Interactive effects of acute experimental pain in trapezius and sored wrist extensor on the electromyography of the forearm muscles during computer work

The Effect of Experimentally Induced Pain in the Cervical, Shoulder, or Orofacial Regions on Cervical Neuromuscular and Kinematic Features: A Systematic Review and Meta-analysis

In this systematic review, we synthesize the literature investigating the effect of experimentally induced pain in the cervical, shoulder, or orofacial regions on cervical neuromuscular and kinematic features. Databases were searched up to November 1, 2023. A total of 29 studies using hypertonic saline injection (n = 27) or glutamate injection (n = 2) as experimental pain models were included. Meta-analyses revealed reduced upper trapezius activation during shoulder flexion/abduction when pain was induced in the upper trapezius (standardized mean difference: -.90, 95% confidence interval: [-1.29; -.51]), splenius capitis (-1.03 [-1.44; -.63]), and supraspinatus (-.63 [-1.25; -.01]), but not in the subacromial space (.22 [-.16; .60]). Furthermore, experimentally induced pain caused a caudal redistribution of activation within the upper trapezius (.96 [.58; 1.34]) but did not change the mediolateral distribution (.11 [-.22; .42]). None of these adaptations persisted after pain resolution. Low-quality evidence supported the absence of an effect of experimental pain on upper trapezius muscle activation during manual dexterity and cervical flexion/extension tasks, as well as on cervical flexor and extensor muscle activation during cervical and jaw tasks. Inconsistent and limited evidence, attributed to the large heterogeneity of task and outcomes, precluded drawing meaningful conclusions about the effects of experimentally induced pain in the cervical region on cervical kinematics. Overall, cervical muscle activation tended to decrease in response to experimentally induced pain, and the decrease of muscle activation depended on the location of the painful stimulus. These adaptations are only partially representative of muscle activation patterns observed in clinical populations. PERSPECTIVE: This systematic review and meta-analysis revealed a reduced or unchanged muscle activation during experimental pain in the cervical, shoulder, or orofacial regions, depending on the task and location of nociceptive stimulation. There was inconsistent evidence on cervical kinematics. These findings enhance our understanding of neuromuscular adaptations to acute experimental pain.

Effects of 1-hour computer use on ulnar and median nerve conduction velocity and muscle activity in office workers

OBJECTIVES

To compare the effects of 1-hour computer use on ulnar and median nerve conduction velocity and muscle activity in office workers with symptomatic neck pain and asymptomatic office workers.

METHODS

A total of 40 participants, both male and female office workers, with symptomatic neck pain (n = 20) and asymptomatic (n = 20), were recruited. Pain intensity, ulnar nerve conduction velocity, median nerve conduction velocity, and muscle activity were determined before and after 1 hour of computer use.

RESULTS

There was a significant increase in pain intensity in the neck area in both groups (P < .001). The symptomatic neck pain group revealed a significant decrease in the sensory nerve conduction velocity of the ulnar nerve (P = .008), whereas there was no difference in the median nerve conduction velocity (P > .05). Comparing before and after computer use, the symptomatic neck pain group had less activity of the semispinalis muscles and higher activity of the anterior scalene muscle than the asymptomatic group (P < .05). The trapezius and wrist extensor muscles showed no significant differences in either group (P > .05).

CONCLUSIONS

This study found signs of neuromuscular deficit of the ulnar nerve, semispinalis muscle, and anterior scalene muscle after 1 hour of computer use among office workers with symptomatic neck pain, which may indicate the risk of neuromuscular impairment of the upper extremities. The recommendation of resting, and encouraging function and flexibility of the neuromuscular system after 1 hour of computer use should be considered.

Deficits in neuromuscular control of increasing force in patients with chronic lateral epicondylitis

Objective: This study investigated the neuromuscular control of increasing and releasing force in patients with chronic lateral epicondylitis (CLE). Methods: Fifteen patients with CLE (10 males, 5 females, 46.5 ± 6.3 years) and fifteen healthy participants (9 males, 6 females, 45.3 ± 2.5 years) participated in this study. In addition to power grip and maximal voluntary contraction (MVC) of wrist extension, force fluctuation dynamics and characteristics of inter-spike intervals (ISI) of motor units (MUs) with various recruitment thresholds in the extensor carpi radialis brevis (ECRB) and extensor carpi radialis longus (ECRL) during a designated force-tracking task with a trapezoidal target (0%-75%-0% MVC) were assessed. Results: Besides a smaller MVC of wrist extension, the patients exhibited significantly greater task errors (p = 0.007) and force fluctuations (p = 0.001) during force increment than the healthy counterparts. Nevertheless, no force variables significantly differed between groups during force release (p > 0.05). During force increment, the amplitudes of the motor unit action potential of the ECRB and ECRL muscles of the patients were smaller than those of the heathy counterparts (p < 0.001). The patient group also exhibited a higher percentage of motor units (MU) with lower recruitment threshold (<5% MVC) in the ECRL/ECRB muscles and a lower percentage of MU with higher recruitment threshold (>40% MVC) in the ECRB muscle, compared to the healthy group. During force increment, the patient group exhibited a higher rate of decrease in inter-spike intervals (ISIs) of motor units with lower recruitment thresholds (<10% MVC) in the ECRB and ECRL muscles, compared to the control group (p < 0.005). Conclusion: The patients with CLE exhibited more pronounced impairment in increasing force than in releasing force. This impairment in increasing force is attributed to deficits in tendon structure and degenerative changes in the larger motor units of the wrist extensors. To compensate for the neuromuscular deficits, the rate of progressive increase in discharge rate of the remaining smaller motor units (MUs) is enhanced to generate force. Significance: The deficits in neuromuscular control observed in CLE with degenerative changes cannot be fully explained by the experimental pain model, which predicts pain-related inhibition on low-threshold motor units.

An Investigation of Maximal Strength of the Upper Limb Bilaterally in Individuals With Lateral Elbow Tendinopathy: A Systematic Review With Meta-Analysis

OBJECTIVE

The aim of this study was to investigate whether there is evidence of bilateral upper limb strength deficits in individuals with unilateral lateral elbow tendinopathy (LET).

METHODS

The electronic databases Medline via Ovid, PubMed, and Scopus were searched from inception to March 2020. Included studies encompassed maximal strength outcomes of any upper limb and appendicular musculature in individuals with LET and an asymptomatic comparator. Study quality was rated using a modified version of the Epidemiological Appraisal Instrument. Hedges g effect sizes (ES) and 95% CIs were calculated for comparisons of maximal strength in the LET group and an asymptomatic control group. Meta-analysis using a random-effects model was performed when possible.

RESULTS

Fourteen studies were included. Quality appraisal resulted in a mean Epidemiological Appraisal Instrument score of 46% (SD = 10%). Meta-analysis revealed strength deficits in shoulder abduction (pooled ES = -0.37 [95% CI = -0.62 to -0.12]) and shoulder external rotation (pooled ES = -0.55 [95% CI = -0.83 to -0.28]) of the symptomatic limb compared with an asymptomatic control group. Meta-analysis also revealed maximal strength deficits in the upper trapezius (pooled ES = -0.26 [95% CI = -0.49 to -0.02]) of the asymptomatic limb compared with an asymptomatic control group. There was also consistent evidence for strength deficits in the serratus anterior, lower trapezius, and wrist extensor muscles and deficits in grip strength of the symptomatic limb as well as strength deficits in the wrist extensor muscles of the asymptomatic limb in individuals with unilateral LET.

CONCLUSION

In individuals with LET, there were maximal strength deficits in shoulder abduction, shoulder external rotation, serratus anterior and lower trapezius muscles, and wrist extension, as well as deficits in grip strength of the symptomatic limb compared with an asymptomatic control group. In addition, there appeared to be strength deficits in the upper trapezius muscle, wrist extension, and metacarpophalangeal joint flexion and extension, as well as deficits in grip strength of the asymptomatic limb in individuals with LET compared with an asymptomatic control group. These results suggest bilateral strength deficits.

IMPACT

These findings highlight the importance of a thorough physical examination and appropriate strengthening intervention for the upper limb with a focus on shoulder and scapular stabilizers, in addition to forearm muscles, in individuals with LET.

LAY SUMMARY

In people with tennis elbow, widespread strength deficits, including weakness of the shoulder, forearm, and wrist muscles, may exist. Interestingly, some of these weaknesses appear on both the affected and the unaffected sides in people with tennis elbow. A physical therapist can help strengthen these areas.

Ergonomic evaluation of the risk factors causing pain in the upper part of the body among IT professionals in India

BACKGROUND: In developing countries, the recent increase in computer-related work has considerably increased the occupational complaint of pain. OBJECTIVE: To examine the effects of workstation design, posture and ergonomic awareness on the prevalence of pain for a year in the upper part of the body (eyes, hands, arms, shoulders, lower back, and upper back) among IT professionals in India. METHOD: To investigate the association of risk factors with the prevalence of pain in different body parts, a newly designed online questionnaire titled “A Questionnaire based on ergonomics for IT Professionals” was developed. The psychometric properties of this questionnaire were tested. 110 computer office workers were recruited from IT companies from major cities in India. RESULTS: The confirmation of reliability and lack of redundancy of items was provided by the calculation of internal consistency (Cronbach’s alpha 0.804) and cross-validation. 60% of participants was male. Mean age was 29.73±6.09 years. The prevalence of pain for a year in the upper part of the body was 38.2%. The frequently reported pains were in the neck (22.7%), lower back area (22.7%), and eye strain (21.8%). CONCLUSION: It was identified that long working hours, excessive usage of smartphones, lack of exercise, incorrect workstation adjustments, and incorrect posture were the risk factors for the prevalence of pain.

Comparison of scapular position and upper extremity muscle strength in patients with and without lateral epicondylalgia: a case-control study

BACKGROUND

The symptoms of lateral epicondylalgia (LE) can be persistent, and recurrence is frequent. Recurrence can be related to proximal segment impairment of the kinetic chain. Knowledge of any relation in the kinetic chain in LE may help treatment. We aimed to investigate scapular position and upper extremity muscle strength in patients with LE and to compare them with controls.

METHODS

The study enrolled 51 patients with LE and 51 age-matched controls. We assessed scapular position asymmetry using the lateral scapular slide test and measured the strength of the upper trapezius (UT), middle trapezius (MT), lower trapezius, and serratus anterior muscles in addition to shoulder abduction, external rotation, and internal rotation and grip strength.

RESULTS

The percentage of participants with scapular asymmetry was greater in the patients than in the controls (P = .005). The involved side regarding shoulder external rotation among the patients was significantly weaker than in the controls (P = .016, P = .009). The involved side of the LE patients was significantly weaker than the uninvolved side in terms of shoulder abduction, external rotation, and internal rotation (P = .013, P = .048, P = .013). The UT/MT ratio on the nondominant side of the controls was significantly greater than that on the involved side of the LE patients (P = .016).

CONCLUSION

Upper extremity muscle strength, grip strength, UT/MT ratio, and scapular position are affected in patients with LE. In addition to the elbow, focusing on the upper segments is essential in the management of LE.

Effects of cognitive loading and force on upper trapezius fatigue

Background

Musculoskeletal disorders (MSDs) are particularly common in the shoulder/neck region for some tasks that involve low force exertions, for example computer work. It has been demonstrated that muscle activity may be stimulated by cognitively demanding tasks. There is a lack of studies on the relationship between qualitative levels of cognitive loading, level of muscle activity, and muscle fatigue.

Aims

To investigate the effects of quantitative levels of cognitive loading on conduction velocity changes and isometric endurance times for the upper trapezius.

Methods

Participants performed a combination of three levels of a cognitively demanding computer task (0, 1.59 and 3 Bits) while simultaneously performing either of two isometric endurance tests (20 and 40% MVC) for the upper trapezius.

Results

Information load had a significant effect (P < 0.05) on normalized conduction velocity slopes for the 40% but not for the 20% maximum voluntary contraction conditions. Information load had a highly significant effect on endurance times for both exertion levels (P < 0.01).

Conclusions

This study found that performing a high-difficulty cognitive task while simultaneously performing increasingly higher levels of static isometric shoulder abduction exertions, fatigued the trapezius muscle quicker than performing an equivalent exertion with low cognitive load. This is particularly relevant to workplaces with increasing levels of automation that require high levels of decision making and computer use.

"Discrete peaks" of excitability and map overlap reveal task-specific organization of primary motor cortex for control of human forearm muscles

The primary motor cortex (M1) presents a somatotopic organization of body parts, but with overlap between muscle/movement representations. This distinct but overlapping M1 organization is believed to be important for individuated control and movement coordination, respectively. Discrete peaks of greater excitability observed within M1 might underpin organization of cortical motor control. This study aimed to examine interactions between M1 representations of synergist and antagonist forearm muscles, compare regions of greater excitability during different functional tasks, and compare characteristics of M1 representation recorded using surface and fine-wire (_fw ) electrodes. Transcranial magnetic stimulation (TMS) was applied over M1 for mapping the representation of 4 forearm muscles (extensor carpi radialis brevis [ECRB], extensor digitorum communis, flexor carpi radialis, and flexor digitorum superficialis) during three tasks: rest, grip, and wrist extension in 14 participants. There are three main findings. First, discrete areas of peak excitability within the M1 representation of ECRB_fw were identified during grip and wrist extension suggesting that different M1 areas are involved in different motor functions. Second, M1 representations of synergist muscles presented with greater overlap of M1 representations than muscles with mainly antagonist actions, which suggests a role in muscle coordination. Third, as larger normalized map volume and overlap were observed using surface than fine-wire electrodes, data suggest that cross-talk from adjacent muscles compromised interpretation of recordings made with surface electrodes in response to TMS. These results provide a novel understanding of the spatial organization of M1 with evidence of "functional somatotopy." This has important implications for cortical control of movement. Hum Brain Mapp 38:6118-6132, 2017. © 2017 Wiley Periodicals, Inc.

Electromyographic analysis of relevant muscle groups during completion of computer tasks using different computer mouse positions

BACKGROUND

We analyzed muscular activity for different computer mouse positions during the completion of a timed computer task and determined whether the different mouse positions could affect muscular activity, productivity and perceived fatigue.

METHODS

The subjects were nine healthy young men. Two mouse positions were studied: the distal position (DP), with the forearm rested on the desk; the proximal position (PP), with only the wrist rested on the desk. The subjects performed a 16-min task in each position. Surface electromyography data were recorded for the upper back and shoulder muscles. Work productivity and muscular activity were measured for each mouse position. A visual analog scale was used to assess subjective fatigue.

RESULTS

Muscular activity was higher in muscle (m.) deltoideus (posterior) for the DP, while it was significantly higher in m. inferior infraspinatus for the PP. The visual analog scale score was significantly higher and work productivity was lower in the PP.

CONCLUSIONS

We found that using a mouse in the DP rather than the PP leads to less activity of the external rotators, less perceived fatigue and more productivity. This suggests that the DP is preferable to the PP for computer work involving a mouse.

Scapular muscle performance in individuals with lateral epicondylalgia

STUDY DESIGN

Descriptive, laboratory-based, cross-sectional study.

OBJECTIVES

To describe scapular musculature strength, endurance, and change in thickness in individuals with unilateral lateral epicondylalgia (LE) compared to the uninvolved limb and the corresponding limb of a matched comparison group.

BACKGROUND

Reported poor long-term outcomes for the nonsurgical management of individuals with LE suggest a less-than-optimal rehabilitation process. Knowledge of scapular muscle function in a working population of individuals with LE may help to further refine conservative management of this condition.

METHODS

Twenty-eight patients with symptomatic LE and 28 controls matched by age and sex were recruited to participate in the study. Strength of the middle trapezius (MT), lower trapezius (LT), and serratus anterior (SA) was measured with a handheld dynamometer. A scapular isometric muscle endurance task was performed in prone. Changes in muscle thickness of the SA and LT were measured with ultrasound imaging. Analysis-of-variance models were used to determine within- and between-group differences.

RESULTS

The involved side of the group with LE had significantly lower values for MT strength (P = .031), SA strength (P<.001), LT strength (P = .006), endurance (P = .003), and change in SA thickness (P = .028) when compared to the corresponding limb of the control group. The involved side of the group with LE had significantly lower strength of the LT (P = .023) and SA (P = .016) when compared to the uninvolved limb; however, these differences were small and of potentially limited clinical significance.

CONCLUSION

When compared to a matched comparison group, there were impairments of scapular musculature strength and endurance in patients with LE, suggesting that the scapular musculature should be assessed and potentially treated in this population. Cause and effect cannot be established, as the weakness of the scapular musculature could be a result of LE.

Computer work and self-reported variables on anthropometrics, computer usage, work ability, productivity, pain, and physical activity

Background

Computer users often report musculoskeletal complaints and pain in the upper extremities and the neck-shoulder region. However, recent epidemiological studies do not report a relationship between the extent of computer use and work-related musculoskeletal disorders (WMSD).

The aim of this study was to conduct an explorative analysis on short and long-term pain complaints and work-related variables in a cohort of Danish computer users.

Methods

A structured web-based questionnaire including questions related to musculoskeletal pain, anthropometrics, work-related variables, work ability, productivity, health-related parameters, lifestyle variables as well as physical activity during leisure time was designed. Six hundred and ninety office workers completed the questionnaire responding to an announcement posted in a union magazine. The questionnaire outcomes, i.e., pain intensity, duration and locations as well as anthropometrics, work-related variables, work ability, productivity, and level of physical activity, were stratified by gender and correlations were obtained.

Results

Women reported higher pain intensity, longer pain duration as well as more locations with pain than men (P < 0.05). In parallel, women scored poorer work ability and ability to fulfil the requirements on productivity than men (P < 0.05). Strong positive correlations were found between pain intensity and pain duration for the forearm, elbow, neck and shoulder (P < 0.001). Moderate negative correlations were seen between pain intensity and work ability/productivity (P < 0.001).

Conclusions

The present results provide new key information on pain characteristics in office workers. The differences in pain characteristics, i.e., higher intensity, longer duration and more pain locations as well as poorer work ability reported by women workers relate to their higher risk of contracting WMSD. Overall, this investigation confirmed the complex interplay between anthropometrics, work ability, productivity, and pain perception among computer users.

Shoulder and forearm oxygenation and myoelectric activity in patients with work-related muscle pain and healthy subjects

We tested hypotheses of (a) reduced oxygen usage, oxygen recovery, blood flow and oxygen consumption; and (b) increased muscle activity for patients diagnosed with work-related muscle pain (WRMP) in comparison to healthy controls. Oxygenation was measured with near infrared spectroscopy (NIRS), and muscle activity with EMG for the extensor carpi radialis (ECR) and trapezius descendens (TD) muscles. Eighteen patients with diffuse neck-shoulder-arm pain and 17 controls (matched in age and sex) were equipped with NIRS and EMG probes. After determining an individual's maximum voluntary contraction (MVC) force, short-term (20 s) isometric contractions for the ECR and TD of 10, 30, 50 and 70 % MVC generated ∆StO₂ and StO₂% recovery (Rslope) from NIRS, and RMS%max from EMG signals. In addition, upper arm venous (VO) and arterial (AO) occlusions generated slopes of total hemoglobin (HbTslope) and deoxyhemoglobin (HHbslope) for the resting ECR as surrogates of blood flow and oxygen consumption, respectively. Mixed model analyses, t tests, and Mann-Whitney test were used to assess differences between groups. There was no significant difference in MVC between groups for either muscle. Also, ∆StO₂%, Rslope for either muscle, and ECR-HbTslope were not different between groups, thus our hypotheses of reduced oxygen use, recovery, and blood flow for patients were not confirmed. However, patients had a significantly lower ECR-HHbslope confirming our hypothesis of reduced consumption. Further, there was no difference in RMS%max during contractions meaning that the hypothesis of increased activity for patients was not confirmed. When taking into account the number of NIRS variables studied, differences we found between our patient group and healthy controls (i.e., in forearm oxygen consumption and shoulder oxygen saturation level) may be considered modest. Overall our findings may have been impacted by the fact that our patients and controls were similar in muscle strength, which is in contrast to previous studies.

Evidence for repetitive load in the trapezius muscle during a tapping task

Many studies describe the trapezius muscle activation pattern during repetitive key-tapping focusing on continuous activation. The objectives of this study were to determine whether the upper trapezius is phasically active during supported key tapping, whether this activity is cross-correlated with forearm muscle activity, and whether trapezius activity depends on key characteristic. Thirteen subjects (29.7 ± 11.4 years) were tested. Surface EMG of the finger's extensor and flexor and of the trapezius muscles, as well as the key on-off signal was recorded while the subject performed a 2-min session of key tapping at 4 Hz. The linear envelopes obtained were cut into single tapping cycles extending from one onset to the next onset signal and subsequently time-normalized. Effect size between mean range and maximal standard deviation was calculated to determine as to whether a burst of trapezius muscle activation was present. Cross-correlation was used to determine the time-lag of the activity bursts between forearm and trapezius muscles. For each person the mean and standard deviation of the cross-correlations coefficient between forearm muscles and trapezius were determined. Results showed a burst of activation in the trapezius muscle during most of the tapping cycles. The calculated effect size was ≥0.5 in 67% of the cases. Cross-correlation factors between forearm and trapezius muscle activity were between 0.75 and 0.98 for both extensor and flexor muscles. The cross-correlated phasic trapezius activity did not depend on key characteristics. Trapezius muscle was dynamically active during key tapping; its activity was clearly correlated with forearm muscles' activity.