The effect of prolonged experimental neck pain on exercise-induced hypoalgesia

Predicting Individual Pain Sensitivity Using a Novel Cortical Biomarker Signature

Importance

Biomarkers would greatly assist decision-making in the diagnosis, prevention, and treatment of chronic pain.

Objective

To undertake analytical validation of a sensorimotor cortical biomarker signature for pain consisting of 2 measures: sensorimotor peak alpha frequency (PAF) and corticomotor excitability (CME).

Design, Setting, and Participants

This cohort study at a single center (Neuroscience Research Australia) recruited participants from November 2020 to October 2022 through notices placed online and at universities across Australia. Participants were healthy adults aged 18 to 44 years with no history of chronic pain or a neurological or psychiatric condition. Participants experienced a model of prolonged temporomandibular pain with outcomes collected over 30 days. Electroencephalography to assess PAF and transcranial magnetic stimulation (TMS) to assess CME were recorded on days 0, 2, and 5. Pain was assessed twice daily from days 1 through 30.

Exposure

Participants received an injection of nerve growth factor (NGF) to the right masseter muscle on days 0 and 2 to induce prolonged temporomandibular pain lasting up to 4 weeks.

Main Outcomes and Measures

The predictive accuracy of the PAF/CME biomarker signature was determined using a nested control-test scheme: machine learning models were run on a training set (n = 100), where PAF and CME were predictors and pain sensitivity was the outcome. The winning classifier was assessed on a test set (n = 50) comparing the predicted pain labels against the true labels.

Results

Among the final sample of 150 participants, 66 were female and 84 were male; the mean (SD) age was 25.1 (6.2) years. The winning classifier was logistic regression, with an outstanding area under the curve (AUC = 1.00). The locked model assessed on the test set had excellent performance (AUC = 0.88; 95% CI, 0.78-0.99). Results were reproduced across a range of methodological parameters. Moreover, inclusion of sex and pain catastrophizing as covariates did not improve model performance, suggesting the model including biomarkers only was more robust. PAF and CME biomarkers showed good to excellent test-retest reliability.

Conclusions and Relevance

This study provides evidence for a sensorimotor cortical biomarker signature for pain sensitivity. The combination of accuracy, reproducibility, and reliability suggests the PAF/CME biomarker signature has substantial potential for clinical translation, including predicting the transition from acute to chronic pain.

Ten Minutes of Core Stabilisation Exercise Result in Local Exercise-Induced Hypoalgesia in Patients With Chronic Unspecific Low Back Pain

BACKGROUND

Core stabilisation training is known to be effective in managing pain in patients suffering from chronic low back pain (CLBP). Yet, acute effects of core stabilisation exercise on exercise-induced hypoalgesia (EIH) are largely unknown. This study aimed to examine the EIH effects of an easy-to-perform core stabilisation exercise in CLBP patients and to explore associations between EIH and potential influencing factors (i.e., physical activity, catastrophizing, kinesiophobia, subjective pain state and exercise exertion).

METHODS

Thirty patients with unspecific CLBP finished this randomised controlled crossover trial. Patients performed a 10-min isometric core stabilisation exercise and a 10-min control session. Before and after, pain sensitivity was measured via pressure pain thresholds [Newton/cm2] locally (low back; PPTlocal) and remotely (forehead, thumb; PPTremote). Correlation analyses were performed between EIH and influencing factors.

RESULTS

A 'Time' × 'Intervention' interaction (p < 0.001) was observed for PPTlocal with post hoc analysis revealing higher values post exercise (p < 0.001; pre: 56.6 ± 20.6, post: 67.5 ± 26.1). No differences were observed for the control session (p = 0.894; pre: 58.5 ± 24.0, post: 58.4 ± 23.3). No such effect was observed for PPTremote (p = 0.014). Post hoc analyses showed no differences following the exercise session (p = 0.103; pre: 41.3 ± 12.5, post: 42.5 ± 13.6), while lower PPTremote post values were observed post control compared to pre values (p = 0.031; 42.5 ± 14.5, post: 41.3 ± 13.7). The only significant moderate correlation was observed between ΔPPTlocal of the exercise session and catastrophizing with rho = -0.381.

CONCLUSION

A 10-min isometric core stabilisation exercise results in local lumbar EIH, while no systemic effects are observed. A higher degree of catastrophizing is associated with lower hypoalgesic responses.

SIGNIFICANCE

This study shows for the first time that a brief and easy-to-perform 10-min core stabilisation exercise produces significant local pain relief (EIH) in patients with unspecific CLBP. The effect is localised to the lumbar region, with no observed impact on remote sites. Higher pain catastrophizing seems to be linked to reduced hypoalgesic response. These findings support the use of short core stabilisation exercises as an effective, immediate, non-pharmacological pain management strategy for these patients.

Quantifying Cervical Rotation Smoothness: Exploring Various Jerk Metrics and Test-Retest Reliability of Jerk, Range of Motion, and Head Repositioning Accuracy

The assessment of smoothness, range of motion (ROM), and head repositioning accuracy (HRA) has gained attention in identifying sensorimotor impairments. Uncertainty persists on the approach for acquiring reliable measures, including choice of smoothness metric, normalization factors, and the required number of measurements for reliable results. This study aimed to address this uncertainty. Thirty healthy participants were included in this single-session randomized cross-over study. The experiment consisted of two parts. One focused on the test-retest assessment of head ROM into right rotation to the end of range from a neutral position using a self-selected movement speed and the HRA when returning to the start-position. In the other part, participants repeated the previous tasks and performed head rotations at slower and faster speeds than their self-selected pace and to the beat of a metronome. All tasks were repeated ten times. For the test-retest, the inter-class-correlation (ICC) values for ROM were between 0.84-0.91, 0.20-0.31 for HRA, and 0.65-0.90 for jerk for 1-10 repetitions. Normalizing jerk through vmean and vpeak had similar variability and appeared equally valid for our data. However, normalizing by vmax ensures desirable properties in the smoothness metric. Lower variability was observed when standardizing movements using a metronome. Based on test-retest findings, three repetitions are recommended, as ICC values show marginal improvement beyond 2-3 repetitions, providing limited additional value.

Acute and long-term effect of specific and non-specific exercises in patients with chronic neck pain: A protocol for a randomized controlled trial

Exercise therapy is the most common approach for people with chronic neck pain (CNP). Although well-established, it remains unknown which type of exercise is the best for treating this condition. Moreover, pain processing can play a role in the persistence of pain and in the response to interventions. Thus, the aim of this randomized controlled trial is to compare the acute and long-term effects of two exercise protocols (specific and non-specific) on pain and pain processing in individuals with CNP. One hundred and ten participants aged between 18 and 65 years who have had non-specific neck pain for more than 3 months will be recruited. They will be randomized and allocated into two groups (specific exercises and non-specific exercises) and both groups will perform an exercise programme twice a week for 8 weeks. Both programmes are divided into two progressive and individualized phases. The primary outcomes are change in pain intensity after 8 weeks of exercise and exercise-induced hypoalgesia, and secondary outcomes are pressure pain threshold, temporal summation of pain, conditioned pain modulation, the Neck Disability Index, the Baecke Physical Activity Questionnaire, and the Global Perception of Change Scale. Outcomes will be assessed at baseline, after 8 weeks of intervention, and at 6-month follow-up.

A 5-day course of repetitive transcranial magnetic stimulation before pain onset ameliorates future pain and increases sensorimotor peak alpha frequency

ABSTRACT

Repetitive transcranial magnetic stimulation (rTMS) has shown promise as an intervention for pain. An unexplored research question is whether the delivery of rTMS prior to pain onset might protect against a future episode of prolonged pain. The present study aimed to determine whether (1) 5 consecutive days of rTMS delivered prior to experimentally induced prolonged jaw pain has a prophylactic effect on future pain intensity and (2) whether these effects were accompanied by increases in corticomotor excitability (CME) and/or sensorimotor peak alpha frequency (PAF). On each day from day 0 to 4, 40 healthy individuals received a single session of active (n = 21) or sham (n = 19) rTMS over the left primary motor cortex. Peak alpha frequency and CME were assessed on day 0 (before rTMS) and day 4 (after rTMS). Prolonged pain was induced via intramuscular injection of nerve growth factor in the right masseter muscle after the final rTMS session. From days 5 to 25, participants completed twice-daily electronic diaries including pain on chewing and yawning (primary outcomes), as well as pain during other activities (eg, talking), functional limitation in jaw function and muscle soreness (secondary outcomes). Compared to sham, individuals who received active rTMS subsequently experienced lower pain on chewing and yawning. Furthermore, active rTMS led to an increase in PAF. This is the first study to show that rTMS delivered prior to prolonged pain onset can protect against future pain. Our findings suggest that rTMS may hold promise as a prophylactic intervention for pain.

A novel cortical biomarker signature predicts individual pain sensitivity

Importance

Biomarkers would greatly assist decision making in the diagnosis, prevention and treatment of chronic pain.

Objective

The present study aimed to undertake analytical validation of a sensorimotor cortical biomarker signature for pain consisting of two measures: sensorimotor peak alpha frequency (PAF) and corticomotor excitability (CME).

Design

In this cohort study (recruitment period: November 2020-October 2022), participants experienced a model of prolonged temporomandibular pain with outcomes collected over 30 days. Electroencephalography (EEG) to assess PAF and transcranial magnetic stimulation (TMS) to assess CME were recorded on Days 0, 2 and 5. Pain was assessed twice daily from Days 1-30.

Setting

Data collection occurred at a single centre: Neuroscience Research Australia.

Participants

We enrolled 159 healthy participants (through notices placed online and at universities across Australia), aged 18-44 with no history of chronic pain, neurological or psychiatric condition. 150 participants completed the protocol.

Exposure

Participants received an injection of nerve growth factor (NGF) to the right masseter muscle on Days 0 and 2 to induce prolonged temporomandibular pain lasting up to 4 weeks.

Main Outcomes and Measures

We determined the predictive accuracy of the PAF/CME biomarker signature using a nested control-test scheme: machine learning models were run on a training set (n = 100), where PAF and CME were predictors and pain sensitivity was the outcome. The winning classifier was assessed on a test set (n = 50) comparing the predicted pain labels against the true labels.

Results

The final sample consisted of 66 females and 84 males with a mean age of 25.1 ± 6.2. The winning classifier was logistic regression, with an outstanding area under the curve (AUC=1.00). The locked model assessed on the test set had excellent performance (AUC=0.88[0.78-0.99]). Results were reproduced across a range of methodological parameters. Moreover, inclusion of sex and pain catastrophizing as covariates did not improve model performance, suggesting the model including biomarkers only was more robust. PAF and CME biomarkers showed good-excellent test-retest reliability.

Conclusions and Relevance

This study provides evidence for a sensorimotor cortical biomarker signature for pain sensitivity. The combination of accuracy, reproducibility, and reliability, suggests the PAF/CME biomarker signature has substantial potential for clinical translation, including predicting the transition from acute to chronic pain.

A 5-day course of rTMS before pain onset ameliorates future pain and increases sensorimotor peak alpha frequency

Repetitive transcranial magnetic stimulation (rTMS) has shown promise as an intervention for pain. An unexplored research question is whether the delivery of rTMS prior to pain onset might protect against a future episode of prolonged pain. The present study aimed to determine i) whether 5 consecutive days of rTMS delivered prior to experimentally-induced prolonged jaw pain could reduce future pain intensity and ii) whether any effects of rTMS on pain were mediated by changes in corticomotor excitability (CME) and/or sensorimotor peak alpha frequency (PAF). On each day from Day 0-4, forty healthy individuals received a single session of active (n = 21) or sham (n = 19) rTMS over the left primary motor cortex. PAF and CME were assessed on Day 0 (before rTMS) and Day 4 (after rTMS). Prolonged pain was induced via intramuscular injection of nerve growth factor (NGF) in the right masseter muscle after the final rTMS session. From Days 5-25, participants completed twice-daily electronic dairies including pain on chewing and yawning (primary outcomes), as well as pain during other activities (e.g. talking), functional limitation in jaw function and muscle soreness (secondary outcomes). Compared to sham, individuals who received active rTMS subsequently experienced lower pain on chewing and yawning. Although active rTMS increased PAF, the effects of rTMS on pain were not mediated by changes in PAF or CME. This study is the first to show that rTMS delivered prior to pain onset can protect against future pain and associated functional impairment. Thus, rTMS may hold promise as a prophylactic intervention for persistent pain.

Acute exercise of painful muscles does not reduce the hypoalgesic response in young healthy women - a randomized crossover study

OBJECTIVES

Exercise-induced hypoalgesia (EIH) is characterized by an increase in pain threshold following acute exercise. EIH is reduced in some individuals with chronic musculoskeletal pain, although the mechanisms are unknown. It has been hypothesized that this may relate to whether exercises are performed in painful or non-painful body regions. The primary aim of this randomized experimental crossover study was to investigate whether the presence of pain per se in the exercising muscles reduced the local EIH response. The secondary aim was to investigate if EIH responses were also reduced in non-exercising remote muscles.

METHODS

Pain-free women (n=34) participated in three separate sessions. In session 1, the maximal voluntary contraction (MVC) for a single legged isometric knee extension exercise was determined. In sessions 2 and 3, pressure pain thresholds (PPT) were assessed at the thigh and shoulder muscles before and after a 3-min exercise at 30 % of MVC. Exercises were performed with or without thigh muscle pain, which was induced by either a painful injection (hypertonic saline, 5.8 %) or a non-painful injection (isotonic saline, 0.9 %) into the thigh muscle. Muscle pain intensity was assessed with an 11-point numerical rating scale (NRS) at baseline, after injections, during and after exercises.

RESULTS

PPTs increased at thigh and shoulder muscles after exercise with painful (14.0-24.9 %) and non-painful (14.3-19.5 %) injections and no significant between-injection EIH differences were observed (p>0.30). Muscle pain intensity was significantly higher following the painful injection compared to the non-painful injection (p<0.001).

CONCLUSIONS

Exercising painful muscles did not reduce the local or remote hypoalgesic responses, suggesting that the pain-relieving effects of isometric exercises are not reduced by exercising painful body regions.

ETHICAL COMMITTEE NUMBER

S-20210184.

TRIAL REGISTRATION NUMBER

NCT05299268.

The impact of prolonged experimental neck pain on walking stability and gait kinematics - A parallel-group study

BACKGROUND

Neck pain is a common problem in the general population, and movement adaptations are a natural response to pain. Previous studies have reported reduced trunk rotation during walking in those suffering from clinical neck pain. However, it is unknown how soon after the onset of pain, movement adaptations are adopted. This study investigated the effect of prolonged experimental neck pain four days after pain onset on gait kinematics during walking.

METHODS

Forty healthy participants were randomized to receive injections of nerve-growth-factor or a control injection of isotonic saline into the right splenius capitis muscle at the end of days 0 and 2. Participants performed two walking tasks, walking and walking while reading on a smartphone, on days 0, 4, and 15. Gait kinematics, spatiotemporal parameters, and gait stability were measured using Xsens Awinda.

FINDINGS

The nerve-growth-factor group reported increased neck pain intensity (median VAS 17.5 [IQR: 2.75-25.75]) on day 4 compared to day 0 and day 15. No pain intensity changes between days were reported for the isotonic-group. For gait kinematics, a main effect of the task was identified, showing that during the smartphone condition, participants had shorter stride lengths and reduced RoM for the trunk, hip, knee, and ankle compared to normal waking (P < 0.006).

INTERPRETATION

Walking while reading on a smartphone, but not mild neck muscle pain, caused changes in the gait kinematics compared to normal walking without neck pain. This finding suggests that movement alterations during walking are not an early feature of prolonged experimental neck pain.

The effect of foot orthoses on gait biomechanics and pain among people with rheumatoid arthritis: A quasi-experimental study

BACKGROUND

Foot pain is frequent among people with rheumatoid arthritis (RA). Foot orthoses (FO) are commonly prescribed with the intention to reduce pain symptoms and improve function.

RESEARCH QUESTION

How do a custom-made FO affect pain, gait biomechanics and daily activity among people with RA?

METHODS

Twenty-five participants with RA and foot pain completed this quasi-experimental study using a control insole for four weeks and then a custom-made FO in the following four weeks. The foot orthoses were customized by plantar foot shape targeting optimal restoration of normal arch height. A visual analog scale was used to monitor changes in ankle/foot, knee, hip joints, and global arthritis pain. In addition, the perceived pain area was measured using a body chart analysis. Kinematics and kinetics of the hip, knee and ankle joints during gait were analyzed using 3D-motion capture. Daily steps were measured with a wrist-based activity tracker for both the control insole and custom-made FO period, respectively.

RESULTS

In comparison to the control insole, the custom-made FO reduced ankle/foot pain intensity (p < 0.001) in addition to a reduction of the perceived pain areas in the feet (p < 0.001), legs (p = 0.012), as well as the arms and hands (p = 0.014). Ankle plantar flexion and eversion moments were also reduced (p < 0.001). No difference in daily steps was observed between the two periods (p = 0.657).

SIGNIFICANCE

This study has demonstrated an ankle/foot pain-relieving effect in conjunction with alterations of the ankle joint moments in people with RA using custom-made FO. The pain relief is plausibly attributed to alterations of the ankle joint moments when using the custom-made FO. However, future studies are needed to explore further into therapeutic implication of custom-made FO in pain management of people with RA.