Matthew M. Marshall

The effects of complex wrist and forearm posture on wrist range of motion

Previous research on wrist functionality has focused almost entirely on range of motion (ROM) in 2 or 3 isolated planes (flexion/extension, radial/ulnar deviation, and forearm pronation/supination), without investigating the potential effects of complex wrist/forearm posture on ROM. A quantitative analysis of these effects on wrist ROM was performed. ROM was measured in one plane using both a manual method and an electrogoniometer while the participant maintained a fixed, secondary wrist and forearm posture. The study revealed that combinations of wrist/forearm postures have significant effects on wrist ROM; the largest effects are those of wrist flexion/extension on radial deviation ROM. The study also found that, consistent with previous research, wrist deviation measurements obtained with an electrogoniometer were significantly different from those obtained manually. Biomechanical theories for the results obtained are discussed. This research could be used to enhance ergonomic evaluation techniques by providing a more accurate risk assessment of certain complex wrist postures, particularly those in which wrist flexion/extension is combined with radial deviation.

Effects of pace and stress on upper extremity kinematic responses in sign language interpreters

Sign language interpreters suffer from high levels of upper extremity disorders and burnout due to the physical and cognitive demands of interpreting. The objective of this research was to quantify the wrist kinematics of interpreting and to assess how speaker pace and psychosocial stress influence wrist kinematics. Professional interpreters interpreted a pre-recorded lecture, while the speaking pace of the lecture varied. One group of subjects was exposed to environmental conditions intended to induce stress. Several wrist kinematic variables of interpreting exceeded previously established high risk benchmarks for development of upper extremity disorders in industrial tasks. Wrist velocity and acceleration increased significantly with pace, with increases ranging from 10.7–18.6%. Increased psychosocial stress resulted in significant increase of left hand (non-dominant) wrist velocity and acceleration, with increases ranging from 14.8–19.5%. These results provide an objective assessment of the biomechanical demands of interpreting and support earlier research into different types of work, which found deleterious effects of psychosocial stress on the biomechanical responses of the lower back.

Verbal Estimation of Peak Exertion Intensity

The objectives of this research were to investigate the accuracy and precision with which trained and untrained participants estimate the magnitude of forceful exertion and to evaluate the mathematical relationship between actual and estimated exertion. Three groups of participants estimated, as a percentage of maximum voluntary contraction (%MVC), the magnitude of submaximal exertion for 12 simulated tasks. In addition to the control group, one group was exposed to one physical benchmark (100% MVC) and another to three benchmarks (25%, 75%, and 100% MVC) prior to force estimation. Error (estimated minus actual) significantly decreased (p < .0001) from 14% MVC to 4% MVC with one benchmark and to -3% MVC with three benchmarks, as compared with the control group. Furthermore, the standard deviation decreased significantly (p < .0001) from the control group (16.6% MVC) to the one-benchmark group (13.8% MVC) to the three-benchmark group (11.6% MVC), indicating improved precision. Significant interaction effects were observed, but their impact on main effects was negligible. Also, linear, power, and logarithmic regression models described the relationship between perceived and actual exertion equally well (R2 = .64-.81). Applications of this research include improving the accuracy and precision of field-based psychophysical estimates of forceful exertion for epidemiological research and other field-based analyses.

Exposure to forceful exertions and vibration in a foundry

The purpose of this research is to describe the results of a study that investigated the exposure of workers in a foundry to ergonomic risk factors. This presentation describes the characteristics of the tools investigated during this research with respect to physical work factors such as muscle activity, upper extremity posture, hand repetition, and exposure to hand/arm vibration. The analysis is based on the use of instrumentation as well as the use of observational methods to quantify these physical work elements.

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.

Symptoms of Musculoskeletal Disorders among Tattoo Artists

Despite the widespread popularity of tattoos in the U.S. and worldwide, little consideration has been given to the occupational risk factors that tattoo artists face. Tattoo artists are exposed to many of the same risk factors faced by occupations such as dentistry and cosmetology, including prolonged static work postures and sustained gripping of hand held tools. However, no research has evaluated the extent to which the tattooing profession is adversely affected by its occupational demands. Utilizing a survey of tattoo artists, this research sought to benchmark the prevalence of symptoms commonly associated with the development of musculoskeletal disorders. The survey results revealed that tattoo artists experience high levels of discomfort in the lower back, neck, shoulders, and upper extremities and that these levels significantly exceed discomfort reported in professions that expose workers to similar ergonomic risk factors.

A Hierarchical Job Analysis System for Assessing Physical Work Barriers

Knowledge of physical work requirements is necessary for determining if a job can be performed by a given person or population. It is also necessary for assessing the risk of fatigue, discomfort and musculoskeletal disease. We have proposed a hierarchical job analysis system that includes four levels of analysis. Level I is based on worker and supervisor interviews and provides descriptions of work tasks, materials, equipment, work environment and activities that may challenge a given persons work capacity or result in excess risk of injury or illness. A Level II analysis is based on direct work site observations and measurements and provides additional quantification of the data obtained from Level I. A Level III analysis is based on expert ratings of ergonomic stresses: repetition, force, contact stress and posture of each task. A Level IV analysis uses instrumentation, e.g., goniometers, electromyography, force gages and accelerometers, to provide quantification of specific task attributes.

The Effects of Complex Wrist and Forearm Posture on Wrist Range of Motion

In order to minimize the risk of repetitive trauma injuries, postures or motions that place joints near the limits of their range of motion (RoM) should be avoided. Before it can be determined that a posture or motion approaches the limit of a joints motion, these limits need to be established. Previous research on wrist functionality has focused almost entirely on RoM in two or three isolated planes (flexion/extension, radial/ulnar deviation, and forearm pronation/supination), without investigating potential effects of complex wrist/forearm posture on RoM. Since most practical applications of this wrist motion data involve more than these isolated planar deviations, the effects of complex wrist/forearm posture on wrist functionality need to be understood.

Adapting Experiential Learning to Develop Problem-Solving Skills in Deaf and Hard-of-Hearing Engineering Students

Individuals who are deaf and hard-of-hearing (DHH) are underrepresented in science, technology, engineering, and mathematics (STEM) professions, and this may be due in part to their level of preparation in the development and retention of mathematical and problem-solving skills. An approach was developed that incorporates experiential learning and best practices of STEM instruction to give first-year DHH students enrolled in a postsecondary STEM program the opportunity to develop problem-solving skills in real-world scenarios. Using an industrial engineering laboratory that provides manufacturing and warehousing environments, students were immersed in real-world scenarios in which they worked on teams to address prescribed problems encountered during the activities. The highly structured, Plan-Do-Check-Act approach commonly used in industry was adapted for the DHH student participants to document and communicate the problem-solving steps. Students who experienced the intervention realized a 14.6% improvement in problem-solving proficiency compared with a control group, and this gain was retained at 6 and 12 months, post-intervention.

Effects of Pace and Work Stress on Upper-Extremity Kinematic Responses in Sign Language Interpreters

Sign language interpreting is an occupation that suffers from high levels of repetitive motion injuries (RMIs) and burnout due to the high physical and cognitive demands of the interpreting task. The objective of this research was to determine the effects of work pace and psychosocial stress on the wrist kinematics of sign language interpreting. It was found that neither pace nor stress affected mean wrist position, but increased pace resulted in a significant increase of both mean velocity and acceleration, with increases ranging from 10.7–18.6%. Increased psychosocial stress resulted in a significant increase of left-hand (non-dominant) mean velocity and acceleration, with increases ranging from 14.8–19.5%. No effect of stress was observed for the right hand. In addition, several wrist kinematic variables of interpreting exceeded previously established high risk industrial benchmarks. The results of this work support earlier research which found deleterious effects of work stress on the biomechanical responses of the lower back.