The Strain Index (SI) has repeatedly shown high levels of validity for differentiating between safe and hazardous tasks for the distal upper extremity (DUE). One limitation of the SI is the lack of reliability data. This study was designed to evaluate the test-retest repeatability of the SI. Fifteen raters, divided into five teams of three, were asked to use the SI to analyze 73 video AVI files of different job tasks; initially as individuals and then as teams. Several months later, raters were asked to repeat individual and team job task assessments. Raters were instructed to analyze tasks using five of six SI task variables, while the sixth was held constant. For three of these task variables, additional data was collected such as peak force and duration of job cycle. Test-retest repeatability was measured using Pearson's R, Spearman's rho, and tetrachoric correlation according to the nature of the variable. Spearman's rho values for individual and team task variable ratings ranged from 0.68 to 0.96 (0.88 average). Pearson's R for task variable data ranged from 0.76 to 0.99 for both teams and individuals with an average of 0.91. The Strain Index's rho values for individuals and teams were 0.70 and 0.84, respectively. For hazard classification, the tetrachoric correlation for individuals was 0.81 and 0.88 for teams. Results of this study support the conclusion that the Strain Index is repeatable when used by teams as well as individuals.

The Strain Index (SI) has repeatedly shown high levels of validity for differentiating between safe and hazardous tasks for the distal upper extremity (DUE). One limitation of the SI is the lack of reliability data. This study was designed to evaluate the test-retest repeatability of the SI. Fifteen raters, divided into five teams of three, were asked to use the SI to analyze 73 video AVI files of different job tasks; initially as individuals and then as teams. Several months later, raters were asked to repeat individual and team job task assessments. Raters were instructed to analyze tasks using five of six SI task variables, while the sixth was held constant. For three of these task variables, additional data was collected such as peak force and duration of job cycle. Test-retest repeatability was measured using Pearson's R, Spearman's rho, and tetrachoric correlation according to the nature of the variable. Spearman's rho values for individual and team task variable ratings ranged from 0.68 to 0.96 (0.88 average). Pearson's R for task variable data ranged from 0.76 to 0.99 for both teams and individuals with an average of 0.91. The Strain Index's rho values for individuals and teams were 0.70 and 0.84, respectively. For hazard classification, the tetrachoric correlation for individuals was 0.81 and 0.88 for teams. Results of this study support the conclusion that the Strain Index is repeatable when used by teams as well as individuals.

Work-related musculoskeletal disorders (MSDs) account for more than 350,000 occupational illnesses and injuries in the United States. Many job risk factors for developing MSDs are found in the automotive industry and the United Automobile Workers (UAW)-Ford Ergonomics Surveillance Tool (EST) has been designed to screen these jobs into high, moderate or low risk for work-related musculoskeletal disorders affecting the distal upper extremity (DUE), lower back (LB) and/or neck and shoulders (NS). The purpose of this effort was to examine the predictive validity of the EST against a sample of target jobs at four Ford plants. Individual jobs for this study were selected by a stratified random assignment. Health records from Ford were reviewed in order to identify first time office visits (FTOVs), which were symptomatic complaints made by individual workers. Jobs that were associated with FTOVs were defined as case jobs for the three body regions. These case jobs were compared with predictions for injury by EST. Sensitivity and specificity were used to test predictive validity. While the sensitivity was poor for all body regions tested, the specificities were fairly strong for DUE and NS when looking at low risk compared to moderate/high risk. The low risk DUE specificity was 0.67 and increased to 0.78 when looking at low/moderate risk compared to high. Low back specificity for low risk was 0.51 but increased to 0.85 when looking at low/moderate risk compared to high. The NS specificity score was 0.81, increasing to 0.85 when looking at low/moderate risk. While the EST does not predict which jobs are high risk for injury, it does screen out safe jobs. Therefore, jobs identified by the EST as low/moderate risk are likely to be safe.

<p>The purpose of this thesis was to evaluate musculoskeletal contributions to joint stiffness in the distal upper extremity. An <em>in-vitro</em> and <em>in-vivo</em> approach was used to examine muscle and ligament contributions to mechanical joint stiffness at the elbow and wrist. In Chapters 2 and 3 an <em>in-vitro</em> approach was used to evaluate ligament contributions to carpal tunnel mechanics. Chapter 2 documented transverse carpal ligament (TCL) mechanical properties and provided a calculation of TCL length when stretched, which confirmed the ligaments importance in carpal tunnel mechanics and carpal bone stability. Chapter 3 quantified mechanical properties of the TCL at six different locations using a biaxial tensile testing method. It was found that the complex TCL fibre arrangement makes the tissue properties location dependent. The TCL contributes to carpal tunnel mechanics and carpal stability and the ligament contributions are different depending on the tissue location tested. Chapters 4 and 5 focused on the effects of hand loads and arm postures on the muscular response to sudden arm perturbations. The elbow flexors demonstrated stiffness contributions immediately prior to a perturbation and were influenced by posture and hand loading. The forearm muscles provided a small contribution to elbow joint stiffness. Chapter 6 also found muscular contributions that increased wrist joint stiffness immediately prior to a sudden perturbation. Additionally, for a small grip-demanding task, forearm muscle co-contraction resulted in large increases in wrist joint stiffness.</p> <p>This thesis has provided a detailed analysis of the TCL which improves our understanding of the carpal tunnel and specific mechanisms of injury. It is the first to document individual muscle contributions to elbow and wrist joint stiffness. The comprehensive analysis of ligament and muscular contributions to joint stiffness has provided insight into joint stability in the distal upper extremity. This can improve our understanding of injury caused by sudden joint loading.</p> / Doctor of Philosophy (PhD)