Pain induced by a single simulated office-work session: time course and association with muscle blood flux and muscle activity

Prolonged slumped sitting causes neck pain and increased axioscapular muscle activity during a computer task in healthy participants - A randomized crossover study

INTRODUCTION

Sitting posture may contribute to spinal pain. Effects of postures on pain, sensitivity and muscle activity during computer tasks were investigated.

METHODS

Twenty-five healthy participants, seated at a workstation without backrest, completed four, 15-min typing tasks: A)Upright with forearm-support; B)Upright without forearm-support; C)Slumped with forearm-support; D)Slumped without forearm-support. Participants rated pain every minute on a numerical rating scale (NRS). RMS-EMG was recorded from upper/lower trapezius (UT, LT), serratus anterior and anterior/middle deltoid. At baseline and after tasks, pressure pain thresholds (PPTs) were recorded bilaterally over the head, UT, and leg.

RESULTS

All tasks caused clinically relevant increased NRS (≥2/10) compared to baseline (P < 0.001). NRS was higher in Task-D (P < 0.003) and lower in Task-B (P < 0.005) than others. PPTs did not change from baseline. Task-D caused higher UT and LT RMS-EMG (P < 0.02) than other tasks.

CONCLUSION

A 15-min task caused pain irrespective of posture with some causing larger changes than others.

Biomechanical Assessments of the Upper Limb for Determining Fatigue, Strain and Effort from the Laboratory to the Industrial Working Place: A Systematic Review

Recent human-centered developments in the industrial field (Industry 5.0) lead companies and stakeholders to ensure the wellbeing of their workers with assessments of upper limb performance in the workplace, with the aim of reducing work-related diseases and improving awareness of the physical status of workers, by assessing motor performance, fatigue, strain and effort. Such approaches are usually developed in laboratories and only at times they are translated to on-field applications; few studies summarized common practices for the assessments. Therefore, our aim is to review the current state-of-the-art approaches used for the assessment of fatigue, strain and effort in working scenarios and to analyze in detail the differences between studies that take place in the laboratory and in the workplace, in order to give insights on future trends and directions. A systematic review of the studies aimed at evaluating the motor performance, fatigue, strain and effort of the upper limb targeting working scenarios is presented. A total of 1375 articles were found in scientific databases and 288 were analyzed. About half of the scientific articles are focused on laboratory pilot studies investigating effort and fatigue in laboratories, while the other half are set in working places. Our results showed that assessing upper limb biomechanics is quite common in the field, but it is mostly performed with instrumental assessments in laboratory studies, while questionnaires and scales are preferred in working places. Future directions may be oriented towards multi-domain approaches able to exploit the potential of combined analyses, exploitation of instrumental approaches in workplace, targeting a wider range of people and implementing more structured trials to translate pilot studies to real practice.

Myofascial Treatment for Microcirculation in Patients with Postural Neck and Shoulder Pain

Vascular impairment is a crucial factor associated with chronic muscle pain, but relevant research from the microcirculatory aspect is lacking. Here, we investigated the differences in neck muscle microcirculation detected through laser-doppler flowmetry (LDF) and cervical biomechanics by a videofluoroscopic image in asymptomatic participants and patients with postural neck and shoulder pain. To understand the mechanism behind the effect of myofascial treatment, transverse friction massage (TFM) was applied and the immediate effects of muscular intervention on microcirculation were monitored. In total, 16 asymptomatic participants and 22 patients (mean age = 26.3 ± 2.4 and 25.4 ± 3.2 years, respectively) were recruited. Their neck muscle microcirculation and spinal image sequence were assessed. The differences in the baseline blood flow between the asymptomatic and patient groups were nonsignificant. However, the standard deviations in the measurements of the upper trapezius muscle in the patients were significantly larger (p < 0.05). Regarding the TFM-induced responses of skin microcirculation, the blood flow ratio was significantly higher in the patients than in the asymptomatic participants (p < 0.05). In conclusion, postintervention hyperemia determined through noninvasive LDF may be an indicator for the understanding of the mechanism underlying massage therapies and the design of interventions for postural pain.

Happy Enough to Relax? How Positive and Negative Emotions Activate Different Muscular Regions in the Back - an Explorative Study

Embodiment theories have proposed a reciprocal relationship between emotional state and bodily reactions. Besides large body postures, recent studies have found emotions to affect rather subtle bodily expressions, such as slumped or upright sitting posture. This study investigated back muscle activity as an indication of an effect of positive and negative emotions on the sitting position. The electromyography (EMG) activity of six back muscles was recorded in 31 healthy subjects during exposure to positive and negative affective pictures. A resting period was used as a control condition. Increased muscle activity patterns in the back were found during the exposure to negative emotional stimuli, which was mainly measured in the lumbar and thorax regions. The positive emotion condition caused no elevated activity. The findings show that negative emotions lead to increased differential muscle activity in the back and thus corroborate those of previous research that emotion affects subtle bodily expressions.

Effects of cycling while typing on upper limb and performance characteristics

Active computer workstations may help reduce workplace sedentarism. However, their impact on the upper limb musculoskeletal system is unknown. Subjects participated in two 60-min computer laptop-based Bike-and-Type sessions at different cycling intensities (LOW, HIGH). Upper trapezius and wrist extensor muscle blood flow, sensitivity and pain thresholds, and typing performance were measured intermittently. Neck/shoulder discomfort increased over time (p < 0.001), and was higher in the HIGH intensity (p = 0.036). Blood flow to the trapezius (p = 0.041) and wrist (p = 0.021) muscles were higher during HIGH, and wrist blood flow increased over time (p = 0.01). Trapezius sensitivity threshold significantly decreased over time (p = 0.003). There were no effects on pressure pain thresholds (interaction p = 0.091). Average typing speed was greater during HIGH (p = 0.046) and increased over time (p < 0.001). Time spent biking while typing effectively improved performance, which may facilitate muscle regeneration, although effects depend on biking intensity.

Discomfort glare and psychological stress during computer work: subjective responses and associations between neck pain and trapezius muscle blood flow

PURPOSE

Exposure to additional environmental stress during computer work, such as visual and psychological demands, is associated with increased eye and neck discomfort, altered moods, and reduced well-being. The aim of this study is to elucidate further how subjective responses in healthy, young females with normal binocular vision are affected by glare and psychological stress during computer work, and to investigate possible associations between trapezius muscle blood flow and neck pain development.

METHODS

43 females participated in a laboratory experiment with a within-subject design. Four 10-min computer work conditions with exposure to different stressors were performed at an ergonomically optimal workstation, under the following series of conditions: no additional stress, visual stress (induced as direct glare from a large glare source), psychological stress, and combined visual and psychological stress. Before and immediately after each computer work condition, questionnaires regarding different visual and eye symptoms, neck and shoulder symptoms, positive and negative state moods, perceived task difficulty, and perceived ambient lighting were completed. Associations between neck pain and trapezius muscle blood flow were also investigated.

RESULTS

Exposure to direct glare induced greater development of visual/eye symptoms and discomfort, while psychological stress exposure made participants feel more negative and stressed. The perception of work lighting during glare exposure was closely related to perceived stress, and associations between visual discomfort and eyestrain, and neck pain were observed in all conditions. Furthermore, participants with high trapezius muscle blood flow overall reported more neck pain, independent of exposure.

CONCLUSIONS

Exposure to visual and psychological stresses during computer work affects the development of symptoms and negative moods in healthy, young females with normal binocular vision, but in different ways. The results also demonstrate the complex interactions involved in symptom development and lighting appraisal during computer work. When optimizing computer workstations, the complexity of the field must be taken into account, and several factors, including visual conditions, must be considered carefully.

Effects of standing on typing task performance and upper limb discomfort, vascular and muscular indicators

Standing is a popular alternative to traditionally seated computer work. However, no studies have described how standing impacts both upper body muscular and vascular outcomes during a computer typing task. Twenty healthy adults completed two 90-min simulated work sessions, seated or standing. Upper limb discomfort, electromyography (EMG) from eight upper body muscles, typing performance and neck/shoulder and forearm blood flow were collected. Results showed significantly less upper body discomfort and higher typing speed during standing. Lower Trapezius EMG amplitude was higher during standing, but this postural difference decreased with time (interaction effect), and its variability was 68% higher during standing compared to sitting. There were no effects on blood flow. Results suggest that standing computer work may engage shoulder girdle stabilizers while reducing discomfort and improving performance. Studies are needed to identify how standing affects more complex computer tasks over longer work bouts in symptomatic workers.

Muscle pain induced by static contraction in rats is modulated by peripheral inflammatory mechanisms

Muscle pain is an important health issue and frequently related to static force exertion. The aim of this study is to evaluate whether peripheral inflammatory mechanisms are involved with static contraction-induced muscle pain in rats. To this end, we developed a model of muscle pain induced by static contraction performed by applying electrical pulses through electrodes inserted into muscle. We also evaluated the involvement of neutrophil migration, bradykinin, sympathetic amines and prostanoids. A single session of sustained static contraction of gastrocnemius muscle induced acute mechanical muscle hyperalgesia without affecting locomotor activity and with no evidence of structural damage in muscle tissue. Static contraction increased levels of creatine kinase but not lactate dehydrogenase, and induced neutrophil migration. Dexamethasone (glucocorticoid anti-inflammatory agent), DALBK (bradykinin B1 antagonist), Atenolol (β1 adrenoceptor antagonist), ICI 118,551 (β2 adrenoceptor antagonist), indomethacin (cyclooxygenase inhibitor), and fucoidan (non-specific selectin inhibitor) all reduced static contraction-induced muscle hyperalgesia; however, the bradykinin B2 antagonist, bradyzide, did not have an effect on static contraction-induced muscle hyperalgesia. Furthermore, an increased hyperalgesic response was observed when the selective bradykinin B1 agonist des-Arg⁹-bradykinin was injected into the previously stimulated muscle. Together, these findings demonstrate that static contraction induced mechanical muscle hyperalgesia in gastrocnemius muscle of rats is modulated through peripheral inflammatory mechanisms that are dependent on neutrophil migration, bradykinin, sympathetic amines and prostanoids. Considering the clinical relevance of muscle pain, we propose the present model of static contraction-induced mechanical muscle hyperalgesia as a useful tool for the study of mechanisms underlying static contraction-induced muscle pain.

Dry needling of the trapezius muscle in office workers with neck pain: a randomized clinical trial

BACKGROUND

Neck pain is a frequent complaint in office workers. This pain can be caused by myofascial trigger points (MTrPs) in the trapezius muscle. This study aimed to determine the effectiveness of deep dry needling (DDN) of active MTrPs in the trapezius muscle.

METHODS

A randomized, single blinded clinical trial was carried out at the Physical Therapy Department at Physiotherapy in Women's Health Research Group at Physical Therapy Department of University of Alcalá, in Alcalá de Henares, Madrid, Spain. Forty-four office workers with neck pain and active MTrPs in the trapezius muscle were randomly allocated to either the DDN or the control group (CG). The participants in the DDN group were treated with DDN of all MTrPs found in the trapezius muscle. They also received passive stretch of the trapezius muscle. The CG received the same passive stretch of the trapezius muscle only. The primary outcome measure was subjective pain intensity, measured using a visual analogue scale (VAS). Secondary outcomes were pressure pain threshold (PPT), cervical range of motion (CROM) and muscle strength. Data were collected at baseline, after interventions and 15 days after the last treatment.

RESULTS

Differences were found between the DDN group and the CG for the VAS (P < 0.001), PPT (P < 0.001), range of motion (AROM) (P < 0.05) and strength (P < 0.05) after intervention and at the 15-day follow-up.

DISCUSSION

Deep dry needling and passive stretch seems to be more effective than passive stretch only. The effects are maintained in the short term. The results support the use of DDN in the management of trapezius muscle myofascial pain syndrome in neck pain.

Prevalence of Myofascial Pain Syndrome in Chronic Non-Specific Neck Pain: A Population-Based Cross-Sectional Descriptive Study

BACKGROUND

Chronic non-specific neck pain is a frequent complaint. It is a recognized medical and socioeconomic problem and a frequent cause of job absenteeism. In recent years, case reports about myofascial pain syndrome (MPS) are emerging among patients suffering from pain. MPS is a regional pain syndrome characterized by myofascial trigger points (MTrP) in palpable taut bands of skeletal muscle that refer pain to a distance, and that can cause distant motor and autonomic effects.

OBJECTIVE

To assess the prevalence of active and latent MTrPs in subjects suffering from chronic non-specific neck pain.

DESIGN

A population-based cross-sectional descriptive study was carried out from January 2012 to December 2014.

SETTING

Three primary healthcare centers in Alcalá de Henares, Madrid (Spain).

SUBJECTS

Two hundred and twenty-four participants diagnosed by their family doctor with chronic non-specific neck pain.

METHODS

Participants were examined by a physical therapist to determine the presence of MPS. Pain descriptions from the subjects and pain body diagrams guided the physical examination. The subjects were not given any information concerning MPS or other muscle pain syndromes.

RESULTS

All participants presented with MPS. MTrPs of the trapezius muscles were the most prevalent, in 93.75% of the participants. The most prevalent active MTrPs were located right (82.1%) and left (79%) in the nearly-horizontal fibers of the upper trapezius muscle. Furthermore, active MTrPs in the levator scapulae, multifidi, and splenius cervicis muscles reached a prevalence of 82.14%, 77.68%, and 62.5%, respectively.

CONCLUSIONS

MPS is a common source of pain in subjects presenting chronic non-specific neck pain.

Changes of Local Blood Flow in Response to Acupuncture Stimulation: A Systematic Review

Objectives. This systematic review aimed to summarize and evaluate the findings of studies investigating the local microcirculatory effects following acupuncture stimulation. Methods. MEDLINE, EMBASE, OASIS, and Cochrane library were searched to identify randomized controlled trials (RCTs) published before January 30, 2015. Studies demonstrating any type of microcirculation response to manual acupuncture in healthy subjects and patients were included. The risk of bias and the reliability of the experimental conditions were evaluated to determine quality assessment. Results. Eight RCTs met the inclusion criteria; there was at least one acupuncture-induced change in a microcirculatory parameter. Of the seven studies in healthy subjects, four reported significant increases in blood flow following acupuncture compared with control, whereas one other study observed reductions in microcirculation immediately after acupuncture needling. The studies that assessed patients with either fibromyalgia or trapezius myalgia found significant increases in blood flow in the skin and muscle. Additionally, the degree and duration of increases in microcirculation varied depending on the condition of the subjects and the manipulation technique. Conclusions. The current evidence regarding the local effects of acupuncture in terms of blood flow remains insufficient for reliable conclusions due to few well-designed studies. Additional well-designed studies are needed to clarify these issues.

Effects of the Workplace Health Promotion Activities Soccer and Zumba on Muscle Pain, Work Ability and Perceived Physical Exertion among Female Hospital Employees

OBJECTIVES

This 40-week workplace physical training RCT investigated the effect of soccer and Zumba, respectively, on muscle pain intensity and duration, work ability, and rating of perceived exertion (RPE) during work among female hospital employees.

METHODS

107 hospital employees were cluster-randomized into two training groups, and a control group. The training was conducted outside working hours as two-three 1-h sessions per week for the first 12 weeks, and continued as one-two 1-h sessions per week for the last 28 weeks. Muscle pain intensity and duration, work ability, and RPE during work were measured at baseline and after 12 and 40 weeks.

RESULTS

After 12 weeks, both the soccer (-1.9, 95% CI, -3.0, -0.8, P = 0.001) and the Zumba group (-1.3, 95% CI, -2.3, -0.3, P = 0.01) reduced the pain intensity (on a scale from 0 to 10) in the neck-shoulder region (eta squared = 0.109), whereas only the soccer group (-1.9, 95% CI, -3.2, -0.7, P = 0.002, eta squared = 0.092) showed a reduction after 40 weeks referencing the control group. After 40 weeks, both the soccer (-16.4 days, 95% CI, -29.6, -3.2, P<0.02) and the Zumba group (-16.6 days, 95% CI, -28.9, -4.2, P<0.01) reduced the pain duration during the past 3 months in the neck-shoulder region (eta squared = 0.077). No significant effects on intensity or duration of pain in the lower back, RPE during work or work ability were found.

CONCLUSIONS

The present study indicates that workplace initiated soccer and Zumba training improve neck-shoulder pain intensity as well as duration among female hospital employees.

TRIAL REGISTRATION

International Standard Randomized Controlled Trial Number Register ISRCTN 61986892.

Reliability of muscle blood flow measurements in orbicularis oculi

PURPOSE

Orbicularis oculi muscle tension and muscle blood flow have been shown to be objective measures of eyestrain during visually demanding activities, such as computer work. In line with this, positive associations between eye-related pain and muscle blood flow in orbicularis oculi have been observed. A hypothesis regarding work situations with cognitive tasks and low-level muscle activity, such as computer work, proposes that muscle pain originates from the blood vessel-nociceptor interactions of the connective tissue of the muscle. Noninvasive muscle blood flow measurements in the orbicularis oculi muscle are preferable to using an invasive technique. The aim of this study was to test reproducibility and stability of muscle blood recordings in orbicularis oculi using photoplethysmography.

METHODS

In the reproducibility tests, 12 subjects were tested twice within 1 to 5 weeks. To study the stability of the method, six of the subjects were randomly selected and tested four more times within 2 to 6 weeks. Test subjects were doing identical visually demanding computer work for 10 minutes in each test.

RESULTS

The short-term repeatability of muscle blood flow measurements was considered good, but the stability of blood flow recordings over time in orbicularis oculi was low because of a greater within-subject maximum variability compared with between-subject average variability.

CONCLUSIONS

Investigators should be aware of the effect of time, possibly attributed to confounding factors such as environmental changes and mental stress, when comparing photoplethysmography muscle blood flow recordings.

A novel assessment of flexibility by microcirculatory signals

Flexibility testing is one of the most important fitness assessments. It is generally evaluated by measuring the range of motion (RoM) of body segments around a joint center. This study presents a novel assessment of flexibility in the microcirculatory aspect. Eighteen college students were recruited for the flexibility assessment. The flexibility of the leg was defined according to the angle of active ankle dorsiflexion measured by goniometry. Six legs were excluded, and the remaining thirty legs were categorized into two groups, group H (n = 15 with higher flexibility) and group L (n = 15 with lower flexibility), according to their RoM. The microcirculatory signals of the gastrocnemius muscle on the belly were monitored by using Laser-Doppler Flowmetry (LDF) with a noninvasive skin probe. Three indices of nonpulsatile component (DC), pulsatile component (AC) and perfusion pulsatility (PP) were defined from the LDF signals after signal processing. The results revealed that both the DC and AC values of the group H that demonstrated higher stability underwent muscle stretching. In contrast, these indices of group L had interferences and became unstable during muscle stretching. The PP value of group H was a little higher than that of group L. These primary findings help us to understand the microcirculatory physiology of flexibility, and warrant further investigations for use of non-invasive LDF techniques in the assessment of flexibility.

A Mechanism-Based Approach to Prevention of and Therapy for Fibromyalgia

Fibromyalgia syndrome (FMS) is characterized by pain referred to deep tissues. Diagnosis and treatment of FMS are complicated by a variable coexistence with regional pain, fatigue, sleep disruption, difficulty with mentation, and depression. The widespread, deep pain of FMS can be a consequence of chronic psychological stress with autonomic dysregulation. Stress acts centrally to facilitate pain and acts peripherally, via sympathetic vasoconstriction, to establish painful muscular ischemia. FMS pain, with or without a coexistent regional pain condition, is stressful, setting up a vicious circle of reciprocal interaction. Also, stress interacts reciprocally with systems of control over depression, mentation, and sleep, establishing FMS as a multiple-system disorder. Thus, stress and the ischemic pain it generates are fundamental to the multiple disorders of FMS, and a therapeutic procedure that attenuates stress and peripheral vasoconstriction should be highly beneficial for FMS. Physical exercise has been shown to counteract peripheral vasoconstriction and to attenuate stress, depression, and fatigue and improve mentation and sleep quality. Thus, exercise can interrupt the reciprocal interactions between psychological stress and each of the multiple-system disorders of FMS. The large literature supporting these conclusions indicates that exercise should be considered strongly as a first-line approach to FMS therapy.

Coffee intake and development of pain during computer work

Background

The present study sought to determine if subjects who had consumed coffee before performing a simulated computer office-work task found to provoke pain in the neck and shoulders and forearms and wrists exhibited different time course in the pain development than the subjects who had abstained from coffee intake.

Findings

Forty eight subjects all working fulltime, 22 with chronic shoulder and neck pain and 26 healthy pain-free subjects, were recruited to perform a computer-based office-work task for 90 min. Nineteen (40%) of the subjects had consumed coffee (1/2 -1 cup) on average 1 h 18 min before start. Pain intensity in the shoulders and neck and forearms and wrists was rated on a visual analogue scale every 15 min throughout the work task.

During the work task the coffee consumers exhibited significantly lower pain increase than those who abstained from coffee.

Conclusions

Subjects who had consumed coffee before starting a pain provoking office work task exhibited attenuated pain development compared with the subjects who had abstained from coffee intake. These results might have potentially interesting implications of a pain-modulating effect of caffeine in an everyday setting. However, studies with a double blind placebo controlled randomized design are needed.

The impact of workplace risk factors on long-term musculoskeletal sickness absence: a registry-based 5-year follow-up from the Oslo health study

OBJECTIVE

To determine the influence of work-related risk factors by gender on long-term sickness absence with musculoskeletal diagnoses (LSM).

METHODS

Data from the Oslo Health Study were linked to the historical event database of Statistics Norway. Eight thousand three hundred thirty-three participants were followed from 2001 through 2005. Generalized linear models were used to compute risk differences for LSM.

RESULTS

In total, 12.6% of the women and 8.8% of the men experienced at least one LSM. Statistically, significant LSM risk increases between 0.039 and 0.086 in association with work environment were found for heavy physical work, low job control (men only), low support from superior (women only), and having shift/night work (men only).

CONCLUSIONS

Women exhibited a higher LSM risk, but the associations with job exposures were stronger for men. This should be addressed when occupational health services give advice on preventive measures.

Dissociation of motor task-induced cortical excitability and pain perception changes in healthy volunteers

BACKGROUND

There is evidence that interventions aiming at modulation of the motor cortex activity lead to pain reduction. In order to understand further the role of the motor cortex on pain modulation, we aimed to compare the behavioral (pressure pain threshold) and neurophysiological effects (transcranial magnetic stimulation (TMS) induced cortical excitability) across three different motor tasks.

METHODOLOGY/PRINCIPAL FINDINGS

Fifteen healthy male subjects were enrolled in this randomized, controlled, blinded, cross-over designed study. Three different tasks were tested including motor learning with and without visual feedback, and simple hand movements. Cortical excitability was assessed using single and paired-pulse TMS measures such as resting motor threshold (RMT), motor-evoked potential (MEP), intracortical facilitation (ICF), short intracortical inhibition (SICI), and cortical silent period (CSP). All tasks showed significant reduction in pain perception represented by an increase in pressure pain threshold compared to the control condition (untrained hand). ANOVA indicated a difference among the three tasks regarding motor cortex excitability change. There was a significant increase in motor cortex excitability (as indexed by MEP increase and CSP shortening) for the simple hand movements.

CONCLUSIONS/SIGNIFICANCE

Although different motor tasks involving motor learning with and without visual feedback and simple hand movements appear to change pain perception similarly, it is likely that the neural mechanisms might not be the same as evidenced by differential effects in motor cortex excitability induced by these tasks. In addition, TMS-indexed motor excitability measures are not likely good markers to index the effects of motor-based tasks on pain perception in healthy subjects as other neural networks besides primary motor cortex might be involved with pain modulation during motor training.

Deep tissue hyperalgesia after computer work

Background and purpose

A growing number of people are using computers. Shoulder and neck pain occur commonly during computer work. Peripheral and central sensitization may play a major role in establishing and maintaining several chronic pain conditions. We have previously reported that a 90 min simulated computer office-work induced substantial pain in the shoulders and neck. We hypothesized that the development of pain during the computer work may be related to sensitization. The aim of the present study was to examine if the 90 min computer work induced deep tissue muscle hyperalgesia manifested as altered pressure pain thresholds (PPTs).

Methods

Twenty-two subjects with chronic shoulder and neck pain (pain group) and 26 healthy and pain free subjects (reference group) performed a standardized computer office-work task with use of a computer-mouse and with time pressure and high precision demands continuously for 90 min. The pressure pain threshold was measured with a pressure algometer in shoulder and forearm muscles (bilaterally in upper trapezius and extensor carpi radialis), and at sternum, before and 15 min and 30 min after the computer work task.

Results

The PPTs before starting the computer work were not different between the groups at any of the five locations. In both groups, the PPTs in the active and inactive side of the upper trapezius as well as in the extensor carpi radialis of the forearm operating the computer mouse were significantly reduced after the 90 min computer work compared with the pre-work levels. In the pain group, also the PPT in the inactive resting forearm was significantly reduced. The changes seen in PPTs from pre-to post-work were not significantly different between the groups, except for the inactive resting forearm where the groups exhibited different time course.

Conclusion

A decrease in pressure pain thresholds of involved muscles suggests that computer office-work can induce deep tissue hyperalgesia within 90 min. The development of pain during the computer work indicates peripheral sensitization as the predominant mechanism. Decreased pressure pain thresholds also in sites distant from pain areas may indicate a contribution from central sensitization in the subjects with chronic shoulder and neck pain.

Implications

The lasting pain after work and the reduced PPTs both in involved and distant musculature may indicate need for frequent pauses during computer work, especially when performed with time pressure and high precision demands, in order to avoid pain to increase and sustain after work, and thus to prevent the possibility of pain to become chronic.

Changed activation, oxygenation, and pain response of chronically painful muscles to repetitive work after training interventions: a randomized controlled trial

The aim of this randomized controlled trial was to assess changes in myalgic trapezius activation, muscle oxygenation, and pain intensity during repetitive and stressful work tasks in response to 10 weeks of training. In total, 39 women with a clinical diagnosis of trapezius myalgia were randomly assigned to: (1) general fitness training performed as leg-bicycling (GFT); (2) specific strength training of the neck/shoulder muscles (SST) or (3) reference intervention without physical exercise. Electromyographic activity (EMG), tissue oxygenation (near infrared spectroscopy), and pain intensity were measured in trapezius during pegboard and stress tasks before and after the intervention period. During the pegboard task, GFT improved trapezius oxygenation from a relative decrease of −0.83 ± 1.48 μM to an increase of 0.05 ± 1.32 μM, and decreased pain development by 43%, but did not affect resting levels of pain. SST lowered the relative EMG amplitude by 36%, and decreased pain during resting and working conditions by 52 and 38%, respectively, without affecting trapezius oxygenation. In conclusion, GFT performed as leg-bicycling decreased pain development during repetitive work tasks, possibly due to improved oxygenation of the painful muscles. SST lowered the overall level of pain both during rest and work, possibly due to a lowered relative exposure as evidenced by a lowered relative EMG. The results demonstrate differential adaptive mechanisms of contrasting physical exercise interventions on chronic muscle pain at rest and during repetitive work tasks.

Muscle oxygenation and glycolysis in females with trapezius myalgia during stress and repetitive work using microdialysis and NIRS

The aim of this investigation was to study female workers active in the labour market for differences between those with trapezius myalgia (MYA) and without (CON) during repetitive pegboard (PEG) and stress (STR) tasks regarding (1) relative muscle load, (2) trapezius muscle blood flow, (3) metabolite accumulation, (4) oxygenation, and (5) pain development. Among 812 female employees (age 30-60 years) at 7 companies with high prevalence of neck/shoulder complaints, clinical examination identified 43 MYA and 19 CON. At rest, during PEG, and STR the trapezius muscle was measured using (1) EMG and MMG, (2) microdialysis, and (3) NIRS. Further, subjective pain ratings were scored (VAS). EMGrms in %MVE (Maximal Voluntary EMG-activity), was significantly higher among MYA than CON during PEG (11.74 +/- 9.09 vs. 7.42 +/- 5.56%MVE) and STR (5.47 +/- 5.00 vs. 3.28 +/- 1.94%MVE). MANOVA showed a group and time effect regarding data from the microdialysis: for MYA versus CON group differences demonstrated lower muscle blood flow and higher lactate and pyruvate concentrations. Potassium and glucose only showed time effects. NIRS showed similar initial decreases in oxygenation with PEG in both groups, but only in CON a significant increase back to baseline during PEG. VAS score at rest was highest among MYA and increased during PEG, but not for CON. The results showed significant differences between CON and MYA regarding muscle metabolism at rest and with PEG and STR. Higher relative muscle load during PEG and STR, insufficient muscle blood flow and oxygenation may account for the higher lactate, pyruvate and pain responses among MYA versus CON.

Physiological responses to low-force work and psychosocial stress in women with chronic trapezius myalgia

Background

Repetitive and stressful work tasks have been linked to the development of pain in the trapezius muscle, although the underlying mechanisms still remain unclear. In earlier studies, it has been hypothesized that chronic muscle pain conditions are associated with imbalance in the autonomic nervous system, predominantly expressed as an increased sympathetic activity. This study investigates whether women with chronic trapezius myalgia show higher muscle activity and increased sympathetic tone at baseline and during repetitive low-force work and psychosocial stress, compared with pain-free controls.

Methods

Eighteen women with chronic trapezius myalgia (MYA) and 30 healthy female controls (CON) were studied during baseline rest, 100 min of repetitive low-force work, 20 min of psychosocial stress (Trier Social Stress Test, TSST), and 80 min recovery. The subjects rated their pain intensity, stress and energy level every 20 min throughout the experiment. Muscle activity was measured by surface electromyography in the trapezius muscle (EMGtrap) and deltoid muscle (EMGdelt). Autonomic reactivity was measured through heart rate (HR), skin conductance (SCL), blood pressure (MAP) and respiration rate (Resp).

Results

At baseline, EMGtrap, stress ratings, and HR were higher in MYA than in CON. Energy ratings, EMGdelt, SCL, MAP and Resp were, however, similar in the two groups. Significant main group effects were found for pain intensity, stress ratings and EMGtrap. Deltoid muscle activity and autonomic responses were almost identical in MYA and CON during work, stress and recovery. In MYA only, pain intensity and stress ratings increased towards the end of the repetitive work.

Conclusion

We found increased muscle activity during uninstructed rest in the painful muscle of a group of women with trapezius myalgia. The present study could not confirm the hypothesis that chronic trapezius myalgia is associated with increased sympathetic activity. The suggestion of autonomic imbalance in patients with chronic local or regional musculoskeletal pain needs to be further investigated.