This study examined changes in task performance during performance of simulated overhead assembly task. The study objectives were to better understand the relationship between fatigue development during overhead work and task performance. This relationship is important, considering that performance changes, or decreases in task quality, have the potential for justifying and driving ergonomic changes that can help to improve worker safety. Sixteen people participated in eight experimental conditions (two levels of duty cycles, two work heights, and two hand positions). Four dependent measures based on endurance, subjective, objective, and physiological fatigue were used to quantify shoulder fatigue and were collected during the experiment. An overhead work task required participants to use a hand tool to strike targets at two reach distances above their head. Task performance was measured as a function of the closeness to the target center and the ability to apply a consistent force throughout the experiment. Data collected in this experiment is intended to provide a research basis for creating design guidelines that will help maximize efficiency and quality while reducing the likelihood of developing shoulder fatigue. / Master of Science

<p>The primary purpose of this thesis was to measure arm strengths, in combinations of exertion directions, and to evaluate the importance of knowing the precise posture of the arm and specific joint locations in 3D space when predicting female arm strength. A stepwise multiple regression approach was utilized in the prediction of female arm strengths, using kinematic measures of hand location, arm posture and 26-force directions from 17 subjects and 8 hand locations as inputs. When including measures of arm posture, the regression model was indeed improved, explaining 75.4% of the variance, with an RMS error of 9.1 N, compared to an explained variance of 67.3% and an RMS error of 10.5 N without those postural variables. A comparison was also made between the empirical strength data from this thesis and the outputs from the University of Michigan’s Center for Ergonomics 3-Dimensional Static Strength Prediction Program (3DSSPP) software. A poor correlation (R-square = 0.305) and high RMS error (39 N) was found, indicating a definite need for further evaluation of the 3DSSPP package, as it is one of the most commonly used ergonomic tools in industry. <strong> </strong></p> / Master of Science (MSc)

<p>Biomechanical and neural factors have both been suggested to contribute to the limited independence of finger movement and involuntary force production. The purpose of this study was to evaluate the degree of finger independence by examining the activity of the four compartments of extensor digitorum (ED) and flexor digitorum superficialis (FDS) using surface electromyography and involuntary force production in the non-task fingers using methods such as the “enslaving effect” (EE) and the “selectivity index” (SI). Twelve male participants performed a series of 5-second sub-maximal exertions at 5, 25, 50 and 75% of maximum using isometric isotonic and ramp finger flexion and extension exertions. Ramp exertions were performed from 0 to 85% of each finger’s maximum force with ascending and descending phases taking 4.5 seconds each with 0.5 seconds of plateau at 85%. Lower EE and higher SI (more selective force production) was found in flexion exertions compared to extension partially due to the higher activity of the antagonist ED compartments counterbalancing the involuntary activation of the non-task FDS compartments. Minimal FDS activity was seen during extension exertions. At forces up to and including 50%, both EE and muscle activity of the non-task compartments were significantly higher in descending exertions than the isotonic or ascending exertions. The selectivity index was also lower during the descending flexion and extension exertions at 25 and 50% MVC exertions. Up to mid-level forces, both finger proximity and contraction mode affects involuntary force production and muscle activation while at higher forces only finger proximity (and not the exertion mode) contributes to finger independence. The fingers were less selective at higher exertion levels (75% MVC) and all 3 exertion modes resulted in similar SI at 75% MVC in all flexion and extension exertions.</p> / Master of Science in Kinesiology

Introduction: External support behaviours, which include leaning (supporting with the non-task hand) or bracing (supporting with the body), are frequently employed by workers in manufacturing settings. However, current ergonomic assessment tools are limited by our limited understanding of these behaviours. Recent studies have investigated these behaviours, however, the designs of these studies are limited in their applicability to real-world scenarios. The purpose of this study was to assess how different task parameters affect the prediction of external support behaviours, as well as the effect of support on task hand, and body, kinematics and kinetics, in a minimally constrained experimental design. Methods: Female participants (n = 18) performed a series of one-handed maximal exertions (in the six orthogonal directions), and one precision task, in four hand Locations. Trials either featured support (as chosen by the participant), or no support. Results & Discussion: Three logistic regression models were developed, with inputs from individual and task characteristics, and they correctly predicted the occurrence of leaning, bracing, or simultaneous leaning and bracing, 74-86% of the time. Leaning and/or bracing were found to provide: 1) oppositional forces to increase task hand force generation, 2) balance, by countering destabilizing moments about the feet, and 3) a reduction in moment arm of the task hand force, with respect to the upper body joints, by bringing the shoulder closer to the task hand. Participants were able to exert 64.8% more force at the task hand as a result of support. Leaning hand placement depended on the task force direction and location. However, the positioning of the leaning hand varied very little. Finally, the precision condition showed that fine motor demands may also affect external support choice. / Thesis / Master of Science in Kinesiology

No description available.