Browsing by Subject "Lifting and carrying -- Physiological aspects"
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Item A biomechanical study of slipping accidents with load carriage(Texas Tech University, 1991-12) Li, Kai WayThe slipping behaviors of ten male subjects under load carrying conditions were studied. The subjects carried 0, 10%, 20%, 30%, and 40% of body weight during different trials while walking on greasy steel plate with the speed of 6.4 km/hr (or 4 mph). The three-dimensional coordinates of the anatomical joints and the ground reaction forces of the subjects were measured and analyzed. The non-parametric Friedman test showed that the subjects were in a more dangerous situation when extra loads were carried. The heavier the load carried, the more severe the slip was. This implies that manual load carriage should be avoided whenever possible if there is any chance of slipping accidents. Both biomechanical and tribological effects were significant on the severity of slipping incidents. The biomechanical effects were the results of the changes of the gait parameters such as heel sliding velocity, stance time, time to slip-start, and so on. The tribological effects were inferred from the alterations of the relative change of the rate of increase of horizontal force versus vertical force and forward impulse. By comparing the time to slip-start and the time to the peak of friction use, it was concluded that friction use did not necessarily indicate the location that slips were most likely to start. The Index for Pedestrian Safety (IPS), or friction use/dynamic coefficient of friction, may be more appropriate than friction use alone to explain the occurrence of slipping since IPS identifies not only the friction demand but also the friction available during the stance phase of gait. Some parameters, based on human sliding patterns, were recommended as the set-up values for dynamic friction measurement devices. It is believed that a good friction measurement device should be able to increase the vertical force from zero to up to 10 KN in a very short period - less dian 0.5 second. A tester that applies constant force on the floor is not recommended to be used for dynamic friction measurements.Item An optimization approach to determine manual lifting motion(Texas Tech University, 1988-12) Lee, Yung-hui TerrenceThe dynamic behavior of a musculoskeletal link system in manual lifting is simulated by a mathematical model which contains a non-linear objective function and a set of linear, as well as non-linear constraints. The model was developed based upon the hypothesis that an individual performs the lifting motion following the principle of minimizing mechanical work done. The input data of the model includes (1) anthropometric parameters of the individual, (2) characteristics of the container (size, weight), (3) initial and final position angles of five major joints, and (4) the task performance time. The output data includes the time history of the five joint angles and the time history of five joint moments. The trajectory is such that it minimizes the mechanical work done while maximizing the utilization of all joints and remaining within the feasible region of the proposed constraints. The simulation results indicated that the differences between the predicted motion and the measured motion is biomechanically feasible and the accuracy is adequate enough with an average U statistics ranging from 0.012 to 0.209.Item Biomechanical stresses during asymmetric lifting: a dynamic three-dimensional approach(Texas Tech University, 1988-12) Chen, Hong-changThe objectives of this study were (1) to establish a three-dimensional dynamic biomechanical model to determine the mechanical stresses on the musculoskeletal system which occur during asymmetric lifting, (2) to examine the difference between symmetric and asymmetric liftings in terms of the loads on the lower spine, and (3) to examine the effects of weights on spinal loads for both symmetric and asymmetric lifting. To accomplish this, a dynamic biomechanical model was developed and designed to study the mechanical stresses imposed on the human body. The model estimated the forces and moments acting on each major joint center, as well as the L5/S1 disc. The dynamic effects of body segment motions and trunk rotation were accounted for in the model. A linear programming optimization technique was used to solve the indeterminate system of internal trunk muscle forces and, in turn, estimated the compressive and shear forces acting on L5/S1. A laboratory experiment was conducted utilizing male subjects who performed a sagittal and two asymmetric lifting tasks consisting of a floor to knuckle height lift using three different weights. The "ExpertVision" motion analysis system was used to track a set of predefined body landmarks and to describe the body motion. This model was validated through the comparison between the model computed force components at ground level and the force components measured by the "Kistler" force platform. A presentation routine was designed to examine the output from the model either in graphical or alphanumerical forms. The biomechanical model, the linear programming module and this presentation routine were constructed and integrated as a package running under a MS-DOS operated microcomputer. Results indicated that the L.P. technique was unable to explain the behavior of trunk muscles under the dynamic experimental situation. The effects of weights on spinal loads showed that heavier weight produced higher stresses than lower weights did. The effects of lifting types--symmetric and asymmetric--on the spinal loads showed that the symmetric lifting yielded higher compression than the asymmetric lifting. On the other hand, the asymmetric lifting created higher antero-posterial and lateral shear forces than the symmetric lifting. Results also indicated that the current biomechanical model predicted significant lateral shear force for symmetric lifting which was assumed to be negligible by most sagittal models.Item Measured and modeled hand forces and resulting forces at the low back during the pull phase of a lifting task(Texas Tech University, 1991-05) Danz, Mary ElizabethThe purpose of this investigation was to compare measured and modeled hand forces applied to the load during two-handed floor-to-knuckle Lifting tasks in the sagittal plane. The goal of this objective was to determine if dynamic biomechanical models should be supplemented with additional information to accurately model hand forces. Hand force was measured with a strain gage instrumented apparatus which simulated a box-type container with handles. The measured hand forces were synchronized with video joint displacement data and load liftoff. Five male subjects performed lifting tasks for two experiments to determine the effects of speed of lifting motion, frequency of lift, percentage of maximum acceptable weight and weight of load on peak hand forces and resulting peak forces at the low-back. A dynamic biomechanical model was used to calculate hand forces and low-back forces. Measured and modeled hand forces were comparable for the middle (carry) portion of the lift, but deviated substantially at the beginning (pull) and ending (placement) phases of the lift. The measured hand forces exhibited a steep spike during the pull phase of the lift which was not evident in the modeled hand forces. The peak magnitudes of the measured hand forces were significantly greater than the modeled values for all lifting tasks. The occurrence of peak measured hand forces was distributed about the liftoff, indicating that peak hand force occasionally occurred just before liftoff. The peak compression and shear forces at the low-back calculated with input of measured hand forces were greater than peak modeled low-back forces for the normal, comfortable speed of lift, and significantly greater for the fast speed of lift. The steep peak at the pull phase in compression and shear forces at the low-back plotted over the duration of the lifting tasks was also evident for most lifting tasks. The results of this investigation indicate that the dynamic biomechanical model should be supplemented with a static model of the pull phase of the lift to more accurately represent the peaking of actual hand forces and the resulting compression and shear forces at the lowback.Item Psychophysical lifting capacity over extended periods(Texas Tech University, 1986-05) Fernandez, Jeffrey E.