"Hydro-kinematic" method for quantifying glide efficiency of swimmers

The purpose of this thesis was to introduce and test methods of quantifying the glide efficiency and the hydrodynamic parameters related to an underwater glide of a human body in a streamlined position and to investigate their relationship with the size and shape characteristics of a body with consideration of actual anthropometry, morphology and posture of body in a streamlined glide position.The thesis comprises three studies. The aim of the first study was to develop and test a method of quantifying glide efficiency in a way that accounts for both the inertial and resistive characteristics of the gliding body as well as the differences in the instantaneous velocities. To achieve this, a displacement function was derived from the equation of motion of the body during a horizontal rectilinear glide. By fitting this function to the position-time data of a body during a rectilinear horizontal glide, a glide factor that indicates the glide efficiency was quantified. This factor represented a combined kinematic and hydrodynamic measure of a glide. As the glide efficiency of a body is influenced by the body shape as well as by the body size, the size-related and shape-related glide efficiencies were determined as separate entities. The validity and applicability of the method was established. Also the glide factor enabled the exact prediction of deceleration during a glide which was not possible knowing the resistive factor alone. It was found that the glide factor increased with decreasing velocity. The method was shown to be able to detect differences in the glide efficiency between subjects and across trials within subjects.The aim of the second study was to develop and test a method of quantifying the hydrodynamic properties of a human body in a streamlined position during an underwater glide so that the values of the resistive factor and the virtual mass can be determined separately. To achieve this aim a displacement function was derived from the equation of motion of the body during an inclined rectilinear glide. By fitting this function to the position-time data of a body during a rectilinear inclined glide, and taking iii advantage of the component of net buoyancy as a constant parameter in the equation of motion, the resistive and inertial parameters were quantified. As the resistive and inertial parameters of a body are influenced by the body shape as well as by the body size, the drag and added mass coefficients were determined to investigate resistive and added inertial properties of a body independent of its size. The validity and applicability of the method was established. The method was able to quantify the hydrodynamic resistance and added inertia parameters considering the glide under realistic conditions. Also added mass of a body during deceleration was quantified with this method. It was found that the added mass decreased with increasing velocity while the resistive force increased.The aim of the third study was to determine the true relationship between the size and the shape characteristics of the body and its hydrodynamic and glide efficiency parameters. In the third study the actual anthropometric measures, morphological indices and postural angles of the body in a streamlined position were determined, in order to quantify the size and shape characteristics of a body in a streamlined position. The correlations between these parameters and the glide efficiency and the resistive and added inertia parameters were obtained. It was found that the gliding ability is more dependent on having a good shape than on having a large body mass with a low crosssectional area. Also the difference of hydrodynamic parameters including the resistive factor and the added mass between two bodies is the result of the differences in the shape characteristics including morphological indices and postural angles rather than due to the differences in size. The results indicated that some of the morphological indices and joint angles investigated in this study were correlated to the glide efficiency and hydrodynamic parameters. The belief that more streamlined objects possess a lower added mass coefficient seems not to be applicable to the human body.The method developed has practical applications in testing swimming suits designed to improve performance. Using the 'Hydro-kinematic' method the suit effect on the ability of a body to entrain added masses of water together with its ability to reduce drag as well as the combined effect on the glide efficiency may be quantified. The results of this study indicate that in talent identification the evaluation should be based on the shape of the body rather than its size. The existence of relationship between some of the morphological indices and the hydrodynamic and glide efficiency parameters would also allow identifying the streamlining degree of a body without the requirement for the direct drag force measurements

A COMPARISON OF TWO FUNCTIONS REPRESENTING VELOCITY OF A HUMAN BODY SUBJECT TO PASSIVE DRAG

The purpose of this study was to compare the goodness of fit of two functions representing horizontal velocity of a human body subject to passive drag. Hyperbolic and exponential functions were fitted to the horizontal velocity data of three glides following push-off from the wall of five swimmers. Measures of goodness of fit included root mean square errors (RMSE), and the coefficient of determination (R2). The hyperbolic function provided a better fit to the actual values of velocity, provided a closer match to the initial velocity, and predicted better the velocities beyond the fitted interval than the exponential function. It was concluded that for the swimmers and range of glide velocities tested, drag was closer to being proportional to the square of velocity than a linear function of velocity

The influence of rocker outsole design on the ground reaction force alignment during walking

Rocker outsole shoe is commonly prescribed to diabetic patients to reduce the risk of plantar ulceration. It is well stablished that the primary biomechanical role of the rocker outsole is to offload the plantar aspect of the forefoot [1]. Shear stresses have been previously affiliated to the etiology of diabetic foot ulcers [2]. However, there is a paucity of research on the effect of the rocker outsole design on the shear components in diabetic patients. While shear impulses can be measured during walking [3], the majority of studies concentrated on the vertical component of the Ground Reaction Force (GRF). Anterior-posterior (AP) shear impulses which are termed positive and negative impulses respectively [4], change the momentum of the body in forward direction. However, Medial-lateral (ML) shear impulses act to push the body away (negative) and towards (positive) the contralateral side [4]. It is envisaged that the rocker outsole design can alter these impulses by changing the contact angles and forces during the shoe-ground interaction. Therefore, the purpose of this study was to investigate the effect of different rocker outsole designs on AP or ML shear impulses

An MRI compatible loading device for the reconstruction of clinically relevant plantar pressure distributions and loading scenarios of the forefoot

This study aims to present a new MRI compatible loading device capable of reconstructing realistic loading scenarios of the human foot for research in the field of foot biomechanics. This device has two different configurations: one used to compress the forefoot and one to bend the metatarsophalangeal joints. Required plantar pressure distribution under the metatarsal heads can be achieved by modifying the distribution of the dorsally applied forces. To validate the device, subject-specific plantar pressures were measured and then reconstructed using the device. For quiet stance the peak pressure reconstruction error was 3% while for mid-stance phase of gait it was 8%. The device was also used to measure the passive bending stiffness of the metatarsophalangeal joints of one subject with low intra-subject variability. A series of preliminary MRI scans confirmed that the loading device can be used to produce static weight-bearing images of the foot (voxel size: 0.23mm×0.23mm×1.00mm). The results indicate that the device presented here can accurately reconstruct subject specific plantar pressure distributions and measure the foot’s metatarsophalangeal passive stiffness. Possible future applications include the validation of finite element models, the investigation of the relationship between plantar pressure and internal stresses/strains and the study of the foot’s inter-segmental passive stiffness

A method for subject-specific modelling and optimisation of the cushioning properties of insole materials used in diabetic footwear

This study aims to develop a numerical method that can be used to investigate the cushioning properties of different insole materials on a subject-specific basis. Diabetic footwear and orthotic insoles play an important role for the reduction of plantar pressure in people with diabetes (type-2). Despite that, little information exists about their optimum cushioning properties. A new in-vivo measurement based computational procedure was developed which entails the generation of 2D subject-specific finite element models of the heel pad based on ultrasound indentation. These models are used to inverse engineer the material properties of the heel pad and simulate the contact between plantar soft tissue and a flat insole. After its validation this modelling procedure was utilised to investigate the importance of plantar soft tissue stiffness, thickness and loading for the correct selection of insole material. The results indicated that heel pad stiffness and thickness influence plantar pressure but not the optimum insole properties. On the other hand loading appears to significantly influence the optimum insole material properties. These results indicate that parameters that affect the loading of the plantar soft tissues such as body mass or a person’s level of physical activity should be carefully considered during insole material selection

An MRI compatible loading device for the reconstruction of clinically relevant plantar pressure distributions and loading scenarios of the forefoot.

The purpose of this study is to demonstrate a new MRI compatible loading device capable of reconstructing realistic loading scenarios of the human foot for research in the field of foot biomechanics. This device has two different configurations: one used to compress the forefoot and one to bend the metatarsophalangeal joints. Required plantar pressure distribution under the metatarsal heads can be achieved by modifying the distribution of the dorsally applied forces. To validate the device, subject-specific plantar pressures were measured and then reconstructed using the device. For quiet stance the peak pressure reconstruction error was 3% while for mid-stance phase of gait it was 8%. The device was also used to measure the passive bending stiffness of the metatarsophalangeal joints of one subject with low intra-subject variability. A series of preliminary MRI scans confirmed that the loading device can be used to produce static weight-bearing images of the foot (voxel size: 0.23 mm × 0.23 mm × 1.00 mm). The results indicate that the device presented here can accurately reconstruct subject specific plantar pressure distributions and measure the foot's metatarsophalangeal passive stiffness. Possible future applications include the validation of finite element models, the investigation of the relationship between plantar pressure and internal stresses/strains and the study of the foot's inter-segmental passive stiffness

A SIMPLE MATHEMATICAL MODELlNG FOR KINEMATIC, DYNAMIC STUDIES OF SWIM TURN PERFORMANCES

A simple mathematical modefing for kinematic and dynamic studies of swim turn performances has been suggested. Side camera was used to obtain timing, hip displacement, velocity and acceleration characteristics of push-off and glide phases in order to justify the proposed modeling. Five elite swimmers were analyzed for a pilot study. It was concluded that this modeling was reliable and useful for feedback to swimmers and coaches on fast and effective turn performances. Water resistance and average leg muscle forces, velocities and accelerations in both push-off and glide phases have been estimated and compared with the results obtained by the other researchers

Multi-segment kinematic model to assess three-dimensional movement of the spine and back during gait.

BACKGROUND Relatively little is known about spine during gait compared to movement analysis of the lower extremities. The trunk is often regarded and analysed as a single rigid segment and there is a paucity of information on inter-segmental movement within the spine and its relationship to pelvis and lower limbs. OBJECTIVES To develop and validate a new multi-segment kinematic model to assess regional three-dimensional movement of the lumbar, lower thoracic and upper thoracic spine during gait. STUDY DESIGN Observational study. METHODS The study was conducted in two parts: (1) to provide validation measures on the kinematic model built in commercially available software and (2) to apply the marker configuration to the spine at T3, T8 and L3 during gait analysis on 10 healthy male volunteers. RESULTS Proposed model revealed excellent concurrent validation measures between an applied input angle to the recorded output angle from the kinematic model. A high reliability was observed during gait analysis, both during a single session and between sessions for all participants. CONCLUSION The thoracic region of the spine should not be modelled as a single rigid segment and the proposed three-dimensional cluster is reliable and repeatable to assess the inter-segmental movement of the spine. CLINICAL RELEVANCE Reliable kinematic data can be collected using the three-dimensional cluster technique, thus, allowing researchers to accurately distinguish between movement patterns of healthy individuals to those with a clinical condition, and provide confidence in data acquisition during the monitoring process of an implemented rehabilitation intervention programme

Finite element modelling of the foot for clinical application: A systematic review

Over the last two decades finite element modelling has been widely used to give new insight on foot and footwear biomechanics. However its actual contribution for the improvement of the therapeutic outcome of different pathological conditions of the foot, such as the diabetic foot, remains relatively limited. This is mainly because finite element modelling is only been used within the research domain. Clinically applicable finite element modelling can open the way for novel diagnostic techniques and novel methods for treatment planning/optimisation which would significantly enhance clinical practice. In this context this review aims to provide an overview of modelling techniques in the field of foot and footwear biomechanics and to investigate their applicability in a clinical setting. Even though no integrated modelling system exists that could be directly used in the clinic and considerable progress is still required, current literature includes a comprehensive toolbox for future work towards clinically applicable finite element modelling. The key challenges include collecting the information that is needed for geometry design, the assignment of material properties and loading on a patient-specific basis and in a cost-effective and non-invasive way. The ultimate challenge for the implementation of any computational system into clinical practice is to ensure that it can produce reliable results for any person that belongs in the population for which it was developed. Consequently this highlights the need for thorough and extensive validation of each individual step of the modelling process as well as for the overall validation of the final integrated system