Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 49-50). Also available via the Internet.

Introduction: The role of muscle forces in determining bone micro-architecture and strength in children is poorly understood as limited evidence relies on surrogate measures of muscle force such as muscle size. The objective of this thesis was to explore the role of muscle area, peak forces from neuromuscular performance tests and physical activity in determining bone properties at the radius and tibia in children. Methods: 37 boys and 42 girls (mean age 10.5; SD 1.6y) had their dominant forearm and lower leg imaged using peripheral quantitative computed tomography (pQCT) and high resolution pQCT (HR-pQCT). Bone mass, density, area and estimated strength were assessed. Muscle area was determined from the pQCT scans and grip strength measured via a handheld dynamometer. Peak force from a single maximal push-up performed on force platforms and the number of standard push-ups completed in a single attempt were recorded. Countermovement and standing long jump maximal forces were recorded, impulse and power were calculated, and average standing long jump distance was measured. Physical activity was measured using the Physical Activity Questionnaire for Children. Sex, maturation (estimated age from peak height velocity), weight and limb length (ulna and tibia) were controlled in the linear regression models. Variance predicted (R2) by models using muscle area, neuromuscular performance measures as independent predictors (squared partial r) of bone properties are reported. Results: Grip strength and muscle area independently predicted 14-18% of the variance in bone area at the distal radius and 9-22% of the variance in bone strength at the distal and shaft sites of radius. Peak push-up force predicted 10% of the variance in trabecular number at the distal radius. Muscle area independently predicted 5-28% and countermovement and standing long jump forces and impulses predicted 6-10% of the variance in bone area, cortical content or density at the tibia shaft. Standing long jump power predicted 5-8% of the variance in bone area and cortical density at the tibia shaft. Physical activity predicted 9% of the variance in trabecular number at the distal tibia. Discussion: Thesis findings support the use of muscle area as a surrogate for muscle forces and identified neuromuscular performance measures that will guide targeted exercise interventions aiming to optimize bone strength development in children.

The present work has arisen from a continuing need to improve the performance of round-steel lifting (hoist) and mining chains, and the hypothesis that this might be done by modification of the link geometry. The finite element (FE) method has been used to analyse the stresses in the chain links. The effects of link length and the bend radius in the crown were considered. The effect of maintaining link length constant and departing from the conventional straight sided (standard) geometry by changing the link shape from eight shape (pinched), through straight sided, to elliptical has been examined. Mining chains made from non-circular section rod have also been investigated. The finite element work has been supported by practical investigations using through-yield strain gauges.

Improvement in the mechanical properties of soil by lime (Ca(OH)2) results from the formation and development of cementitious phases. The newly formed phases interlock and bond the soil particles together increasing the strength of the soil and improving its durability. In the present work the engineering properties including plasticity, density, compressive strength, porosity, permeability and frost heave resistance were investigated for cylindrical specimens of a Devonian Red-Marl containing various amounts of lime (2-14 wt%), cured for up to 24 weeks at different temperatures (25, 50 and 75°C) and in different environments (sealed, unsealed, air, nitrogen and carbon dioxide). Mineralogical analysis of Red-Marl as well as montmorillonite, kaolinite and illite and also the reaction products of these materials with lime (10-20wt%) were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy with energy dispersive analysis (TEM/EDAX) and thermogravimetric analysis (TG). The Red-Marl was found to consist of illite/glauconite, quartz and feldspar with minor amounts of chlorite and haematite. It was observed that curing temperature has a dramatic effect on the reaction between soil and lime and on the engineering properties of the cured soil-lime samples. At normal curing temperatures the plasticity index decreases markedly and the strength increases only marginally with increasing lime content and curing time. At elevated temperatures, the strength sharply increases in a moist environment whereas lack of sufficient moisture virtually stops any further reaction. It was observed that carbonation of lime does not contribute to any great extent to the increase in strength and should be minimized. The addition of a small amount of NaCl in conjunction with lime may accelerate the reaction slightly. It was observed that the nature of clay soil alters by adding lime and the cured materials show a greater durability with a significant improvement in properties such as pore structure, permeability, volume stability and frost resistance. The analyses of the newly formed cementitious material shows it to consist of almost amorphous gel forming foil-like membranes and fine filaments which interconnect the soil particles. Morphological development and microstructural analyses of the gel suggest that it is formed as a result of the progressive breakdown of the original clay particles by reaction with lime.

The primary objective of the present study was to examine the effects of three resistance training programs that varied in either inter-set rest interval length or volume of training on the development of strength and muscle fiber size. Male subjects with a minimum of 1- year of regular resistance training experience were randomly assigned to one of three, 8- week training groups. The first set of all three programs was similar in that 10 repetitions to failure were performed. In program A (n=5) the load (78% 1-RM) remained constant for all subsequent sets. Program B (n=7) also used a constant load (80% 1-RM), however the rest interval was reduced from 3 minutes (as in Program A) to 1 minute. Subjects in this group performed additional sets to equate training volume with Program A. The training load for Program C (n=7) was progressively reduced (80% to 70% 1-RM) before each subsequent set to ensure the completion of 10 repetitions. Therefore, the volume performed was greater than that of Programs A and B. Single arm elbow flexion 1-RM increased by 12.3 +/- 3.5% in Program A, 16.5 +/-3.5% in Program B, and 14.1 +/- 4.7% in Program C. Gains in 10-RM equaled 16.3 +/-4.1%, 18.0 +/- 5.0% and 13.9 +/- 3.1% for Programs A, B and C, respectively. Although these increases in strength were significant (p<.05), there were no differences in the magnitude of change between the three groups. Increases in the cross-sectional area of type I and type II muscle fibers were similar after all three training programs. The second objective of this investigation was to measure the acute neuromuscular fatigue produced during a single session of each of the training protocols incorporated in the longitudinal part of this study. Force and IEMG during maximal isometric voluntary contractions (MVIC) along with blood lactate were assessed prior to and upon the completion of each protocol. Subjects performed 3 sets of single-arm elbow flexion to failure using a training load of approximately 77.3% 1-RM in Protocol A. During Protocol B, subjects utilized the same constant resistance but the rest-intervals between each set were 1 minute. Protocol C was designed to maintain the repetitions completed per set at 10 while utilizing 3-minute rest interval. During Protocol C, the load used during the first set was equal to that used during Protocol A and was then reduced by about approximately 5% for each of the two subsequent sets. Protocol A and Protocol B resulted in similar reductions in MVIC, whereas Protocol C (24.8 +/- 7.2%) resulted in a significantly (p<.05) greater reduction in MVIC than Protocol A (20.2 +/- 7.7%). Protocols A and B elicited similar reductions in the force-time curve of the MVIC. A significantly greater reduction in the final 300ms of the force-time curve was observed following Protocol C (in comparison to Protocol A) (p<.05). There were no significant changes in IEMG after subjects performed protocols A and B. A significant time effect (with no interaction effect) in IEMG was observed following the comparison of Protocol A with Protocol C. Blood lactate increased significantly in response to all three protocols with no differences between the protocols. The third objective of this study was to compare the magnitude of resistance training-induced acute fatigue before and after the completion of 8 weeks of resistance training specific to the fatigue protocols used. The magnitude of resistance training-induced acute neuromuscular fatigue remained unchanged following the resistance training programs. The results appear to indicate that acute neuromuscular fatigue produced during resistance training may not be associated with the chronic increases in muscle strength and size. / Graduate

Magister Artium (Sport, Recreation and Exercise Science) - MA(SRES) / Over the years, cricket has progressed into a game of immense physical prowess, and evolved from a traditional and conservative game into a professional sport requiring very high levels of fitness and skill. The ability to throw a ball at high velocity and with great accuracy is critical for successful performance in many ball sports, including cricket. The aim of this study focussed on examining the relationship between isokinetic strength of the shoulder complex and throwing velocity amongst club cricketers in the age group of 18-32 years. The study used a quantitative methodology with a cross-sectional research design. A convenient sample of 40 male cricketers from the University of the Western Cape was tested. Isokinetic strength of external rotators (ER), internal rotators (IR) and ratios were measured using the Biodex Pro System 4 isokinetic dynamometer at two speeds, namely, 60º•sec-¹ and 90º•sec-¹. Throwing velocity was measured using a calibrated Cordless Speed/Radar Gun. The major findings of this study were the significant correlations between IR at 60º•sec-¹ and throwing velocity for the first team (r = 0.72; p = 0.01), second team (r = 0.67; p = 0.03), third team (r = 0.73; p = 0.01) and fourth team (r = 0.69; p = 0.02). The correlation between the strength ratio at 60º•sec-¹ and throwing velocity was significant for the first team (r = 0.76; p = 0.01), second team (r = 0.83; p = 0.002), third team (r = 0.70; p = 0.02) and fourth team (r = 0.94; p = 0.0001). In conclusion, shoulder strength plays a significant role in the throwing velocity amongst club cricketers. Specifically, the shoulder internal rotators were found to be a major influence in throwing velocity. Furthermore, the shoulder strength ratio is a strong predictor of shoulder strength performance.

The basic assumption of limit design, that moments are equalized by the formation of a mechanism has proven applicable to steel beams and certain types of frames. It is not known, however, if the theory applies to light metal alloys. Steel possesses a considerable amount of strain hardening which is essential to the formation of plastic hinges in the beam, but some aluminum alloys which have little strain hardening may not be suitable for limit design. Two beam tests were carried out on a twice statically indeterminate beam made of Alcan 65S-T6 aluminum alloy to determine whether the mechanism predicted by the theory of limit design is realized before failure occurs in the beam. Moments and deflections of the beam near failure are compared with theoretical predictions obtained from the theory of limit design and the theory of inelastic bending. The latter, developed by Dr. A. Hrennikoff in 1918, is more "exact" than the theory of limit design. Test results showed that the beam failed at one of the early plastic hinges, before the mechanism was fully developed. It demonstrated that limit design is not always applicable to beams made of aluminum alloys which have very little strain hardening. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The finite element technique is a powerful method to study the dynamic response of a structure taking into account the effects of ground conditions. However, limitations of computer storage capacity and cost presently prevent its general application to three-dimensional problems. In this thesis it is shown that three-dimensional problems can be analyzed by applying appropriate modification factors to two-dimensional (plane strain) analyses. Modification factors are first determined analytically by comparing the dynamic response of both strip and rectangular footings (uniform shear stress) for a range of input frequencies. It is found that for input frequencies which are less than the fundamental period of the soild layer the modification factor is essentially independent of the input frequency. This suggests that the modification factors could be obtained from static analyses. Modification factors based on static stiffness analyses for both uniform shear stress and uniform shear displacement (rigid foundation) conditions were obtained and were found to be in close agreement with those obtained from the dynamic analyses. Variation of the modification factor with both the depth of the layer and the ratio of the sides of the rectangular base are given in graphical form. These factors may be applied to finite element place strain analysis to predict the dynamic response of three-dimensional structures. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Room temperature tensile tests were performed on aged Fe-Cu and tempered Fe-C martensites to study the strengthening of ferrite, due to dispersions of non-coherent second phase particles over a range of particle sizes. Electron Microscopy was used to determine the structure parameters. Strengthening was observed-in both the aged Fe-Cu, with a soft second phase and the tempered Fe-C martensite with a hard second phase dispersion. In the aged Fe-Cu, the yield strength seems to be due to the bowing out of dislocations between particles - an Orowan- type of mechanism where as in the tempered Fe-C martensite, the strengthening is possibly due to several mechanisms involving cementite dispersions, grain boundaries and excess carbon in solution. Aged Fe-Cu, did not exhibit any appreciable increase in work hardening over that of pure iron. But in the tempered Fe-C martensite, the work hardening was higher than that of pure iron and increased with cementite particle size. It was not possible to explain the observed work hardening behaviour with the help of the existing work hardening theories. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate