Hypoalgesia after exercises with painful vs. non-painful muscles in healthy subjects – a randomized cross-over study

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Simon Hansen ◽  
Kristian Kjær Petersen ◽  
Emilie Sloth ◽  
Line Appelon Manum ◽  
Anita Kjær McDonald ◽  
...  

Abstract Objectives Exercise-induced hypoalgesia (EIH) is a decrease in the pain sensitivity after exercise. Individuals with chronic pain show less EIH after one exercise session compared with pain-free individuals possibly due to pain in exercising muscles. The primary aim of this randomized controlled cross-over study was to compare the EIH response at the exercising thigh muscle following exercises performed with painful vs. non-painful muscles. Secondary aims were to explore if a reduced EIH response was confined to the painful muscle, and whether the muscle pain intensity and the EIH responses were negatively associated. Methods In two sessions, 34 pain-free participants received a painful (hypertonic saline, 5.8%) injection and a control (isotonic saline, 0.9%) injection in the right thigh muscle before performing a 3 min isometric wall squat exercise. Pressure pain thresholds (PPTs) were assessed at both thighs and the left neck/shoulder at baseline, after injections and after exercise. Pain intensities in the thighs were rated on numerical rating scales (NRS: 0–10). Results Hypertonic saline induced moderate thigh pain at rest (NRS: 4.6 ± 2.1) compared to the control injection (NRS: 0.3 ± 0.4; p<0.001). EIH at the thighs and neck/shoulder were not different between sessions (Injected thigh: 0 kPa; 95% CI: −51 to 52; Contralateral thigh: −6 kPa; 95% CI: −42 to 30; neck/shoulder: 19 kPa; 95% CI: −6 to 44). No significant associations between pain intensity ratings immediately after the Painful injection and EIH responses at any assessment sites were found (right thigh: β=0.08, 95% CI: −12.95 to 20.64, p=0.64, left thigh: β=−0.33, 95% CI: −27.86 to 0.44, p=0.06; neck/shoulder: β=−0.18, 95% CI: −15.11 to 4.96, p=0.31). Conclusions Pain in the area of an exercising muscle did not reduce local or systemic EIH responses. Trial registration number NCT04354948.

2020 ◽  
Author(s):  
Sofia Louca Jounger ◽  
Johanna Svedenlöf ◽  
Reija Elenius ◽  
Christoffer Källkrans ◽  
Emil Scheid ◽  
...  

Abstract Background Intramuscular injection of hypertonic saline evokes pain with similar characteristics as clinical myalgia and is thus, considered a valid human experimental model. The aim of this study was to investigate if intramuscular injection of sterile water can be used as a human experimental pain model by comparing it with hypertonic and isotonic saline, and to analyze if the effects differ between men and women. Methods This randomized double blind and placebo-controlled study included 15 healthy women and 15 healthy age-matched men (mean (SD) age of 23.6 (2.4) years). The study comprised of three separate sessions, with at least one week of wash out between each session. Sterile water (i.e. the test-substance), hypertonic saline (active control), and isotonic saline (passive control) were injected intramuscularly into one of the masseter muscles in a randomized order. Pain intensity (VAS) was assessed every 15 th s after the injection and pain duration (s) as well as pain drawing area (au) were recorded. Pressure pain thresholds (kPa) were assessed every 5 min after injection during 30 min. Results All substances evoked pain ( P < 0001), but sterile water and hypertonic saline induced pain with higher intensity ( P < 0.001), longer duration ( P < 0.001), and larger pain drawing area ( P < 0.001) than isotonic saline. The pain intensity was higher for hypertonic saline than sterile water 45-165 s after injection ( P < 0.015), but there were no significant differences between them regarding maximum pain intensity, pain duration or pain drawing area. There was no significant difference in PPT values with time or between substances. The pain duration was longer in the men compared to the women for all substances ( P < 0.006), while the pain drawing area was larger in women after injection of hypertonic saline ( P < 0.003), but not after injection of the other substances. No other sex differences were found. Conclusion Injection of sterile water had similar effects as hypertonic saline on pain variables, but no effect on PPT. Hence, the model mimics clinical myalgia and may offer a novel and simpler alternative to hypertonic saline injections.


Pain Medicine ◽  
2020 ◽  
Author(s):  
Rocco Cavaleri ◽  
Lucy S Chipchase ◽  
Simon J Summers ◽  
Jane Chalmers ◽  
Siobhan M Schabrun

Abstract Objective Although acute pain has been shown to reduce corticomotor excitability, it remains unknown whether this response resolves over time or is related to symptom severity. Furthermore, acute pain research has relied upon data acquired from the cranial “hotspot,” which do not provide valuable information regarding reorganization, such as changes to the distribution of a painful muscle’s representation within M1. Using a novel, rapid transcranial magnetic stimulation (TMS) mapping method, this study aimed to 1) explore the temporal profile and variability of corticomotor reorganization in response to acute pain and 2) determine whether individual patterns of corticomotor reorganization are associated with differences in pain, sensitivity, and somatosensory organization. Methods Corticomotor (TMS maps), pain processing (pain intensity, pressure pain thresholds), and somatosensory (two-point discrimination, two-point estimation) outcomes were taken at baseline, immediately after injection (hypertonic [n = 20] or isotonic saline [n = 20]), and at pain resolution. Follow-up measures were recorded every 15 minutes until 90 minutes after injection. Results Corticomotor reorganization persisted at least 90 minutes after pain resolution. Corticomotor depression was associated with lower pain intensity than was corticomotor facilitation (r = 0.47 [P = 0.04]). These effects were not related to somatosensory reorganization or peripheral sensitization mechanisms. Conclusions Individual patterns of corticomotor reorganization during acute pain appear to be related to symptom severity, with early corticomotor depression possibly reflecting a protective response. These findings hold important implications for the management and potential prevention of pain chronicity. However, further research is required to determine whether these adaptations relate to long-term outcomes in clinical populations.


2004 ◽  
Vol 91 (3) ◽  
pp. 1250-1259 ◽  
Author(s):  
Dario Farina ◽  
Lars Arendt-Nielsen ◽  
Roberto Merletti ◽  
Thomas Graven-Nielsen

The aim of this human study was to investigate the relationship between experimentally induced muscle pain intensity (i.e., amount of nociceptive activity) and motor unit (MU) firing decrease and MU conduction velocity (CV). In 12 healthy subjects, nociceptive afferents were stimulated in the right tibialis anterior muscle by three intramuscular injections of hypertonic saline (0.2, 0.5, and 0.9 ml) separated by 140 s. The subjects performed six isometric contractions (20 s long) at 10% of the maximal voluntary contraction during the experimental muscle pain. The same set of six contractions was performed without any infusion before the painful condition on the right leg. The procedure was repeated for the left leg with infusion of isotonic (nonpainful) saline. Intramuscular and surface electromyographic (EMG) signals were collected to assess MU firing rate and CV. The firing rate of the active MUs [range: 7.4-14.8 pulses/s (pps)] did not change significantly in the three control conditions (without infusion for the right and left leg and with infusion of isotonic saline in the left leg). There was, on the contrary, a significant decrease (on average, mean ± SE, 1.03 ± 0.21 pps) of the firing rates during the painful condition. Moreover, MU firing rates were inversely significantly correlated with the subjective scores of pain intensity. Single MU CV was 3.88 ± 0.03 m/s (mean ± SE, over all the MUs) with no statistical difference among any condition, i.e., the injection of hypertonic saline did not alter the muscle fiber membrane properties of the observed MUs. Progressively increased muscle pain intensity causes a gradual decrease of MU firing rates. This decrease is not associated with a change in MU membrane properties, indirectly assessed by CV. This study demonstrates a central inhibitory motor control mechanism with an efficacy correlated to the nociceptive activity.


2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Sofia Louca Jounger ◽  
Niklas Eriksson ◽  
Helena Lindskog ◽  
Anna Oscarsson ◽  
Vivian Simonsson ◽  
...  

Abstract This study investigated if repeated buffered acidic saline infusions into the masseter muscles induced muscle pain and mechanical sensitization. Fourteen healthy men participated in this double-blind, randomized, and placebo-controlled study. Two repeated infusions (day 1 and 3) were given in the masseter muscles with either a buffered acidic saline solution (pH 5.2) or an isotonic saline solution (pH 6) as control. After 10 days of wash-out, the experiment was repeated with the other substance. Pressure pain thresholds (PPT), pain intensity, maximum unassisted mouth opening (MUO), and pain drawings were assessed before, directly following, and after each infusion at 5, 15, and 30 min and on day 4 and 7. Fatigue and pain intensity were assessed after a one-minute chewing test 30 min after infusions and day 4 and 7. Acidic saline induced higher pain intensity than control day 3 up to 5 min after infusions, but did not affect PPT. The chewing test did not evoke higher fatigue during chewing or MUO or after acidic saline infusion compared to control. Repeated acidic saline infusions in the masseter muscles induced a short-lasting muscle pain without mechanical hyperalgesia or functional pain. Hence, this model might not be superior to already existing experimental muscle pain models.


Cephalalgia ◽  
1992 ◽  
Vol 12 (2) ◽  
pp. 101-106 ◽  
Author(s):  
Kai Jensen ◽  
Michael Norup

The study was aimed at developing a reference model for experimental pain and tenderness in the human temporal muscle by the local injection of hypertonic saline, potassium chloride and acidic phosphate buffer, using isotonic saline as control. The design was randomized and double-blind. Twenty healthy subjects had 0.2 ml test solution injected into one temporal muscle and saline into the other. Following each injection, pain was rated on a 10-point ordinal scale and pressure-pain thresholds were measured every minute for 10 min by a pressure algometer. Hypertonic saline ( n = 11) and potassium chloride ( n = 12) induced significantly more pain than isotonic saline ( ANOVA, p < 0.0001). Compared to control injections, hypertonic saline and potassium chloride induced a significant reduction in pressure-pain threshold (ANOVA, p < 0.0001 and p < 0.05). Forty-eight percent of the injections led to the referral of pain most often to the jaws. A positive correlation between the relative occurrence of referred pain and pain intensity was observed ( p < 0.001) as was a negative correlation between the decrease in pressure-pain threshold and pain intensity ( p < 0.05).


2011 ◽  
Vol 115 (1) ◽  
pp. 136-143 ◽  
Author(s):  
François Kerbaul ◽  
Benoît Rondelet ◽  
Vincent Bénas ◽  
Dominique Grisoli ◽  
Arnaud De Waroquier ◽  
...  

Background Normovolemic hemodilution is known to inhibit hypoxic pulmonary vasoconstriction. How the coupling between the pulmonary arterial (PA) circulation and the right ventricle (RV) is affected by normovolemic hemodilution and by the composition of replacement solutions remains unknown. Therefore, the effects of isotonic and hypertonic saline hydroxyethylstarch solutions on the pulmonary circulation and RV, in control and hypoxic conditions, were compared. Methods Anesthetized piglets (n = 14) were equipped with manometer-tipped catheters in the RV and main PA and an ultrasonic flow probe around the main PA. The pulmonary circulation was assessed by pressure-flow relations and vascular impedance, RV afterload by effective arterial elastance (Ea), RV contractility by end-systolic elastance (Ees), and RV-PA coupling by the Ees/Ea ratio. Measurements were done in control (Fio2 0.40) and hypoxic (Fio2 0.12) conditions before and after acute normovolemic hemodilution with either 20 ml/kg isotonic saline hydroxyethylstarch (hydroxyethylstarch 130/0.4 6% in NaCl 0.9%, Voluven, Fresenius-Kabi, Sevres, France) or 5 ml/kg hypertonic saline hydroxyethylstarch (hydroxyethylstarch 200/0.5 6% in NaCl 7.2%, HyperHES, Fresenius-Kabi) solutions. Results Hypoxic pulmonary vasoconstriction was associated with proportional increases in Ea and Ees and did not affect RV-PA coupling. Hemodilution attenuated the hypoxic response. Hemodilution with isotonic saline hydroxyethylstarch did not affect the RV-PA coupling, whereas hemodilution with hypertonic saline hydroxyethylstarch increased Ees and the Ees/Ea ratio. Conclusion In experimental normovolemic hemodilution, both in control and in hypoxic conditions, RV-PA coupling is unaffected by isotonic saline hydroxyethylstarch but improved by hypertonic saline hydroxyethylstarch, mainly because of an increase in RV contractility.


2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Morten Pallisgaard Støve ◽  
Rogerio Pessoto Hirata ◽  
Thorvaldur Skuli Palsson

Abstract Objectives The effect of stretching on joint range of motion is well documented, and although sensory perception has significance for changes in the tolerance to stretch following stretching the underlining mechanisms responsible for these changes is insufficiently understood. The aim of this study was to examine the influence of endogenous pain inhibitory mechanisms on stretch tolerance and to investigate the relationship between range of motion and changes in pain sensitivity. Methods Nineteen healthy males participated in this randomized, repeated-measures crossover study, conducted on 2 separate days. Knee extension range of motion, passive resistive torque, and pressure pain thresholds were recorded before, after, and 10 min after each of four experimental conditions; (i) Exercise-induced hypoalgesia, (ii) two bouts of static stretching, (iii) resting, and (iv) a remote, painful stimulus induced by the cold pressor test. Results Exercise-induced hypoalgesia and cold pressor test caused an increase in range of motion (p<0.034) and pressure pain thresholds (p<0.027). Moderate correlations in pressure pain thresholds were found between exercise-induced hypoalgesia and static stretch (Rho>0.507, p=0.01) and exercise-induced hypoalgesia and the cold pressor test (Rho=0.562, p=0.01). A weak correlation in pressure pain thresholds and changes in range of motion were found following the cold pressor test (Rho=0.460, p=0.047). However, a potential carryover hypoalgesic effect may have affected the results of the static stretch. Conclusions These results suggest that stretch tolerance may be linked with endogenous modulation of pain. Present results suggest, that stretch tolerance may merely be a marker for pain sensitivity which may have clinical significance given that stretching is often prescribed in the rehabilitation of different musculoskeletal pain conditions where reduced endogenous pain inhibition is frequently seen.


2021 ◽  
Vol 10 (14) ◽  
pp. 3056
Author(s):  
Ada Holak ◽  
Michał Czapla ◽  
Marzena Zielińska

Background: The all-too-frequent failure to rate pain intensity, resulting in the lack of or inadequacy of pain management, has long ceased to be an exclusive problem of the young patient, becoming a major public health concern. This study aimed to evaluate the methods used for reducing post-traumatic pain in children and the frequency of use of such methods. Additionally, the methods of pain assessment and the frequency of their application in this age group were analysed. Methods: A retrospective analysis of 2452 medical records of emergency medical teams dispatched to injured children aged 0–18 years in the area around Warsaw (Poland). Results: Of all injured children, 1% (20 out of 2432) had their pain intensity rated, and the only tool used for this assessment was the numeric rating scale (NRS). Children with burns most frequently received a single analgesic drug or cooling (56.2%), whereas the least frequently used method was multimodal treatment combining pharmacotherapy and cooling (13.5%). Toddlers constituted the largest percentage of patients who were provided with cooling (12%). Immobilisation was most commonly used in adolescents (29%) and school-age children (n = 186; 24%). Conclusions: Low frequency of pain assessment emphasises the need to provide better training in the use of various pain rating scales and protocols. What is more, non-pharmacological methods (cooling and immobilisation) used for reducing pain in injured children still remain underutilized.


1972 ◽  
Vol 36 (5) ◽  
pp. 569-583 ◽  
Author(s):  
J. Stovall King ◽  
Don L. Jewett ◽  
Howard R. Sundberg

✓ A possible mechanism by which intrathecal infusion of partially frozen saline might relieve patients of chronic pain has been studied by applying hypertonic saline to the dorsal rootlets of cats in vitro. The supernatant of partially thawed normal saline was found to be hypertonic. Persistent block of C fibers, detected by a collision method, occurred after the rootlets had been exposed to saline from 500 to 2500 mOsm/L for 15 min followed by 15 min of isotonic saline. Few of the A fibers were blocked by this procedure, but both A and C fibers were blocked when solutions of 3500 mOsm/L were used. Differential blockage of C fibers could also be produced with hypotonic saline and with distilled water. Localized cooling, to 2°C for 25 min, had no persistent effect on C fiber conduction, and when cooling was combined with hypertonic saline there was no potentiation of the differential blockade caused by the saline. Hypertonic solutions of sucrose or sodium nitrate produced no persistent differential block; most A and C fibers recovered. However, choline chloride was as effective as sodium chloride in giving a differential blockade. It seems that chloride ion plays a major role in establishing the persistent C fiber blockade observed when dorsal rootlets are exposed to hypertonic saline.


2021 ◽  
Vol 20 (1) ◽  
Author(s):  
Takayuki Seto ◽  
Hidenori Suzuki ◽  
Tomoya Okazaki ◽  
Yasuaki Imajo ◽  
Norihiro Nishida ◽  
...  

Abstract Background The spinal nerve ligation (SNL) rat is well known as the most common rodent model of neuropathic pain without motor deficit. Researchers have performed analyses using only the von Frey and thermal withdrawal tests to evaluate pain intensity in the rat experimental model. However, these test are completely different from the neurological examinations performed clinically. We think that several behavioral reactions must be observed following SNL because the patients with neuropathic pain usually have impaired coordination of the motions of the right–left limbs and right–left joint motion differences. In this study, we attempted to clarify the pain behavioral reactions in SNL rat model as in patients. We used the Kinema-Tracer system for 3D kinematics gait analysis to identify new characteristic parameters of each joint movement and gait pattern. Results The effect of SNL on mechanical allodynia was a 47 ± 6.1% decrease in the withdrawal threshold during 1–8 weeks post-operation. Sagittal trajectories of the hip, knee and ankle markers in SNL rats showed a large sagittal fluctuation of each joint while walking. Top minus bottom height of the left hip and knee that represents instability during walking was significantly larger in the SNL than sham rats. Both-foot contact time, which is one of the gait characteristics, was significantly longer in the SNL versus sham rats: 1.9 ± 0.15 s vs. 1.03 ± 0.15 s at 4 weeks post-operation (p = 0.003). We also examined the circular phase time to evaluate coordination of the right and left hind-limbs. The ratio of the right/left circular time was 1.0 ± 0.08 in the sham rats and 0.62 ± 0.15 in the SNL rats at 4 weeks post-operation. Conclusions We revealed new quantitative parameters in an SNL rat model that are directly relevant to the neurological symptoms in patients with neuropathic pain, in whom the von Frey and thermal withdrawal tests are not used at all clinically. This new 3D analysis system can contribute to the analysis of pain intensity of SNL rats in detail similar to human patients’ reactions following neuropathic pain.


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