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

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.