the increased competitive experience of male athletes was observed. Female athletes did not appear to benefit from the experience effect on their pain tolerance. Conclusions. The study confirmed a significant difference in pain perception associated with the athletes’ gender and agonistic experience. Separate explanations related to the pattern of pain inhibition and the acquired reduction in pain sensitivity are reported.

Psychosocial subgroups in high-performance athletes with low back pain: eustress-endurance is most frequent, distress-endurance most problematic!

OBJECTIVES

In non-athletes, fear-avoidance and endurance-related pain responses appear to influence the development and maintenance of low back pain (LBP). The avoidance-endurance model (AEM) postulates three dysfunctional pain response patterns that are associated with poorer pain outcomes. Whether comparable relationships are present in athletes is currently unclear. This cross-sectional case-control study explored frequencies and behavioral validity of the AEM-based patterns in athletes with and without LBP, as well as their outcome-based validity in athletes with LBP.

METHODS

Based on the Avoidance-Endurance Fast-Screen, 438 (57.1% female) young adult high-performance athletes with and 335 (45.4% female) without LBP were categorized as showing a "distress-endurance" (DER), "eustress-endurance" (EER), "fear-avoidance" (FAR) or "adaptive" (AR) pattern.

RESULTS

Of the athletes with LBP, 9.8% were categorized as FAR, 20.1% as DER, 47.0% as EER, and 23.1% as AR; of the athletes without LBP, 10.4% were categorized as FAR, 14.3% as DER, 47.2% as EER, and 28.1% as AR. DER and EER reported more pronounced endurance- and less pronounced avoidance-related pain responses than FAR, and vice versa. DER further reported the highest training frequency. In athletes with LBP, all dysfunctional groups reported higher LBP intensity, with FAR and DER displaying higher disability scores than AR.

CONCLUSIONS

The results indicate that also in athletes, patterns of endurance- and fear-avoidance-related pain responses appear dysfunctional with respect to LBP. While EER occurred most often, DER seems most problematic.

IMPLICATIONS

Endurance-related pain responses that might be necessary during painful exercise should therefore be inspected carefully when shown in response to clinical pain.

Pain sensitivity increases more in younger runners during an ultra-marathon

OBJECTIVES

Ultra-endurance research interest has increased in parallel with an increased worldwide participation in these extreme activities. Pain-related data for the growing population of ultra-endurance athletes, however, is insufficient. More data is especially needed regarding the variation in the aging populations of these athletes. We have previously shown that peripheral and central pain sensitivity increases during an ultra-marathon. To further clarify these changes in pain sensitivity during ultra-endurance competition we investigated these variations in two age populations: Younger runners ≤ 39-year-old (younger) and an older group of runners being ≥ 40 years of age (older).

METHODS

Subjects were recruited from ultra-marathon competitions held over a three-year period in Florida, USA. All courses were flat with either hard macadam surface or soft sandy trails; run in hot, humid weather conditions. Pressure pain threshold (PPT) was measured with a pressure algometer on the distal, dominant arm before and immediately after an ultra-marathon. Conditioned pain modulation (CPM) was also measured pre and post, immediately after the PPT by placing the non-dominant hand in a cold-water bath maintained at 13.5 ± 1.5 °C. The difference between the pre and post measurements for both PPT and CPM were calculated and referred to as ΔPPT and ΔCPM, respectively for analysis. Data were analyzed with a Mixed 2 × 2 (Within X Between) MANOVA.

RESULTS

Both PPT and CPM decreased during the ultra-marathons (p<0.05) in the younger group of runners. In the older runners there was not a statistically significant decrease in PPT during the ultramarathons whereas CPM did significantly decrease statistically (p=0.031). The ΔPPT was less in the older group compared to the younger group (p=0.018). The difference between the younger and older groups ΔCPM approached statistical significance at p=0.093.

CONCLUSIONS

This statistical evidence suggests that the overall increase in peripheral and possibly central pain sensitivity was different between our age groups. Pain sensitivity during the ultra-marathon increased more in our younger group of runners than in our older group. This study suggests that there is an unidentified factor in an older population of ultra-marathon runners that results in an attenuated increase in pain sensitivity during an ultra-endurance activity. These factors may include a decreased innate immune response, lower fitness level, lower exertion during the ultra-marathon, variation in endorphin, enkephalin, endocannabinoid and psychological factors in the older age runners.

Dissociation of Endogenous Pain Inhibition Due to Conditioned Pain Modulation and Placebo in Male Athletes Versus Nonathletes

Animals and humans are able to inhibit pain by activating their endogenous pain-inhibition system. Endurance athletes possess a higher pain-tolerance threshold and a greater conditioned pain modulation (CPM) effect than nonathletes, suggesting better endogenous pain inhibition. In addition to CPM, placebo is another prominent paradigm used to test endogenous pain inhibition. However, whether the placebo effect and the CPM effect share the same mechanisms of pain inhibition has not been investigated. If there is a shared mechanism, then endurance athletes should show not only a better CPM effect than nonathletes but also a greater placebo effect. Here, we investigated 16 male endurance athletes and 17 male nonathletes in well-established placebo and CPM paradigms to assess whether endurance athletes have a better endogenous pain-inhibition system than nonathletes. As expected, we find a significantly greater CPM effect in athletes than in nonathletes. In contrast, we could only find a significant placebo effect in nonathletes. Explorative analyses reveal negative associations between the placebo effect and heart rate variability as well as between the placebo effect and interoceptive awareness. Together, the results demonstrate a dissociation of endogenous pain inhibition of CPM and placebo effect between endurance athletes and nonathletes. This suggests that both effects are based, at least in part, on different biological mechanisms.

Painful Cutaneous Electrical Stimulation vs. Heat Pain as Test Stimuli in Conditioned Pain Modulation

Different paradigms can assess the effect of conditioned pain modulation (CPM). The aim of the present study was to compare heat pain, as an often used test stimulus (TS), to painful cutaneous electrical stimulation (PCES), having the advantage of the additional recording of PCES-related evoked potentials. In 28 healthy subjects we applied heat and PCES at the dominant hand as test stimulus (TS) to compare the CPM-effect elicited by hand immersion into cold water (10 °C) as conditioning stimulus (CS). Subjects rated the pain intensity of TS at baseline, during and 5 min after CS application and additionally of CS, on a numerical rating scale (NRS) (0–100). The ‘early’ (during CS–before CS) and ‘late’ (after CS–before CS) CPM-effects were analyzed. Parallel to the PCES, the related evoked potentials were recorded via Cz to evaluate any changes in PCES-amplitudes. CS reduced significantly the pain intensity of both PCES and heat pain as TS. On a group level, the CPM-effect did not differ significantly between both paradigms. Both early and late CPM-effect based on PCES correlated significantly with the CS pain intensity (r = −0.630 and −0.503, respectively), whereas using heat pain the correlation was not significant. We found a significant reduction of PCES-amplitudes during CS, but this did not correlate with the PCES-induced pain intensity. Correlation with the CS painfulness (r = −0.464) did not achieve the significance level after Bonferroni correction. The extent of the CPM effects was similar in both testing paradigms at group level, despite intraindividual differences. Future studies should further elicit the exact mechanisms explaining the modality of these specific differences.

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

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

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

Conservative management of fifth metacarpal head fracture in a professional cricketer: A case study and literature review

This is a unique presentation of common injury in a young professional athlete. The sensitivity of typical acute clinical signs in athletes is not known. Adequate splinting and early graded mobilization are key for successful rehabilitation, which was shorter than reported in the literature.

Pain Processing in Elite and High-Level Athletes Compared to Non-athletes

Background

Previous studies shows that elite and high-level athletes possess consistently higher pain tolerance to ischemic and cold pain stimulation compared to recreationally active. However, the data previously obtained within this field is sparse and with low consistency.

Purpose

The aim of the present study was to examine the difference in pain perception between elite and high-level endurance athletes (cross country skiers and runners), elite soccer players and non-athletes, as well to explore the impact of psychological factors on pain processing.

Methods

Seventy one healthy volunteers (33 females and 38 males) participated in the study. Soccer players (n = 17), cross country skiers (n = 12), and long-distance runners (n = 3) formed the athlete group, with 39 non-athletes as controls. Big-five personality traits, fear of pain and Grit (perseverance and passion for long-term goals) were measured prior to induction of experimental pain. Pain threshold and intensity was induced by a PC-controlled heat thermode and measured by a computerized visual analog scale. Pain tolerance was measured by the cold pressor test (CPT).

Results

Elite and high-level athletes had increased pain tolerance, higher heat pain thresholds, and reported lower pain intensity to thermal stimulation. Endurance athletes (cross country skiers and long-distance runners) had better tolerance for cold pain compared to both soccer-players and non-athletes. Furthermore, endurance athletes reported lower pain intensity compared to non-athletes, whereas both endurance athletes and soccer players had higher heat pain thresholds compared to non-athletes. Fear of Pain was the only psychological trait that had an impact on all pain measures.

Conclusion

The present findings suggest that sports with long durations of physically intense activity, leveling aerobic capacity, are associated with increased ability to tolerate pain and that the amount of training hours has an impact on this tolerance. However, the small sample size implies that the results from this study should be interpreted with caution.

Conditioned pain modulation in elite athletes: a systematic review and meta-analysis

Background and aims Elite athletes reportedly have superior pain tolerances, but it is unclear if results extend to conditioned pain modulation (CPM). The aim of our study was to synthesize existing literature in order to determine whether CPM is increased in elite athletes compared to healthy controls. Methods A systematic review and random-effects meta-analysis was conducted. Cochrane Central Register of Controlled Trials, SPORTDiscus, PsycINFO, CINAHL, Web of Science, and PubMed were searched for English-language studies that examined CPM in adult elite athlete populations. Results Seven studies were identified; all were of poor to fair methodological quality. There was no overall difference in CPM between elite athletes and controls (Hedges g = 0.37, CI95 -0.03-0.76; p = 0.07). There was heterogeneity between studies, including one that reported significantly less CPM in elite athletes compared to controls. An exploratory meta-regression indicated that a greater number of hours trained per week was associated with higher CPM. Conclusions The overall number and quality of studies was low. Despite nominally favoring higher CPM in elite athletes, aggregate results indicate no significant difference compared to healthy controls. A possible factor explaining the high degree of variability between studies is the number of hours elite athletes spent training. Implications Based on available evidence, athletes do not have remarkable endogenous pain modulation compared to controls. High quality experimental studies are needed to address the effect of hours trained per week on CPM in athletes.

Is There a Relationship Between Workload and Occurrence of Back Pain and Back Injuries in Athletes?

The back is subjected to a great deal of strain in many sports. Up to 20% of all sports injuries involve an injury to the lower back or neck. Repetitive or high impact loads (e.g., running, gymnastics, skiing) and weight loading (e.g., weightlifting) affect the lower back. Rotation of the torso (e.g., golf, tennis) causes damage to both, the lumbar and thoracic spine. The cervical spine is most commonly injured in contact sports (e.g., boxing, football). One of the factors that increases the odds of injuries in athletes is excessive and rapid increases in training loads. In spite of currently emerging evidence on this issue, little is known about the balance between physiological loading on the spine and athletic performance, versus overloading and back pain and/or injury in athletes. This scoping review aims (i) to map the literature that addresses the association between the training load and the occurrence of back pain and/or injury, especially between the Acute:Chronic Workload Ratio (ACWR) and back problems in athletes of individual and team sports, and (ii) to identify gaps in existing literature and propose future research on this topic. A literature search of six electronic databases (i.e., MEDLINE, PubMed, Web of Science, SCOPUS, SportDiscus, and CINAHL) was conducted. A total of 48 research articles met the inclusion criteria. Findings identified that fatigue of the trunk muscles induced by excessive loading of the spine is one of the sources of back problems in athletes. In particular, high training volume and repetitive motions are responsible for the high prevalence rates. The most influential are biomechanical and physiological variations underlying the spine, though stress-related psychological factors should also be considered. However, limited evidence exists on the relationship between the ACWR and back pain or non-contact back injuries in athletes from individual and team sports. This may be due to insufficiently specified the acute and chronic time window that varies according to sport-specific schedule of competition and training. More research is therefore warranted to elucidate whether ACWR, among other factors, is able to identify workloads that could increase the risk of back problems in athletes.

En Pointe: Dancers Report Their Pain Less Variably Than Do Controls

The subjective nature of pain and the lack of a gold standard for objective measurement hinders effective assessment, diagnosis, and treatment. Some individuals, such as professional dancers, are better in assessing and reporting bodily sensations. This observational study aimed to assess whether dancers report their pain less variably, than other people do. After consenting, subjects completed the focused analgesia selection test (FAST), which assesses subjects' variability of pain reports. FAST outcomes, ICC and R² reflect the magnitude of variability of pain reports observed. In addition, subjects underwent a taste task, which similarly assesses variability of tastes (salty and sweet) intensity reports and completed the Multidimensional Assessment of Interoceptive Awareness questionnaire. Thirty-three professional dancers and 33 healthy aged-matched controls were recruited. The dancers exhibited less variability of pain reports then controls (P = .013), but not in case of tastes-reports. Years of practice was positively correlated with pain reporting variability (r = .447, P = .009, and r = .380, P = .029; for FAST ICC and R², respectively). Multidimensional Assessment of Interoceptive Awareness subscores correlated with pain reporting variability: R² and ICC with emotional awareness (r = .260, P = .040, and r = .274, P = .030, respectively), and R² with trusting [r = .254, P = .044]). PERSPECTIVE: The difference between dancers and controls in the magnitude of variability of pain reports is probably due to the dancers' extensive training, which focuses on attention to body signals. Our results suggest that training can improve subjective pain reports, which are essential for quality clinical care.

Influence of self-reported physical activity and sleep quality on conditioned pain modulation in the orofacial region

OBJECTIVES

To evaluate the influence of self-reported physical activity and sleep quality on conditioned pain modulation (CPM) in the orofacial region.

MATERIALS AND METHODS

Ninety healthy participants aged 18-50 years old were evenly distributed according to the level of physical activity into low, moderate, and high level. The classification of physical activity was based on modified criteria of the International Physical Activity Questionnaire (IPAQ), considering intensity, duration, and frequency of physical activity. The Pittsburgh Sleep Quality Index (PSQI) assessed sleep quality and the individuals were then classified as good or poor sleepers. CPM was assessed using the pressure pain threshold (PPT) of the anterior temporalis as test stimulus and hand immersion in hot water as conditioning stimulus. ANOVA was applied to the data and Tukey's posttest was applied when the main effects or interactions were significant (p < 0.050).

RESULTS

There was no significant main effect of neither physical activity nor sleep quality on pain modulation. However, individuals who reported high level of physical activity and good quality of sleep had a greater pain modulation (- 0.60 ± 0.34) when compared with those who reported moderate (- 0.10 ± 0.25) and low level of physical activity (- 0.10 ± 0.52) and good sleep quality (p < 0.028).

CONCLUSIONS

Pain modulation seems to be more efficient in individuals who report a good sleep quality and a high level of physical activity.

CLINICAL RELEVANCE

Conditioned pain modulation is highly variable in healthy people. Therefore, a multifactorial approach should be taken into consideration in the evaluation of the efficacy of endogenous analgesia.

Pain inhibition is not affected by exercise-induced pain

Introduction:

Offset analgesia (OA) and conditioned pain modulation (CPM) are frequently used paradigms to assess the descending pain modulation system. Recently, it was shown that both paradigms are reduced in chronic pain, but the influence of acute pain has not yet been adequately examined.

Objectives:

The aim of this study is to investigate OA and CPM after exercise-induced pain to evaluate whether these tests can be influenced by delayed-onset muscle soreness (DOMS) at a local or remote body site.

Methods:

Forty-two healthy adults were invited to 3 separate examination days: a baseline appointment, the consecutive day, and 7 days later. Participants were randomly divided into a rest (n = 21) and an exercise group (n = 21). The latter performed a single intensive exercise for the lower back. Before, immediately after, and on the following examination days, OA and CPM were measured at the forearm and the lower back by blinded assessor.

Results:

The exercise provoked a moderate pain perception and a mild delayed-onset muscle soreness on the following day. Repeated-measurements analysis of variance showed no statistically significant main effect for either OA or CPM at the forearm or lower back (P > 0.05).

Conclusion:

Delayed-onset muscle soreness was shown to have no effect on the inhibitory pain modulation system neither locally (at the painful body part), nor remotely. Thus, OA and CPM are robust test paradigms that probably require more intense, different, or prolonged pain to be modulated.

Pain Expansion and Severity Reflect Central Sensitization in Primary Care Patients with Greater Trochanteric Pain Syndrome

OBJECTIVES

The aims of this study were twofold: 1) to evaluate the differences in pain sensitivity of patients with greater trochanteric pain syndrome (GTPS) and 2) to examine the association between pain expansion, pain severity, and pain-related central sensitization somatosensory variables in patients with GTPS.

STUDY DESIGN

A cross-sectional study.

SETTING

Primary health care centers.

SUBJECTS

The sample consisted of 49 participants with a mean age of 48.28 ± 8.13 years and included eight males (16.3%) and 41 females (83.7%).

METHODS

Conditioned pain modulation (CPM), pain location, temporal summation, pressure pain detection threshold (PPDT), and pain intensity were recorded. Pain severity was determined with the Graded Chronic Pain Scale (GCPS).

RESULTS

Several participants (34.7%) showed a negative conditioned pain modulation and a statistically significant negative moderate correlation (P < 0.05; r = -0.316) between conditioned pain modulation and right view percentage of pain location. Temporal summation at the major trochanter showed a statistically significant low negative correlation (P < 0.05; r = -0.298). The GCPS exhibited a statistically significant moderately positive correlation (P < 0.01; r = 0.467) with the PPDT at the trochanter and a significant correlation with the postero-superior iliac spine (P < 0.01; r = 0.515) and epicondyle (P < 0.01; r = 0.566).

CONCLUSIONS

Patients with GTPS presented altered CPM, a relationship with more pain areas associated with negative CPM, and a positive association between pain severity and mechanical hyperalgesia at remote sites. Thus, physicians could apply these outcome measurements to assess primary care patients with GTPS and determine the central sensitization presence to prescribe adequate multimodal treatment approaches.

Understanding the pain profile in patients with haemophilia: Impaired descending pain inhibition as measured by conditioned pain modulation

INTRODUCTION

Haemophilic arthropathy is associated with pain that often becomes chronic, likely caused by peripheral and central mechanisms. In the field of haemophilia, to our knowledge, the role of the descending pain pathway, which can also be involved in these pain processes, has not been examined to date.

AIM

In light of the dearth of existing literature, we sought to evaluate the function of endogenous descending pain modulation in patients with haemophilia.

METHODS

Thirty adult patients with moderate to severe haemophilia A or B (median [interquartile range] age 51.0 [42.0-54.0]) and 23 healthy adult controls (age 46.5 [36.8-54.3]) underwent conditioned pain modulation (CPM) in order to examine the function of endogenous pain modulation. The CPM response was determined by scoring a test stimulus (heat) alone as well as under the influence of a conditioning stimulus (cold) on the basis of a numeric rating scale (NRS) (0 = 'no pain' to 100 = 'worst possible pain').

RESULTS

Patients with haemophilia demonstrated a statistically significant reduced CPM response when compared with the age-matched healthy controls (median (interquartile range) NRS score: patients: -10 (-17.5-[-7.5]) vs controls: -20 (-30.0-[-13.75]); P = .002). The determined difference in the CPM response between both cohorts showed a medium effect size of r = .433.

CONCLUSION

The results of this study indicate that an impaired degree of endogenous pain modulation could be present in patients with haemophilia. Therefore, the function of the descending pain pathway should be considered regarding an individual and comprehensive pain management.

Pain Catastrophizing in College Athletes

BACKGROUND

Pain is the most common patient-reported symptom but the perception of pain is complex, differs between individuals and is not directly proportional to the extent of injury. The relationship between aberrant pain coping strategies such as pain catastrophizing and the presence of pain in competitive athletes should be further established to employ the most optimal treatment.

HYPOTHESIS

The hypotheses were that numeric pain rating and pain catastrophizing (Pain Catastrophizing Scale, PCS) scores would have a moderate to strong relationship in college athletes, and athletes with either a current injury or previous injury, or playing with pain, would have significantly higher pain catastrophizing scores compared with noninjured/nonpainful athletes.

STUDY DESIGN

Cross-sectional study.

LEVEL OF EVIDENCE

III.

METHODS

College athletes completed a demographic form, injury questionnaire, numeric pain rating, and the PCS. All athletes were medically cleared for sports participation at the time of survey completion. A total PCS score was calculated in addition to a rumination, magnification, and helplessness score. Spearman rank was utilized to measure the strength of relationship between the PCS score and pain rating.

RESULTS

A total of 291 athletes from 15 different sports completed the questionnaires (males: 156, females: 135; age: 19 [2] y). Negligible correlations existed between the PCS score and pain (r = .27). Athletes who were currently injured or previously injured had significantly higher PCS scores compared with uninjured athletes (P < .01).

CONCLUSIONS

Approximately one-third of college athletes reported playing injured and/or with pain, but the relationship between pain rating and PCS score was negligible. The individualistic nature of pain perception and coping strategies would suggest that clinicians may want to consider screening for pain catastrophizing either prior to athletic participation or for athletes not following an expected recovery after injury in an effort to enhance individualized patient care.

Sedentary behaviour facilitates conditioned pain modulation in middle-aged and older adults with persistent musculoskeletal pain: a cross-sectional investigation

INTRODUCTION

Higher physical activity (PA) and lower sedentary behaviour (SB) levels have demonstrated beneficial effects on temporal summation (TS) and conditioned pain modulation (CPM) in healthy adults. This cross-sectional study investigated the relationships between PA and SB and TS/CPM responses in individuals with chronic musculoskeletal pain.

METHODS

Sixty-seven middle-aged and older adults with chronic musculoskeletal pain were recruited from the community. Questionnaires measuring demographics, pain, and psychological measures were completed. Physical activity/SB levels were measured using the International Physical Activity Questionnaire-short form and Sedentary Behaviour Questionnaire, respectively. Semmes monofilament was used to assess mechanical TS (MTS) at the most symptomatic (MTS-S) and a reference region (MTS-R); change in the pain scores (baseline-10th application) was used for analysis. Conditioned pain modulation procedure involved suprathreshold pressure pain threshold (PPT-pain4) administered before and after (CPM30sec, CPM60sec, and CPM90sec) conditioning stimulus (2 minutes; ∼12°C cold bath immersion). For analysis, PPT-pain4 (%) change scores were used.

RESULTS

PPT-pain4 (%) change scores at CPM30sec and CPM60sec demonstrated significant weak positive correlations with SB levels and weak negative correlations with PA measures. After adjusting for confounding variables, a significant positive association was found between SB (h/d) and PPT-pain4 (%) change scores at CPM30sec and CPM60sec. No significant associations between MTS and PA/SB measures.

CONCLUSION

Sedentariness is associated with higher pain inhibitory capacity in people with chronic musculoskeletal pain. The observed relationship may be characteristic of a protective (sedentary) behaviour to enhance pain modulatory mechanism. Prospective longitudinal studies using objective PA/SB measures are required to validate the observed relationship in a larger sample size.

Higher Cortical Facilitation and Serum BDNF Are Associated with Increased Sensitivity to Heat Pain and Reduced Endogenous Pain Inhibition in Healthy Males

Background

Although the brain-derived neurotrophic factor (BDNF) has been intensively investigated in animal models of chronic pain, its role in human pain processing is less understood.

Objective

To study the neurophysiology of BDNF modulation on acute experimental pain, we performed a cross-sectional study.

Methods

We recruited 20 healthy male volunteers (19-40 years old) and assessed their serum BDNF levels, quantitative sensory testing, and cortical excitability parameters using transcranial magnetic stimulation.

Results

Linear regression models demonstrated that the BDNF (β = -5.245, P = 0.034) and intracortical facilitation (β = -3.311, P = 0.034) were inversely correlated with heat pain threshold (adjusted R2 = 44.26). The BDNF (β = -3.719, P ≤ 0.001) was also inversely correlated with conditioned pain modulation (adjusted R2 = 56.8).

Conclusions

Our findings indicate that higher serum BDNF and intracortical facilitation of the primary motor cortex are associated with increased sensitivity to heat pain and high serum BDNF with reduced pain inhibition during noxious heterotopic stimulation.

The relationship between sensitivity to pain and conditioned pain modulation in healthy people

BACKGROUND

The relationship between sensitivity to pain and conditioned pain modulation (CPM) - a paradigm reflecting the activity of the endogenous descending analgesic system - is still unclear. This study aimed at investigating CPM magnitude in two distinct subgroups of healthy subjects, presenting low vs. high sensitivity to pain (LSP vs. HSP, respectively), by employing two different thermal paradigms of CPM.

METHOD

Ninety-five healthy subjects (out of 293 tested) were identified as LSP (n = 48) or HSP (n = 47) according to their tolerance time to noxious cold stimulation (Cold Pressor Test, 1 °C). All subjects were exposed to two different paradigms of CPM: 1) Fixed temperature 'test-pain' (TP) where phasic, fixed painful heat stimuli of 47 °C were administered before and during a prolonged 'conditioning stimulus' (cold water at 12 °C for 30 s); and 2) Individually based 'pain-60' where TP was determined as the temperature that induced pain at a magnitude of 60 on a 0-100 rating scale (with the same conditioning stimulus).

RESULT

Using both thermal paradigms, LSP subjects showed decreased CPM magnitudes in comparison to HSP (p < 0.0001 in both paradigms). Within each group, no differences in the magnitudes of CPM were found between the two paradigms.

CONCLUSION

These findings show that regardless of the thermal CPM paradigm employed, healthy individuals exhibiting low sensitivity to pain have a low pain inhibition profile and vice-versa. It is suggested that in healthy subjects, pain sensitivity predisposes the magnitude of CPM and not the other way around.

Training volume is associated with pain sensitivity, but not with endogenous pain modulation, in competitive swimmers

OBJECTIVES

To investigate the association of pain sensitivity and endogenous analgesia capacity, and training volume in a group of competitive swimmers.

DESIGN

An observational multi-center study.

SETTING

Multiple competitive swimming clubs.

PARTICIPANTS

102 healthy competitive swimmers.

MAIN OUTCOME MEASURES

Training volume was estimated using self-reported information. Static and dynamic measures of pain were assessed using pressure pain thresholds (PPTs) and conditioned pain modulation (CPM), the latter as a measure of endogenous pain inhibition. Selected demographic and psychosocial measures were considered as possible confounding factors.

RESULTS

Moderate positive correlations (0.38 < r < 0.44; p < 0.01) exist between self-reported training volume and PPTs at widespread body areas in competitive swimmers. These results were maintained during linear regression analysis while addressing possible confounding factors such as age and selected psychosocial factors. No associations were found between self-reported training volume and conditioned pain modulation (-0.08 < r < 0.06; p > 0.05).

CONCLUSIONS

Self-reported swim training volume is associated with pain sensitivity in competitive swimmers. Swimmers who train more show higher pressure pain thresholds, indicating lower pain sensitivity. Swim training volume is not associated with endogenous nociceptive inhibitory capacity as determined using CPM.

Acetaminophen ingestion improves muscle activation and performance during a 3-min all-out cycling test

Acute acetaminophen (ACT) ingestion has been shown to enhance cycling time-trial performance. The purpose of this study was to assess whether ACT ingestion enhances muscle activation and critical power (CP) during maximal cycling exercise. Sixteen active male participants completed two 3-min all-out tests against a fixed resistance on an electronically braked cycle ergometer 60 min after ingestion of 1 g of ACT or placebo (maltodextrin, PL). CP was estimated as the mean power output over the final 30 s of the test and W′ (the curvature constant of the power–duration relationship) was estimated as the work done above CP. The femoral nerve was stimulated every 30 s to measure membrane excitability (M-wave) and surface electromyography (EMGRMS) was recorded continuously to infer muscle activation. Compared with PL, ACT ingestion increased CP (ACT: 297 ± 32 W vs. PL: 288 ± 31 W, P < 0.001) and total work done (ACT: 66.4 ± 6.5 kJ vs. PL: 65.4 ± 6.4 kJ, P = 0.03) without impacting W′ (ACT: 13.1 ± 2.9 kJ vs. PL: 13.6 ± 2.4 kJ, P = 0.19) or the M-wave amplitude (P = 0.66) during the 3-min all-out cycling test. Normalised EMGRMS amplitude declined throughout the 3-min protocol in both PL and ACT conditions; however, the decline in EMGRMS amplitude was attenuated in the ACT condition, such that the EMGRMS amplitude was greater in ACT compared with PL over the last 60 s of the test (P = 0.04). These findings indicate that acute ACT ingestion might increase performance and CP during maximal cycling exercise by enhancing muscle activation.

Endogenous Pain Inhibitory Function: Endurance-Trained Athletes vs Active Controls

Objective

Athletes are at risk for developing chronic pain conditions, but the role of exercise in the modulation of pain in athletes has not been well established. The aim of this study was to investigate conditioned pain modulation (CPM) and exercise-induced hypoalgesia (EIH) responses between 13 endurance-trained athletes and 13 normally active controls.

Methods

In a cross-sectional, nonrandomized study with two independent groups of college-aged males and females, pressure pain thresholds (PPTs) were assessed in the vastus lateralis (VL) and brachioradialis (BR) using a pressure algometer before and after a conditioning stimulus, an isometric hand grip exercise to failure, and a 30-minute run.

Results

PPTs increased following the conditioning stimulus, indicating a CPM response, to a similar degree in the BR (19.3% ± 26.5% vs 18.6% ± 16.2%, P = 0.93) and VL (18.9% ± 25.9% vs 28.7% ± 27.4%, P = 0.73) in the athletes and controls. PPTs increased following isometric exercise to a similar extent in athletes and controls in the BR (23.9% ± 22.8% vs 28.2% ± 24.0%, P = 0.75) and VL (15.8% ± 14.8% vs 15.5% ± 11.6%, P = 0.94). Following 30 minutes of running, EIH was similar between athletes and controls in the VL (21.2% ± 17.2% vs 13.8% ± 13.3%, P = 0.23) but was attenuated in the BR of the athletes (6.1% ± 16.9% vs 20.9% ± 20%, P = 0.047).

Conclusions

Athletes and controls exhibited similar endogenous pain inhibitory function both locally and systemically following CPM and isometric, upper body exercise. After the 30-minute run, BR EIH was reduced in the athletes compared with controls, suggesting a reduced systemic response following familiar exercise—perhaps due to the exercise being perceived as less painful and/or effortful.

Sport-related injury and pain classification

Pain is common in athletes, and pain management in sport has traditionally been equated with injury management. Although both pain and injury interfere with sport performance, they are not synonymous. Acute musculoskeletal injury commonly manifests as nociceptive pain, inflammatory pain, or both. Pain that persists beyond expected injury recovery must account for all potential contributors to pain, including ongoing biomechanical abnormalities, underlying pathophysiology, and psychosocial issues. Pain chronification involves multiple pathophysiologic and neurobehavioral processes that lead from acute injury-related pain to subacute and chronic pain, and must be distinguished from an ongoing biomechanical overuse pattern. The foundation of pain management in athletes is proper pain classification, which involves assessing for any combination of nociceptive/inflammatory pain, neuropathic pain, central sensitization, and autonomic/motor/affective manifestations of pain. Understanding this foundation is critical because there are scant evidence-based guidelines for the management of pain in sport. This chapter will explore the relationship of sport-related injury and pain, and will provide a management framework that is consistent with International Olympic Committee consensus.

Quantitative sensory testing in physically active individuals and patients who underwent multidisciplinary pain therapy in the longitudinal course

Objective

The aim of this study was to evaluate possible differences of quantitative sensory testing (QST) results in healthy individuals (group control, n=20), physically active individuals (group sport, n=30) and in patients suffering from chronic musculoskeletal pain (group pain, n=30).

Methods

Thermal detection thresholds, thermal pain thresholds and blunt pressure pain thresholds were measured at various sites (T0). Additionally, group pain was treated in multidisciplinary pain therapy for 4 weeks. All groups were retested after 4 weeks to evaluate the reliability of QST measurements and to investigate possible early changes following treatment (T1).

Results

Importantly, QST-measurements showed stable test results for group sport and group control at both time points. Athletes demonstrated the highest pain thresholds in general (cold pain threshold mean in degree Celsius for the hand: 5.76, lower back right: 7.25, lower back left: 7.53; heat pain threshold mean in degree Celsius for the hand: 46.08, lower back right: 45.77, lower back left: 45.70; and blunt pressure pain mean in kilograms for the hand: 3.54, lower back right: 5.26, lower back left: 5.46). Patients who underwent therapy demonstrated significant differences at T1 (cold pain threshold hand mean in degree Celsius for the hand: 11.12 [T0], 15.12 [T1]; and blunt pressure pain mean in kilograms for the lower back right: 2.87 [T0], 3.56 [T1]). They were capable of enduring higher blunt pressure, but on the other hand cold pain tolerance had decreased (P=0.045 and P=0.019, respectively).

Conclusions

In conclusion, we were able to demonstrate significant differences of QST results among the three groups and we detected early changes following multidisciplinary pain therapy, which will be discussed.

Central and peripheral pain sensitization during an ultra-marathon competition

Background and aims

The participation in ultra-marathons and other ultra-endurance events has increased exponentially over the past decade. There is insufficient data on variation in pain mechanisms in exercise overall but especially in the ultra-endurance athlete population. To further understand peripheral and central pain sensitization we have investigated pressure pain threshold and conditioned pain modulation during three separate ultra-marathon competitions.

Methods

Each ultra-marathon investigated was held in the state of Florida, USA, over flat, sandy and paved surfaces under generally warm to hot, humid conditions. Pressure pain threshold was measured utilizing a Baseline © Dolorimeter. The blunt end of the dolorimeter stylus was placed onto the distal dominant arm, equidistant between the distal radius and ulna, three times in a blinded manner to insure that the testing technician did not influence the subject’s responses. Conditioned pain modulation was measured immediately after the PPT measures by placing the non-dominant hand in a cool water bath maintained at 15°C. The same dolorimeter measurement was repeated two more times on the dominant arm while the non-dominant hand remained in the water. Data was analyzed with a paired t-test.

Results

Pressure pain threshold was significantly decreased (p<0.05) at 25, 50 and 100 miles. Conditioned pain modulation was also significantly decreased (p<0.05) at 25, 50 and 100 miles of an ultra-marathon competition.

Conclusions

Together these data suggest an increased peripheral and/or central pain sensitization starting at 25 miles and continuing throughout an ultra-marathon competition run in these conditions. This is the first study that provides evidence of a decreased peripheral pain threshold and decreased central pain inhibition from ultra-marathon running. Decreases in both the peripheral pain threshold and central inhibition may result from nociceptor plasticity, central sensitization or a combination of both.

Implications

Based on previous research that has indicated a central sensitization resulting from inflammation and the well-documented inflammatory response to the rigors of ultra-marathon competition, we suggest the decreased peripheral pain threshold and decreased descending pain inhibition results from this inflammatory response of running an ultra-marathon.

Muscle Strength and Neuromuscular Control in Low-Back Pain: Elite Athletes Versus General Population

The purpose of the study was to investigate the athletic-based specificity of muscle strength and neuromuscular control of spine stability in chronic non-specific low-back pain (LBP). Thirty elite athletes and 29 age-matched non-athletes with (15 athletes and 15 non-athletes) and without LBP (15 athletes and 14 non-athletes) participated in the study. Muscle strength was measured during maximal isometric trunk flexion and trunk extension contractions. The neuromuscular control of spine stability was analyzed by determining trunk stiffness, trunk damping, and onset times of the lumbar and thoracic erector spinae muscles after sudden perturbations (quick release experiments) as well as maximum Lyapunov exponents (local dynamic stability) using non-linear time series analysis of repetitive lifting movements. LBP was assessed using the visual analog scale. We found lower maximal trunk extension moments (p = 0.03), higher trunk damping (p = 0.018) and shorter onset times (p = 0.03) of the investigated trunk muscles in LBP patients in both athletes and non-athletes. Trunk stiffness and the local dynamic stability did not show any differences (p = 0.136 and p = 0.375, respectively) between LBP patients and healthy controls in both groups. It can be concluded that, despite the high-level of training in athletes, both athletes and non-athletes with LBP showed the same deconditioning of the lumbar extensor muscles and developed similar strategies to ensure spine stability after sudden perturbations to protect the spine from pain and damage. The findings highlight that specific training interventions for the trunk muscles are not only crucial for individuals of the general population, but also for well-trained athletes.

Psychological Factors Associated With Ultramarathon Runners' Supranormal Pain Tolerance: A Pilot Study

Athletes seem to have higher pain tolerance than the normally active population. It is unknown whether psychological factors contribute to their supranormal pain tolerance. The aim of this pilot study was to examine pain-related psychological processes in ultramarathon runners ('ultrarunners') and to explore whether psychological factors mediate the elevated pain tolerance displayed by ultrarunners. Forty participants took part in the study: 20 ultrarunners and 20 age- and gender-matched controls. Participants underwent the cold pressor test using water cooled to 0.1 to 0.5°C and completed the Pain Catastrophizing Scale, Pain Anxiety Symptoms Scale-20, Pain Vigilance and Awareness Questionnaire, and Pain Resilience Scale. Immersion time on the cold pressor test was significantly longer for the ultrarunners (P = .007) and they also had lower scores on all Pain Anxiety Symptoms Scale-20 subscales (P ≤ .030). The 2 groups did not differ significantly on the other questionnaires. Mediation analysis revealed that reduced pain-related escape and avoidance behaviors accounted for 40% of the difference in immersion time between the groups (P = .020). Our results suggest that ultrarunners have lower levels of pain-related anxiety than the general population and that their supranormal pain tolerance is partially mediated by reduced pain-related escape and avoidance behaviors. PERSPECTIVE: This study investigated whether psychological factors contribute to the supranormal pain tolerance displayed by ultrarunners. It found that ultrarunners have lower levels of pain-related anxiety than nonrunning controls and that reduced pain-related escape and avoidance behaviors partially mediate their elevated pain tolerance.

Cuff Pressure Pain Detection Is Associated with Both Sex and Physical Activity Level in Nonathletic Healthy Subjects

Purpose

The aim of this study was to evaluate pressure pain sensitivity on leg and arm in 98 healthy persons (50 women) using cuff algometry. Furthermore, associations with sex and physical activity level were investigated.

Method

Normal physical activity level was defined as Godin Leisure-Time Exercise Questionnaire (GLTEQ) score ≤ 45 and high activity level as GLTEQ > 45. A pneumatic double-chamber cuff was placed around the arm or leg where a single chamber was inflated. The cuff inflation rate (1 kPa/s) was constant, and pain intensity was registered continuously on a 10 cm electronic visual analogue scale (VAS). The pain detection threshold (PDT) was defined as when the pressure was perceived as painful, and pain tolerance (PTT) was when the subject terminated the cuff inflation. For PTT, the corresponding VAS score was recorded (VAS-PTT). The protocol was repeated with two chambers inflated.

Result

Only single cuff results are given. For women compared with men, the PDT was lower when assessed in the arm ( P = 0.002), PTTs were lower in the arm and leg ( P < 0.001), and the VAS-PTT was higher in the arm and leg ( P < 0.033). Highly active participants compared with less active had higher PDT ( P = 0.027) in the leg. Women showed facilitated spatial summation ( P < 0.014) in the arm and leg and a steeper VAS slope (i.e., the slope of the VAS pressure curve between PDT and PPT) in the arm and leg ( P < 0.003).

Conclusion

This study indicates that reduced pressure pain sensitivity is associated both with male sex and physical activity level.

Stress and Alterations in the Pain Matrix: A Biopsychosocial Perspective on Back Pain and Its Prevention and Treatment

The genesis of chronic pain is explained by a biopsychosocial model. It hypothesizes an interdependency between environmental and genetic factors provoking aberrant long-term changes in biological and psychological regulatory systems. Physiological effects of psychological and physical stressors may play a crucial role in these maladaptive processes. Specifically, long-term demands on the stress response system may moderate central pain processing and influence descending serotonergic and noradrenergic signals from the brainstem, regulating nociceptive processing at the spinal level. However, the underlying mechanisms of this pathophysiological interplay still remain unclear. This paper aims to shed light on possible pathways between physical (exercise) and psychological stress and the potential neurobiological consequences in the genesis and treatment of chronic pain, highlighting evolving concepts and promising research directions in the treatment of chronic pain. Two treatment forms (exercise and mindfulness-based stress reduction as exemplary therapies), their interaction, and the dose-response will be discussed in more detail, which might pave the way to a better understanding of alterations in the pain matrix and help to develop future prevention and therapeutic concepts.

Pain Adaptability in Individuals With Chronic Musculoskeletal Pain Is Not Associated With Conditioned Pain Modulation

Healthy humans can be divided into the pain adaptive (PA) and the pain nonadaptive (PNA) groups; PA showed a greater decrease in pain rating to a cold pressor test (CPT) than PNA. This study examined if the dichotomy of pain adaptability existed in individuals with chronic musculoskeletal pain. CPTs at 2°C and 7°C were used to assess the status of pain adaptability in participants with either chronic nonspecific low back pain or knee osteoarthritis. The participants' potency of conditioned pain modulation (CPM) and local inhibition were measured. The strengths of pain adaptability at both CPTs were highly correlated. PA and PNA did not differ in their demographic characteristics, pain thresholds from thermal and pressure stimuli, or potency of local inhibition or CPM. PA reached their maximum pain faster than PNA (t₄₁ = -2.76, P < .01), and had a gradual reduction of pain unpleasantness over 7 days whereas PNA did not (F_6,246 = 3.01, P = .01). The dichotomy of pain adaptability exists in musculoskeletal pain patients. Consistent with the healthy human study, the strength of pain adaptability and potency of CPM are not related. Pain adaptability could be another form of endogenous pain inhibition of which clinical implication is yet to be understood.

PERSPECTIVE

The dichotomy of pain adaptability was identified in healthy humans. The current study confirms that this dichotomy also exists in individuals with chronic musculoskeletal pain, and could be reliably assessed with CPTs at 2°C and 7°C. Similar to the healthy human study, pain adaptability is not associated with CPM, and may reflect the temporal aspect of pain inhibition.

Suicide Behavior and Chronic Pain: An Exploration of Pain-Related Catastrophic Thinking, Disability, and Descriptions of the Pain Experience

This study examined differences in suicidal ideation (SI) and suicide attempts (SAs) among veterans with chronic pain. Pain-specific variables, including catastrophic thinking, disability, and sensory, affective, and evaluative pain descriptors, were a focus. Structured diagnostic and clinical interviews were conducted to examine SI/SA and mental health. Veterans completed the Structured Clinical Interview for DSM-IV and the Columbia-Suicide Severity Rating Scale to assess Axis I symptoms and suicidal behavior(s). Self-report questionnaires were used to evaluate the participants' subjective experience of chronic pain, which included the McGill Pain Questionnaire, Pain Catastrophizing Scale, and Pain Disability Index. The findings add to previous literature by suggesting pain-related catastrophic thinking specifically is related to elevated risk for SA, whereas affective and sensory pain are associated with SI. The study results support the need to assess pain from a multifaceted perspective and to examine the different experiences of pain, such as sensory and affective constructs, when discussing suicide risk in veterans.

The psychology of elite cycling: a systematic review

This systematic review sought to synthesise what is currently known about the psychology of elite cycling. Nine electronic databases were searched in March 2017 for studies reporting an empirical test of any psychological construct in an elite cycling sample. Fourteen studies (total n = 427) met inclusion criteria. Eight studies were coded as having high risk of bias. Themes extracted included mood, anxiety, self-confidence, pain, and cognitive function. Few studies had similar objectives meaning that in many instances findings could not be synthesised in a meaningful way. Nevertheless, there was some cross-study evidence that elite cyclists have more positive mood states (relative to normative scores), pre-race anxiety impairs performance (among male cyclists), and associative strategies are perceived as helpful for pain management. Among single studies coded as having low risk of bias, evidence suggests that implicit beliefs affect decision making performance, elite cyclists are less susceptible to mental fatigue (than non-elite cyclists), and better leadership skills relates to greater social labouring. Limitations include non-standardisation of measures, lack of follow-up data, small sample sizes, and overall poor research quality. The findings of this systematic review might be used to inform research and theory development on the psychology of elite endurance cycling.

Diagnosis of psychosocial risk factors in prevention of low back pain in athletes (MiSpEx)

Background

Low back pain (LBP) is a common pain syndrome in athletes, responsible for 28% of missed training days/year. Psychosocial factors contribute to chronic pain development. This study aims to investigate the transferability of psychosocial screening tools developed in the general population to athletes and to define athlete-specific thresholds.

Methods

Data from a prospective multicentre study on LBP were collected at baseline and 1-year follow-up (n=52 athletes, n=289 recreational athletes and n=246 non-athletes). Pain was assessed using the Chronic Pain Grade questionnaire. The psychosocial Risk Stratification Index (RSI) was used to obtain prognostic information regarding the risk of chronic LBP (CLBP). Individual psychosocial risk profile was gained with the Risk Prevention Index - Social (RPI-S). Differences between groups were calculated using general linear models and planned contrasts. Discrimination thresholds for athletes were defined with receiver operating characteristics (ROC) curves.

Results

Athletes and recreational athletes showed significantly lower psychosocial risk profiles and prognostic risk for CLBP than non-athletes. ROC curves suggested discrimination thresholds for athletes were different compared with non-athletes. Both screenings demonstrated very good sensitivity (RSI=100%; RPI-S: 75%-100%) and specificity (RSI: 76%-93%; RPI-S: 71%-93%). RSI revealed two risk classes for pain intensity (area under the curve (AUC) 0.92(95% CI 0.85 to 1.0)) and pain disability (AUC 0.88(95% CI 0.71 to 1.0)).

Conclusions

Both screening tools can be used for athletes. Athlete-specific thresholds will improve physicians' decision making and allow stratified treatment and prevention.

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.

A longitudinal exploration of pain tolerance and participation in contact sports

BACKGROUND/AIMS

Athletes who choose to engage in contact sports do so with the knowledge that participation will bring pain in the form of contact with others, injury, and from exertion. Whilst athletes who play contact sports have been shown to have higher pain tolerance than those who do not, it is unclear whether this is a result of habituation over time, or as a result of individual differences at the outset. The aim was to compare pain responses over an athletic season in athletes who participated in contact sport and those who disengaged from it.

METHODS

One hundred and two new contact athletes completed measures of cold and ischaemic pain tolerance, perceived pain intensity, pain bothersomeness, pain coping styles and attendance at the start, middle (4 months) and end (8 months) of their season. The athletes were drawn from martial arts, rugby and American football. Cluster analysis placed 47 athletes into a participating category and 55 into a non-participating cluster.

RESULTS

Participating athletes had higher ischaemic pain tolerance at the start (r=0.27, p=0.05), middle (r=0.41, p<0.0001) and end of the season (r=0.57, p<0.0001) compared to non-participating athletes. In addition participating athletes were more tolerant to cold pain at the end of the season (r=0.39, p<0.0001), compared to non-participating athletes. Participating athletes also exhibited higher direct coping, catastrophized less about injury pain and also found contact pain to be less bothersome physically and psychologically compared to non-participating athletes. Participating athletes were more tolerant of ischaemic pain at the end of the season compared to the start (r=0.28, p=0.04). Conversely non-participating athletes became significantly less tolerant to both pain stimuli by the end of the season (cold pressor; r=0.54, p<0.0001; ischaemia; r=0.43, p=0.006). Pain intensity as measured by a visual analogue scale did not change over the season for both groups.

CONCLUSIONS

Those who cease participation in contact sports become less pain tolerant of experimental pain, possibly a result of catastrophizing. The results suggest that athletes who commit to contact sports find pain less bothersome over time, possibly as a result of experience and learning to cope with pain. Athletes who continue to participate in contact sports have a higher pain tolerance, report less bothersomeness and have higher direct coping than those who drop out. In addition, tolerance to ischaemic pain increased over the season for participating athletes.

IMPLICATIONS

Having a low pain tolerance should not prevent athletes from taking part in contact sports, as pain becomes less bothersome in athletes who adhere to such activities. Participating in contact sports may result in maintained cold pain tolerance, increased ischaemic pain tolerance, reduced catastrophizing and better coping skills. Coaches can therefore work with athletes to develop pain coping strategies to aid adherence to contact sports.