Changes in interstitial noradrenaline, trapezius muscle activity and oxygen saturation during low-load work and recovery

Peripheral muscle oxygenation, pain, and disability indices in individuals with and without nonspecific neck pain, before and after myofascial reorganization®: A double-blind randomized controlled trial

To investigate whether myofascial reorganization® in the trapezius muscle (MRT) improves peripheral muscle oxygenation and pain tolerance and decreases neck disability index (NDI) scores in individuals with and without nonspecific neck pain (NP) using a double-blind randomized controlled trial. Seventy-five subjects were equally and randomly assigned to three groups: the intervention groups (experimental [EG] and sham sSG]) and the control group (CG). Several inclusion criteria were applied to the intervention groups: male or female, aged 18-32 years, self-reported NP in the last 3 months without a defined cause; at least "soft" pain in session 1 of the NDI, and at least a score of 1 on the Visual Analogue Scale (VAS). The CG was required to have NDI and VAS scores of 0 at recruitment. Intervention: The EG underwent MRT for 10 min, once a week for 6 weeks. Patients with NP in the SG underwent classical massage for the same duration and frequency. Patients in the CG had no pain and underwent no intervention. Data collection was performed using the NDI Questionnaire, a pressure algometer for pain evaluation, and near-infrared spectroscopy for muscle oxygenation measurements. It was registered as NCT03882515 at ClinicalTrials.gov. The NDI score in both the EG (p<0.001) and SG (p<0.001) decreased after 6 weeks of intervention compared to the CG. The CG demonstrated a lower basal tissue saturation (TSI) index than the EG (p<0.001) and SG (p = 0.02). The EG demonstrated higher oxyhemoglobin values than the SG (p<0.001) and CG (p = 0.03). The CG had higher pain tolerance than the EG (p = 0.01) and SG (p<0.001) post-intervention. MRT increased trapezius muscle oxygenation after 6 weeks of intervention.

A randomized clinical trial comparing non-thrust manipulation with segmental and distal dry needling on pain, disability, and rate of recovery for patients with non-specific low back pain

Objective: The purpose of this study was to examine the within and between-group effects of segmental and distal dry needling (DN) without needle manipulation to a semi-standardized non-thrust manipulation (NTM) targeting the symptomatic spinal level for patients with non-specific low back pain (NSLBP). Methods: Sixty-five patients with NSLBP were randomized to receive either DN (n = 30) or NTM (n = 35) for six sessions over 3 weeks. Outcomes collected included the oswestry disability index (ODI), patient specific functional scale (PSFS), numeric pain rating scale (NPRS), and pain pressure thresholds (PPT). At discharge, patients perceived recovery was assessed. Results: A two-way mixed model ANOVA demonstrated that there was no group*time interaction for PSFS (p = 0.26), ODI (p = 0.57), NPRS (p = 0.69), and PPT (p = 0.51). There was significant within group effects for PSFS (3.1 [2.4, 3.8], p = 0.018), ODI (14.5% [10.0%, 19.0%], p = 0.015), NPRS (2.2 [1.5, 2.8], p = 0.009), but not for PPT (3.3 [0.5, 6.0], p = 0.20). Discussion: The between-group effects were neither clinically nor statistically significant. The within group effects were both significant and exceeded the reported minimum clinically important differences for the outcomes tools except the PPT. DN and NTM produced comparable outcomes in this sample of patients with NSLBP. Level of evidence: 1b.

Can cognitive activities during breaks in repetitive manual work accelerate recovery from fatigue? A controlled experiment

Neurophysiologic theory and some empirical evidence suggest that fatigue caused by physical work may be more effectively recovered during “diverting” periods of cognitive activity than during passive rest; a phenomenon of great interest in working life. We investigated the extent to which development and recovery of fatigue during repeated bouts of an occupationally relevant reaching task was influenced by the difficulty of a cognitive activity between these bouts. Eighteen male volunteers performed three experimental sessions, consisting of six 7-min bouts of reaching alternating with 3 minutes of a memory test differing in difficulty between sessions. Throughout each session, recordings were made of upper trapezius muscle activity using electromyography (EMG), heart rate and heart rate variability (HRV) using electrocardiography, arterial blood pressure, and perceived fatigue (Borg CR10 scale and SOFI). A test battery before, immediately after and 1 hour after the work period included measurements of maximal shoulder elevation strength (MVC), pressure pain threshold (PPT) over the trapezius muscles, and a submaximal isometric contraction. As expected, perceived fatigue and EMG amplitude increased during the physical work bouts. Recovery did occur between the bouts, but fatigue accumulated throughout the work period. Neither EMG changes nor recovery of perceived fatigue during breaks were influenced by cognitive task difficulty, while heart rate and HRV recovered the most during breaks with the most difficult task. Recovery of perceived fatigue after the 1 hour work period was also most pronounced for the most difficult cognitive condition, while MVC and PPT showed ambiguous patterns, and EMG recovered similarly after all three cognitive protocols. Thus, we could confirm that cognitive tasks between bouts of fatiguing physical work can, indeed, accelerate recovery of some factors associated with fatigue, even if benefits may be moderate and some responses may be equivocal. Our results encourage further research into combinations of physical and mental tasks in an occupational context.

Experimentally induced stress validated by EMG activity

Experience of stress may lead to increased electromyography (EMG) activity in specific muscles compared to a non-stressful situation. The main aim of this study was to develop and validate a stress-EMG paradigm in which a single uncontrollable and unpredictable nociceptive stimulus was presented. EMG activity of the trapezius muscles was the response of interest. In addition to linear time effects, non-linear EMG time courses were also examined. Taking into account the hierarchical structure of the dataset, a multilevel random regression model was applied. The stress paradigm, executed in N = 70 subjects, consisted of a 3-minute baseline measurement, a 3-minute pre-stimulus stress period and a 2-minute post-stimulus phase. Subjects were unaware of the precise moment of stimulus delivery and its intensity level. EMG activity during the entire experiment was conform a priori expectations: the pre-stimulus phase showed a significantly higher mean EMG activity level compared to the other two phases, and an immediate EMG response to the stimulus was demonstrated. In addition, the analyses revealed significant non-linear EMG time courses in all three phases. Linear and quadratic EMG time courses were significantly modified by subjective anticipatory stress level, measured just before the start of the stress task. Linking subjective anticipatory stress to EMG stress reactivity revealed that subjects with a high anticipatory stress level responded with more EMG activity during the pre-stimulus stress phase, whereas subjects with a low stress level showed an inverse effect. Results suggest that the stress paradigm presented here is a valid test to quantify individual differences in stress susceptibility. Further studies with this paradigm are required to demonstrate its potential use in mechanistic clinical studies.

The influence of dry needling of the trapezius muscle on muscle blood flow and oxygenation

OBJECTIVE

The purpose of this study was to investigate the effect of dry needling on the blood flow and oxygen saturation of the trapezius muscle.

METHODS

Twenty healthy participants participated in this study. One single dry needling procedure was performed in the right upper trapezius, at a point located midway between the acromion edge and the seventh cervical vertebrae. Using the oxygen to see device, blood flow and oxygen saturation were evaluated at the treated point and 3 distant points (similar point in the left upper trapezius and 30 mm laterally from this midpoint). Measurements were taken at baseline and in the recovery period (0, 5, and 15 minutes posttreatment).

RESULTS

After removal of the needle, the blood flow and oxygen saturation increased significantly from the pretreatment level in the treated point (P ≤ .001), and these values remained high throughout the 15-minute recovery period. There were only minor changes in the distant points.

CONCLUSIONS

These results suggest that dry needling enhances the blood flow in the stimulated region of the trapezius muscle but not in a distant region used in this study.

Muscle- and task-dependent responses to concurrent physical and mental workload during intermittent static work

Many workers experience combined physical and mental demands in their jobs, yet the contribution of these demands to the development of musculoskeletal disorders is unclear. The purpose of this study was to investigate muscle- and task-dependent responses to concurrent demands during intermittent static work. Twenty-four participants performed shoulder, wrist, and torso exertions at three levels of physical workload (PWL) in the absence (control) and presence (concurrent) of a mental arithmetic task. Compared to the control, concurrent demand conditions resulted in decreased muscle activity (4-9% decrease), increased cardiovascular load (2-4% increase), and impaired motor co-ordination (9-24% increase in force fluctuation). Furthermore, these outcomes were more prominent at higher PWL levels and within postural (shoulder and torso) muscles. Mental task performance exhibited greater interference with the physical task at low and high PWL levels. Thus, it may be important to consider these muscle- and task-specific interactions of concurrent demands during job design to address worker health and performance issues.

PRACTITIONER SUMMARY

Occupational tasks place both physical and mental demands on workers. These demands can adversely affect physiological responses and performance, and are muscle- and task-dependent. Findings from this research may facilitate the development of ergonomics interventions, such as task redesign and tool/workstation design, that may help reduce risk of workplace injuries.

The use of muscle near-infrared spectroscopy in sport, health and medical sciences: recent developments

Near-infrared spectroscopy (NIRS) has been shown to be one of the tools that can measure oxygenation in muscle and other tissues in vivo. This review paper highlights the progress, specifically in this decade, that has been made for evaluating skeletal muscle oxygenation and oxidative energy metabolism in sport, health and clinical sciences. Development of NIRS technologies has focused on improving quantification of the signal using multiple wavelengths to solve for absorption and scattering coefficients, multiple pathlengths to correct for the influence of superficial skin and fat, and time-resolved and phase-modulated light sources to determine optical pathlengths. In addition, advances in optical imaging with multiple source and detector pairs as well as portability using small wireless detectors have expanded the usefulness of the devices. NIRS measurements have provided information on oxidative metabolism in various athletes during localized exercise and whole-body exercise, as well as training-induced adaptations. Furthermore, NIRS technology has been used in the study of a number of chronic health conditions. Future developments of NIRS technology will include enhancing signal quantification. In addition, advances in NIRS imaging and portability promise to transform how measurements of oxygen utilization are obtained in the future.

Changes in mechanical load and extensor muscle activity in the cervico-thoracic spine induced by sitting posture modification

The influence of whole body sitting posture on cervico-thoracic posture, mechanical load and extensor muscle activity was examined in 23 asymptomatic adults. Cervical and upper thoracic extensor muscle activity measured in guided slouched and lumbo-pelvic neutral postures was normalised to that measured in a self-selected habitual posture. Head and neck posture and gravitational load moment measurements were obtained in each posture. Sagittal head translation, upper cervical extension and load moment were significantly greater in the slouched posture (p < 0.001). Contrasting patterns of cervical and thoracic extensor activity were observed in the slouched and neutral postures, with cervical extensor activity 40% higher in the slouched posture (p < 0.0001). Thoracic extensor activity was significantly higher in the lumbo-pelvic neutral posture than the habitual posture (p = 0.002). The significant changes in extensor muscle activity with postural modification appear to be induced by the associated change in mechanical load moment of the head. STATEMENT OF RELEVANCE: More neutral sitting postures reduce the demand on the cervical extensor muscles and modify the relative contribution of cervical and thoracic extensors to the control of head and neck posture. Postures that promote these patterns of muscular activity may reduce cervical spine loading and the development of posture-related neck pain.

Combining microdialysis and near-infrared spectroscopy for studying effects of low-load repetitive work on the intramuscular chemistry in trapezius myalgia

Epidemiological research provides strong evidence for a link between repetitive work (RW) and the development of chronic trapezius myalgia (TM). The aims were to further elucidate if an accumulation of sensitising substances or impaired oxygenation is evident in painful muscles during RW. Females with TM (n = 14) were studied during rest, 30 minutes RW and 60 minutes recovery. Microdialysate samples were obtained to determine changes in intramuscular microdialysate (IMMD) [glutamate], [PGE₂], [lactate], and [pyruvate] (i.e., [concentration]) relative to work. Muscle oxygenation (%StO₂) was assessed using near-infrared spectroscopy. During work, all investigated substances, except PGE₂, increased significantly: [glutamate] (54%, P < .0001), [lactate] (26%, P < .005), [pyruvate] (19%, P < .0001), while the %StO₂ decreased (P < .05). During recovery [PGE₂] decreased (P < .005), [lactate] remained increased (P < .001), [pyruvate] increased progressively (P < .0001), and %StO₂ had returned to baseline. Changes in substance concentrations and oxygenation in response to work indicate normal increase in metabolism but no ongoing inflammation in subjects with TM.

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.