Browsing by Author "Dr. Gary A. Mirka, Committee Chair"

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The effects of sloped ground on the hip, knee, and ankle joint kinetics and kinematics during manual lifting tasks.
(2002-08-21) Shin, Gwanseob; Dr. Eric Klang, Committee Member; Dr. Carolyn Sommerich, Committee Member; Dr. Gary A. Mirka, Committee Chair
The biomechanical effects of sloped ground on hip, knee, and ankle joint moments and lifting posture during sagittally symmetric manual lifting were investigated using a two-dimensional five-segment dynamic biomechanical model. Subjects' motions were traced and recorded at 60Hz by Flock of Birds magnetic tracking system as they lifted a 10 kg cubic box on five sloped grounds; two declined slopes (-20°, -10°), two inclined slopes (+20°, +10°), and flat ground (0°), using three lifting techniques; back lift, freestyle lift, and leg lift. Fifteen trials were tested and each trial involved repetitive lifting (6 to 9 lifts per trial) for 50 seconds. The kinetic and kinematic effects were examined by computing the peak net reactive moments at the hip, knee, and ankle joints, and measuring peak segment flexion angles of the trunk, thigh, and leg (shank). Results indicated that the peak joint moments and peak segment angles were significantly affected by slope angle and lifting technique (α = 0.05). The inclined slope angles (10° and 20°) caused up to 6.8 % and 14.3 % larger peak hip moments than flat ground during the freestyle and leg lifts, respectively. The lowest peak hip moment (236.48 Nm) was observed during the leg lift on flat ground and the largest peak hip moment (302.62 Nm) occurred during the back lifts on flat ground. The components contribution analyses showed that the two static components (vertical reaction static force on the shoulder joint and the trunk mass) were main contributors to the responses of peak hip moment to changes in slope angle. The leg lift technique produced significantly less peak joint moments than other lifting techniques regardless of slope angle. The mean peak hip moment was 16.0 % and 10.5 % less in the leg lift technique (251.0 Nm) than in the back (298.8 Nm) and freestyle lift (280.4 Nm) respectively. Specifically, trunk angular acceleration acted as a major contributor to the significant difference in peak hip moments between the back lift and the leg lift. The trunk angular acceleration, peak flexion angles of the trunk, thigh, and shank separated the leg lift from the back lift.
Evaluating the Effects of Age on the Variability in Lifting Technique
(2005-08-16) Freeman, Jacklyn H; Dr. Peter Mente, Committee Member; Dr. David Kaber, Committee Member; Dr. Gary A. Mirka, Committee Chair
As individuals age, they under go numerous changes that can affect their lifting technique. These changes include muscle strength and flexibility reductions, and decreases in postural control. The rate and degree of these declines vary from individual to individual, which can lead to variability in their lifting technique. The objective of this research was to evaluate the inter- and intra-subject variability of the trunk kinematics and ground reaction forces on the lifting technique used to perform a lifting task. Variability of the lifting technique is important to consider when evaluating the safety of lifting tasks. A higher variability of a lifting technique means that some individuals perform the lifting task using more extreme techniques than others. Thus, a lifting task with high variability can lead to a greater risk of injury if the variability is not taken into account when testing the safety of the lifting task. The hypothesis was that an older subject group would have a higher inter- and intra-subject variability than a younger subject group. It was hypothesized that older subjects would have greater inter-subject variability because of the varying experiences and backgrounds of the older subjects, which would lead to variances in the lifting technique between subjects. It was hypothesized that older subjects would exhibit greater intra-subject variability because older subjects are more likely to lose their balance during a lifting task and would experience weakened muscles faster than younger subjects, both of which would lead to variance in the lifting technique within a subject. Two subject groups were used in this study — a younger subject group and an older subject group. Subjects were asked to perform lifting tasks that included two levels of load and three levels of lifting asymmetry angle. Trunk kinematic data were captured using a Lumbar Motion Monitor, and ground reaction force data were captured with a force platform. The inter- and intra-subject variability of the trunk kinematic data and force platform data were calculated using equations derived from the Modified Levene's test. Two statistical models were created — one model for the inter-subject variability dependent variables and one model for the intra-subject dependent variables. Multiple Analysis of Variance (MANOVA) and subsequent univariate Analysis of Variance (ANOVA) techniques were used to analyze the effects of age, weight, and angle (and their interactions) on the dependent variables. The results did not support the hypothesis, as age was neither a significant main effect nor a factor in any significant interactions for any of the dependent variables. For inter-subject variability, the MANOVA showed that weight*angle was significant and for intra-subject variability, the MANOVA showed that angle was significant. The general trend of increasing intra-subject variability was demonstrated with increasing angle. One possible explanation for why age was not a significant factor in the inter-subject variability dependent variables is the relatively homogenous nature of the older subject group. An explanation for why age was not a significant factor in the intra-subject variability dependent variables is that since older subjects exhibit decreased flexibility, they were more constrained in how they performed the lifting task. Future work should consist of choosing a heterogeneous older subject group with varying backgrounds among subjects. Recording the flexibility and muscle strengths of all subjects would be beneficial for comparison between the older and younger subject groups.
Predicting Trunk Kinematics from Static Task Parameters
(2002-07-25) Nay, David Todd; Dr. David A. Dickey, Committee Member; Dr. Gary A. Mirka, Committee Chair; Dr. Carolyn M. Sommerich, Committee Member
Many of the current ergonomic assessment tools available to industry take static "snapshots" of manual material handling (MMH) tasks to assess the hazards of a job. These tools are valuable to industry in that they provide a quick and inexpensive assessment of the task. However, these tools do not evaluate the trunk kinematics occurring during the task. As previous research has shown, trunk kinematics play an important role in assessing the stress placed on a person's low back. The goal of this study was to provide a model that predicts the trunk kinematics as a result of static task parameter inputs. A three-dimensional electrogoniometer worn on the subject's low back (Lumbar Motion Monitor (LMM)) was used to record the effects of task parameters on trunk kinematics during a lifting task. Task parameters consisted of the inputs to the NIOSH Lifting Equation: the beginning and ending asymmetry location (five levels), horizontal distance (two levels), vertical height (three levels), and weight (two levels). Study results showed a good ability to predict the trunk kinematics in the sagittal plane, but a very low ability in the coronal and transverse planes. Using the results of this study to calculate the LMM Model's Probability of High Risk Group Membership (PHRGM) resulted in an average absolute error of 8.07. Improvements in the ability to accurately predict the PHRGM were achieved when the MMH lifts evaluated were kept within the parameters of this research. The results of this research provide ergonomists with trunk kinematics information from the static task parameters that can be used during the ergonomic assessment of a MMH lift.
Productivity and Ergonomic Investigation of Bent-Handle Pliers.
(2002-07-02) Duke, Kelly Scott; Dr. Michael S. Woglater, Committee Member; Dr. Carolyn M. Sommerich, Committee Member; Dr. Gary A. Mirka, Committee Chair
Musculoskeletal disorders (MSDs) cost industry billions of dollars in workers' compensation costs each year. Ergonomics is concerned with understanding the causes of MSDs and developing solutions to reduce these costs. Awkward postures have been implicated as a risk factor for the development of some MSDs, and a design principle to "bend the tool, not the wrist" has been advocated in many ergonomic textbooks. However, despite numerous laboratory investigations showing positive outcomes of application of this design principle to various hand tools, there is indication of lack of acceptance in industry for these bent-handle tools. In an attempt to understand the lack of industry acceptance, this investigation sought to determine if this design principle imposed constraints on users and/or negatively affected productivity, which may explain why they are not being widely used in industry. The experiment used two different tasks (a computer-jumper installation task, and a spring assembly task) to compare the use of bent-handle pliers versus straight-handle pliers. Additionally, the effects of work surface orientation (vertical versus slanted at 45°) was evaluated, as was the effect of constraining the user's coupling of the tool. The dependent variables in the experiment were productivity and postural outcomes (arm elevation, wrist deviation in the radial/ulnar plane, and wrist deviation in flexion/extension). An important point that must be made is that overall the results clearly suggested that the expected outcomes (both productivity and postural) are very task specific. This in itself says a lot about the general recommendation to "bend the tool", that being that the recommendation cannot be made without clearly understanding the other task characteristics involved, and that it should therefore not be proposed as a general design recommendation. For the computer-jumper task the bent-handle pliers resulted in 5.3% faster task performance compared to the straight-handle pliers, while for the spring assembly task the performance was 4.9% faster with the straight-handle pliers. The explanation provided is that the bent-handle pliers seem to be preferable for tasks that require minimal or no tool rotation out of the sagittal plane, losing their advantage when multi-plane rotation is required. When subjects were constrained to holding the pliers with a power grip or oblique grip (modified power grip) arm elevation was reduced 50% and ulnar deviation was reduced by 12% when using the bent-handle pliers on the computer-jumper task, while on the spring assembly task ulnar deviation was reduced 22%. These results suggest that there are postural advantages to the bent-handle pliers (for the tasks used in this experiment) when the pliers-coupling is restricted to these grips. In the test of constrained versus unconstrained the results showed that for the computer-jumper task the postural benefits of the bent-handle pliers were lost when the subject could hold the straight-handle pliers any way desired, while for the spring assembly task this was not seen. In addition to showing that the postural benefits may only be seen when the pliers are held in a specific way, these results (along with others discussed in the paper) illustrate that the expectations associated with this design concept are very task-specific. Finally, removal of the coupling constraint also showed that subjects were more likely hold the straight-handle pliers in unconventional manners. In summary, it appears that the specificity of the bent-handle tool design, may make it better in very specific circumstances, but if the use requires increasing degrees of manipulation, it is less likely to be superior to a simpler design.
Visual Posture Observation Error and Training
(2003-06-04) Covalla, Elizabeth Danielle; Dr. Gary A. Mirka, Committee Chair; Dr. Nelson Couch, Committee Member; Dr. Carolyn M. Sommerich, Committee Member
The purpose of this study was to determine people's ability to visually estimate postural angles of the shoulder, trunk, and wrist. One application of these findings is to determine the effect of estimation error on common risk analysis tools that incorporate posture. Considerations are given to the effect of training, video mode, gender, body region, and subject characteristics on estimation error. Absolute error, algebraic error, and subject confidence are used to characterize visual estimation abilities. Results indicate that visual estimation error ranges between 7 and 10 degrees. Error further increased with wrist postures and female observers. Due to estimation errors, analysis tools that include posture are less accurate in predicting risk of injury. Eight, 12, and 14 percent of shoulder, trunk, and wrist postures, respectively, were misclassified causing Rapid Upper Limb Assessment (RULA) scores to shift by at least one point. For the Strain Index, forty percent of wrist postures were misclassified by participants causing as much as a two-thirds change in the final score.