1,937 research outputs found
Mass-spring modelling of vault springboard contact
Vaulting is a discipline in Men's and Women's Artistic Gymnastics. While the springboard
contact is not judged, the success of the rest of the vault is underpinned by it. The purpose of
this study was to develop an understanding of the mechanics of the springboard contact
phase of gymnastic vaulting.
An analysis of hopping in place, forward hopping and running jumps on a force platform
showed that the force-mass centre displacement relationship during ground contact
approximated that of a mass rebounding on a linear spring. Subsequently, two mass-spring
models were developed using a symbolic mathematics package. Both models represented the
gymnast as a rigid cylinder, with personalized linear and angular inertia characteristics,
connected at its mass centre to a linear spring. A one spring model combined the springiness
of the gymnast and the springboard in a single linear spring, while a two spring model
treated them as separate linear springs.
Handspring vaults performed by an elite male gymnast at a range of approach speeds and
springboard settings were analysed to provide model inputs. Springboard properties were
empirically determined and revealed that the springboard stiffness varied appreciably
depending upon feet contact position. Given the touchdown kinematics and takeoff angle of
the gymnast, the models estimated spring stiffness and linear and angular takeoff velocities,
the spring stiffness and takeoff vertical velocity estimates showing some sensitivity to spring
angle at touchdown. Simulations in which the touchdown kinematics and spring stiffnesses
were systematically adjusted, identified their influence on takeoff kinematics and provided
an insight into the mechanics of springboard. contact.
Estimated (leg) spring stiffnesses were consistent with those reported in the literature for
other activities and'simulation results showed that simple rebounds accounted for the
majority of the takeoff velocities. Spring angle at touchdown was found to be most effective at modifying each of the takeoff variables, however to produce a selective effect on takeoff required a combination of adjustments to the touchdown. In proposing strategies for gymnasts, their ability to control each of the touchdown variables has to be considered
Gait analysis methods in rehabilitation
Introduction: Brand's four reasons for clinical tests and his analysis of the characteristics of valid
biomechanical tests for use in orthopaedics are taken as a basis for determining what
methodologies are required for gait analysis in a clinical rehabilitation context.
Measurement methods in clinical gait analysis: The state of the art of optical systems capable
of measuring the positions of retro-reflective markers placed on the skin is sufficiently advanced
that they are probably no longer a significant source of error in clinical gait analysis. Determining
the anthropometry of the subject and compensating for soft tissue movement in relation to the
under-lying bones are now the principal problems. Techniques for using functional tests to
determine joint centres and axes of rotation are starting to be used successfully. Probably the last
great challenge for optical systems is in using computational techniques to compensate for soft
tissue measurements. In the long term future it is possible that direct imaging of bones and joints
in three dimensions (using MRI or fluoroscopy) may replace marker based systems.
Methods for interpreting gait analysis data: There is still not an accepted general theory of
why we walk the way we do. In the absence of this, many explanations of walking address the
mechanisms by which specific movements are achieved by particular muscles. A whole new
methodology is developing to determine the functions of individual muscles. This needs further
development and validation. A particular requirement is for subject specific models incorporating
3-dimensional imaging data of the musculo-skeletal anatomy with kinematic and kinetic data.
Methods for understanding the effects of intervention: Clinical gait analysis is extremely
limited if it does not allow clinicians to choose between alternative possible interventions or to
predict outcomes. This can be achieved either by rigorously planned clinical trials or using
theoretical models. The evidence base is generally poor partly because of the limited number of
prospective clinical trials that have been completed and more such studies are essential. Very
recent work has started to show the potential of using models of the mechanisms by which people
with pathology walk in order to simulate different potential interventions. The development of
these models offers considerable promise for new clinical applications of gait analysis
Predicting maximum eccentric strength from surface EMG measurements
The origin of the well documented discrepancy between maximum voluntary and in vitro tetanic
eccentric strength has yet to be fully understood. This study aimed to determine whether surface
EMG measurements can be used to reproduce the in vitro tetanic force â velocity relationship from
maximum voluntary contractions. Five subjects performed maximal knee extensions over a range
of eccentric and concentric velocities on an isovelocity dynamometer whilst EMG from the
quadriceps were recorded. Maximum voluntary (MVC) force â length â velocity data were
estimated from the dynamometer measurements and a muscle model. Normalised amplitude â
length â velocity data were obtained from the EMG signals. Dividing the MVC forces by the
normalised amplitudes generated EMG corrected force â length â velocity data. The goodness of
fit of the in vitro tetanic force â velocity function to the MVC and EMG corrected forces was
assessed. Based on a number of comparative scores the in vitro tetanic force â velocity function
provided a significantly better fit to the EMG corrected forces compared to the MVC forces
(p †0.05), Furthermore, the EMG corrected forces generated realistic in vitro tetanic force â
velocity profiles. A 58 ± 19% increase in maximum eccentric strength is theoretically achievable
through eliminating neural factors. In conclusion, EMG amplitude can be used to estimate in vitro
tetanic forces from maximal in vivo force measurements, supporting neural factors as the major
contributor to the difference between in vitro and in vivo maximal force
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Kinetic Asymmetries During Submaximal and Maximal Speed Running
An important issue for sports scientists, coaches and athletes is an understanding of the factors within a running stride that can enhance or limit maximal running speed. Previous research has identified many sprint-related parameters as potential kinetic limiters of maximal Center of Mass velocity (Chapman and Caldwell, 1983b; Weyand et al., 2001). Bilateral asymmetry is present for many of these parameters during running; however the degree to which such asymmetries change as running speed increases is unknown. It was hypothesized that asymmetries in key sprinting parameters would be larger at maximal speed than all other tested speeds. Kinematics and kinetics were collected from nine female competitive speed and power athletes (age = 21 ±3 years, mass = 60.58 ±7.48 kg, height = 1.64 ±0.07 m) who completed maximal and submaximal sprinting trials on a force-instrumented treadmill. A repeated-measures ANOVA was completed for each parameter to examine the asymmetry differences across speed. The only parameter for which asymmetry was statistically greater (p\u3c0.05) during maximal speed than all other speeds was effective vertical stiffness, in which the level of asymmetry increased incrementally with speed (r2=0.97). Therefore the hypothesis that asymmetries would increase with speed for all key parameters is rejected. Bilateral asymmetries in effective vertical stiffness appeared to be related to asymmetries in both vertical and A/P propulsive impulse at maximal speed. Furthermore, asymmetries in effective vertical stiffness may force runners to resort to a less stable and less coordinated gait, limiting their ability to further increase stride frequency, and thus limiting maximal speed
An inquiry into the theory, causes and consequences of monitoring indicators of health and safety at work
This paper engages in an interdisciplinary survey of the current state of knowledge related to the theory, determinants and consequences of occupational safety and health (OSH). First, it synthesizes the available theoretical frameworks used by economists and psychologists to understand the issues related to the optimal provision of OSH in the labour market. Second, it reviews the academic literature investigating the correlates of a comprehensive set of OSH indicators, which portray the state of OSH infrastructure (social security expenditure, prevention, regulations), inputs (chemical and physical agents, ergonomics, working time, violence) and outcomes (injuries, illnesses, absenteeism, job satisfaction) within workplaces. Third, it explores the implications of the lack of OSH in terms of the economic and social costs that are entailed. Finally, the survey identifies areas of future research interests and suggests priorities for policy initiatives that can improve the health and safety of workers
Control of the upper body accelerations in young and elderly women during level walking
<p>Abstract</p> <p>Background</p> <p>The control of the head movements during walking allows for the stabilisation of the optic flow, for a more effective processing of the vestibular system signals, and for the consequent control of equilibrium.</p> <p>In young individuals, the oscillations of the upper body during level walking are characterised by an attenuation of the linear acceleration going from pelvis to head level. In elderly subjects the ability to implement this motor strategy is reduced. The aim of this paper is to go deeper into the mechanisms through which the head accelerations are controlled during level walking, in both young and elderly women specifically.</p> <p>Methods</p> <p>A stereophotogrammetric system was used to reconstruct the displacement of markers located at head, shoulder, and pelvis level while 16 young (age: 24 ± 4 years) and 20 older (age: 72 ± 4 years) female volunteers walked at comfortable and fast speed along a linear pathway. The harmonic coefficients of the displacements in the medio-lateral (ML), antero-posterior (AP), and vertical (V) directions were calculated via discrete Fourier transform, and relevant accelerations were computed by analytical double differentiation. The root mean square of the accelerations were used to define three coefficients for quantifying the attenuations of the accelerations from pelvis to head, from pelvis to shoulder, and from shoulder to head.</p> <p>Results</p> <p>The coefficients of attenuation were shown to be independent from the walking speed, and hence suitable for group and subject comparison.</p> <p>The acceleration in the AP direction was attenuated by the two groups both from pelvis to shoulder and from shoulder to head. The reduction of the shoulder to head acceleration, however, was less effective in older women, suggesting that the ability to exploit the cervical hinge to attenuate the AP acceleration is challenged in this population. Young women managed to exploit a pelvis to shoulder attenuation strategy also in the ML direction, whereas in the elderly group the head acceleration was even larger than the pelvis acceleration.</p> <p>Conclusion</p> <p>The control of the head acceleration is fundamental when implementing a locomotor strategy and its loss could be one of the causes for walking instability in elderly women.</p
Evaluation of mechanical load in the musculoskeletal system : development of experimental and modeling methodologies for the study of the effect of exercise in human models
Doutoramento em Motricidade Humana, na especialidade de BiomecĂąnicaA major concern of Biomechanics research is the evaluation of the mechanical load and power that the human body develops and endorses when performing high to moderate sport activities. With the purpose of increasing performance and reducing the risk of injury, substantial advances were accomplished to pursuit this goal, either on the laboratory techniques as well as modelling and simulation. Traditionally, the main focus was the assessment of kinematics, kinetics and electromyography data to describe the main mechanics and neuromuscular behaviour, when performing a certain movement. The use of methodologies that enable the quantification of the effect of a particular joint moment of force in the entire body or the contribution of an individual muscle force to accelerate the centre of mass of the body is quite relevant in biomechanical analysis. This is particularly important when dealing with explosive movements such as those that occur in sports activities, or in the clinical field when dealing with abnormal movement. At the same time, the advances in imaging technology allows us the use of some of those techniques to gather subject-specific information, particularly the muscle architectural parameters that are crucial to the production of force, such as muscle volume, muscle physiological cross-section area and muscle pennation angle. In the course of this dissertation, we investigated the use and/or combination of different methodologies to study the effect of mechanical load in the lower limb musculoskeletal system during a cyclic stretch-shortening exercise. We aimed at using an integrated approach to better characterize the behaviour of the musculoskeletal system when subjected to this type of mechanical load.RESUMO: Uma das principais preocupaçÔes da investigação em BiomecĂąnica Ă© a avaliação da carga mecĂąnica que o corpo desenvolve e que consegue suportar quando realiza açÔes desportivas com nĂvel de desempenho de moderado a elevado. Com o objetivo de melhorar a performance mas reduzindo o risco de lesĂŁo, tĂȘm sido realizados avanços significativos quer nas tĂ©cnicas laboratoriais e equipamentos, quer nas tĂ©cnicas de modelação e simulação. A investigação tradicional em biomecĂąnica tem o seu foco na avaliação da cinemĂĄtica, cinĂ©tica e função neuromuscular para descrever a mecĂąnica do corpo e o comportamento neuromuscular, durante a execução de um determinado movimento. No entanto, a utilização de metodologias que permitam a quantificação do efeito de um determinado momento de força articular em todos os segmentos corporais ou a contribuição de um momento de força muscular individual na aceleração do centro de massa do corpo Ă© bastante relevante na anĂĄlise biomecĂąnica. Isto Ă© particularmente importante quando se lida com movimentos explosivos, tais como os que ocorrem em actividades desportivas, ou no Ăąmbito clĂnico quando se tratam de condiçÔes nĂŁo normais ou patolĂłgicas. Ao mesmo tempo, os avanços na tecnologia de imagem permitem a utilização de algumas destas tĂ©cnicas para recolher informaçÔes especĂficas do sujeito, nomeadamente no que diz respeito aos parĂąmetros arquitectĂłnicos do mĂșsculo, que sĂŁo cruciais para a produção da força, tal como o volume muscular, a ĂĄrea de secção transversal fisiolĂłgica ou o Ăąngulo de penação. No decurso deste trabalho, foi investigada a utilização e/ou combinação de diferentes metodologias para estudar o efeito da carga mecĂąnica no sistema musculo-esquelĂ©tico do membro inferior durante um exercĂcio de alongamento-encurtamento realizado de forma cĂclica. O principal objetivo foi utilizar uma abordagem integrada para melhor caracterizar o comportamento do sistema mĂșsculo-esquelĂ©tico, quando submetido a este tipo de carga mecĂąnica.FCT - Fundação para a CiĂȘncia e a Tecnologi
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