Exercise-induced Hypoalgesia Research Articles

Brain Mechanisms of Exercise-Induced Hypoalgesia: To Find a Way Out from "Fear-Avoidance Belief".

It is well known that exercise produces analgesic effects (exercise-induced hypoalgesia (EIH)) in animal models and chronic pain patients, but the brain mechanisms underlying these EIH effects, especially concerning the emotional aspects of pain, are not yet fully understood. In this review, we describe drastic changes in the mesocorticolimbic system of the brain which permit the induction of EIH effects. The amygdala (Amyg) is a critical node for the regulation of emotions, such as fear and anxiety, which are closely associated with chronic pain. In our recent studies using neuropathic pain (NPP) model mice, we extensively examined the association between the Amyg and EIH effects. We found that voluntary exercise (VE) activated glutamate (Glu) neurons in the medial basal Amyg projecting to the nucleus accumbens (NAc) lateral shell, while it almost completely suppressed NPP-induced activation of GABA neurons in the central nucleus of the Amyg (CeA). Furthermore, VE significantly inhibited activation of pyramidal neurons in the ventral hippocampus-CA1 region, which play important roles in contextual fear conditioning and the retrieval of fear memory. This review describes novel information concerning the brain mechanisms underlying EIH effects as a result of overcoming the fear-avoidance belief of chronic pain.

Pain modulation through exercise : Exercise-induced hypoalgesia in physiotherapy

Exercise prescription is acentral tenet of physiotherapy. One of the numerous benefits of exercise is its influence on endogenous pain modulation. Exercise-induced hypoalgesia (EIH) refers to ashort-term change in pain sensitivity following an acute bout of exercise. Interest in this phenomenon has grown considerably with over 150articles published, including four systematic reviews in 2020 alone.This narrative review provides an overview of EIH including adefinition and summary of the underlying mechanisms and mediating factors. Recent systematic reviews assessing EIH in people with and without musculoskeletal complaints were evaluated using AMSTAR2. Review findings confirm the presence of EIH. For asymptomatic people, confidence in the evidence was low to very low due to high heterogeneity of included studies, risk of bias, and study eligibility. For people with pain, there is very low confidence, at best, that subgroups or isometric exercise show altered EIH. Despite the growing body of evidence, challenges within the available evidence due to its complex nature are highlighted. Recommendations regarding outcome measures and exercise parameters are required, and further understanding of reliability and validity of EIH is needed. There is ademand to further elucidate these parameters and contextual factors to advance our understanding of EIH. Additional clinical research, especially in patient populations, is required to then provide implications for rehabilitation.

The impact of isometric handgrip exercise and training on health-related factors: A review.

Isometric handgrip exercise has been suggested to promote some health-related factors (e.g., lowering blood pressure). However, there is a need to evaluate whether this type of exercise can be included as an option to elicit these health-related outcomes. The purpose of the article was to systematically review the acute and chronic effects of isometric handgrip exercise on resting blood pressure, pain sensation, cognitive functionand blood lipids and lipoproteins. A systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. A total of 89 studies met our inclusion criteria. Most randomized controlled trials (17/26) reported reductions in resting blood pressure (mostly systolic blood pressure) following isometric handgrip training. There were inconsistent results in isometric handgrip exercise-induced hypotension (i.e., acute response). There was convincing evidence observed in randomized controlled trials (4/6) for isometric handgrip exercise-induced hypoalgesia. Some randomized controlled trials (2/2) supported an improvement in memory performance, but not interference control (0/2), after a session of isometric handgrip exercise. None of the included studies found any effects of isometric handgrip training on blood lipids and lipoproteins. Isometric handgrip exercise appears to be an effective method to improve certain health-related factors. The acute reductions in pain and blood pressure may share a similar central mechanism. However, training-induced reductions in resting blood pressure may be driven by changes in the periphery. Additional work is needed to better understand if (and to what extent) isometric handgrip exercise (or training) influences cognitive function and blood lipids and lipoproteins.

Effect of prolonged experimental neck pain on exercise-induced hypoalgesia.

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

Hypoalgesia following isometric handgrip exercise with and without blood flow restriction is not mediated by discomfort nor changes in systolic blood pressure

ABSTRACT The purpose was to examine the effect of isometric handgrip exercise with and without blood flow restriction on exercise-induced hypoalgesia at a local and non-local site, and its underlying mechanisms. Sixty participants (21 males & 39 females, 18–35 years old) completed 3 trials: four sets of 2-minute isometric handgrip exercise at 30% of maximum handgrip strength; isometric handgrip exercise with blood flow restriction at 50% of arterial occlusion pressure; and a non-exercise time-matched control. Pain thresholds increased similarly in both exercise conditions at a local (exercise conditions: ~0.45 kg/cm2, control: ~-0.04 kg/cm2) and non-local site (exercise conditions: ~0.37 kg/cm2, control: ~-0.16 kg/cm2). Blood flow restriction induced greater feelings of discomfort compared to exercise alone [median difference (95% credible interval) of 4.5 (0.5, 8.6) arbitrary units]. Blood pressure increased immediately after exercise (systolic: 10.3 mmHg, diastolic: 7.7 mmHg) and decreased in recovery. There was no within participant correlation between changes in discomfort and pressure pain threshold. A bout of isometric handgrip exercise with or without blood flow restriction can provide exercise-induced hypoalgesia at a local and non-local site. However, discomfort and changes in systolic blood pressure do not explain this response.

Weather-Related Pain or Meteoropathy has been Attracting Attention

Recent topic concerning weather-related pain or meteoropathy is described. Such symptoms are observed in patients with rheumatoid arthritis (RA), fibromyalgia, osteoarthritis, or headache, neck pain, stiff shoulder, back pain. Patients often feel pain when atmospheric pressure showed lower pressure of 1003-1007 hPa or decrease of 6-10 hPa. From psychosomatic point of view, decreased self-efficacy or higher catastrophic thinking are involved. Several questionnaires are useful for the evaluation, such as Pain Disability Assessment Scale (PDAS), Hospital Anxiety and Depression Scale (HADS), Pain Self–Efficacy Questionnaire (PSEQ), and Pain Catastrophizing Scale (PCS). For treatment, exercise–induced hypoalgesia (EIH) would be effective.

The effect of exercise intensity on exercise-induced hypoalgesia in cancer survivors: A randomized crossover trial.

Pain is experienced by people with cancer during treatment and in survivorship. Exercise can have an acute hypoalgesic effect (exercise‐induced hypoalgesia; EIH) in healthy individuals and some chronic pain states. However, EIH, and the moderating effect of exercise intensity, has not been investigated in cancer survivors. This study examined the effect of low‐ and high‐intensity aerobic exercise on EIH in cancer survivors after a single exercise session as well as a brief period of exercise training (2‐weeks, three exercise sessions per week). Participants (N = 19) were randomized to low‐ (30%–40% Heart Rate Reserve (HRR) or high‐ (60%–70% HRR) intensity stationary cycling for 15–20 min. Pressure pain thresholds (PPT) were assessed over the rectus femoris and biceps brachii before and after a single exercise session and again after a short training period at the assigned intensity. Then, following a 6‐week washout period, the intervention was repeated at the other intensity. After the first exercise session, high‐intensity exercise resulted in greater EIH over the rectus femoris than low intensity (mean difference ± SE: −0.51 kg/cm2 ± 0.15, Cohen's d = 0.78, p = 0.004). After a 2‐week training period, we found no difference in EIH between intensities (0.01 kg/cm2 ± 0.25, d = 0.00 p = 0.99), with comparable moderate effect sizes for both low‐ and high‐intensity exercise, indicative of EIH. No EIH was observed over the biceps brachii of the arm at either low or high intensity. Low‐intensity exercise training may be a feasible option to increase pain thresholds in cancer survivors.

Aerobic Exercise Attenuates Pain Sensitivity: An Event-Related Potential Study

In this study, electroencephalography (EEG) was utilized to explore the neurophysiological mechanisms of aerobic exercise-induced hypoalgesia (EIH) and provide a theoretical basis for the application of aerobic exercise in pain assessment and treatment. Forty-five healthy subjects were randomly divided into moderate-intensity aerobic exercise [70% heart rate reserve (HRR)], low-intensity aerobic exercise (50% HRR), or control groups (sitting). Aerobic exercise was performed with cycling. Pressure pain threshold (PPT), heat pain threshold (HPT), event-related potential (ERP) induced by contact heat stimulus and pain scoring were measured before and after the intervention. We found that moderate-intensity aerobic exercise can increase the PPT (rectus femoris: t = −2.71, p = 0.017; tibialis anterior muscle: t = −2.36, p = 0.033) and HPT (tibialis anterior muscle: t = −2.219, p = 0.044) of proximal intervention sites rather than distal sites, and decreased pain scorings of contact heat stimulus. After moderate-intensity aerobic exercise, alpha oscillation power reflecting the central descending inhibitory function was enhanced (t = −2.31, p < 0.05). Low-intensity aerobic exercise mainly reduced the pain unpleasantness rating (Block 1: t = 2.415, p = 0.030; Block 2: t = 3.287, p = 0.005; Block 4: t = 2.646, p = 0.019; Block 5: t = 2.567, p = 0.022). Aerobic exercise had an overall EIH effect. Its hypoalgesic effect was related to exercise intensity and affected by the site and type of pain stimulus. Moderate-intensity aerobic exercise effectively reduced the sensitivity to various painful stimuli, and low-intensity aerobic exercise selectively inhibited the negative emotional pain response. The hypoalgesic mechanism of aerobic exercise involves the enhancement of the central descending inhibitory function.

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

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.

Effects of Exercise-induced Hypoalgesia and Its Neural Mechanisms.

Exercise-induced hypoalgesia is frequently documented in the literature. However, the underlying neural mechanism of this phenomenon remains unclear. Here, we explored the effects of different intensities of isometric exercise on pain perception with a randomized controlled design and investigated its neural mechanisms through tracing the dynamic changes of heat-evoked brain responses. Forty-eight participants were randomly assigned to one of the three groups with different exercise intensities (i.e., high, low, and control). Their subjective pain reports and brain responses elicited by heat stimuli before and after exercise were assessed. We observed 1) the increased pressure pain thresholds and heat pain thresholds on the dorsal surface of the hand and the biceps brachii muscle of the exercised limb (closed to the contracting muscle), and the decreased pressure pain ratings at the indexed finger of the unexercised limb; 2) more reduction of pain sensitivity on both the biceps brachii muscle and the dorsal surface of the hand induced by the high-intensity isometric exercise than the low-intensity isometric exercise; and 3) both the high-intensity and the low-intensity isometric exercise induced the reduction of N2 amplitudes and N2-P2 peak-to-peak amplitudes, as well as the reduction of event-related potential magnitudes elicited by the heat stimuli on the exercised limb. The hypoalgesic effects induced by the isometric exercise were not only localized to the moving part of the body but also can be extended to the distal part of the body. The exercise intensities play a vital role in modulating these effects. Exercise-induced hypoalgesia could be related to the modulation of nociceptive information transmission via a spinal gating mechanism and also rely on a top-down descending pain inhibitory mechanism.

Pain and executive function: no association between remote exercise-induced hypoalgesia and cognitive inhibition in pain-free participants.

Cognitive inhibition, which denotes the ability to suppress predominant or automatic responses, has been associated with lower pain sensitivity and larger conditioned pain modulation in humans. Studies exploring the association between cognitive inhibition and other pain inhibitory phenomena, like exercise-induced hypoalgesia (EIH), are scarce. The primary aim was to explore the association between cognitive inhibition and EIH at exercising (local) and non-exercising (remote) muscles after isometric exercise. The secondary aim was to explore the association between cognitive inhibition and pressure pain sensitivity. Sixty-six pain-free participants (28.3±8.9 years old, 34 women) completed two cognitive inhibition tasks (stop-signal task and Stroop Colour-Word task), a 3-min isometric wall squat exercise, and a quiet rest control condition with pre- and post-assessments of manual pressure pain thresholds at a local (thigh) and a remote site (shoulder). In addition, cuff pressure pain thresholds, pain tolerance and temporal summation of pain were assessed at baseline. No association was found between remote EIH and cognitive inhibition (Stroop interference score: r=0.12, [-0.15; 0.37], p=0.405, BF01=6.70; stop-signal reaction time: r=-0.08, [-0.32; 0.17], p=0.524, BF01=8.32). Unexpectedly, individuals with worse performance on the Stroop task, as indicated by a higher Stroop interference score, showed higher local EIH (r=0.33; [0.10; 0.53], p=0.007, BF01=0.29). No associations were observed between pain sensitivity and any of the cognitive inhibition performance parameters. The present findings do not support previous evidence on positive associations between exercise-induced hypoalgesia and cognitive inhibition, as well as baseline pain sensitivity and cognitive inhibition.

Wrist, but Not Back, Isometric Contraction Induced Widespread Hypoalgesia in Healthy Participants.

Objective: Exercise may reduce pain sensitivity. This phenomenon called exercise-induced hypoalgesia is observed in different types of exercises and involves the activation of endogenous pain modulation systems. Although the effect of limb exercise on pain sensitivity has often been tested, few studies explored the impact of back exercises that are often used to treat low back pain. The main objective is to measure the effect of back-muscle exercise on pain sensitivity and compare it to the effect of a limb-muscle exercise.Methods: Twenty-three participants who were pain-free performed a 4-min wrist flexion isometric contraction followed by a 4-min low back extension, separated by a 20-min break. Pressure pain thresholds were tested at two low back (S1 spinous process, lumbar erector spinae muscle) and two wrist (capitate bone, wrist flexor muscles) sites before and after each exercise. For each exercise, sites were considered as remote or local in relation to the muscles contracted during the exercise. An independent sample of 11 participants was recruited to confirm the influence of low back extension on pain sensitivity.Results: Wrist exercise induced a larger increase in pain sensitivity than back exercise at the remote site. Only wrist exercise induced a hypoalgesia effect at both the local and the remote sites. Back exercise induced a similar effect in the independent sample.Conclusions: This study showed that back and wrist exercises induced a distinct effect on pain sensitivity in participants who were pain-free. The wrist exercise induced a systemic reduction in pain sensitivity (locally and remotely), whereas the back exercise did not. This differential effect may be present because wrist exercise induced most fatigue compared with the back exercise.

Effect Of Blood Flow Restricted Handgrip Exercise On Exercise-induced Hypoalgesia At Local And Non-local Muscles

Effect Of Blood Flow Restricted Handgrip Exercise On Exercise-induced Hypoalgesia At Local And Non-local Muscles

Exercise-Induced Hypoalgesia Profile in a Rat Neuropathic Pain Model Predicts Pain Severity Following Infraorbital Nerve Injury and Is Associated with Local Cytokine Levels, Systemic Endocannabinoids, and Endogenous Opioids.

To investigate the role of exercise-induced hypoalgesia (EIH) in the development of neuropathic pain (NP) following infraorbital nerve (ION) injury and to explore possible underlying mechanisms defining the differences between rats with high and low EIH. EIH was evaluated by measuring the percentage of withdrawal responses to a series of 30 mechanical stimuli applied to the hind paw before and after 180 seconds of exercise on a rotating rod. The rats were assigned to low- and high-EIH groups based on reduction in the percent of withdrawal responses following exercise. NP was induced in high- and low-EIH rats via ION constriction injury. Rats were tested with graded nylon monofilaments to establish the withdrawal threshold. Increasingly stiff monofilaments were applied to the ION territory until there was a clear withdrawal by the rat. This was repeated a total of three times. A decreased withdrawal threshold indicates allodynia. Testing was performed at baseline and at 3, 10, and 17 days following the injury. On day 17 postinjury, IONs were harvested for the assessment of interleukin (IL)-6, IL-1β, and IL-10 levels. Samples from high-EIH and low-EIH surgically naïve rats served as control for the cytokines study. In this second part of the study, the effects of cannabinoid 1 (CB1) and cannabinoid 2 (CB2) antagonists and naltrexone on EIH profiles and on the withdrawal thresholds to mechanical stimulation were measured. EIH and withdrawal thresholds in high- and low-EIH rats were measured before and after administration of antagonists. Low-EIH rats developed significantly more pronounced allodynia in the ION territory following injury compared to high-EIH rats. At 17 days postinjury, ION IL-1β levels were higher in low-EIH rats, and IL-10 levels were higher in high-EIH rats. CB1 antagonist blocked the analgesic effect induced by exercise in high- but not in low-EIH rats. The CB2 antagonist had no significant effect on high- or low-EIH rats. Naltrexone blocked the effects of EIH in both high- and low-EIH rats. Exercise induced a significant analgesic effect in high-EIH but not in low-EIH rats. CB1 or CB2 antagonist administration had no effect on pre-exercise responses to mechanical stimulation, while naltrexone administration resulted in significant allodynia in both low- and high-EIH rats. This study demonstrated substantial differences between rats with high and low EIH. The results suggest that following ION injury, high-EIH rats may have a more prominent or activated endocannabinoids system and that their inflammatory response is moderated, with higher levels of IL-10 and lower levels of IL-1β.

Association of pain intensity and patterns with response to exercise in knee osteoarthritis

Purpose: While exercise is recommended as the first-line intervention for people with chronic knee pain due to osteoarthritis (OA), a significant proportion of individuals do not respond to exercise interventions and may even report more pain. A normal response to a bout of exercise is characterized by reductions in pain and pain threshold, a phenomenon known as exercise induced hypoalgesia (EIH). Some individuals with chronic pain show an impaired EIH response immediately after exercise which may contribute to non-response after exercise interventions.

27042 Pressure-pain thresholds at baseline and in response to isometric exercise in Achilles tendinopathy

ABSTRACT IMPACT: Baseline presentation in AT (higher upper trapezius PPT with no difference at calf or tendon) may suggest a mechanism for persistent symptoms: with more advantageous central pain processing and no tradeoff peripherally, they may choose to continue their usual activities without regard for further damage to the affected tendon. OBJECTIVES/GOALS: Exercise-induced hypoalgesia, a reduction in pain with exercise, is often observed in healthy populations but is not well established in Achilles tendinopathy (AT). The aim was to compare pressure-pain threshold (PPT) at baseline and after fatiguing isometric exercise in AT and healthy controls. METHODS/STUDY POPULATION: 21 participants were recruited for the study: 7 AT (26.5 ±8.8 yrs), 14 control (22.1 ±3.2 yrs). After a familiarization session, participants completed an experimental session that involved performance of intermittent maximal voluntary isometric contractions (MVICs) (2s:2s duty cycle) in a Biodex3 dynamometer (Biodex Medical, Shirley, NY) for 4 minutes. PPT was measured at the medial gastrocnemius (calf), Achilles tendon, and upper trapezius at baseline and immediately following the fatiguing isometric task using a Somedic Algometer (Somedic AB, Sweden). Data are expressed as Mean(SD). Change in PPT is expressed as a percentage of baseline PPT. Units for PPT are kPa. A priori alpha was set to 0.05. RESULTS/ANTICIPATED RESULTS: There was no change in tendon or calf PPT following isometric exercise in AT (tendon: p=0.78; calf: p=0.76), while both increased (i.e., exercise-induced hypoalgesia) in controls (tendon: 9.5(17.8), p=0.03; calf: 21.3(22.7), p&lt;0.01). Neither group experienced a post-exercise change in upper trapezius PPT (AT: p=0.35; control: p=0.37). There was no between-group difference in baseline calf (p=0.14) or tendon (p=0.19) PPT. However, baseline and post-exercise upper trapezius PPT were significantly higher in AT (baseline: 335.6(194.8); post-exercise: 321.2(170.1)) than in controls (baseline: 193.7(75.1), p&lt;0.01; post-exercise: 198.1(79.1), p&lt;0.01). DISCUSSION/SIGNIFICANCE OF FINDINGS: These findings suggest: (1) in persons with AT, central pain processing is altered at baseline, but unaffected in response to isometric fatiguing exercise; and (2) in persons with AT, peripheral pain processing is unaffected at baseline, but is altered in response to this mode and dosage of fatiguing isometric exercise.

The Effects of Wheel-Running Using the Upper Limbs Following Immobilization After Inducing Arthritis in the Knees of Rats

This study investigated the effects of wheel-running using the upper limbs following immobilization after inducing arthritis in the knees of rats. Forty male Wistar rats (aged 8 weeks) divided into four groups randomly: arthritis (AR), immobilization after arthritis (Im), wheel-running exercise with the upper limbs following immobilization after arthritis induction (Im+Ex) and sham arthritis induction (Con). The knee joints of the Im and Im+Ex groups were immobilized with a cast for 4 weeks. In the Im+Ex group, wheel-running exercise was administered for 60 min/day (5 times/week). The swelling and the pressure pain threshold (PPT) of the knee joint were evaluated for observing the condition of inflammatory symptoms in affected area, and the paw withdraw response (PWR) was evaluated for observing the condition of secondary hyperalgesia in distant area. Especially, in order to evaluate histological inflammation in the knee joint, the number of macrophage (CD68-positive cells) in the synovium was examined. The expression of calcitonin gene-related peptide (CGRP) in the spinal dorsal horn (L2-3 and L4-5) was examined to evaluate central sensitization. The Im+Ex group showed a significantly better recovery than the Im group in the swelling, PPTs, and PWRs. Additionally, CGRP expression of the spinal dorsal horn (L2-3 and L4-5) in the Im+Ex group was significantly decreased compared with the Im group. According to the results, upper limb exercise can decrease pain in the affected area, reduce hyperalgesia in distant areas, and suppress the central sensitization in the spinal dorsal horn by triggering exercise-induced hypoalgesia (EIH).

The effect of acute-experimental pain models on offset analgesia.

Offset analgesia (OA) is characterized by a disproportionately large decrease in pain perception after a slight decrease in noxious stimulation. In patients with ongoing pain, this response is reduced. The effect is pronounced in painful body areas. The influence of acute pain has not been sufficiently investigated. The aim of this study was to investigate the influence of two experimental acute pain models, measured within the area of acute pain and on the non-affected opposite side, thereby considering the possible somatotopic nature of OA. Healthy, pain-free volunteers (n=75) were randomly assigned to one of three groups (cold water, exercise and control group). The 'cold water group' immersed one hand into cold water for 3min (Cold Pressor Task), while the 'exercise group' performed an isometric grip exercise for 3min. There was no manipulation in the control group. Each experimental pain stimulus was performed at both (dominant, non-dominant) forearms. The individualized OA paradigm consisted of offset and constant temperature trials. Offset analgesia was measured immediately before, during and after the experimental pain stimuli. A significant difference in OA was shown during experimental pain when compared to the control condition (exercise vs. control: p<0.001, cold vs. control: p=0.001), with no difference between the experimental conditions (p>0.05). Immediately following the pain stimulation, results were marginally non-significant (p=0.05). Experimental painful stimulation reduced OA. This result should be interpreted with caution due to potential influences of conditioned pain modulation or exercise-induced hypoalgesia as well as possible floor effects. Temporal contrast of pain perception is inhibited in acute pain states. This study showed that reduced offset analgesia is observed when pain is experimentally induced using noxious cold and exercise stimuli.

Interrelated hypoalgesia, creep, and muscle fatigue following a repetitive trunk flexion exposure

Repetitive trunk flexion can damage spinal tissues, however its association with low back pain in the workplace may be confounded by factors related to pain sensitivity. Muscle fatigue, exercise-induced hypoalgesia, and creep-induced neuromuscular changes following repetitive trunk flexion may all affect this assumed exposure-pain relationship. This study’s purpose was to determine how mechanical pain sensitivity in the low back is affected by a repetitive trunk flexion exposure and identify factors associated with changes in low back pain sensitivity. Pressure pain thresholds, perceptions of sub-threshold stimuli, and muscle fatigue in the trunk and tibia, as well as lumbar spine creep were tracked in 37 young healthy adults before and up to 40 min after a 10-min repetitive trunk flexion exposure. Pressure pain thresholds (p = 0.033), but not perceptions of sub-threshold stimuli (p > 0.102) were associated with approximately a 12.5% reduction in pain sensitivity 10 min after completing the exposure, while creep and local muscle fatigue effects were only observed immediately following the exposure. Creep and fatigue interactions and the corresponding tibial measure co-varied with individual low back pressure pain thresholds. The net hypoalgesic effects of repetitive trunk flexion have the potential to partially mask possibly injurious loads, which could contribute to the severity or incidence of lower back injuries related to these exposures.

Acute Effects of a Brief Physical Exercise Intervention on Somatosensory Perception, Lumbar Strength, and Flexibility in Patients with Nonspecific Chronic Low-Back Pain.

BackgroundEvidence-based clinical guidelines consider physical exercise one of the best nonpharmacological interventions for low-back pain (LBP), but it is necessary to clarify the exercise-induced hypoalgesia effect of different modalities of exercise in chronic pain populations.PurposeThis study focused on exploring acute changes in tactile and pressure-pain perception and lumbar strength and flexibility in patients with nonspecific chronic LBP (NSCLBP) after performing one of three 20-minute physical exercise modalities.MethodsA total of 81 patients with NSCLBP were pseudorandomly distributed into three groups of 20-minute physical exercise — 1) aerobic (n=21, mean age 42±9.72 years, nine men), 2) stretching (n=21, mean age 40±11.37 years, ten men), and 3) strengthening (n=20, mean age 35.80±11.56 years, ten men) — and 4) a control group (n=19, mean age 38.64±10.24 years, eight men), and completed self-reported questionnaires during the same period. Tactile and pressure-pain thresholds and isometric lumbar muscle endurance and flexibility were assessed before and after this brief exercise-based intervention.ResultsAll groups were comparable in terms of sociodemographic and clinical data, cardiovascular capacity, and self-reported data onphysical disability, mood, motivation, psychological response to stimulus properties of physical exercise, and physical activity enjoyment. Our analyses revealed higher tactile sensitivity (p<0.001) and pressure-pain thresholds (p<0.001) at the forefinger than other body locations. We also found lower pain sensitivity (p=0.010) and pressure pain–intensity ratings (p=0.001) and higher lumbar flexibility (p<0.001) after intervention. After calculation of absolute pre–post differences, higher tactile sensitivity was observed at the gluteus medius muscle than the erector spinal muscle only after aerobic intervention (p=0.046).ConclusionThese results add some evidence about different modalities of exercise-induced hypoalgesia in NSCLBP. However, the fact that we also found improvements in the control group limits our conclusions.