Neck and shoulder muscle activity during standardized work-related postural tasks

Effects of error rates and target sizes on neck and shoulder biomechanical loads during augmented reality interactions

Augmented reality (AR) interactions have been associated with increased biomechanical loads on the neck and shoulders. To provide a better understanding of the factors that may impact such biomechanical loads, this repeated-measures laboratory study evaluated the effects of error rates and target sizes on neck and shoulder biomechanical loads during two standardized AR tasks (omni-directional pointing and cube placing). Twenty participants performed the two AR tasks with different error rates and target sizes. During the tasks, angles, moments, and muscle activity in the neck and shoulders were measured. The results showed that the target sizes and error rates significantly affected angles, moments, and muscle activity in the neck and shoulder regions. Specifically, the presence of errors increased neck extension, shoulder flexion angles and associated moments. Muscle activity in the neck (splenius capitis) and shoulder (anterior and medial deltoids) also increased when the errors were introduced. Moreover, interacting with larger targets resulted in greater neck extension moments and shoulder abduction angles along with higher muscle activity in the splenius capitis and upper trapezius muscles. These findings indicate the importance of reducing errors and incorporating appropriate target sizes in the AR interfaces to minimize risks of musculoskeletal discomfort and injuries in the neck and shoulders.

Characterizing exposure to physical risk factors during veterinary surgery with wearable sensors: a pilot study

Occupational ApplicationsVeterinarians provide comprehensive health services for animals, but despite exposure to similar occupational and safety hazards as medical physicians, physical risk factors for these doctors and healthcare teams have not been characterized. In this pilot study, we used wearable sensor technology and showed that veterinary surgeons commonly experience static and demanding postures while performing soft tissue and orthopedic surgeries. Observations showed that muscle activation was highest in the right trapezius. Job factors such as surgical role (attending vs. assisting) and surgical specialty (soft tissue vs. orthopedics) appeared to influence exposure to physical risk factors. These findings suggest a need to consider the unique demands of surgical specialties in order to address the key risk factors impacting injury risks among veterinarians. For example, static postures may be a priority for soft tissue surgeons, while tools that reduce force requirements are more pressing for orthopedic surgeons.Technical AbstractBackground: Although musculoskeletal fatigue, pain, and injuries are commonly reported among surgeons in veterinary medicine, few studies have objectively characterized the exposure to physical risk factors among veterinary surgeons.Purpose: This study aimed to characterize muscle activation and postures of the neck and shoulders during live veterinary surgeries in the soft tissue and orthopedic specialties.Methods: Forty-four ergonomic exposure assessments (exposures) were collected during 26 surgical procedures across five surgeons. Exposures were collected from both soft tissue (n = 23) and orthopedic (n = 21) specialties. Physical risk factors were characterized by: 1) directly measuring muscle activation and posture of the neck and shoulders, using surface electromyography and inertial measurement units, respectively; and 2) collecting self-reported workload, pain, and stiffness.Results: Across the 44 exposures, neck and back symptoms respectively worsened after the surgery in 27% and 14% of the exposures. Veterinary surgeons exhibited neck postures involving a mean of 17° flexion during the surgical procedures. Static postures were common, occurring during 53-80% of the procedures. Compared to soft tissue procedures (e.g., 13.2% MVC in the right trapezius), higher muscle activity was observed during orthopaedic procedures (e.g., 27.6% MVC in the right trapezius).Conclusions: This pilot study showed that physical risk factors (i.e., muscle activity and posture of the neck/shoulder) can be measured using wearable sensors during live veterinary surgeries. The observed risk factors were similar to those documented for medical physicians. Further studies are needed to bring awareness to opportunities for improving workplace ergonomics in veterinary medicine and surgery.

Design and ergonomic assessment of a passive head/neck supporting exoskeleton for overhead work use

Overhead work is an important risk factor associated with musculoskeletal disorders of the neck and shoulder region. This study aimed to propose and evaluate a passive head/neck supporting exoskeleton (HNSE) as a potential ergonomic intervention for overhead work applications. Fourteen male participants were asked to perform a simulated overhead task of fastening/unfastening nut in 4 randomized sessions, characterized by two variables: neck extension angle (40% and 80% of neck maximum range of motion) and exoskeleton condition (wearing and not wearing the HNSE). Using the HNSE, significantly alleviated perceived discomfort in the neck (p-value = 0.009), right shoulder (p-value = 0.05) and left shoulder (p-value = 0.02) and reduced electromyographic activity of the right (p-value = 0.005) and left (p-value = 0.01) sternocleidomastoid muscles. However, utilizing the exoskeleton caused a remarkable increase in right (p-value = 0.04) and left (p-value = 0.05) trapezius electromyographic activities. Performance was not significantly affected by the HNSE. Although the HNSE had promising effects with respect to discomfort and muscular activity in the static overhead task, future work is still needed to investigate its effect on performance and to provide support for the generalizability of study results.

The Ergonomic Association between Shoulder, Neck/Head Disorders and Sedentary Activity: A Systematic Review

Background

Work-associated upper limb and neck disorders are common occupational disorders throughout the world. These disorders are usually observed more in workers who spend a long time sitting, referred to as sedentary activity (SA). The immediate and distorted risk of sedentary-related problems was considered high in Europe, Australia, and the United States. Even though mediation is convenient, it is likely to reduce office workers' risks of developing cervical and upper body pain due to sedentary work. This systematic review addresses risk factors and evaluates the relationship between SA and upper body disorders in office workers (i.e., shoulder and neck/head).

Methods

PubMed, Scopus, and Web of Science were searched for articles published between January 2010 and August 2021 in the English language. The three keywords “sedentary,” “upper body elements,” and “work” (and their derivatives) were searched to identify studies and carry out this systematic review. The articles were searched so that all three keywords or at least a derivation of each keyword should appear. Findings. Of the 40 articles that met the enclosure criteria, 32 studies examined the association of SA and upper body elements during both office and computer work. However, three articles were evaluated in the sit-stand work environment, and in the remaining five studies, one was evaluated during teaching, two during hospital work, and two during mixed working conditions.

Conclusions

Research related to SA focuses mainly on extended risk factors, but there was no focus on other aspects, such as muscle and tendon contractions. As there is a convincing connection between SA and the upper body, our close examination identifies the need to institutionalize a system for collecting, analyzing, and describing the impact and short-term effects of SA on the upper body. Additionally, some suggestions were made to minimize the risk in a sedentary working environment.

Fatigue, Stress, and Performance during Alternating Physical and Cognitive Tasks-Effects of the Temporal Pattern of Alternations

In occupational life, performing cognitive work tasks in between fatiguing physical work tasks may allow recovery and reduce stress without losing productive working time. The temporal pattern of such alternations is likely a determinant of the recovery effect, influencing both stress and fatigue; the difficulty of the cognitive task (CT) would also be a likely determinant. The aim of this study was to determine to what extent the temporal pattern of alternations between a repetitive physical task and a CT of different difficulties influenced perceived fatigability, performance fatigability, stress-related outcomes, and performance. Fifteen women performed four work sessions comprising 110 min of repeated bouts of a repetitive physical task (pipetting), alternating with a CT (n-back). Sessions differed in bout cycle time (short: 7 + 3 min versus long: 14 + 6 min) and CT difficulty (CTdiff; easy versus difficult). Fatigue was assessed from recordings of maximal voluntary contraction force in shoulder elevations and handgrip pre- and post-work, electromyography (EMG) from the right trapezius and right forearm extensors during work, and repeated self-ratings of fatigue and pain throughout the session. Stress was assessed using electrocardiography (heart rate variability), salivary alpha-amylase, and self-reports. Perceived fatigue increased significantly over time for all protocols and more in long-cycle than short-cycle conditions. EMG activity did not increase markedly over time in any condition. Neither objective nor subjective indicators suggested that stress increased over time, regardless of the temporal pattern. Pipetting performance remained stable in all conditions. Cognitive performance, measured by the proportions of correct positive and false positive answers, differed between CTdiff levels but remained stable over time, with no significant difference between temporal patterns. In summary, temporal patterns of alternating tasks influenced fatigue to some extent but had no obvious influence on stress indicators or performance. Thus, designing job rotation with alternating physical and cognitive work should consider the temporal patterns of alternations to minimize fatigue.

Musculoskeletal disorders and selecting an appropriate tool for ergonomic risk assessment in the dental profession

BACKGROUND

Work-related Musculoskeletal Disorders (WMSDs) are major challenges in the occupational health services industry. Dental practitioners are regularly subjected to ergonomic risks, which can cause Musculoskeletal Disorders (MSDs) in various body regions.

OBJECTIVE

This comparative cross-sectional study aimed to investigate MSDs and select a proper ergonomic risk assessment method in dental practice.

METHODS

This study was conducted on 70 dentists and 70 administrative staff of dental offices (comparison group) from Shahroud, Iran. The Cornell Musculoskeletal Discomfort Questionnaire (CMDQ) and two observational ergonomic risk assessment methods, including Quick Exposure Check (QEC) and Rapid Entire Body Assessment (REBA), were utilized.

RESULTS

The results suggested that the mean score of musculoskeletal discomforts was significantly higher in dentists than in the administrative personnel. Additionally, the results of multiple regression analysis technique inferred that job tenure, working hours, and age had a significant impact on total MSDs. Regular exercise was found to significantly reduce neck discomfort complaints. It was also found that QEC was more effective in predicting musculoskeletal discomforts compared to REBA.

CONCLUSION

Considering the high incidence of WMSDs in dentists, various interventional measures revolving around ergonomically redesigned workstations, enhanced physical working conditions, and ergonomic training courses are suggested.

A novel passive neck orthosis for patients with degenerative muscle diseases: Development & evaluation

The current study evaluated the effect of a passive neck orthosis, developed for patients suffering from progressive muscular diseases, on neck muscle activity in 10 adult healthy participants. The participants performed discrete head movements involving pure neck flexion (-10 to 30°), pure neck rotation (up to 30° left and right) and combined neck flexion-rotation (-10 to 30°) in steps of 10° by moving a cursor on a screen to reach predefined targets and staying on target for 10 s. Surface electromyography (EMG) was recorded from upper trapezius and sternocleidomastoid muscles and amplitudes were averaged over the static phases in trials with and without the orthosis. Moreover, the variability in head position and time required to perform the tasks were compared between conditions. Wearing the orthosis caused significant reductions (p = 0.027) in upper trapezius activity (a change of 0.2-1.5% EMGmax) while working against gravity. The activity level of the sternocleidomastoid muscle increased (p ≤ 0.025) by 0.3-1.0% EMGmax during pure and combined rotations without any pain reported. The orthosis showed potential to reduce the activity level of the upper trapezius muscle, the main load bearing muscle of the neck. Further study will be carried out to evaluate the effect in different patient groups.

Evaluation of a Passive Upper-Limb Exoskeleton Applied to Assist Farming Activities in Fruit Orchards

Work-related musculoskeletal disorder (WMSD) is a common occupational injury. Among the occupational injuries of agricultural workers, 93% are related to WMSD, with the shoulder being the second most affected area. This paper presents a passive upper-limb exoskeleton (PULE) with a gas spring and four-bar mechanism developed to aid the daily activities associated with orchard farming. The PULE is used to assist the arm-lifting process, reducing the physical exertion of farmers and the risk of developing WMSD. Electromyography (EMG) measurements of 26 participants were obtained to evaluate the difference in physical exertion with and without the PULE. Two arm activities: fruit thinning, with the arms raised and maintained at 100°, and pesticide spraying, with the hands swinging from 0° to 100° and back, were simulated. Using the PULE decreased muscle tension of the anterior deltoid (AD) by 17.64–19.86%. The PULE also decreased the AD activity by 37.67–39.57% during the actual orchard farming operations. The Qualisys motion capture system indicated that the difference in the lifting angle of the upper limb with and without the PULE was less than 1° and not significant (α > 0.05). Thus, the PULE did not affect the flexibility of the wearer in orchard farming activities.

Evaluation of the biomechanical stress in the neck and shoulders during augmented reality interactions

This study aimed to characterize the biomechanical stresses in the neck and shoulder, self-reported discomfort, and usability by different target distance or size during augmented reality (AR) interactions. In a repeated-measures laboratory-based study, 20 participants (10 males) performed three standardized AR tasks (3-dimensional (3-D) cube, omni-directional pointing, and web-browsing tasks) with three target distances (0.3, 0.6, and 0.9 m from each participant denoted by near, middle, far targets) for the 3-D cube and omni-directional pointing tasks or three target sizes: small (30% smaller than default), medium (default: 1.0 × 1.1 m), and large (30% larger than default) for the web-browsing task. Joint angle, joint moment, muscle activity, self-reported discomfort and comfort in the neck and shoulders; and subjective usability ratings were measured. The results showed that shoulder angle (flexion and abduction), shoulder moment (flexion), middle deltoid muscle activity significantly increased as the target distance increased during the 3-D cube task (p's < 0.001). Self-reported neck and shoulder discomfort significantly increased after completing each task (p's < 0.001). The participants preferred the near to middle distance (0.3-0.6 m) or the medium to large window size due to task easiness (p's < 0.005). The highest task performance (speed) was occurred at the near distance or the large window size during the 3-D cube and web-browsing tasks (p's < 0.001). The results indicate that AR interactions with the far target distance (close to maximum reach envelop) may increase the risk for musculoskeletal discomfort in the shoulder regions. Given the increased usability and task performance, the near to middle distance (less than 0.6 m) or the medium to large window size (greater than 1.0 × 1.1 m) would be recommended for AR interactions.

A Pilot Study Evaluating the Prevalence of Cervical Spine Dysfunction Among Students of Dentistry at the Medical University

Introduction: Cervical pain affects most people at some stage, especially middle-aged. It is one of the symptoms of cervical spine dysfunction. The prevalence of neck pain varies and depends on the population studied.

Aim: The aim of the study was to assess the prevalence of cervical spine dysfunction among dentistry students from a medical university.

Materials and Methods: The study was conducted on a group of 112 randomly chosen, generally healthy students (73 women and 39 men) of the faculty of medicine, division of dentistry at a medical university, aged 20–32, average 22.88 ± 2.7. The survey was based on a questionnaire about possible symptoms and disorders of the cervical spine in the 6 preceeding months. A bodychart was used to visualize ailments in relation to the scheme of human body, and a Graded Chronic Pain Scale was applied to assess levels of pain. Additionally, the Perceived Stress Scale and Neck Disability Index were evaluated.

Results: With respect to the questionnaire about possible symptoms of cervical spine disorders in the 6 preceeding months, 22.32% of students declared headaches 2–3 times a week, and 45.53% 2–3 times a month. 42.85% of the participants reported difficulties with concentration, 56.25% showed attention issues, and 25% had problems with memory. Moreover, 9.82% of the subjects suffered from depression, and 27.67% declared mood disorders. The bodychart revealed the occurrence of pain within the cervical spine in 47.32% of the respondents. 31.25% of students declared discomfort in the suboccipital area. In 57.14% of people, low intensity of chronic pain without functional disorders was noted. A moderate level of stress was reported in 58.03% of students. Mild cervical spine disorders were found in 53.57% of cases.

Conclusion: The relatively high prevalence of symptoms of the cervical spine dysfunction, chronic pain, stress, and neck disability among young people may indicate that numerous spinal disorders identified in dentists result not only from their profession, in which spine is significantly overloaded, but also individual predispositions including biopsychosocial profile and the changing lifestyle habits of young people.

Evaluation of a passive exoskeleton for static upper limb activities

The aim of this study was to evaluate the effect of a passive upper body exoskeleton on muscle activity, perceived musculoskeletal effort, local perceived pressure and subjective usability for a static overhead task. Eight participants (4 male, 4 female) held a load (0 kg and 2 kg) three times overhead for a duration of 30 s each, both with and without the exoskeleton. Muscle activity was significantly reduced for the Biceps Brachii (49%) and Medial Deltoid (62%) by the device for the 2 kg load. Perceived effort of the arms was significantly lower with the device for the 2 kg load (41%). The device did not have a significant effect on trunk or leg muscle activity (for the 2 kg load) or perceived effort. Local perceived pressure was rated below 2 (low pressure levels) for all contact areas assessed. Half of the participants rated the device usability as acceptable. The exoskeleton reduced muscle activity and perceived effort by the arms, and had no significant negative effect on the trunk and lower body with regards to muscle activity, perceived effort and localised discomfort.

The effects of forearm support and shoulder posture on upper trapezius and anterior deltoid activity

[Purpose] To assess the effects of forearm support and shoulder posture on upper trapezius and anterior deltoid activity. [Subjects and Methods] Twenty-three female university students were evaluated. Muscle activity was assessed by a portable surface electromyography (sEMG) system (Myomonitor IV, Delsys, USA). Upper trapezius and anterior deltoid activity were recorded in five shoulder flexion postures: 0°, 15°, 30°, 45° and 60° and in two conditions: with the forearm supported and unsupported. Descriptive data analysis was performed and statistical analysis was conducted by a multivariate analysis of variance with three repeated factors (posture, support and side). [Results] Three-way interactions were not significant. Two-way interaction was significant for support and posture for both muscles, indicating that the muscular activity depends on the forearm support and shoulder posture. The forearm support reduced upper trapezius and anterior deltoid activity for all shoulder flexion angles. The mean and standard deviation for this decrease was 7.8 (SD=4.6)% of the maximal voluntary contraction for anterior deltoid and 3.8 (SD=2.0)% of the maximal voluntary contraction for upper trapezius. In the unsupported condition, increasing the shoulder flexion angle caused an increase in the upper trapezius and anterior deltoid activation. [Conclusion] These results highlight the importance of using forearm support and to maintain neutral shoulder posture, when the upper arms are not supported, to reduce muscle activation. Thus, this study provides evidence about the effect of these recommendations to reduce muscular activity.

Evidence for Startle Effects due to Externally Induced Lower Limb Movements: Implications in Neurorehabilitation

Passive limb displacement is routinely used to assess muscle tone. If we attempt to quantify muscle stiffness using mechanical devices, it is important to know whether kinematic stimuli are able to trigger startle reactions. Whether kinematic stimuli are able to elicit a startle reflex and to accelerate prepared voluntary movements (StartReact effect) has not been studied extensively to date. Eleven healthy subjects were suspended in an exoskeleton and were exposed to passive left knee flexion (KF) at three intensities, occasionally replaced by fast right KF. Upon perceiving the movement subjects were asked to perform right wrist extension (WE), assessed by extensor carpi radialis (ECR) electromyographic activity. ECR latencies were shortest in fast trials. Startle responses were present in most fast trials, yet being significantly accelerated and larger with right versus left KF, since the former occurred less frequently and thus less expectedly. Startle responses were associated with earlier and larger ECR responses (StartReact effect), with the largest effect again upon right KF. The results provide evidence that kinematic stimuli are able to elicit both startle reflexes and a StartReact effect, which depend on stimulus intensity and anticipation, as well as on the subjects' preparedness to respond.