In this PhD thesis, a novel experimental technique has been implemented to study the variables controlling the undulatory locomotion of a tiny worm. Well known for its elegant slithering motion and simple biology, the millimetre-sized nematode Caenorhabditis elegans was chosen to serve as a model organism for our work. The emphasis of this thesis, as embodied by three separate research projects, has been to study the passive and active biomechanical properties of C. elegans, as well as to investigate inter-worm interactions. Micropipette deflection has been used to directly probe forces in a time-resolved manner and with high dynamic resolution. The viscoelastic material properties of C. elegans were explored on a biologically and structurally relevant length scale, and the elastic properties of the body were quantified. Furthermore, the soft tissue was found to behave as a shear-thinning fluid: a non-Newtonian property that has interesting implications on the undulatory locomotion strategy of the nematode. Micropipette deflection furthermore allowed for measurements of the active swimming dynamics of C. elegans. Our experiments quantified the drag coefficients of the tiny worm as well as the viscous forces present in its swimming motion. Swimming experiments were performed in a normal buffer solution, in the confinement of solid boundaries, as well as in fluids with increased viscosities, and the dynamics of the gait modulating worm was investigated. Finally, the binary interactions between two swimming nematodes were studied, utilizing the high micromechanical control provided by the micropipette-based technique. Our findings provide new insight into the physics of undulatory locomotion and active materials in general. / Thesis / Doctor of Philosophy (PhD)

Previous analyses of mandibular biomechanics have incorporated a wide variety of approaches and variables in attempts at describing the relationships between the forces generated by the muscle and the forces of resistance at the dentition and temporomandibular joints. The most difficult element to determine in man has been the role of the joint forces which require indirect analyses. A critical literature review points out the problems associated with previous analyses of mandibular mechanics and predictions of joint loading and the need for the incorporation of all relevant anatomical and physiological parameters in order to realistically quantify these relationships. A computerized mathematical model of human mandibular biomechanics for static functions is presented which allows the determination of forces occurring at the dentition and the joints due to the individual muscle force contributions. Utilizing the principles of static equilibrium the model provides for the determination of these forces for any individual for whom the necessary input parameters have been derived. Anatomically, this model requires the designation of the three dimensional coordinates of the origin and insertion points of nine pairs of masticatory muscles, any position of tooth contact, and the temporomandibular joint positions. Determination of the forces generated by the individual muscle groups, and therefore the overall muscle force resultant acting on the system, is given by the product of a number of physiological parameters. These include the physiological cross-section, the intrinsic force per unit of cross-sectional area, and the relative activation level of each muscle for the specific static function. Also required is the three dimensional orientation of tooth resistance force at the designated position of tooth contact, as well as that of the left joint force in the frontal plane. This information reduces the variables in the equilibrium equations to a determinate number which has a single unique solution for each of the tooth and two joint resistance forces. The magnitudes as well as three dimensional orientations of the resultant vectors of the muscles, the tooth resistance force and the two temporomandibular joints are thereby determined mathematically. Both bilaterally symmetrical and unilateral clenching functions as well as three intervals near the intercuspal position of chewing were tested with this model using data derived from literature sources from real subjects. This data was incorporated into a hypothetical average individual data file. Using this data, derivation of the magnitudes and orientations of muscle and tooth forces were made providing predictions as to the nature of temporomandibular joint loading for this individual. The extent of muscle force generated for static maximal clenching tasks modeled was a maximum of 1000 to 1200 N during intercuspal clenching. The orientation of muscle force with respect to the occlusal plane varied from about 90 degrees in the lateral plane, for more posterior molar functions, to 64 degrees for incisal functions. Maximal tooth resistance forces were around 500 to 600 N at the molars versus only 130 to 140 N at the incisors. Unilateral functions showed the working side joint to be more heavily loaded than the balancing side especially for a more posterior function (i.e. molar). Less muscle and therefore tooth force was produced unilaterally but with the benefit of even less residual joint force. Thus, unilateral functions appear to be much more efficient in terms of the distribution of forces between the dentition and joints. Variation in tooth orientation produced variations in both the orientation and magnitudes of the joint forces exhibiting a functional interrelationship of these forces. Based on the analysis in general, the joints were predicted to be capable of resisting up to 300 N of force per side directed anterosuperiorly at about 60 to 100 degrees in the lateral plane. More divergent forces at the joints were found to be of substantially lower magnitude in the lateral and frontal planes. These findings are in good agreement with other studies. / Dentistry, Faculty of / Graduate

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The biomechanics of the overhead throw has been extensively studied in regards to baseball pitching. However, an understanding of the proper mechanics needed to successfully throw a football has not previously been investigated. Thus, the purpose of this study was to investigate the kinematics, kinetics, and electromyography of the football throws in elite quarterbacks. Three collegiate quarterbacks were evaluated using a multi-camera motion capture system and electromyography electrodes. The results of this study are able to give a breakdown in the types of mechanics needed in each of the phases of the throw. This study demonstrated that during the early cocking phase, most of the movement seen in the upper body occurs in the frontal plane to abduct the shoulder. During the late cocking phase, the shoulder holds a constant abduction angle and begins to externally rotate. The shoulder reaches a value of 117° of external rotation, much less than has previously been reported. During the acceleration phase, the shoulder rapidly internally rotates as well as horizontally adducts. Once the ball is released, the shoulder has to produce large forces and muscle activity to slow down the rotation. These results will be able to give coaches and players a tool for what to look for when evaluating the mechanics of an individual.

The experiments presented in this thesis provide novel insight into two scarcely studied areas in the field of lateral hip impact biomechanics. The high energy nature of hip impacts requires high sampling rates for accurate study of hip impact dynamics. However, to date only optical motion capture, with relatively lower sampling rates (240-400 Hz), has been used to measure pelvic deflection during hip impact experiments with human participants. As such, the results from the first study compared the differences between two measurement systems (3D optical motion tracking and 2D high speed videography) in measuring common variables of impact biomechanics (peak force, time to peak force, peak deflection, time to peak deflection and energy absorbed). Although significant differences were seen between systems in measuring TFmax and Emax, the magnitude of differences were at or below 5% of the total magnitude of each measured variable. Furthermore, averaging impacts within a subject reduced the differences between systems for Emax. Furthermore, this study showed the effect of sampling rate on measuring hip impact dynamics, and how sampling at lower frequencies affects the aforementioned variables. Tests on the effect of sampling rate found differential effects contingent on the dependent variable measured. Sampling as low at 300 Hz, significantly reduced measures of Fmax and Dmax, but only by on average 0.7 and 0.5 %, respectively. Whereas measures of TFmax and TDmax increased by on average 9.5 and 6.8 %. Sampling Emax at 500 Hz and 300 Hz increased measures of impact absorption by 2.2 and 2.8 % respectively. Sampling at 4500 Hz was the lowest sampling rate that was not significantly different from 9000 Hz across all dependent variables. The second study in this thesis investigates the influence of contact area on load distribution during lateral hip impacts. In summary, this study shows that all three time-varying signals (Ft, FTt and Dt ) were significantly correlated with time-varying contact area (Ct). These results lend support to the possibility of modeling lateral hip impacts with contact models, but provide little support for a Hertzian model adaptation. Analysis on the relationships between body mass and BMI found both anthropometric measures to correlate significantly with peak impact force, but not with peak impact force directed to the greater trochanter. These results bring into question the feasibility of modeling hip fracture risk with body mass or BMI as inputs, without further investigating the distribution of impact force to the greater trochanter. In this study only contact area was significantly correlated with all measures of GT specific loading, and has never before been implemented in predictive modelling of hip fracture risk. Finally, this study found that although effective mass, total body mass and BMI were significantly correlated with the contact area at peak force, they only accounted for 21, 22 and 33% of the variance in CA. Altogether, this study sheds new light on the role that contact area plays in lateral hip impact loading and the importance of understanding load distribution during lateral hip impacts. It also highlights the importance of moving towards predictive models that incorporate more robust estimate of body composition and geometry, with hopes that these will better help estimate the risk of hip fracture. Overall, this thesis provides insight into the expected differences between measuring hip impact dynamics with two, relatively different measurement techniques. In addition, it highlights the need for further study on the relationship between contact geometry and hip fracture risk, something not currently implemented in most hip fracture risk models.

Prolonged periods in sitting or standing may negatively influence worker health. Integration of sit-stand workstations has attempted to mitigate these deleterious effects, and has generated positive results in terms of postural discomfort, injury risk and worker fatigue. Identification of how identical tasks are affected by sitting and standing is necessary to take advantage of loading differences between these configurations. The purpose of this research was to determine if differences in workplace configurations between seated and standing postures created changes in posture or muscular activity levels during manual materials handling tasks. Twenty male and twenty female participants performed four manual materials handling tasks: a 40N static push, a 40N static pull, a weighted bottle transfer set at 15% of the participant’s maximal arm elevation force, and a light assembly task in sitting and standing. Upper extremity electromyography was collected at 8 sites, and changes in local joint moments and body discomfort were calculated. Interactions between task and sit/stand configuration resulted in increases of up to 500% in some joint moments, 94% in EMG activity and 880% in some local body discomfort regions when tasks were completed in sitting. A main effect of sitting appeared primarily in joint moments and muscle activity, and generally resulted in increased loading in sitting. Important exceptions existed, which included resultant wrist joint loading 8.2 times larger in standing, and foot/shank discomfort increasing by up to 609%. Task differentially affected all EMG outputs, as well as most local joint moments and body discomfort regions. Future recommendations regarding upper extremity exposures during manual materials handling tasks should consider placing workers in standing postures instead of seated ones to minimize musculoskeletal loading to the upper extremity. In addition, the effects of task and sit/stand configuration should be considered in order to leverage differences between these positions, with tasks in standing generally resulting in decreased musculoskeletal disorder risks.

Thesis (PhD) - Swinburne University of Technology, Faculty of Engineering and Industrial Sciences, 2006. / A thesis submitted for the degree of Doctor of Philosophy, [Faculty of Engineering and Industrial Sciences], Swinburne University of Technology, 2006. Typescript. Includes bibliographical references (p. 251-256)

ACL (anterior cruciate ligament) injuries of the knee joint alter biomechanics and may cause abnormal loading conditions that place patients at a higher risk of developing osteoarthritis (OA). There are multiple types of ACL reconstruction (ACLR), but all types aim to restore anterior tibial translation and internal tibial rotation following surgery. Analyzing knee joint contact loads provide insight into the loading conditions following ACLR that may contribute to the long-term development of OA. Ten ACLR subjects, who underwent the same reconstruction, performed gait and cycling experiments while kinematic and kinetic data were collected. Inverse dynamic analyses were performed on processed data using OpenSim to calculate reconstructed and contralateral knee joint contact loads which were then compared between gait and cycling at both moderate and high resistances. Significant differences were found between gait and cycling at either resistance for tibiofemoral (TF) compressive, anterior shear, lateral shear forces, and internal abduction and internal rotation moments for both ACLR and contralateral knees. Anterior shear force was largest for cycling at a high resistance, however, since the ACL provides a posterior restoring force and is more engaged at low flexion angles, adjusting for flexion angles when measuring AP shear forces should be considered. Overall, the calculated loading conditions suggest cycling provided better joint stability by limiting anterior tibial translation and internal tibial rotation compared to gait. The results suggest cycling is a better rehabilitation exercise to promote graft healing and limit abnormal loading conditions that increase the risk of developing OA.