Bilateral trapezius activity during a dual task depends on age and sex - Results of an experimental laboratory study.

To determine differences in muscle activity amplitudes and variation of amplitudes when using different information and communication technologies (ICT). Office workers use different ICT to perform tasks. Upper body musculoskeletal complaints are frequently reported by this occupational group. Increased muscle activity and insufficient variation are potential risk factors for musculoskeletal complaints. Muscle activity of right and left upper trapezius and right wrist extensor muscle bundle (extensor carpi radialis longus and brevis) of 24 office workers (performing their usual tasks requiring different ICT at work and away from work) were measured continuously over 10 to 12 hours. Muscle activity variation was quantified using two indices, amplitude probability distribution function and exposure variation analysis. There was a trend for electronics-based New ICT tasks to involve less electromyography (EMG) variation than paper-based Old ICT tasks. Performing Combined ICT tasks (i.e., using paper- and electronics-based ICT simultaneously) resulted in the highest muscle activity levels and least variation; however, these Combined ICT tasks were rarely performed. Tasks involving no ICT (Non-ICT) had the greatest muscle activity variation. Office workers in this study used various ICT during tasks at work and away from work. The high EMG amplitudes and low variation observed when using Combined ICT may present the greatest risk for musculoskeletal complaints, and use of Combined ICT by workers should be kept low in office work. Breaking up combined, New, and Old ICT tasks, for example, by interspersing highly variable Non-ICT tasks into office workers' daily tasks, could increase overall muscle activity variation and reduce risk for musculoskeletal complaints.

Upper limb and trunk muscle activation during an unexpected descent on the outstretched hands in young and older women

Most previous studies of concurrent physical and cognitive demands have addressed tasks of limited relevance to occupational work, and with dissociated physical and cognitive task components. This study investigated effects on muscle activity and heart rate variability of executing a repetitive occupational task with an added cognitive demand integral to correct task performance. Thirty-five healthy females performed 7.5 min of standardized repetitive pipetting work in a baseline condition and a concurrent cognitive condition involving a complex instruction for correct performance. Average levels and variabilities of electromyographic activities in the upper trapezius and extensor carpi radialis (ECR) muscles were compared between these two conditions. Heart rate and heart rate variability were also assessed to measure autonomic nervous system activation. Subjects also rated perceived fatigue in the neck-shoulder region, as well as exertion. Concurrent cognitive demands increased trapezius muscle activity from 8.2% of maximum voluntary exertion (MVE) in baseline to 9.0% MVE (p = 0.0005), but did not significantly affect ECR muscle activity, heart rate, heart rate variability, perceived fatigue or exertion. Trapezius muscle activity increased by about 10%, without any accompanying cardiovascular response to indicate increased sympathetic activation. We suggest this slight increase in trapezius muscle activity to be due to changed muscle activation patterns within or among shoulder muscles. The results suggest that it may be possible to introduce modest cognitive demands necessary for correct performance in repetitive precision work without any major physiological effects, at least in the short term.

IntroductionThe most common work-related musculoskeletal disorder worldwide is neck pain, especially among individuals who extensively use computers in a seated position. One biomedical cause of this neck pain is the prolonged activity of the muscles around the neck. Electromyography (EMG) has been used to evaluate the frequency and intensity of muscle activity. “Relative rest time (RRT)” is an index derived indicating the proportion of time below a certain threshold to the total task time. This study aimed to investigate the measurement errors and minimum detectable change (MDC) of RRT of the pericervical muscles during prolonged typing tasks in individuals with neck symptoms and to examine the differences in measurement errors at 3 µV and 6 µV thresholds.MethodsThis test-retest reliability study was conducted twice with a one-week interval to examine measurement errors of the RRT using surface EMG. The number of participants was set to 30 subjects who had neck symptoms with a Neck Disability Index of 16% or higher. The primary outcome measure was RRT of the following: the pericervical muscles of the right side during a 60-minute typing task; the splenius capitis muscle, upper trapezius (UT) muscle, middle trapezius muscle, sternocleidomastoid muscle, serratus anterior muscle, longissimus muscle, and pectoralis major muscle. RRT was calculated as the percentage of time that muscle activity was below the threshold for more than 0.250 seconds continuously during a 60-minute typing task. The standard error of measurement (SEM) and MDC were calculated with the two thresholds of 3 µV and 6 µV. The SEMs of the two thresholds were compared using a paired method.ResultsUltimately, the data of 26 participants were analyzed. The SEM (MDC) values of the RRT at the 3 µV and 6 µV thresholds were 19.22 (53.27) and 9.52 (26.39) for the splenius capitis muscle, 3.24 (8.97) and 0.38 (1.05) for the sternocleidomastoid muscle, 15.47 (42.88) and 18.79 (52.08) for the UT muscle, 21.28 (58.99) and 2.28 (6.32) for the middle trapezius muscle, 13.67 (37.90) and 11.64 (32.27) for the serratus anterior muscle, 16.81 (46.60) and 3.32 (9.20) for the longissimus muscle, and 8.97 (24.87) and 4.24 (11.74) for the pectoralis major muscle, respectively. The SEMs of the RRT with the 6 µV threshold were statistically significantly lower than those with the 3 µV threshold in all pericervical muscles, except for the UT muscle.ConclusionThis study identified the SEM and MDC of the RRT for the pericervical muscles during prolonged typing tasks in individuals with neck symptoms. Except for the UT muscle, the SEMs of the RRT with the 6 µV threshold were statistically smaller than those with the 3 µV threshold. Therefore, when using the RRT in intervention studies that aim to reduce muscle activity during typing in those with neck symptoms, the 6 µV threshold measurement would be recommended for the RRT of the pericervical muscles except for the UT muscle.

Background: Humans' role in small industries as a source of labor is still dominant, mostly manual work. The research was conducted on manual workers in small agel fiber industries in Yogyakarta. Manual work is related to human strength and endurance. Ergonomic problems often arise in manual labor, including neck pain, back pain, and leg pain called musculoskeletal disorders. Non-ergonomic working conditions also increase the electrical activity of muscles. This study aims to reduce electrical muscle activity and musculoskeletal complaints by repairing an ergonomic workstation in the agel fiber twisting process.Methods: This research is an experimental study with 15 female subjects. The electrical activity of muscles is measured when working under conventional conditions (Period 1) and repairing an ergonomic work station (Period 2). The electrical activity of the muscles was measured using surface electromyography. Musculoskeletal complaints were measured before and after intervention with conventional conditions (Period 1) and ergonomic work station repair (Period 2). Musculoskeletal complaints were measured using the Nordic Body Map Questionnaire. The measurement data between the two periods were analyzed by using the paired samples t-test and the Wilcoxon signed-rank test.Results: The results showed a decrease in the upper trapezius muscles' electrical activity by 35.46% and the erector spinae muscles' electrical activity by 22.43%. The average of musculoskeletal complaints decreased by 23.77%, measured after working in period 1 and period 2.Conclusion: Ergonomic work station can reduce the electrical activity of the upper trapezius muscles, electrical activity of the erector spinae muscles, and musculoskeletal complaints in workers twisting the agel fiber rope.

OCCUPATIONAL APPLICATIONSWhile completing a sub-maximum forceful wrist flexion task for two 1-hour sessions, the temporal patterns of forearm muscle activity of 10 females changed along with corresponding changes in torque, duty-cycle, and torque-time integral. These temporal changes in muscle activity promote variation in muscle activity during repetitive tasks, and as a result may prove to be a protection mechanism for musculoskeletal disorder development. In addition, the changes observed in torque, duty-cycle, or torque-time integral indicate that even during very defined simulated occupational tasks, workers may find ways to interject variation into a task that may also contribute to this protection.TECHNICAL ABSTRACT Background: Jobs requiring repetitive motion are common in many industries, and such jobs can be associated with the development of musculoskeletal disorders. Temporal changes in muscle activity patterns throughout repetitive tasks, if they occur, may promote variation in muscle activity and therefore may prevent the development of musculoskeletal disorders during repetitive work. Purpose: To assess temporal changes in activity patterns of the forearm muscles during a prolonged (2-hour) repetitive wrist flexion task. Methods: Ten females completed a repeated-measures study by performing a task requiring 80° wrist flexions at a rate of 15 flexions per minute overcoming a resistant force set at 25% of their maximum voluntary isometric wrist flexion torque for two 1-hour sessions, with a 5-minute break between the two sessions. Muscle activity of six forearm flexor and extensor muscles was measured using surface electromyography during the first and last 5 minutes of each of the 2-hour sessions. Task performance parameters including torque, cycle time, angle, duty cycle, work, and torque-time integral were also recorded and calculated during the 5-minute periods. Results: Compared to the first 5 minutes of the first hour, mean extensor carpi ulnaris activity was significantly lower during the last 5 minutes of both hours, and the muscle activity percentage of time in gaps was significantly higher for the last 5 minutes of the first hour and both 5-minute periods of the second hour. Torque, duty cycle, and torque-time integral were also significantly lower during the last 5 minutes of the first hour and both 5-minute periods of the second hour compared to the first 5 minutes of the first hour. Conclusions: The observed temporal changes indicate some variation in muscle activity during the repetitive task, which may affect musculoskeletal disorder development. These results provide some preliminary insight into mechanisms that may prevent the development of musculoskeletal disorder development during repetitive tasks.

In this study we sought to describe upper-extremity proximal and distal muscle activity in typically developing children during a handwriting task and to explore the relationship between muscle activity and speed and quality of writing. We evaluated 35 third- and fourth-grade Israeli children using the Alef-Alef Ktav Yad Hebrew Handwriting Test. Simultaneously, we recorded the participants' upper trapezius and thumb muscle activity by surface electromyography. Using the coefficient of variation (standard deviation divided by mean amplitude) as a measure of variability within each muscle, we analyzed differences in muscle activity variability within and between muscles. The proximal muscle displayed significantly less variability than the distal muscles. Decreased variability in proximal muscle activity was associated with decreased variability in distal muscle activity, and decreased variability in the distal muscles was significantly associated with faster speed of writing. The lower amount of variability exhibited in the proximal muscle compared with the distal muscles seems to indicate that the proximal muscle functions as a stabilizer during a handwriting task. In addition, decreased variability in both proximal and distal muscle activity appears to be more economical and is related to faster writing speed. Knowledge of the type of proximal and distal muscle activity used during handwriting can help occupational therapists plan treatment for children with handwriting disabilities.

This study aimed at investigating whether patients with neck-shoulder complaints from different aetiologies (work-related musculo-skeletal disorders, WMSD; whiplash associated disorders, WAD) show comparable muscle activation patterns, characterised by higher activation and lower relaxation levels of the trapezius muscles compared to healthy controls. Twenty healthy controls, 21 WMSD and 20 WAD patients with non-acute neck-shoulder pain were recruited for this cross-sectional study. Surface electromyography (sEMG) recordings were performed at the upper trapezius muscles during reference contractions, standardised computer tasks (typing and unilateral stress task), and rest measurements. sEMG was continuously recorded during these measurements. Outcome measures were root mean square (RMS) to study muscle activity, and relative rest time (RRT) to study muscle relaxation. Statistical analysis comprised the bootstrap technique and Kruskall-Wallis tests. Results showed no clear evidence for abnormal muscle activation patterns in WMSD and WAD patients compared to healthy controls. However, a tendency was observed for higher RMS levels during the reference contractions and computer tasks in both patient groups compared to healthy controls, and lower RRT levels at the non-dominant side during stress. Both patient groups also showed larger variability in RMS and RRT values. This variability has more often been reported in literature and may suggest the existence of subgroups of pain patients with corresponding different muscle activation patterns not related to aetiology. Future research may focus on identifying these subgroups of patients with neck-shoulder pain.

Daily muscle activity and quiescence in non-frail, pre-frail, and frail older women

To examine the effect of concurrent physical and cognitive demands as well as age on indicators of muscle fatigue at the wrist. There are few studies examining risk indicators for musculoskeletal disorders associated with work-related physical and cognitive demands that often occur simultaneously in the workplace. Twenty-four gender-balanced older and 24 gender-balanced younger (mean age 60 and 23years) participants performed four 30min dual tasks. Tasks differed by the muscular load level during force tracking: 5% and 10% of maximum voluntary contraction force (MVC) and concurrent cognitive demands on the working memory: easy and difficult. Muscle fatigue was assessed by MVC decline and changes in surface electromyography (increased root mean square: RMS, decreased median frequency: MF) at the extensor digitorum (ED) and extensor carpi ulnaris (EU). A decline in MVC was found in all participants when tracking was performed at 10% MVC (mean ± SD: 137.9 ± 49.2 - 123.0 ± 45.3N). Irrespective of age, muscular, or cognitive load, RMS increased (ED 12.3 ± 6.5 - 14.1 ± 7.0% MVE, EU 15.4 ± 7.6 - 16.9 ± 8.6% MVE) and MF decreased (ED 85.4 ± 13.6 - 83.2 ± 12.8Hz, EU 107.2 ± 17.1 - 104.3 ± 16.7Hz) in both muscles. However, changes in MF of EU tended to be more pronounced in the older group at higher cognitive and lower muscular load, without reaching statistical significance. Maximum voluntary contraction indicated no interaction between muscle fatigue, cognitive load, or age. However, the tendencies toward altered muscle activity due to an increase in cognitive load and older age suggest muscular adaptations while maintaining tracking performance during the onset of fatigue signs in the sEMG signal. If the tendencies in muscle activity are confirmed by further studies, ergonomic assessments in industrial workplaces should consider cognitive load and age when describing the risk of musculoskeletal disorders.

Can surface electromyography differentiate muscle activity between upper trapezius muscles with active versus latent trigger points?: A cross-sectional study

A prospective study of the relationship between musculoskeletal or psychological complaints and muscular responses to standardized cognitive and motor tasks in a working population

Background The Y-raise exercise (Y) is known as an effective intervention for increasing lower trapezius (LT) muscle activation. Interventions such as pectoralis minor (PM) stretching might improve scapular alignment, while therapeutic taping might influence muscle activity and shoulder posture. However, the combined effect of these interventions on trapezius muscle activity during the Y-raise exercise has not been fully investigated. Purpose The purpose of this study was to compare the muscle activity of the upper trapezius (UT) and LT, as well as the LT/UT activity ratio, between a standard Y and a Y-raise performed with LT taping after pec minor stretching (YLTPS) in healthy individuals. Study design Cross-sectional study Methods Fifteen healthy individuals participated in this study. UT, LT, and serratus anterior activities were measured using surface electromyography during the Y and the YLTPS. A paired t-test was used to compare the muscle activities. The significance level was set at α = 0.05. Results Compared to the Y, the YLTPS condition showed significantly lower UT activity, higher LT activity, and a greater LT/UT muscle activity ratio (p<0.05). However, there was no significant difference in SA activity between the conditions (p>0.05). Conclusions The YLTPS might be recommended to selectively enhance LT activation and improve the LT/UT activity ratio in healthy subjects.

We investigated muscle activity, intra-subject variability in muscle activity and co-contraction during vertical jumps and landings in children and adults. Ten male children and 10 male adults completed 10 countermovement jumps (CMJ), 10 drop jumps (DJ) from 30cm, 10 low and high landings from 30 and 60cm for the children and 60 and 90cm for the adults. The adults also performed ten DJ from 60cm. EMG was recorded from nine lower limb muscles in the right leg and normalized to isometric MVC. Statistical parametric mapping was used to reveal differences in the muscle activity and intra-subject variability in the muscle activity. Co-contraction was quantified for two thigh muscle pairs and one plantar flexor/dorsiflexor muscle pair and group differences were assessed (two-way ANOVA). No significant differences were observed in the less eccentric demanding CMJ while significantly higher muscle activity magnitude and intra-subject variability were observed for the children during the initial part of the contact phase of DJ and landings, indicating a less consistent muscle activity pattern in the children. This may indicate that vertical jumps/landings involving a high amount of eccentric muscle contraction constrain the muscle activation in children, possibly because of immature motor control.

Virtual reality (VR) technology offers an exciting way to emulate real-life walking conditions that may better elicit changes in emotional state. We aimed to determine whether VR technology is a feasible way to elicit changes in state anxiety during walking. Electrocardiogram data were collected for 18 older adult women while they navigated a baseline walking task, a dual walking task, and four walking VR environments. Using heart rate variability (HRV) analysis, we found that all four of the VR environments successfully elicited a significantly higher level of state anxiety as compared to the walking baseline, with 84% of participants eliciting a significantly lower HRV in each of the four VR conditions as compared to baseline walking. VR was also found to be a more reliable tool for increasing state anxiety as compared to a dual task, where only 47% of participants demonstrated a significantly lower HRV as compared to baseline walking. VR, therefore, could be promising as a tool to elicit changes in state anxiety and less limited in its ability to elicit changes as compared to a traditional dual task condition.