Physical exposure of sign language interpreters: baseline measures and reliability analysis

Upper extremity biomechanics in native and non-native signers

BACKGROUND

Individuals fluent in sign language (signers) born to non-signing, non-deaf parents (non-natives) may have a greater injury risk than signers born to signing, deaf parents (natives). A comprehensive analysis of movement while signing in natives and non-natives has not been completed and could provide insight into the greater injury prevalence of non-natives.

OBJECTIVE

The objective of this study was to determine differences in upper extremity biomechanics between non-natives and natives.

METHODS

Strength, 'micro' rests, muscle activation, ballistic signing, joint angle, and work envelope were captured across groups.

RESULTS

Non-natives had fewer rests (p = 0.002) and greater activation (p = 0.008) in non-dominant upper trapezius. For ballistic signing, natives had greater anterior-posterior jerk (p = 0.033) and for joint angle, natives demonstrated greater wrist flexion-extension range of motion (p = 0.040). Natives also demonstrated greater maximum medial-lateral (p = 0.015), and greater minimum medial-lateral (p = 0.019) and superior-inferior (p = 0.027) positions.

CONCLUSIONS

We observed that natives presented with more rests and less activation, but greater ballistic tendencies, joint angle, and envelope compared to non-natives. Additional work should explore potential links between these outcomes and injury risk in signers.

Structural remodeling of the lumbar multifidus, thoracolumbar fascia and lateral abdominal wall perimuscular connective tissues: Medium-term test-retest reliability of ultrasound measures

INTRODUCTION

Growing interest is being paid to the lumbar multifidus (LM) intramuscular fatty infiltrations and fibrosis that are secondary to low back pain as well to the remodeling of perimuscular connective tissues (fasciae) such as the thoracolumbar fascia and fascia sheets separating the abdominal wall muscles. Magnetic resonance imaging and computed tomography have traditionally been used but rehabilitative ultrasound imaging (RUSI) is much more affordable and practical, which can accelerate research and clinical applications on this topic. The aim of this study was to test the medium-term (8 weeks) test-retest reliability of the corresponding RUSI measures.

METHODS

Thirty-four participants with non-acute LBP and 30 healthy controls performed a RUSI assessment before and after an 8-week time interval. LM echogenicity was quantified to assess fatty infiltrations and fibrosis while fasciae were quantified with thickness measures. Relative and absolute reliability were estimated using the generalizability theory as a framework, allowing to partition the different sources of error.

RESULTS

Overall, the reliability findings were quite acceptable, with negligible systematic effects. Excellent relative reliability was reached in half of the investigated RUSI measures, particularly when averaging measures across trials. However, neither relative, nor absolute reliability results support the use of these RUSI measurements on an individual basis (e.g. clinical applications) but they are useful on a group basis (e.g. research applications).

DISCUSSION

The different sources of error were distributed unequally across RUSI measures, pointing to different measurement strategies to mitigate the underlying errors.

CONCLUSIONS

The use of the generalizability theory allowed identifying the sources of error of the different RUSI measures. For each category of measure, depending of the distribution of errors, it was possible to recommend specific measurement strategies to mitigate them.

The Modified Strain Index: A Composite Measure of Injury Risk for Signers

Up to 81% of individuals who are fluent in sign language (signers) report pain. Non-native signers (with non-signing, non-deaf parents) report greater pain than natives (≥1 signing, deaf parent). The goal of this study was to develop a composite measure of injury risk (the modified Strain Index for signers) based on previously identified biomechanics unique to signers and examine scores across sub-groups of natives and non-natives. Non-natives were hypothesized to have greater pain and higher composite scores than natives. Ten natives and 15 non-natives used a numeric scale to rate pain while signing. Measures included 'micro' rests, muscle activation, ballistic signing, non-neutral joint angle, and work envelope. Descriptive statistics were used to create categorical ratings and backward elimination multiple linear regression to establish rank order of the biomechanical tasks. Participant performance was rated, and the product of the multipliers across tasks created a score. Pain intensity was associated with the composite score (r = 0.46; p = 0.02), however there was no difference between natives (score = 13.39 ± 3.1) and non-natives (score = 19.55 ± 4.7; p = 0.34). This work presents an approach to incorporate multiple biomechanical factors into a single, composite measure unique to signers, however further evidence-based adjustments are needed to enhance its robustness.

Trapezius muscle activity variation during computer work performed by individuals with and without neck-shoulder pain

This study aimed at determining the extent to which individuals with neck-shoulder pain and non-symptomatic individuals differ in muscle activation patterns, when performing computer work, as quantified by exposure variation analysis (EVA). As a secondary aim, we also aimed to quantify the day-to-day reliability of EVA variables describing trapezius muscle activation in a non-symptomatic control group. Thirteen touch-typing computer users (pain: n = 5, non-symptomatic: n = 8) completed three pre-selected computer tasks in the laboratory. Upper trapezius muscle activity was recorded using electromyography and analyzed using EVA with five amplitude and five duration categories. Individuals with neck-shoulder pain spent less time at low amplitudes and exhibited longer uninterrupted periods of muscle activation compared to their non-symptomatic counterparts. Thus, non-symptomatic workers tended to switch between exposure levels more often than individuals with pain. For a majority of EVA variables, ICCs ranged from 0.6 to 0.9, and between-days coefficients of variation were between 0.4 and 2.2.

Can exposure variation be promoted in the shoulder girdle muscles by modifying work pace and inserting pauses during simulated assembly work?

This study investigated the acute effects of changing the work pace and implementing two pause types during an assembly task. Eighteen healthy women performed a simulated task in four different conditions: 1) slow or 2) fast work pace with 3) passive or 4) active pauses every two minutes. The root mean square (RMS) and exposure variation analysis (EVA) from the trapezius and serratus anterior muscles, as well as the rate of perceived exertion (RPE) from the neck-shoulder region, were observed. Decreased RMS and RPE as well as more variable muscle activity (EVA) were observed in the slow work pace compared with the fast one. The pause types had a limited effect, but active pauses resulted in increased RMS of the clavicular trapezius. The findings revealed the importance of work pace in the reduction of perceived exertion and promotion of variation in muscle activation during assembly tasks. However, the pause types had no important effect on the evaluated outcomes.

Paramedics on the job: dynamic trunk motion assessment at the workplace

Many paramedics' work accidents are related to physical aspects of the job, and the most affected body part is the low back. This study documents the trunk motion exposure of paramedics on the job. Nine paramedics were observed over 12 shifts (120 h). Trunk postures were recorded with the computer-assisted CUELA measurement system worn on the back like a knapsack. Average duration of an emergency call was 23.5 min. Sagittal trunk flexion of >40° and twisting rotation of >24° were observed in 21% and 17% of time-sampled postures. Medical care on the scene (44% of total time) involved prolonged flexed and twisted postures (∼ 10s). The highest extreme sagittal trunk flexion (63°) and twisting rotation (40°) were observed during lifting activities, which lasted 2% of the total time. Paramedics adopted trunk motions that may significantly increase the risk of low back disorders during medical care and patient-handling activities.

Quebec Research on Work-related Musculoskeletal Disorders

This paper aimed to demonstrate the contribution of the research performed by the musculoskeletal disorders (MSD) Research Axis group of the Quebec Occupational Health and Safety Research Network towards better understanding of work-related MSD (WMSD) development and prevention. Although the group targets its work to the Quebec population, its work has significant impact around the world, placing MSD axis members and knowledge and expertise created in Quebec on the international map. Results from the contribution of members are relevant, primarily in the demonstration of the implication of physical workload as well as organizational and psychosocial work-related factors in the development of WMSDs. Also, members have demonstrated that gender, sex, social class, age and ethno-cultural groups interact in various ways with WMSD determinants. Efforts are devoted towards improving understanding of the physiological responses linked with MSDs, which could also lead to new workplace practices in rehabilitation. The group emphasizes the integration of prevention procedures from the design stage to the workplace intervention. Members have proposed research-based tools for best practices at work and also an original conceptual model as a key, novel element of a theoretical conceptualization of WMSDs. Moreover, the group focuses on improving WMSD surveillance, using multiple sources of information, providing information on newly identified health risks and developing new methods of assessing risk in order to effectively prevent disability in the working population. Finally, results from research of the MSD axis group have implications for orienting legal processes, improving legal recognition of MSDs as occupational diseases, and contributing to the evolution of legal thinking. However, much remains to be done. To that end, the group plans and encourages new initiatives for further advancement. In conclusion, the originality of the work places the group in a favourable position to address the complexity underlying WMSDs, combining expertise that enriches fundamental, clinical and population-based research.

Biomechanical Comparison of American Sign Language Interpretation and Conversation

Sign language interpreting is an occupation that requires a combination of high physical and cognitive demands. Professional sign language interpreters frequently suffer from work-related musculoskeletal disorders, but the problem does not seem to be as widespread for Deaf people who, similar to interpreters, frequently use a signed language. This study compares the biomechanics of American Sign Language (ASL) interpreting with the biomechanics of ASL used in casual conversation between professional interpreters and Deaf students. Results indicate that interpreters use, on average, 22% larger wrist deviations and 7% higher levels of wrist velocity when they interpret, compared to when they use ASL in conversation. During conversation, no significant differences in wrist kinematics were observed between the Deaf students and interpreters who participated in the conversation. However, the Deaf students tended to sign with larger wrist deviation than the interpreters.

Reliability of different thresholds for defining muscular rest of the trapezius muscles in computer office workers

This study aimed at documenting the reliability of different thresholds used for defining the muscular rest of the trapezius muscles of 27 computer office workers, using surface electromyography (EMG) signals collected in the field. Measurement strategies for increasing the reliability of the results were also explored. Ten different thresholds to define muscular rest were compared: 1) five normalised (individualised) thresholds; 2) three absolute thresholds (in muV); 3) two absolute but individualised thresholds. The reliability was assessed using both a 15-min standardised computer task and 45 min of regular computer work. The main findings were: 1) overall, in a repeated measures study design, muscular rest variables were more reliable with the use of absolute thresholds when compared to normalised and individualised thresholds; 2) excellent reliability (index of dependability >0.75) can be reached when averaging the scores over 2 days; 3) using a standardised task instead of regular work does not necessarily lead to more reliable results.

Comparison of three computer office workstations offering forearm support: impact on upper limb posture and muscle activation

The aims of the study were: 1) to determine whether resting the forearms on the work surface, as compared to chair armrests, reduces muscular activation; 2) to compare the sensitivity of different electromyographic (EMG) summary parameters. Eighteen healthy subjects performed computer work (with keyboard and mouse alternately) for 20 min while resting their forearms on a work surface adjustable in height (Workstation A), on the chair's armrests with an adjustable workstation (Workstation B) or on their chair's armrests with a non-adjustable workstation (Workstation C). The EMG amplitude of the trapezius and deltoid muscles was little influenced by the workstations, whereas their EMG variability increased with Workstation A, which was interpreted as a positive effect. However, the EMG amplitude of the mouse-side extensor digitorum muscle was higher with Workstation A. Alternating between resting the forearms on the work surface and on the chairs' armrests could solicit different muscles during computer work, and could be considered as a strategy for preventing musculoskeletal disorders. The new exposure variation analysis summary parameters used were sensitive to small workstation changes, thus supporting their use in future studies.