Maintaining dynamic balance during walking is a major challenge in many patient populations including older adults and post-stroke hemiparetic subjects. To maintain dynamic balance, whole-body angular-momentum has to be regulated through proper foot placement and generation of the ground-reaction-forces. Thus, the overall goal of this research was to understand the mechanisms and adaptations used to maintain dynamic balance during walking by analyzing whole-body angular-momentum, foot placement and ground-reaction-forces in older adults and post-stroke subjects. The analysis of healthy older adults showed that they regulated their frontal-plane angular-momentum poorly compared to the younger adults. This was mainly related to the increased step width, which when combined with the dominant vertical ground-reaction-force, created a higher destabilizing external moment during single-leg stance. The results also suggested that exercise programs targeting appropriate foot placement and lower extremity muscle strengthening, particularly of the ankle plantarflexors and hip abductors, may enhance balance control in older adults. During post-stroke hemiparetic walking, ankle-foot-orthosis and locomotor therapy are used in an effort to improve the overall mobility. However, the analyses of healthy subjects walking with and without a solid ankle-foot-orthosis showed that they can restrict ankle plantarflexor output and limit the successful regulation of angular-momentum and generation of forward propulsion. Thus, the prescription of solid ankle-foot-orthosis should be carefully considered. The analysis of hemiparetic subjects walking pre- and post-therapy showed that locomotor training did not improve dynamic balance. However, for those subjects who achieved a clinically meaningful improvement in their self-selected walking speed, their change in speed was correlated with improved dynamic balance. Also, improved balance was associated with narrower mediolateral paretic foot placement, longer anterior nonparetic steps, higher braking ground-reaction-force peaks and impulses, higher (lower) propulsive ground-reaction-force peaks and impulses from the paretic (nonparetic) leg, and higher vertical ground-reaction-force impulses from both legs during the late stance. Further, simulation analyses of hemiparetic walking highlighted the importance of ankle plantarflexors, knee extensors and hip abductors in maintaining balance and revealed the existence of compensatory mechanisms due to the paretic leg muscle weakness. Collectively, these studies showed the importance of ankle plantarflexors and hip abductors in maintaining dynamic balance. / text

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The objective of the work carried out in this thesis was to develop analytical and computational tools to model and investigate musculoskeletal human joints. It was recognised that the FEA was used by many researchers in modelling human musculoskeletal motion, loading and stresses. However the continuum mechanics played only a minor role in determining the articular joint motion, and its value was questionable. This is firstly due to the computational cost and secondly due to its impracticality for this application. On the other hand, there isn’t any suitable software for precise articular joint motion analysis to deal with the local joint stresses or non standard joints. The main requirement in orthopaedics field is to develop a modeller software (and its associated theories) to model anatomic joint as it is, without any simplification with respect to joint surface morphology and material properties of surrounding tissues. So that the proposed modeller can be used for evaluating and diagnosing different joint abnormalities but furthermore form the basis for performing implant insertion and analysis of the artificial joints. The work which is presented in this thesis is a new frame work and has been developed for human anatomic joint analysis which describes the joint in terms of its surface geometry and surrounding musculoskeletal tissues. In achieving such a framework several contributions were made to the 6DOF linear and nonlinear joint modelling, the mathematical definition of joint stiffness, tissue path finding and wrapping and the contact with collision analysis. In 6DOF linear joint modelling, the contribution is the development of joint stiffness and damping matrices. This modelling approach is suitable for the linear range of tissue stiffness and damping properties. This is the first of its kind and it gives a firm analytical basis for investigating joints with surrounding tissue and the cartilage. The 6DOF nonlinear joint modelling is a new scheme which is described for modelling the motion of multi bodies joined by non-linear stiffness and contact elements. The proposed method requires no matrix assembly for the stiffness and damping elements or mass elements. The novelty in the nonlinear modelling, relates to the overall algorithmic approach and handling local non-linearity by procedural means. The mathematical definition of joint stiffness is also a new proposal which is based on the mathematical definition of stiffness between two bodies. Based on the joint stiffness matrix properties, number of joint stiffness invariants was obtained analytically such as the centre of stiffness, the principal translational stiffnesses, and the principal rotational stiffnesses. In corresponding to these principal stiffnesses, their principal axes have been also obtained. Altogether, a joint is assessed by six principal axes and six principal stiffnesses and its centre of stiffness. These formulations are new and show that a joint can be described in terms of inherent stiffness properties. It is expected that these will be better in characterising a joint in comparison to laxity based characterisation. The development of tissue path finding and wrapping algorithms are also introduced as new approaches. The musculoskeletal tissue wrapping involves calculating the shortest distance between two points on a meshed surface. A new heuristic algorithm was proposed. The heuristic is based on minimising the accumulative divergence from the straight line between two points on the surface and the direction of travel on the surface (i.e. bone). In contact and collision based development, the novel algorithm has been proposed that detects possible colliding points on the motion trajectory by redefining the distance as a two dimensional measure along the velocity approach vector and perpendicular to this vector. The perpendicular distance determines if there are potentially colliding points, and the distance along the velocity determines how close they are. The closest pair among the potentially colliding points gives the “time to collision”. The algorithm can eliminate the “fly pass” situation where very close points may not collide because of the direction of their relative velocity. All these developed algorithms and modelling theories, have been encompassed in the developed prototype software in order to simulate the anatomic joint articulations through modelling formulations developed. The software platform provides a capability for analysing joints as 6DOF joints based on anatomic joint surfaces. The software is highly interactive and driven by well structured database, designed to be highly flexible for the future developments. Particularly, two case studies are carried out in this thesis in order to generate results relating to all the proposed elements of the study. The results obtained from the case studies show good agreement with previously published results or model based results obtained from Lifemod software, whenever comparison was possible. In some cases the comparison was not possible because there were no equivalent results; the results were supported by other indicators. The modelling based results were also supported by experiments performed in the Brunel Orthopaedic Research and Learning Centre.

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The intuitive link between a runner’s gait and their metabolic cost of running, or running economy (RE), has led to many trying to compare the running mechanics of economical runners to those of less economical runners. However using this approach has created controversy about whether running mechanics meaningfully contribute to RE. Additionally only a limited number of studies use a broad, explorative, inter-disciplinary approach, encompassing physiological parameters, flexibility, kinematics, kinetics and muscular activity. The purpose of this thesis was to primarily assess ‘self-optimisation’ through considering acute and short-term adaptations to running mechanics and RE. To assess the biomechanical and physiological mechanisms behind changes to RE three studies were conducted, in addition to a fourth study which investigated biomechanical familiarisation. Study one investigated whether there were any biomechanical or physiological changes in beginner runners after 10 weeks of running and whether any of these changes contributed to a change in RE. There was an 8.4% improvement in RE (224  24 vs. 205  27 mL.kg-1.min-1) and an increase in treadmill time-to-exhaustion (16.4  3.2 vs. 17.3  2.7 min), but no change in ̇ 2max, minute ventilation or heart rate. Several kinematic, kinetic and flexibility measures were found to change over time, but joint moments and stiffness remained similar, with knee extension at toe-off, rearfoot velocity at touch down and timing of peak dorsiflexion explaining 94.3% of the variance in change in RE. Results from study one suggested that changes in muscular activity might have contributed to kinematic differences, and subsequently an economical gait. Specifically, as joint moments were unchanged after 10 weeks it is possible that muscular coactivation may have changed since varying levels of agonist-antagonist activation can produce the same joint moment. Consequently study two examined the relationship between muscular coactivation and the metabolic cost of running, as thus far there was conflicting evidence. Results showed that in trained, recreational runners greater thigh coactivation was associated with a greater metabolic cost of running. Furthermore, the speed of running was found to affect the level of coactivation at the shank and of the flexor-flexor muscle pair, with less coactivation reported at faster submaximal speeds. The final part of the thesis focused on a manipulation investigation into barefoot (BFT), minimalist shod (MS) and shod (SH) running. Applying the novel findings from studies one and two to this topical area would hopefully provide new insight into the 3 BFT running debate. Prior to applying this knowledge of kinematic and muscular activity changes in relation to RE whilst running BFT, an investigation into the time required to become familiar with barefoot treadmill running was needed. Results revealed that barefoot familiarisation was characterised by less plantarflexion and greater knee flexion at touch down, whilst stride length appeared to be adopted instantaneously. Reliability (intra-class correlations) and accuracy (standard error of mean) of the kinematic data appeared strongest once individuals had been running for 20 mins. Furthermore there were no significant differences in the kinematics after 20 mins of running. The final study considered how changing the levels of proprioception and cushioning (BFT, MS and SH) influenced RE and the potential running mechanics that contributed to any changes in RE. The ramifications of such changes on injury risk were also considered by investigating impact accelerations, effective mass and pronation. Additionally, the effect of naturally changing stride length from a shorter BFT stride to a longer SH stride on RE were examined. Heightened proprioception and no external cushioning (BFT running) appeared to improve RE by at least 5% regardless of stride length, when compared to SH running with a SH stride length. However less proprioception and no external cushioning (MS running) only improves RE, compared to SH running with a SH stride length, when runners run with their SH stride length, rather than their shorter BFT stride length (~2.5% shorter). Improvements in RE are attributed to a lower vertical oscillation and effective mass, greater dependency on efficient, Type I muscles i.e. tibialis anterior, and less plantarflexion at toe-off. However higher impact accelerations, earlier heel off and low pronation angles, suggest there may be an increase in injury risk. Therefore the findings from this thesis have demonstrated that runners naturally selfoptimise the way they run. This is seen both as an acute (changes in footwear) and short-term (10 weeks) response to changing running gait. Study two demonstrated that economical runners appear to use different muscular strategies, with study one and four showing they also adopt specific movement patterns that may promote efficient storage and release of elastic energy. Additionally study three found that runners can become familiar with BFT treadmill running in 20 minutes. It is also important to note that economical biomechanical adjustments do not always favour a reduction in injury risk. But the thesis findings seem to suggest that perhaps performance denominates in terms of self-optimisation, rather than injury prevention.

<p>Abstract Cranial base angle, vertebral dimensions, vertebral curvature, and locomotive behavior differ among Homo, Pan, and Gorilla; but many distinctions are obfuscated by dimensional and behavioral overlap among the genera and their fossil relatives. To address these issues, cranial and vertebral measurements (suites) were examined among Homo, Gorilla, and Pan as representative hominines for their posture and locomotion or positional-locomotory complexes. An additional analysis considered Australopithecus afarensis (A.L. 288-1 and A.L. 333) for comparative purposes. Using size-adjusted values with applied Bonferroni adjusted alpha levels, significant results for both the Kruskal-Wallis H-test and Mann-Whitney U-tests indicated statistically significant differences among species for cranial base angle (p = 0.000) and vertebral body dimensions with coronal and sagittal facet orientation (p = 0.000 ? 0.003). Detected significance was present for thoracic and lumbar curvature (p = 0.000) and positional-locomotory complex (p = 0.000) among species, albeit only cranial base angle was significant for the Pan-Gorilla comparison. Moreover, post hoc Spearman?s rho tests indicated significant results (p = 0.000 ? 0.009) with strong positive and negative correlations throughout the column for each species. However, no pattern among vertebral measurements throughout the vertebral column was detected. Lastly, Multinomial Logistic Regression yielded a correct classification percentage with significant model fit (p = 0.000) of 86.4% for the cranial base, 82.8-97.0% for all subsequent vertebrae, and 80.3% for thoracic and lumbar curvature among species. Positional locomotory complexes were also significant (p = 0.000) and yielded a correct classification percentage of 82.2% among bipeds and the two modes of knuckle-walking practiced by Pan and Gorilla respectively. However, misclassifications between human and nonhuman primates for cranial base angle and calculated vertebral curvature suggest that these variables are not viable for assessing either genera or positional-locomotory complexes. Lastly, both Australopithecus afarensis specimens (A.L. 288-1 and A.L. 333) were incorrectly classified. The A.L. 288-1 specimen identified as Homo and the misclassification of A.L. 333 as Pan suggest either species or vertebra misidentification. Overall, the data indicate that both vertebral corpus dimensions and coronal and sagittal facet orientations differ significantly among hominine taxa and can distinguish species and their respective posturo-locomotory complex. As for the evolutionary implications, human bipedalism is distinct as related to cranial base angle and vertebral measurements; however significant differences between Pan and Gorilla suggest homoplasy among measurements and denote parallelism for the emergence of knuckle-walking.

Since its first measurement in 1679, the usefulness of the location of whole body centre of mass (COM) data has progressed from having largely theoretical value into being an instrument with several diagnostic and applied scientific uses. This thesis describes first the biomechanical and measurement theory foundation of COM research and then details the historical development of methods to measure COM location and the various applied uses of this variable. Original research data presented in this thesis then go on to provide the first direct measurements of COM movement in walking humans. A second study quantifies the accuracy of the most commonly used current technique to quantify COM location (the kinematic segmental method) by determining the limits of agreement between it and a direct measurement method (the reaction-board), in lying and running subjects. In the latter studies a novel reaction-board measurement method is developed making use of life-sized projections of subjects in various stride positions and used to place runners into recumbent static running positions. These data demonstrate that reaction-board and segmental methods report COM locations with a mean difference of 1.6cm and agree to within limits of 6.0cm for the location of COM in recumbent individuals. The final study described in this thesis compares single COM measurements made using two kinematic segmental methods (models) to a direct suspension technique of measuring COM location. The suspension technique used is adapted from the original method of determining COM location upon which kinematic segmental methods derive their origin. The data show that both cadaver-derived kinematic models of COM, and kinematic models derived from live human data, differ from a direct COM suspension method, and that cadaver based estimates display greater accuracy (agreement with the direct suspension method). This study also uniquely provides information on the effect of whole body mass, body fat or body water on the accuracy of segmental models in male subjects.

Thesis. 1977. M.S.--Massachusetts Institute of Technology. Dept. of Physics. / Microfiche copy available in Archives and Science. / Includes bibliographical references. / by Patricia Canty. / M.S.

Aims: To determine improvements in third metacarpal (Mc3) condylar microanatomy attributable to preconditioning exercise. To investigate developmental causes of Mc3 condylar fracture. Methods: Twelve Thoroughbred horses were raised at pasture; six received preconditioning exercise from 10 days. Calcein labels were administered 19 and 11 days prior to euthanasia at 18 months. Six horses also received 2 seasons of race-training and were euthanised at 3 years. Slices were taken from the distal Mc3 condyle in the frontal and dorsal- and palmar-oblique frontal planes, scanned with DXA and macerated (frontal slices) or embedded in PMMA (oblique slices). Articular calcified cartilage (ACC) and subchondral bone (SCB) in oblique slices were imaged using confocal scanning light microscopy and quantitative backscattered electron scanning electron microscopy. ACC and SCB in the palmar slice lateral parasagittal grooves were imaged using μCT and nanoindentation tested. Results: Characteristic spatial variations in ACC and SCB histomorphometric parameters were present, none of which was significantly related to preconditioning exercise. Thickened, aberrantly mineralised ACC was found in 13/24 parasagittal grooves in the palmar slices and on the sagittal ridge of 4/12 dorsal slices of 18-month-old horses. Deep to thickened ACC, SCB had an open marrow structure, having not adopted the buttress morphology of the normal SCB plate. SCB in 3-year-old horses had incorporated early ACC defects as notches in parasagittal grooves and a hyaline cartilage island in a sagittal ridge. ACC was less stiff and SCB more stiff in affected than unaffected parasagittal grooves. Chondroclastic resorption in the parasagittal groove may be retarded as early as 3-6 months, possibly due to localised inhibition of ACC mineralisation. Linear defects in the Mc3 parasagittal groove may develop prior to entry to race training and are not significantly affected by preconditioning exercise. Early identification of affected individuals should aid in reducing condylar fracture risk.

Sound arriving at the ear causes the vibration of the sensory tissues, including the basilar membrane (BM), inside the cochlea and, in turn, leads to inner hair cell excitation and auditory nerve fiber (ANF) responses. The goal of this study is to better understand the mechanics of inner hair cell excitation which leads to hearing. BM motion and ANF tuning are generally very similar, but the ANF had appeared to be unresponsive to a plateau mode of BM motion that occurs at frequencies above an ANF's characteristic frequency (CF). We recorded ANF responses from the gerbil, concentrating on this supra-CF region. We observed a supra-CF plateau in ANF responses at high stimulus level, indicating that the plateau mode of BM motion can be excitatory. Quantitative aspects of our findings suggest that the differential longitudinal motion that occurs within the traveling wave but not the plateau mode increases the sensitivity of inner hair cell excitation. The main findings of this study include: The detection of the plateau threshold within the supra-CF region of the ANF tuning curve. A larger BM motion was necessary for an ANF to reach a threshold response within the plateau region than the traveling wave region, based on the previous lack of ANF plateau threshold detection and a comparison to the BM plateau levels in the literature. Stimuli used in this study, even though unnaturally high in level, advanced our understanding of cochlear mechanics. However, at high sound pressure levels used, the middle ear generated subharmonic distortions that could produce confounding effects in the plateau responses. Hence, we also characterized the subharmonics and were able to rule out the possibility that they were solely responsible for the plateau responses we observed.