Mouth rinsing and ingesting salty or bitter solutions does not influence corticomotor excitability or neuromuscular function.

PURPOSE: To explore the effect of tasting unpleasant salty or bitter solutions on lower limb corticomotor excitability and neuromuscular function. METHODS: Nine females and eleven males participated (age: 27 ± 7 years, BMI: 25.3 ± 4.0 kg m-2). Unpleasant salty (1 M) and bitter (2 mM quinine) solutions were compared to water, sweetened water, and no solution, which functioned as control conditions. In a non-blinded randomized cross-over order, each solution was mouth rinsed (10 s) and ingested before perceptual responses, instantaneous heart rate (a marker of autonomic nervous system activation), quadricep corticomotor excitability (motor-evoked potential amplitude) and neuromuscular function during a maximal voluntary contraction (maximum voluntary force, resting twitch force, voluntary activation, 0-50 ms impulse, 0-100 impulse, 100-200 ms impulse) were measured. RESULTS: Hedonic value (water: 47 ± 8%, sweet: 23 ± 17%, salt: 71 ± 8%, bitter: 80 ± 10%), taste intensity, unpleasantness and increases in heart rate (no solution: 14 ± 5 bpm, water: 18 ± 5 bpm, sweet: 20 ± 5 bpm, salt: 24 ± 7 bpm, bitter: 23 ± 6 bpm) were significantly higher in the salty and bitter conditions compared to control conditions. Nausea was low in all conditions (< 15%) but was significantly higher in salty and bitter conditions compared to water (water: 3 ± 5%, sweet: 6 ± 13%, salt: 7 ± 9%, bitter: 14 ± 16%). There was no significant difference between conditions in neuromuscular function or corticomotor excitability variables. CONCLUSION: At rest, unpleasant tastes appear to have no influence on quadricep corticomotor excitability or neuromuscular function. These data question the mechanisms via which unpleasant tastes are proposed to influence exercise performance.

Mouth Rinsing and Ingestion of Unpleasant Salty or Bitter Solutions Does Not Improve Cycling Sprint Performance in Trained Cyclists.

The purpose of this study was to investigate the influence of mouth rinsing and ingesting unpleasant salty or bitter solutions on cycling sprint performance and knee extensor force characteristics. Eleven male and one female trained cyclists (age: 34 ± 9 years, maximal oxygen uptake 56.9 ± 3.9 ml·kg-1·min-1) completed a ramp test and familiarization followed by four experimental trials. In each trial, participants completed an all-out 30-s cycling sprint with knee extensor maximal voluntary contractions before and immediately after the sprint. In a randomized, counterbalanced, cross-over order, the four main trials were: a no solution control condition, water, salty (5.8%), or bitter (2 mM quinine) solutions that were mouth rinsed (10 s) and ingested immediately before the cycling sprint. There were no significant differences between conditions in mean power (mean ± SD, no solution: 822 ± 115 W, water: 818 ± 108 W, salt: 832 ± 111 W, bitter: 818 ± 105 W); peak power (no solution: 1,184 ± 205 W, water: 1,177 ± 207 W, salt: 1,195 ± 210 W, bitter: 1,184 ± 209 W); or fatigue index (no solution: 51.5% ± 5.7%, water: 50.8% ± 7.0%, salt: 51.1% ± 5.9%, bitter: 51.2% ± 7.1%) during the sprint. Maximal force and impulse declined postexercise; however, there were no significant differences between conditions in knee extensor force characteristics. The present data do not support the use of unpleasant salty or bitter solutions as an ergogenic aid to improve sprint exercise performance.

Exploring Patient Perceptions of Noninvasive Brain Stimulation: A Systematic Review.

OBJECTIVE: To synthesize and critically appraise literature exploring patient perceptions regarding the therapeutic use of noninvasive brain stimulation. MATERIAL AND METHODS: A systematic search of CINHAL, PUBMED, Web of Science, and Medline was performed. Reference lists of relevant articles were also screened. Studies exploring participant perceptions regarding the therapeutic use of noninvasive brain stimulation were eligible for inclusion. Perceptions were divided into three domains: knowledge, experience, and attitudes. Noninvasive brain stimulation was defined as any neuromodulation technique that alters brain activity but does not require invasive methods such as surgery. No restrictions were placed upon study design or participant population. Two reviewers performed data extraction and risk of bias assessment. Data relating to methodological characteristics, participant demographics, type of noninvasive brain stimulation, and nature of perceptions (knowledge, experience, or attitudes) were extracted. RESULTS: Four studies comprising data from 163 participants met the inclusion criteria. All studies investigated perceptions of repetitive transcranial magnetic stimulation (rTMS) in psychiatric populations. Most participants perceived rTMS to be safe and beneficial, demonstrated low levels of fear, and were willing to recommend the intervention to others. No studies were found investigating patient perception of transcranial direct current stimulation (tDCS). CONCLUSION: The findings from this review suggest that rTMS is well accepted as a therapeutic treatment among psychiatric populations, providing support for its clinical utility. Future work is needed to determine if similar findings exist for other conditions (eg, chronic pain) and for other therapeutic forms of brain stimulation (eg, tDCS).

The Relationship Between Corticomotor Reorganization and Acute Pain Severity: A Randomized, Controlled Study Using Rapid Transcranial Magnetic Stimulation Mapping.

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.

Fear of movement is associated with corticomotor depression in response to acute experimental muscle pain.

Acute musculoskeletal pain is associated with reductions in corticomotor output that persists even after pain resolves. Factors that contribute to corticomotor depression following acute pain are unknown. This study examined whether psychological factors, including pain catastrophising, kinesiophobia, and implicit theories of pain, were associated with corticomotor depression following acute experimental muscle pain. Forty-two healthy individuals participated. Participants completed three questionnaires: Pain Catastrophising Scale, Tampa Scale of Kinesiophobia, and Implicit Theories of Pain Scale. Acute pain was induced into the right extensor carpi radialis brevis (ECRB) muscle by injection of hypertonic saline. Corticomotor depression was assessed as a reduction in motor-evoked potentials measured from ECRB muscle in response to transcranial magnetic stimulation before, immediately after, and at 10, 20, and 30 min following pain resolution. Corticomotor depression was present at each time point relative to baseline (p < 0.001). Higher levels of kinesiophobia were associated with less corticomotor depression 10-min post pain resolution (r = 0.32, p = 0.03), but not at any other time point (p > 0.11). When corticomotor depression was compared between individuals with 'high' and 'low' kinesiophobia, a similar relationship was observed: Individuals with high compared to low kinesiophobia displayed less corticomotor depression immediately after (p = 0.02) and 10 min post pain (p = 0.02), but not at 20 or 30 min (p = 0.05 for both). No relationship was observed with any other psychological variable (p > 0.15). These data provide preliminary support for a relationship between pain-related fear of movement and corticomotor depression in response to acute pain. These findings may have implications for clinical musculoskeletal pain disorders.

Cerebral peak alpha frequency reflects average pain severity in a human model of sustained, musculoskeletal pain.

Heightened pain sensitivity, the amount of pain experienced in response to a noxious event, is a known risk factor for development of chronic pain. We have previously reported that pain-free, sensorimotor peak alpha frequency (PAF) is a reliable biomarker of pain sensitivity for thermal, prolonged pains lasting tens of minutes. To test whether PAF can provide information about pain sensitivity occurring over clinically relevant timescales (i.e., weeks), EEG was recorded before and while participants experienced a long-lasting pain model, repeated intramuscular injection of nerve growth factor (NGF), that produces progressively developing muscle pain for up to 21 days. We demonstrate that pain-free, sensorimotor PAF is negatively correlated with NGF pain sensitivity; increasingly slower PAF is associated with increasingly greater pain sensitivity. Furthermore, PAF remained stable following NGF injection, indicating that the presence of NGF pain for multiple weeks is not sufficient to induce the PAF slowing reported in chronic pain. In total, our results demonstrate that slower pain-free, sensorimotor PAF is associated with heightened sensitivity to a long-lasting musculoskeletal pain and also suggest that the apparent slowing of PAF in chronic pain may reflect predisease pain sensitivity.NEW & NOTEWORTHY Pain sensitivity, the intensity of pain experienced after injury, has been identified as an important risk factor in the development of chronic pain. Biomarkers of pain sensitivity have the potential to ease chronic pain burdens by preventing disease emergence. In the current study, we demonstrate that the speed of pain-free, sensorimotor peak alpha frequency recorded during resting-state EEG predicts pain sensitivity to a clinically-relevant, human model of prolonged pain that persists for weeks.

Hand therapy versus corticosteroid injections in the treatment of de Quervain's disease: A systematic review and meta-analysis.

STUDY DESIGN: Systematic review with meta-analysis. INTRODUCTION: Although corticosteroid injections are often cited as best practice in the treatment of de Quervain's disease, no reviews have compared their effectiveness to a multimodal definition of hand therapy. PURPOSE: To compare the effectiveness of corticosteroid injections with that of i) hand therapy alone and ii) combined hand therapy/corticosteroid injection approaches in the treatment of de Quervain's disease. METHODS: Searches of key databases were performed to identify experimental studies published between January 1950 and November 2014. Outcome measures included treatment success, pain, quality of life, and function. RESULTS: Both corticosteroid injections and hand therapy improved pain and function from baseline, but between-group differences were not significant (across 6 studies). However, significantly more participants were treated successfully when combined orthosis/corticosteroid injection approaches were compared to i) orthoses (RR 0.53, 95% CI 0.35-0.80) and ii) injections alone (RR 0.76, 95% CI 0.64-0.89). CONCLUSION: Combined orthosis/corticosteroid injection approaches are more effective than either intervention alone in the treatment of de Quervain's disease. LEVEL OF EVIDENCE: 1a.

Neuroinflammatory activation in sensory and motor regions of the cortex is related to sensorimotor function in individuals with low back pain maintained by nociplastic mechanisms: A preliminary proof-of-concept study.

BACKGROUND: Chronic pain involves communication between neural and immune systems. Recent data suggest localization of glial (brain immune cells) activation to the sensorimotor regions of the brain cortex (S1/M1) in chronic low back pain (LBP). As glia perform diverse functions that impact neural function, activation might contribute to sensorimotor changes, particularly in LBP maintained by increased nervous system sensitivity (i.e., nociplastic pain). This preliminary proof-of-concept study aimed to: (i) compare evidence of neuroinflammatory activation in S1/M1 between individuals with and without LBP (and between nociceptive and nociplastic LBP phenotypes), and (ii) evaluate relationships between neuroinflammatory activation and sensorimotor function. METHODS: Simultaneous PET-fMRI measured neuroinflammatory activation in functionally defined S1/M1 in pain-free individuals (n = 8) and individuals with chronic LBP (n = 9; nociceptive: n = 4, nociplastic: n = 5). Regions of S1/M1 related to the back were identified using fMRI during motor tasks and thermal stimuli. Sensorimotor measures included single and paired-pulse transcranial magnetic stimulation (TMS) and quantitative sensory testing (QST). Sleep, depression, disability and pain questionnaires were administered. RESULTS: Neuroinflammatory activation was greater in the lower back cortical representation of S1/M1 of the nociplastic LBP group than both nociceptive LBP and pain-free groups. Neuroinflammatory activation in S1/M1 was positively correlated with sensitivity to hot (r = 0.52) and cold (r = 0.55) pain stimuli, poor sleep, depression, disability and BMI, and negatively correlated with intracortical facilitation (r = -0.41). CONCLUSION: This preliminary proof-of-concept study suggests that neuroinflammation in back regions of S1/M1 in individuals with nociplastic LBP could plausibly explain some characteristic features of this LBP phenotype. SIGNIFICANCE STATEMENT: Neuroinflammatory activation localized to sensorimotor areas of the brain in individuals with nociplastic pain might contribute to changes in sensory and motor function and aspects of central sensitization. If cause-effect relationships are established in longitudinal studies, this may direct development of therapies that target neuroinflammatory activation.

Bilateral Corticomotor Reorganization and Symptom Development in Response to Acute Unilateral Hamstring Pain: A Randomized, Controlled Study.

Accumulating evidence demonstrates that pain induces adaptations in the corticomotor representations of affected muscles. However, previous work has primarily investigated the upper limb, with few studies examining corticomotor reorganization in response to lower limb pain. This is important to consider, given the significant functional, anatomical, and neurophysiological differences between upper and lower limb musculature. Previous work has also focused on unilateral corticomotor changes in response to muscle pain, despite an abundance of literature demonstrating that unilateral pain conditions are commonly associated with bilateral motor dysfunction. For the first time, this study investigated the effect of unilateral acute hamstring pain on bilateral corticomotor organization using transcranial magnetic stimulation (TMS) mapping. Corticomotor outcomes (TMS maps), pain, mechanical sensitivity (pressure pain thresholds), and function (maximal voluntary contractions) were recorded from 28 healthy participants at baseline. An injection of pain-inducing hypertonic (n = 14) or pain-free isotonic (n = 14) saline was then administered to the right hamstring muscle, and pain ratings were collected every 30 seconds until pain resolution. Follow-up measures were taken immediately following pain resolution and at 25, 50, and 75 minutes post-pain resolution. Unilateral acute hamstring pain induced bilateral symptom development and changes in corticomotor reorganization. Two patterns of reorganization were observed-corticomotor facilitation and corticomotor depression. Corticomotor facilitation was associated with increased mechanical sensitivity and decreased function bilaterally (all P < .05). These effects persisted for at least 75 minutes after pain resolution. PERSPECTIVE: These findings suggest that individual patterns of corticomotor reorganization may contribute to ongoing functional deficits of either limb following acute unilateral lower limb pain. Further research is required to assess these adaptations and the possible long-term implications for rehabilitation and reinjury risk in cohorts with acute hamstring injury.

The relationship between sustained hamstring pain and reorganisation of somatosensory representations: a randomised, controlled study.

ABSTRACT: Recurrent hamstring injuries are highly prevalent amongst sporting populations. It has been hypothesised that pain from an initial hamstring injury may induce reorganisation of somatosensory representations that could contribute to reinjury. However, because of the cross-sectional nature of existing research, it remains unknown whether somatosensory changes are a cause or effect of pain or if they are driven by other potentially confounding factors. Here, we explored the effect of experimentally induced sustained hamstring pain on tasks that interrogate somatosensory and spatial representations. Fifty healthy participants were randomly allocated to an experimental group that performed an eccentric exercise protocol on the right hamstring to induce delayed onset muscle soreness or a control group performing a repetition-matched concentric exercise protocol. The tactile cortical representation was assessed using two-point discrimination and tactile localisation, whereas the proprioceptive representation was assessed using a left-right judgement task. Peripersonal spatial representations were assessed using an auditory localisation task. Assessments were performed at baseline and day 2. No between-group differences in tactile acuity were observed. However, improvements in left-right judgments and worsening of auditory localisation occurred in the experimental group compared with the control group. This study provides preliminary evidence showing that somatosensory changes occur in response to sustained hamstring pain. Experimentally induced, sustained hamstring pain elicited enhancements in proprioceptive processing and deficits in peripersonal spatial processing, suggesting a shift in the allocation of attentional resources from the external (peripersonal) to internal (body) environment. These findings may hold important implications for reinjury risk and rehabilitation following hamstring pain.

Effectiveness of non-pharmacological treatments for vestibular and oculomotor dysfunction in patients with persistent post-concussive symptoms: protocol for a systematic review and meta-analysis.

INTRODUCTION: Concussion is a form of mild traumatic brain injury that disrupts brain function. Although symptoms are mostly transient, recovery can be delayed and result in persistent postconcussive symptoms (PPCS). Vestibular and oculomotor dysfunction are among the most debilitating impairments associated with PPCS. However, pharmacological interventions for these impairments are associated with deleterious side effects. Accordingly, increasing research has examined the utility of non-pharmacological interventions for PPCS. The aim of this review is to synthesise and evaluate the effectiveness of non-pharmacological interventions for the treatment of vestibular and oculomotor dysfunction for patients with PPCS. METHODS AND ANALYSIS: Systematic searches of MEDLINE, PubMed, Web of Science and Scopus will identify randomised controlled trials employing non-pharmacological treatments for vestibular and/or oculomotor dysfunction for PPCS. Such interventions may include, but are not limited to, vestibular rehabilitation, optokinetic stimulation and vestibulo-ocular reflex exercises. Assessments of oculomotor function will include versional eye movements, vergence eye movements, visual-fixation movements and accommodation response. Assessments of vestibular function will include the Fukuda Step test, functional balance tests, force displacement tests, and subjective reports of balance disruption or vertigo. Where appropriate, meta-analyses of standardised mean differences will be conducted using a random effects model for continuous outcomes. For dichotomous outcomes (improved vs not improved following treatment), effects will be expressed as relative risk. The impact of heterogeneity will be calculated using the I2 statistic. The Physiotherapy Evidence Database scale will be used to determine the methodological quality of individual studies and Grading of Recommendations, Assessment, Development and Evaluations used to assess the certainty and quality of evidence for each outcome. ETHICS AND DISSEMINATION: Ethical approval is not required for this review. Findings will be disseminated through peer-reviewed publications and conference presentations. PROSPERO REGISTRATION NUMBER: CRD42021254720.

The Influence of Stress on Student Performance during Simulation-based Learning: A Pilot Randomized Trial.

Background: Simulation-based learning is an important educational medium that is being implemented increasingly for the purpose of improved patient care and safety. However, there is evidence to suggest that simulation-based education (SBE) may increase anxiety, as illustrated through self-reporting and physiological responses. Despite such data, no studies have investigated whether anxiety and stress can be manipulated through SBE scenario design and delivery to facilitate optimal learning conditions. Objective: This pilot study examined perceived anxiety and physiological stress experienced by entry-level physiotherapy students while learning a skill using SBE and the relationship between this anxiety and their subsequent skill performance. Methods: Final-year physiotherapy students were randomly allocated to one of three SBE experiences: low, medium, or high stress. The experiences were designed to induce increasing levels of stress and anxiety. Performance of the learned skill (endotracheal airway suctioning) was measured after the SBE using a bespoke assessment form. Cortisol levels, heart rate, and perceived anxiety measurements (State-Trait Anxiety Inventory and visual analog scale) were also collected. Results: Twenty-seven participants completed the trial. There were significant differences in perceived stress and physiological response between the groups. The low-stress group demonstrated significantly better performance of airway suctioning than the higher-stress groups (P = 0.02). Higher anxiety was correlated with poorer skill performance (r = -0.410). Conclusions: Students report SBE to be stressful, and scenarios themselves can influence the stress and anxiety experienced. Greater stress is associated with poor learning outcomes during SBE. Healthcare educators involved in SBE scenario design need to consider the stress levels experienced. Future research to determine optimal stress and embed measurement of stress in SBE experiences is warranted.

Investigating interindividual variability in corticomotor reorganization during sustained hamstring pain: A randomized experimental study.

BACKGROUND: Increasing evidence suggests that pain drives maladaptive corticomotor changes that may increase susceptibility to injury and promote symptom recurrence. However, few studies have evaluated the influence of interindividual corticomotor responses to musculoskeletal pain. Existing research in this area has also been limited largely to the upper limb. This is a pertinent point, given the functional and neurophysiological differences between upper and lower limb muscles, as well as the fact that most acute sporting injuries occur in the lower limb. Accordingly, this study explored the variability of corticomotor responses to experimentally-induced sustained hamstring pain and whether specific patterns of corticomotor reorganization were associated with poorer outcomes (mechanical sensitivity, pain, or functional limitation). METHOD: Thirty-six healthy individuals participated. Following random allocation on Day 0, the experimental group performed an eccentric exercise protocol of the right hamstring muscles to induce delayed onset muscle soreness. The control group performed repetition-matched concentric exercise that did not induce soreness. Measures of mechanical sensitivity, pain, function, and corticomotor organization were collected at baseline and on Day 2. RESULTS AND CONCLUSIONS: Corticomotor responses to sustained hamstring pain were variable. Individuals who developed corticomotor facilitation in response to hamstring pain experienced greater mechanical sensitivity than those who developed corticomotor depression. These novel data could have implications for rehabilitation following lower limb pain or injury.

The Effect of Theta Burst Stimulation Over the Primary Motor Cortex on Experimental Hamstring Pain: A Randomized, Controlled Study.

Theta burst stimulation (TBS) over the primary motor cortex (M1) is an emerging technique that may have utility in the treatment of musculoskeletal pain. However, previous work exploring the analgesic effects of noninvasive brain stimulation has been limited largely to the arm or hand, despite 80% of acute musculoskeletal injuries occurring in the lower limb. This is a pertinent point, given the functional and neurophysiological differences between upper and lower limb musculature, as well as evidence suggesting that reorganization of corticomotor pathways is region-specific. This study investigated the effect of excitatory TBS on pain, function, and corticomotor organization during experimentally induced lower limb pain. Twenty-eight healthy participants attended 2 experimental sessions. On Day 0, participants completed 10 sets of 10 maximal eccentric contractions of the right hamstring muscles to induce delayed onset muscle soreness. Four consecutive blocks of either active or sham TBS were delivered on Day 2. Measures of mechanical sensitivity, pain (muscle soreness, pain intensity, pain area) function (single-leg hop distance, maximum voluntary isometric contraction, lower extremity functional scale), and corticomotor organization were recorded before and after TBS on Day 2. Pain and function were also assessed daily from Days 2 to 10. Active TBS reduced mechanical sensitivity compared to sham stimulation (P = .01). Corticomotor organization did not differ between groups, suggesting that improvements in mechanical sensitivity were not mediated by changes in M1. Subjective reports of pain intensity and function did not change following active TBS, contrasting previous reports in studies of the upper limb. PERSPECTIVE: M1 TBS reduces mechanical sensitivity associated with experimentally induced hamstring pain. Though further work is needed, these findings may hold important implications for those seeking to expedite recovery or reduce muscle sensitivity following hamstring injury.

Exploring patient perceptions of repetitive transcranial magnetic stimulation as a treatment for chronic musculoskeletal pain: a qualitative study.

OBJECTIVE: Repetitive transcranial magnetic stimulation (rTMS), a form of non-invasive brain stimulation, is a novel avenue for the management of chronic musculoskeletal pain. Despite evidence for the effectiveness of rTMS in chronic pain conditions, the clinical uptake of rTMS remains limited and little is known regarding patient perceptions of this therapeutic technique. DESIGN: Qualitative study using a phenomenological approach, reported in accordance with the Consolidated criteria for Reporting Qualitative research checklist. SETTING: Sydney, Australia. PARTICIPANTS: Fifteen participants were recruited from the community and completed the study. All participants had a diagnosis of chronic musculoskeletal pain, a history of seeking treatment and no prior experience with rTMS. METHODS AND ANALYSIS: All participants completed a semistructured interview to explore overall knowledge, preconceived concerns and attitudes regarding rTMS as a treatment for chronic musculoskeletal pain. The interviews were transcribed verbatim and analysed thematically. RESULTS: The key themes that influenced an individual's hypothetical acceptance of rTMS for chronic pain management were (1) the individual's initial impression of the equipment appearance, (2) the participant's individual history and familiarity with technology, (3) the accessibility and availability of rTMS and (4) knowledge regarding pain physiology and rTMS. CONCLUSIONS: This was the first qualitative study to explore the perception of rTMS as a treatment among people with chronic musculoskeletal pain. RTMS appears to be accepted as a treatment option among individuals with chronic musculoskeletal pain. Developing targeted strategies to address accessibility, funding support and medical endorsements may encourage use of rTMS in a clinical chronic pain setting.

Transcranial Direct Current Stimulation Accelerates The Onset of Exercise-Induced Hypoalgesia: A Randomized Controlled Study.

Exercise-induced hypoalgesia (EIH) describes acute reductions in pain that occur following exercise. Current evidence suggests that the magnitude of EIH is small-to-moderate at best, warranting exploration of novel avenues to bolster these effects. Transcranial direct current stimulation (tDCS) has been shown to relieve pain and represents a promising intervention that may enhance EIH. This study aimed to determine whether anodal tDCS of the primary motor cortex (M1) can augment EIH in healthy individuals experiencing experimentally-induced musculoskeletal pain. Twenty-four healthy subjects attended 2 experimental sessions ("Day 0" and "Day 2"). On Day 0, subjects were injected with nerve growth factor into their right extensor carpi radialis brevis to induce persistent elbow pain. On Day 2, each subject received active or sham tDCS over M1 followed by an isometric grip exercise. Pain intensity, muscle soreness, sensitivity (pressure pain thresholds), and conditioned pain modulation were assessed prior to the nerve growth factor injection, on Day 2 before tDCS, immediately post-exercise, and 15 minutes post-exercise. Active tDCS expedited the onset of EIH, inducing immediate reductions in pain intensity that were not present until 15 minutes post-exercise in the sham group. However, active tDCS did not reduce muscle soreness or sensitivity when compared to sham tDCS. PERSPECTIVE: These findings suggest that active tDCS accelerates the onset of EIH in healthy individuals experiencing experimentally-induced pain. This may represent a promising means of enhancing adherence to exercise protocols. However, larger randomised controlled trials in persistent pain populations are required to confirm the clinical impact of these findings.

Corticomotor reorganization during short-term visuomotor training in the lower back: A randomized controlled study.

INTRODUCTION: Accumulating evidence suggests that motor skill training is associated with structural and functional reorganization of the primary motor cortex. However, previous studies have focussed primarily upon the upper limb, and it is unclear whether comparable reorganization occurs following training of other regions, such as the lower back. Although this holds important implications for rehabilitation, no studies have examined corticomotor adaptations following short-term motor training in the lower back. METHOD: The aims of this study were to (a) determine whether a short-term lumbopelvic tilt visuomotor task induced reorganization of the corticomotor representations of lower back muscles, (b) quantify the variability of corticomotor responses to motor training, and (c) determine whether any improvements in task performance were correlated with corticomotor reorganization. Participants were allocated randomly to perform a lumbopelvic tilt motor training task (n = 15) or a finger abduction control task involving no lumbopelvic movement (n = 15). Transcranial magnetic stimulation was used to map corticomotor representations of the lumbar erector spinae before, during, and after repeated performance of the allocated task. RESULTS: No relationship between corticomotor reorganization and improved task performance was identified. Substantial variability was observed in terms of corticomotor responses to motor training, with approximately 50% of participants showing no corticomotor reorganization despite significant improvements in task performance. CONCLUSION: These findings suggest that short-term improvements in lower back visuomotor task performance may be driven by changes in remote subcortical and/or spinal networks rather than adaptations in corticomotor pathways. However, further research using tasks of varying complexities and durations is required to confirm this hypothesis.

Repetitive transcranial magnetic stimulation of the primary motor cortex expedites recovery in the transition from acute to sustained experimental pain: a randomised, controlled study.

Repetitive transcranial magnetic stimulation (rTMS) of the primary motor cortex (M1) is increasingly being investigated as a means of alleviating chronic pain. However, rTMS interventions are typically initiated once pain has already become chronic and maladaptive patterns of neural activity are likely to have been established. A critical question is whether M1 rTMS applied soon after pain onset can prevent the development of maladaptive neural activity and promote recovery. This study investigated the effect of 5 consecutive days of excitatory M1 rTMS on pain, functional limitation, mechanical hyperalgesia, descending inhibitory pain control, and M1 organisation in the transition from acute to sustained pain. Thirty healthy participants attended 8 sessions over a 16-day period. On days 0, 2, and 4, nerve growth factor was injected into the right forearm to induce progressively developing muscle soreness and mechanical hyperalgesia. Active or sham excitatory rTMS was delivered on days 4 to 8. Clinical and neurophysiological outcomes were recorded on days 0, 2, 4, 6, 8, 11, and 14. Active rTMS promoted recovery of muscle soreness, pain, and mechanical hyperalgesia when compared with sham rTMS (all between-group P < 0.05). Corticomotor excitability and descending inhibitory pain control did not differ between groups. These findings suggest that active excitatory M1 rTMS promotes recovery of muscle soreness, pain, and mechanical hyperalgesia in the transition from acute to sustained experimental pain. The analgesic effects of M1 rTMS do not seem to be modulated by descending inhibitory pain control or local changes in corticomotor excitability.

Effect of sustained experimental muscle pain on joint position sense.

INTRODUCTION: Joint position sense (JPS) is impaired in clinical musculoskeletal pain conditions, but when this impairment develops in the transition from initial to prolonged pain is not known. OBJECTIVES: This study assessed whether progressively developing sustained experimentally induced muscle pain impacts JPS in healthy individuals. METHODS: Twenty-eight healthy individuals received injection of nerve growth factor (NGF) into the right extensor carpi radialis brevis muscle on days 0 and 2 to induce sustained pain and hyperalgesia. Wrist JPS was assessed 2 days before day 0 (day -2), before the injection on days 0 and 2, and on days 4 and 14. Joint position sense was quantified as the ability to return the wrist to a neutral position following movements in the direction of radial and ulnar deviation. A 3-dimensional motion analysis system was used to calculate absolute, relative, and joint-angle repositioning errors. Numerical rating scale scores of pain intensity, body chart pain drawings, and pressure pain thresholds (PPTs) were recorded on each day. RESULTS: Compared with baseline, pressure pain thresholds decreased while pain intensity and area increased at day 2 (P < 0.001) and day 4 (P < 0.001) before returning to baseline on day 14 (P > 0.13). Relative to day 0, there was no change in wrist JPS at day 2, 4, and 14 following movements in either target direction (P > 0.05). CONCLUSION: Despite the presence of sustained muscle pain and hyperalgesia for 4 days at the elbow, no statistical change in wrist joint position error was observed. These findings suggest that pain and hyperalgesia lasting as long as 4 days does not impair JPS.

Motor adaptation varies between individuals in the transition to sustained pain.

Musculoskeletal pain is associated with altered motor control that, despite short-term benefit, is hypothesised to have long-term consequences, contributing to the development of chronic pain. However, data on how motor control is altered when pain is sustained beyond a transient event are scarce. Here, we investigated motor adaptation, and its relationship with corticomotor excitability, in the transition to sustained muscle pain. Twenty-eight healthy individuals were injected with nerve growth factor into the right extensor carpi radialis brevis muscle on days 0 and 2. Motor adaptation and corticomotor excitability were assessed on day -2, before injection on days 0 and 2, and again on days 4 and 14. Motor adaptation was quantified during a radial-ulnar movement as kinematic variability of wrist flexion-extension and pronation-supination, and as electromyographic (EMG) variability of extensor carpi radialis brevis activity. Pain, muscle soreness, and functional limitation were assessed from days 0 to 14. Pain, muscle soreness, and functional limitation were evident at days 2 and 4 (P < 0.001). Electromyographic variability reduced at days 4 and 14 (P < 0.04), with no change in kinematic variability (P = 0.9). However, data revealed variation in EMG and kinematic variability between individuals: some displayed increased motor variability, whereas others a decrease. Individuals who displayed an increase in EMG variability after 4 days of pain also displayed an increase in corticomotor excitability (r = 0.43, P = 0.034). These findings suggest individual adaptation of the motor system in the transition to sustained pain that could have implications for clinical musculoskeletal pain disorders.