Thèses sur le sujet « Biomechanical variable »

Antipronation foot orthosis are commonly used by health care professionals to treat a variety of lower limb conditions thought to be caused by excessive foot pronation. However, despite their widespread use, laboratory based research indicates that antipronation foot orthosis cause variable joint moment/motion biomechanical responses. If a specific biomechanical response is required to treat a specific clinical condition, it follows that practitioners cannot tailor foot orthosis confidently to alleviate symptoms thought to be associated with excessive pronation. A conceptual framework representing a biomechanical system of foot function was proposed to explain how external forces, foot structure, and neuromuscular factors cause these variable joint moment/motion responses to foot orthosis. Two studies (study 1 & study 2) sought to understand how external forces influenced joint moment/motion responses. Study 1 examined if systematic changes in external forces created by varying APFO geometry correlate to changes in joint moment/motion responses. To answer this research question a pilot study (n = 11) developed suitable increments in anti-pronation orthotic geometry that could systematically alter external forces under the plantar foot. The main study (n = 20) demonstrated that varying orthotic arch geometry and medial heel wedge geometry could systematically alter external forces (measured as peak pressure and centre of pressure) and joint moment/motion responses in foot structures. However, study 1 showed that changes in external forces created by varying APFO geometry are generally not strongly correlated (r < 0.6) to changes in joint moment/motion responses thus indicating that other factors (e.g. structural/neuromuscular) influence biomechanical responses to foot orthoses. On the basis that forces applied to the sole of the foot pass through plantar soft tissues prior to being applied to bones of a joint to affect moments and kinematics, study 2 characterised how soft tissue respond to change in external forces due to change in orthotic geometry. A pilot study (n = 10) developed a reliable method that could be used to quantify soft tissue thickness between the surface of an orthosis and bones overlying the medial arch. The results for the main study (n = 27) found that antipronation orthosis systematically compressed soft tissue structures under the plantar foot. The studies reported in this thesis show that antipronation orthosis can be tailored to systematically alter tissue compression, external forces and joint moment/motion responses. However, systematically altering external forces under the plantar foot with antipronation foot orthosis is not strongly correlated with changes in joint moment/motion responses. This suggests moment/motion responses are strongly influenced by structural features and/or neuromuscular action in combination with external forces. The work presented in this thesis offers a foundation for future studies seeking to understand how foot orthoses alters foot biomechanics.

The current clinical management of abdominal aortic aneurysm (AAA) disease is based on measuring the aneurysm maximum diameter to decide when timely intervention can be recommended to a patient. However, other parameters may also play a role in causing or predisposing the AAA to either an early or delayed rupture relative to its size. Therefore, patient-specific assessment of rupture risk based on physical principles such as individualized biomechanics can be conducive to the development of a vascular tool with translational potential. To that end, the present doctoral research materialized into a framework for image based patient-specific vascular biomechanics assessment. A robust generalized approach is described herein for image-based volume mesh generation of complex multidomain bifurcated vascular trees with the capability of incorporating regionally varying wall thickness. The developed framework is assessed for geometrical accuracy, mesh quality, and optimal computational performance. The relative influence of the shape and the constitutive wall material property on the AAA wall mechanics was explored. This study resulted in statistically insignificant differences in peak wall stress among 28 AAA geometries of similar maximum diameter (in the 50 – 55 mm range) when modeled with five different hyperelastic isotropic constitutive equations. Relative influence of regionally varying vs. uniform wall thickness distribution on the AAA wall mechanics was also assessed to find statistically significant differences in spatial maxima of wall stresses, strains, and strain energy densities among the same 28 AAA geometries modeled with patient-specific non-uniform wall thickness and two uniform wall thickness assumptions. Finally, the feasibility of estimating in vivo wall strains from individual clinical images was evaluated. Such study resulted in a framework for in vivo 3D strain distributions based on ECG gated, unenhanced, dynamic magnetic resonance images acquired for 20 phases in the cardiac cycle. Future efforts should be focused on further development of the framework for in vivo estimation of regionally varying hyperelastic, anisotropic constitutive material models with active mechanics components and the integration of such framework with an open source finite element solver with the goal of increasing the translational potential of these tools for individualized prediction of AAA rupture risk in the clinic.

Abnormal lower-limb mechanics during functional activities have been reported as being associated with several knee injuries. Hence it is important to develop screening tests to identify healthy individuals who may be susceptible to knee injury and then to design individual intervention programmes. There is limited literature exploring the associations between lower-limb biomechanical variables during athletic tasks associated with knee-joint injuries. A better understanding of inter-task performance would offer insights into the consistency of motor patterns employed by healthy individuals during common screening tasks. This thesis comprises four themed studies. The first study aimed to examine the reliability of using 3D motion analysis to measure the biomechanical variables during single-leg squats (SLS), single-leg landing (SLL), running and sidestep cutting tasks. The findings of first study revealed that within-day measurements are more reliable than those between days across all tasks, while transverse-plane variables are less reliable compared to other planes of movement. The second study established reference values for lower-limb biomechanical variables during these tasks in a large population sample (90 healthy participants). Furthermore, gender differences in biomechanical variables were also assessed. Significant differences were noticed in knee-flexion, knee-valgus and hip-adduction peak angles across all tasks and both genders. The third study examined the relationships between lower-limb biomechanical variables during these tasks. A significant relationship has been reported across all tasks between the following variables: peak knee-abduction angle and moment, hip-internal and hip-adduction rotation angles. The findings support the hypothesis that those individuals who exhibit misalignment strategies, specifically in frontal and transverse planes, during SLS & SLL will also show the same movements during running and cutting tasks. However, it must be stressed that the use of squat or landing alone should not be considered as a replacement to find individuals at risk of running or cutting mechanics since several variable showed weak or no correlation. The final study aimed to examine the effectiveness of an augmented feedback protocol on SLS performance and if changing squat performance would be reflected in a change in performance in SLL, running and side-step cutting tasks. Training resulted in a significant reduction in knee-valgus angle and moment and hip-flexion angles during single-leg squatting. Additionally, these improvements remained a few days later, proposing motor patterns might have improved and these improvements would sustain, thus reducing the risk of injury in the longer time. Furthermore, significant reductions in knee-valgus angle and moment were also noticed in landing after squat feedback training, but no significant improvements were transferred to run and cut tasks. This thesis has expanded the understanding about using 3D movement-analysis systems and established reference values when performing common screening tasks. Furthermore, feedback was used to improve performance strategies, which could reduce the risk of knee injuries in a quick and easy manner. However, the results of this study do not confirm that the alterations reported in biomechanical variables were solely due to the SLS feedback-training programme.

Background Whole-body vibration (WBV) as a training modality is established in the fields of sport, fitness, rehabilitation, and clinical intervention. WBV exercises are performed thereby while standing on a motor driven oscillating platform device. Therefore, the scientific interest in WBV is a steadily increasing field in sports science and research. It has been shown that WBV training elicits various biological and physiological effects in men. Nevertheless, there are only a small number of studies examining WBV effects on neuromuscular performance of the lower extremities in elderly people. Furthermore, the results of these studies show many discrepancies that may be caused by limitations referring to the different applied training protocols and vibration loads. In addition, there is still a deficit of information for effective but safe recommendations for WBV application for trunk and neck muscles. Therefore, this doctoral thesis deals with three major aspects of WBV as an exercise modality in strength training: (1) the recommendation of optimal vibration loads (VbLs) for the lower extremities as an essential element of the WBV exercise parameters in older adults, (2) the evaluation of these VbLs in a WBV training intervention for elderly people with regard to feasibility and chronic effects on neuromuscular performance of the lower limbs, and (3) the allocation of information for effective but safe advices for VbLs for trunk and neck muscles. These aspects are further specified toward five hypotheses (H1, H2, H3, H4, and H5) by findings and limitations of the current state of literature. Methods The five hypotheses are evaluated within three research papers (studies 1 to 3). The first study (S1) evaluated the optimal VbL determined by the combination of three biomechanical variables (vibration frequency, vibration amplitude, and knee angle) in older adults (H1). Therefore, the neuromuscular activity of the quadriceps femoris and hamstring muscles in 51 healthy subjects were measured during WBV exposure using surface electromyography (EMG). Maximal voluntary contractions (MVCs) were conducted prior to the measurements to normalise the EMG signals. A three-way mixed ANOVA was performed to analyse the different effects of the biomechanical variables on muscle activity. Study 2 (S2) represents a randomised controlled trial to assess the results of S1 implemented in a WBV training protocol and therefore to evaluate the feasibility and effectiveness of a six-week WBV intervention (H2, H3, and H4). A total of 21 subjects was allocated randomly into either a WBV training or control group. While the WBV group completed a six-week WBV training programme the control group was asked not to change their current level of physical activity during the study. Before and after the intervention period, jump height was measured during a countermovement jump (CMJ). In addition, isokinetic knee extension and flexion strength parameters were recorded using a motor-driven dynamometer. The Borg scale for ratings of perceived exertion (RPE scale) was used to evaluate the intensity of WBV exercises within each training session. Changes from pre- to posttest were analysed by a paired sample t-test (within-group comparisons) and independent sample t-test (between-group comparisons). The intention of study 3 (S3) was to analyse the impact of biomechanical variables on neuromuscular activity of different trunk and neck muscles during WBV (H5) filling the lack of information in current literature. Those biomechanical variables were assumed, which current literature suggests as having the lowest risk of negative side effects on the head. Surface EMG was used to record the neuromuscular activity in 28 healthy subjects. EMG signals were normalised to prior measured MVC. Different effects of the biomechanical variables were analysed by an ANOVA for repeated measurements. Results The findings of S1 showed that the biomechanical variables affect the level of neuromuscular activity of thigh muscles in older adults in different dimensions which confirms H1. The maximum levels of muscle activity were significantly reached at high amplitude and high frequency, whereas the factor “knee angle” only significantly affected the quadriceps femoris. Furthermore, WBV led to a higher muscle activation of the quadriceps femoris (74.1 % MVC) than of the hamstring muscles (27.3 % MVC). The main findings in S2 were an increased multi-joint strength performance of the lower limbs during a countermovement jump in the WBV group, whereas values of the control group remained unchanged after the intervention, thus confirming H2. There were no statistically significant differences in isokinetic maximal strength, mean power, or work values in knee extension or flexion in both groups (rejecting H3). In addition, the subjective perceived exertion of the WBV exercises and respective training parameters ranged between moderate rating levels of 7 and 13 of the Borg scale and indicate WBV intervention as a feasible and safe training program for elderly people, which is consistent with H4. Finally, the outcomes of S3 confirmed H5 as the biomechanical variables affect the level of neuromuscular activity of the trunk and neck in different dimensions. The maximum levels of muscle activity were significantly reached at high amplitude and high frequency, while knee angles had similar effects on the VbL. WBV led to a higher muscle activation of the lower back muscles (27.2% MVC) than of neck muscles (8.5 % MVC) and the abdominal muscles (3.6 % MVC). Conclusion A maximised VbL for WBV training in older adults depends on specific combinations of the biomechanical variables (vibration frequency, vibration amplitude, and knee angle). In addition, a WBV training based on this age-specific high VbL is a feasible, suitable and effective training program for elderly people to prevent age-related reduction of muscle performance in the lower extremities. Furthermore, the combination of biomechanical variables recommended in literature as safe for preventing harmful transmissions to the head, only elicit low to moderate muscle activation of the upper body. The findings of this thesis represent fundamental research in the field of WBV and may help to improve further research in this area. Finally, this thesis may help coaches and therapists to enhance the quality of WBV training in practical application
Hintergrund Ganzkörpervibration (Whole-Body Vibration, WBV) hat sich als Trainingsanwendung im Sport-, Fitness, Rehabilitationsbereich und klinischen Bereich etabliert, wobei die Übungen dabei im Stehen auf einer Vibrationsplatte durchgeführt werden. In diesem Zusammenhang ist auch das wissenschaftliche Interesse am Vibrationstraining ein stetig wachsendes Feld in den Bereichen der Sportwissenschaft und Forschung. Bisher konnte gezeigt werden, dass Vibrationstraining verschiedene biologische als auch physiologische Reaktionen beim Menschen hervorruft. Dennoch gibt es nur wenige Untersuchungen, die sich mit den Auswirkungen des Vibrationstrainings auf die neuromuskuläre Leistung der unteren Extremitäten bei älteren Menschen beschäftigen. Des Weiteren weißen die Ergebnisse dieser wenigen Studien viele Widersprüchlichkeiten auf, welche durch die unterschiedlich verwendeten Trainingsvorgaben und Vibrationsbelastungen verursacht sein könnten. Darüber hinaus besteht noch ein großes Defizit an grundlegenden Informationen hinsichtlich effektiver, aber dennoch sicherer Vorgaben in der Anwendung des Vibrationstrainings im Bereich der Rumpf- und Nackenmuskulatur. Vor diesem Hintergrund beschäftigt sich die vorliegende Dissertation mit drei wesentlichen Aspekten des Vibrationstrainings: (1) die Empfehlung von optimalen Vibrationsbelastungen (VbL) als wesentlicher Bestandteil des Vibrationstrainingsplans der unteren Extremitäten älterer Menschen, (2) die Evaluierung dieser VbL anhand einer auf Vibrationstraining basierter Intervention mit älteren Menschen hinsichtlich Durchführbarkeit und Auswirkungen auf die neuromuskuläre Leistung der unteren Gliedmaßen, und (3) Angaben für effektive und sichere VbL für Rumpf- und Nackenmuskulatur bereitzustellen. Mit der Aufarbeitung von Ergebnissen und Defiziten des aktuellen Forschungsstands werden diese Aspekte durch die Formulierung von fünf Hypothesen (H1, H2, H3, H4, and H5) weiter spezifiziert. Methodik Die fünf Hypothesen werden in drei wissenschaftlichen Veröffentlichungen (Studie 1 bis 3) untersucht. Die erste Studie (S1) befasste sich mit der optimalen VbL für ältere Personen (H1), welche durch die Kombination von drei biomechanischen Variablen (Vibrationsfrequenz, Vibrationsamplitude und Kniewinkel) bestimmt wird. Hierzu wurde die neuromuskuläre Aktivität der vorderen und hinteren Oberschenkelmuskulatur von 51 gesunden Probanden unter Vibration mittels Oberflächen-Elektromyografie (EMG) gemessen. Vor den Messungen wurden maximale muskuläre Kontraktionen durchgeführt, um die EMG zu normalisieren. Um die unterschiedlichen Auswirkungen der biomechanischen Variablen zu analysieren wurde eine drei-faktorielle Varianzanalyse durchgeführt. Studie 2 (S2) entspricht einer randomisierten kontrollierten Studie, welche die Ergebnisse aus S1 in einem Trainingsplan verwendet, um die Durchführbarkeit und Effektivität eines sechs wöchigen Vibrationstrainings zu untersuchen (H2, H3, und H4). Hierfür wurden 21 Probanden zufällig einer Vibrationstrainings- oder einer Kontrollgruppe zugeteilt. Während die Vibrationsgruppe ein sechs wöchiges Vibrationstraining absolvierte, wurden die Teilnehmer der Kontrollgruppe gebeten ihre körperliche Aktivität während des Studienzeitraums nicht zu verändern. Vor und nach dem Untersuchungszeitraums wurde die Sprunghöhe während eines „countermovement jump“ (CMJ) erfasst. Weiterhin wurden isokinetische Kraftmessgrößen der Kniegelenkbeugung und –streckung an einem Dynamometer ermittelt. Die Borgskala zur Erfassung des subjektiven Belastungsempfindens wurde eingesetzt, um die Intensität der Übungen des Vibrationstrainings innerhalb einer Trainingseinheit zu messen. Veränderungen der Messgrößen zwischen Eingangs- und Abschlusstest wurden statistisch mit einem t-Test für abhängige (innerhalb einer Gruppe) und einem t-Test für unabhängige Stichproben (zwischen den Gruppen) untersucht. Ziel der dritten Studie (S3) war es den Einfluss der biomechanischen Variablen auf die muskuläre Aktivierung verschiedener Rumpf- und Nackenmuskeln (H5). Hierzu wurden solche biomechanische Variablen ausgesucht, welche laut derzeitigem Wissensstand jeweils das geringste Risiko von Nebenwirkungen für den Kopf ausüben. Mittels Oberflächen-EMG wurde die muskuläre Aktivität von 28 Probanden erfasst. EMG Signale wurden zu vorangegangenen MVC Messungen normalisiert. Die Unterschiedlichen Effekte der biomechanischen Variablen wurden mittels einer Varianzanalyse für Messwiederholungen analysiert. Ergebnisse Die Ergebnisse von S1 konnten zeigen, dass die biomechanischen Variablen den neuromuskulären Aktivierungsgrad der Oberschenkelmuskulatur bei älteren Personen unterschiedlich beeinflussen und somit H1 bestätigen. Der höchste Grad der Aktivierung wurde deutlich mit einer großen Amplitude und hohen Frequenz erreicht, wobei der Kniewinkel ausschließlich die vordere Oberschenkelmuskulatur beeinflusst. Zudem, führte der Vibrationseinfluss zu einer größeren Muskelaktivität der Oberschenkelvorderseite (74.1 % MVC) als der –rückseite (27.3 % MVC). Die Resultate von S2 hinsichtlich des CMJ Tests bestätigen H2, da es in der Vibrationstrainingsgruppe zu einer gesteigerten gelenksübergreifender Kraftleistung in den Beinen kam, aber keine Veränderungen in der Kontrollgruppe feststellbar waren. Hingegen kam es in keiner Gruppe zu statistisch signifikanten Veränderungen der isokinetischen Messgrößen (Maximalkraft, Kraftleistung, Muskelarbeit), wodurch H3 abgelehnt wird. Das subjektive Belastungsempfinden der Übungen und des Belastungsgefüges des Vibrationstrainings liegt zwischen moderaten Bewertungsstufen von 7 bis 13 der Borgskala und weist daraufhin, dass Vibrationstraining ein praktikables und sicheres Übungsprogramm für ältere Menschen ist und somit H4 bestätigt. Die Ergebnisse von S3 konnten H5 bestätigen, da die biomechanischen Variablen den neuromuskulären Rumpf- und Nackenmuskulatur unterschiedlich beeinflussen. Der höchste Grad der Aktivierung wurde deutlich mit einer großen Amplitude und hohen Frequenz erreicht, wobei der Kniewinkel sich ähnlich auf die VbL auswirkt. Der Vibrationsstimulus führte zudem zu einer höheren Aktivierung der unteren Rückenmuskulatur (27.2% MVC) als der Nacken- (8.5 % MVC) und Bauchmuskulatur (3.6 % MVC). Schlussfolgerungen Die maximale muskuläre Belastung älterer Personen in einem Vibrationstrainings hängt von bestimmten Kombinationen der biomechanischen Variablen (Vibrationsfrequenz, Vibrationsamplitude und Kniewinkel). Zudem ist ein Vibrationstraining, das auf altersspezifischen Vibrationsbelastungen basiert ein machbares, angemessenes und effektives Trainingsprogramm für älteren Menschen, um einem altersbedingten Abnehmen der muskulären Leistungsfähigkeit vorzubeugen. Weiterhin führt die Verbindung von biomechanischen Variablen, welche laut bisherigem Forschungsstand als sicher gegen schädliche Vibrationsübertragungen zum Kopf gelten, nur zu leichten bis moderaten Muskelaktivierung im Oberkörper. Die Ergebnisse dieser Dissertation liefern einen Beitrag zur Grundlagenforschung auf dem Gebiet des Vibrationstrainings und können weiteren Forschungsarbeiten hilfreich sein. Darüber hinaus kann diese Arbeit helfen die Qualität von Vibrationstrainingsangeboten zu verbessern und somit zum praktischen Nutzen beitragen

Knee-ankle-foot orthoses (KAFOs) are full leg braces for individuals with knee extensor weakness, designed to support the person during weight bearing activities by preventing knee flexion. KAFOs typically result in an unnatural gait pattern and are primarily used for level ground walking. A novel variable resistance orthotic knee joint was designed and evaluated to address these limitations. This low profile design fits beneath normal clothing. Mechanical and biomechanical testing demonstrated that the design resisted knee motion during stance phase, released the knee joint without restricting the knee’s range of movement, and provided flexion resistance during stair descent. Design modifications and related testing procedures were developed to further improve joint performance and to validate the design prior to testing on individuals with knee extensor weakness.

Due to their prevalence and associated high rehabilitation costs, this thesis aimed to better understand factors influencing the risk of tibial (TSF) and third metatarsal (MT3SF) stress fractures in Royal Marine recruit training. In Study 1, the standard issue combat assault boot and neutral trainer were assessed during running. Running in the boot caused restricted ankle motion, greater forefoot loading, greater ankle stiffness and a more laterally applied horizontal force vector at the instant of peak braking, suggesting that the risk of incurring MT3SF was greater in this condition. In Study 2, bending stresses were modelled along the length of the third metatarsal of five participants, using individual bone geometry and dynamic gait data. Stresses were modelled for running when barefoot, and when shod in the standard issue footwear. Estimated peak bending stresses were significantly greater in the combat assault boot than the gym trainer, predominantly due to increased plantar loading. Individual bone geometry was however dominant in determining peak bending stresses. In Study 3, a large (n=1065) prospective study was conducted to identify differences in baseline characteristics between recruits sustaining a TSF or MT3SF and those who complete training uninjured. Ten TSF and 14 MT3SF cases were compared to 120 uninjured legs. Results suggest that risk of TSF is greater in those recruits with reduced ability to resist loading and attenuate impact during gait. Results for MT3SF suggest that ankle and foot position at touchdown, and the timing and magnitude of forefoot loading, are important factors influencing risk of this injury. The observation of lower age and BMI in both stress fracture groups was linked to lower bone strength and earlier fatigue mechanisms. This thesis has increased the understanding of MT3SF in particular, and provides information on specific factors which may be associated with MT3SF and TSF in RM recruits during basic training.

The general purpose of this project was to gain further insight into the effect of ageing on swing phase biomechanics during walking. A particular emphasis was placed on the effect of ageing on the critical gait variables anterior-posterior heel contact velocity (A-P HCV) and minimum toe clearance (MTC). In addition, techniques were developed to i) obtain three-dimensional (3D) joint kinematics from an electromagnetic tracking system (ETS) and ii) quantify a compensatory synergy in a multiple degree-of-freedom (DOF) precision task, namely gait. Intra-trial, intra-day/inter-tester and inter-day/intratester repeatability of gait kinematics acquired using the ETS-based technique was equivalent or superior to that obtained using optoelectronic and video based systems. Compared with young participants, the elderly exhibited a greater A-P HCV and greater MTC variability. The postural configuration of the elderly at the time of MTC (timeMTC) was different to that of the young, while no marked differences in joint angle variability at timeMTC were identified. Both the young and elderly were found to exhibit compensatory synergies between kinematic DOFs that acted to minimise MTC variability. The overall strength of these synergies was similar for the young and elderly however the number of DOFs involved in the synergy was less for the elderly than the young. In conclusion, healthy elderly individuals exhibit changes in their walking pattern that may place them a greater risk of a slip and or trip-related fall than their younger counterparts.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Physiotherapy and Exercise Science
Griffith Health
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Through whatever misfortune people have always had the need for artificial limbs. This study questions current thinking in the field of prosthetics, aiming to address the most prevalent issues affecting the amputee today, such as, fit, comfort and practicality, which have an inarguable baring on patient prostheses satisfaction. Through examination, more obscure problems encountered by users were explained, indicating how design issues and methodologies affect the present and future manufacturing process. As a result of this research a development model for the increased effectiveness of prostheses fitrnent and improvements in patient prosthetic satisfaction have been made. This has included suggestions for potential improvements in limb fitting center protocol, patient education and awareness strategies for the assessment of delivered patient needs and requirements Methods implemented during the research consisted of a comprehensive literature review of current infonnation, technical reports and patient satisfaction findings and assessment techniques. 1bis was accompanied with an investigation and evaluation of the prosthetics industry, including limb fitting, patient requirements, product/service shortfalls, rehabilitation technique and patient lifestyle. Additionally interviews and questionnaires with practitioners and users were undertaken aiding the evaluation of patient satisfaction and the identification of potential improvements in artificial limb fitment procedure. The results revealed several areas that deserved more detailed investigation, notably relating to the hypotheses, that the relationship between the levels of fit, comfort and practicality archived within the prostheses has an effect on the patient's satisfaction. Through the examination ofthis main hypothesis one of the most significant factors which emerged was the effect ofthe communication level held between the patient and prosthetist. The results of"this enquiry indicated that improved patient knowledge with respect oftheir situation and an increased ability to accurately relay issues of concern to the prosthetist, facilitated the delivery of satisfactory prostheses, in turn improving its fit, comfort and practicality. In conclusion, previous conjecture as to the limited effectiveness of current prosthetics in re-establishing patients activity levels were assessed, and suggestions generated by the results of patients dissatisfaction with their limbs. These findings facilitated the realisation of new educational, protocol-based methodologies, tools and theories.

Variable Resistance Training (VRT), loading elastic band tension on a barbell, has shown improvements in force, power, and velocity. Studied extensively in the squat and bench press, VRT is less researched in the context of the deadlift. Additionally, while no acute VRT deadlift studies exist where intensity was ≥ 90% 1- RM, some heavy VRT studies suggest that at approximately 90% 1-RM, less band tension (BT) is required to enhance force and power than seen at lower intensities in existing research. Therefore, the purpose of this study was to determine the effects of VRT on peak relative vertical ground reaction force (VGRF), average and peak velocity, and time of peak force (VGRF time), in heavy, traditional deadlifts. METHODS: Seven resistance trained, college-aged males were recruited for this study. Over the course of approximately eight weeks, subjects completed five training sessions including familiarization, and testing the deadlift at 90% 1-RM with no bands (NB), 10%BT, 20%BT, or 30%BT. All training sessions were performed on dual force plates and with a linear position transducer to determine kinetic and kinematic outcomes. RESULTS: There were significant differences between conditions for both peak [F (3,18) = 13.607, p < 0.001] and average velocity [F (3, 18) = 14.077, p < 0.001]. No significant differences were detected between conditions for peak relative VGRF [F (3, 12) = 2.41, p= 0.118], or VGRF time [F (3, 12) = 1.843, p= 0.193]. PRACTICAL APPLICATIONS: The results of this study suggest velocity is improved with 20% to 30%BT when deadlifting approximately 90% 1-RM. For maximum force, traditional, NB deadlifts might be optimal considering the lack of improvement with the addition of bands. Despite the lack of significance between conditions, the large relative percent decrease in VGRF time from NB to 10%BT suggests that this small amount of BT may be advantageous for rapid force development with heavy loads

Background: European and Italian statistics have reported in the past decade a significant increase of work-related musculoskeletal disorders including the construction sector. Objectives: To check this issue, the EPM Research Unit in collaboration with the Craftmanship Territorial Joint Committee in Bergamo, have started a research in the field of musculoskeletal disorders with special reference to lumbar spine and upper limbs. Methods: The health survey was carried out by ad hoc trained staff. Results: between November 2009 and November 2010, data on 2755 subjects with a variety of jobs were obtained, over 50% being masons. The whole sample and the group of masons were investigated and both exhibited prevalence of upper limb diseases definitely higher than the reference group of non-exposed subjects. At the same time, risk assessment on painters and carpenters was performed, showing very hogh levels of risk o upper limb biomechanical overload due to awkward postures and force application. Conclusions: Hence the need for active research to be included in the protocol of health surveillance (with appropriate clinical protocol), of upper limb and spine MSDs. They also highlight the need for other biomechanical overload exposure data aimed at reconstructing risk profiles (from biomechanical overload) but above all at identifying the technological and organizational solutions to erase this particular risk.

Ce travail de thèse s’est déroulé dans le cadre d’une convention CIFRE entre mon laboratoire de rattachement C3S (EA4660) et le département Recherche et Développement (R&D) de l’équipe cycliste professionnelle FDJ. Les différentes études que nous avons conduites se sont articulées autour de l’amélioration de la performance sportive chez le cycliste à travers une variable centrale qui est la puissance mécanique qu’il développe lors de la locomotion (Pméca) selon deux axes principaux : 1) l’évaluation et le suivi du potentiel physique avec pour but l’amélioration du processus d’entraînement et 2) l’optimisation de l’interface homme – machine à partir de l’analyse du matériel et des équipements utilisés par les cyclistes dans l’équipe FDJ
This thesis has been completed as part of a CIFRE agreement between the laboratory C3S(EA4660) and the Research and Development (R&D) department of the FDJ professionalcycling team. The various studies that we conducted centred on analysing sport performanceoptimisation in cyclists through a central variable: the mechanical power output (PO)developed during locomotion. There were two main areas of focus: 1) evaluation andmonitoring of physical potential, with the aim of improving the training process, and 2)optimisation of the human–machine interface via analysis of the materials and equipmentused by the FDJ team cyclists

The majority of previous research investigating the role of vision in controlling adaptive gait has predominantly focused on over-ground walking or obstacle negotiation. Thus there is a paucity of literature investigating visuomotor control of step descent. This thesis addressed the importance of the lower visual field (lvf) in regulating step descent landing control, and determined when visual feedback is typically used in regulating landing control prior to/during step descent. When step descents were completed from a stationary starting position, with the lvf occluded or degraded, participants adapted their stepping strategy in a manner consistent with being uncertain regarding the precise location of the foot/lower leg relative to the floor. However, these changes in landing control under conditions of lvf occlusion were made without fundamentally altering stepping strategy. This suggests that participants were able to plan the general stepping strategy when only upper visual field cues were available. When lvf was occluded from either 2 or 1 step(s) prior to descending a step during on-going gait, stepping strategy was only affected when the lvf was occluded in the penultimate step. Findings suggest that lvf cues are acquired in the penultimate step/few seconds prior to descent and provide exproprioceptive information of the foot/lower leg relative to the floor which ensures landing is regulated with increased certainty. Findings also highlight the subtle role of online vision used in the latter portion of step descent to 'fine tune' landing control.

abstract: Modern, advanced statistical tools from data mining and machine learning have become commonplace in molecular biology in large part because of the “big data” demands of various kinds of “-omics” (e.g., genomics, transcriptomics, metabolomics, etc.). However, in other fields of biology where empirical data sets are conventionally smaller, more traditional statistical methods of inference are still very effective and widely used. Nevertheless, with the decrease in cost of high-performance computing, these fields are starting to employ simulation models to generate insights into questions that have been elusive in the laboratory and field. Although these computational models allow for exquisite control over large numbers of parameters, they also generate data at a qualitatively different scale than most experts in these fields are accustomed to. Thus, more sophisticated methods from big-data statistics have an opportunity to better facilitate the often-forgotten area of bioinformatics that might be called “in-silicomics”. As a case study, this thesis develops methods for the analysis of large amounts of data generated from a simulated ecosystem designed to understand how mammalian biomechanics interact with environmental complexity to modulate the outcomes of predator–prey interactions. These simulations investigate how other biomechanical parameters relating to the agility of animals in predator–prey pairs are better predictors of pursuit outcomes. Traditional modelling techniques such as forward, backward, and stepwise variable selection are initially used to study these data, but the number of parameters and potentially relevant interaction effects render these methods impractical. Consequently, new modelling techniques such as LASSO regularization are used and compared to the traditional techniques in terms of accuracy and computational complexity. Finally, the splitting rules and instances in the leaves of classification trees provide the basis for future simulation with an economical number of additional runs. In general, this thesis shows the increased utility of these sophisticated statistical techniques with simulated ecological data compared to the approaches traditionally used in these fields. These techniques combined with methods from industrial Design of Experiments will help ecologists extract novel insights from simulations that combine habitat complexity, population structure, and biomechanics.
Dissertation/Thesis
Masters Thesis Industrial Engineering 2018

碩士
國立臺灣科技大學
機械工程系
101
Spinal disc degeneration or lumbar nerve root compression can be treated by surgical operations. One of surgical operations is anterior lumbar interbody fusion (ALIF). In this surgical procedure, the lumbar disc is incised and removed. Then, an intervertebral cage or a small block of bone graft is placed between the vertebrae. Finally, an anterior vertebral plate is held in front of lumbar vertebrae by bone screws. However, the clinical complications of anterior lumbar vertebral plate system still occur. The fixation stability of anterior vertebral plates might be affected by different screw orientation. Past studies have tried to improve this clinical performance by changing the screw orientation, but their conclusions are inconsistency. Thus, the purpose of this study was to investigate the fixation stability of vertebral plate with variable-angle screws for the anterior lumbar interbody fusion surgery . Three-dimensional solid models of the spinal implants were developed by using SolidWorks, and the nonlinear finite element models were developed to investigate the fixation stability by using ANSYS Workbench. The parametric study and the optimization study of anterior vertebral plate systems were conducted by using Taguchi robust design methods and neurogenetic algorithms, respectively. The results of the numerical studies were validated using the biomechanical tests. For the parameteric study, the consequence of this research was that the contribution of sagittal plane (SI plane) was more influential than transverse plane (ML plane), and L5SI was particularly important design parameter. For the optimal study, optimum design obtained from neurogenetic algorithms was superior to that obtained from Taguchi Methods. The optimum design obtained from neurogenetic algorithms was 15°in SI plane of L4 vertebra, 15° in ML plane of L4 vertebra, -8.2° in SI plane of L5 vertebra, and 15°in ML plane of L5 vertebra. For the biomechanical tests, the numerical results could be validated and the correlation coefficient between the numerical models and the experimental tests was 0.909. The results of this study could directly provide the surgical suggestion and biomechanical rationale to orthopedic surgeons. In addition, those numerical models could also be used to evaluate a new design of anterior vertebral plate.

碩士
中國文化大學
體育學系運動教練碩博士班
106
Purpose: The promotion of pétanque in the world has been a hundred year. Taiwan has worked hard for ten years and still has no professional sportswear. The purpose of this study was to investigate the difference in parameters: ground reaction, foot pressure and kinematics produced by pétanque athletes wearing casual flat shoes with general insoles and casual flats shoes with arch support insoles at 6.5 meters shooting. Methods: 19 pétanque athletes were named as subjects. There were 9 males and 10 females. They must receive at least one year of pétanque special training, and there should be no leg or foot injury within half a year. After the experiment, the Xsens as motion capture analysis system was used to organize the kinematics parameters, and the F-scan was used to analyze the plantar pressure data. The AMTI force plate used to collect the ground reaction force data. Compare the difference of the shoes of the pétanque athletes’ data. Results: There was a significant difference in the total area of plantar contact at the moment of front swing and the ball leaves hand, the dorsiflexion angle of frontal ankle, the proportion of plantar contact area of the left foot in the moment of front swing, the proportion of plantar contact area of the right foot in the moment the ball leaves the hand, the offset of the pressure center and the pressure center offset area in the left and right direction during front swing. Conclusion: The arch support insole does not affect the performance of the 6.5m shooting and the upper limb movement mode, but it can improve the lower limb stability.

Immune system functionality and lymphocyte activity are gaining traction as a relevant therapeutic source for potentially addressing diseases such as cancer and autoimmune disorders. One such promising technique, adoptive cell therapy, revolves around successful ex vivo T cell activation and the ability to elicit a specific immune response. Key studies have recently suggested that mechanical forces play an important role in the ability of T cells to expand and proliferate and that T cell activation is sensitive to the mechanical properties of activating substrates. T cells initiate adaptive immune responses through interactions with antigen presenting cells (APCs). When T cells interact with APCs, they form the immune synapse, a multistep process that leads to downstream signaling and cellular function. Previous research has suggested that this process is both dynamic and mechanically sensitive. Gaining insight into the mechanisms through which T cells carry out mechanosensing and the associated effector functionalities will be advantageous in developing approaches for controlling T cell activation through mechanics and will allow for more accurate and efficient methods of promoting cell expansions for targeted therapies. This dissertation serves to generate a new mechanically dynamic 3D system to be utilized towards these understandings and contribute to the fields of immunology and mechanobiology. We first establish the development of a novel variable rigidity system actuated by magnetic field application. Validation experiments conclude that this device provides rapid, dynamic, and reversible control of substrate rigidity, without affecting the physical or biochemical properties of the system. The novel system is first used to explore mechanistic activity of T cells during activation in the face of a dynamic biomechanical environmental; we discover that T cells modulate the deflection and protrusive nature of their physical behaviors towards their targets in response to variable rigidity changes. We then utilize the magnetically driven system to characterize the biological mechanisms involved in these mechanosensitively associated behavior phenotypes. We demonstrate that activation patterns of T cells, defined by cytokine secretion profiles and TCR stimulation, correspond with varying cellular deformation directionality of activating substrates of variable increasing rigidity. In this process we discover a possible rigidity threshold upon which TCR triggering is sustained. Furthermore we reveal cytoskeleton components associated with identified mechanosensitive behaviors that cells produce in response to dynamic biomechanical cues. Together this work highlights the dynamic physicality and biomechanical mechanisms of T cell activation in response to a variable rigidity environment. These conclusions reveal insights into T cell mechanosensing activity within the natural mechanically complex atmosphere of the body. Encompassing those understandings, this thesis will help address current scientific gaps between mechanobiology and immunology and advance the biomechanical parameters of cell expansion driven adoptive immunotherapies.

Background Whole-body vibration (WBV) as a training modality is established in the fields of sport, fitness, rehabilitation, and clinical intervention. WBV exercises are performed thereby while standing on a motor driven oscillating platform device. Therefore, the scientific interest in WBV is a steadily increasing field in sports science and research. It has been shown that WBV training elicits various biological and physiological effects in men. Nevertheless, there are only a small number of studies examining WBV effects on neuromuscular performance of the lower extremities in elderly people. Furthermore, the results of these studies show many discrepancies that may be caused by limitations referring to the different applied training protocols and vibration loads. In addition, there is still a deficit of information for effective but safe recommendations for WBV application for trunk and neck muscles. Therefore, this doctoral thesis deals with three major aspects of WBV as an exercise modality in strength training: (1) the recommendation of optimal vibration loads (VbLs) for the lower extremities as an essential element of the WBV exercise parameters in older adults, (2) the evaluation of these VbLs in a WBV training intervention for elderly people with regard to feasibility and chronic effects on neuromuscular performance of the lower limbs, and (3) the allocation of information for effective but safe advices for VbLs for trunk and neck muscles. These aspects are further specified toward five hypotheses (H1, H2, H3, H4, and H5) by findings and limitations of the current state of literature. Methods The five hypotheses are evaluated within three research papers (studies 1 to 3). The first study (S1) evaluated the optimal VbL determined by the combination of three biomechanical variables (vibration frequency, vibration amplitude, and knee angle) in older adults (H1). Therefore, the neuromuscular activity of the quadriceps femoris and hamstring muscles in 51 healthy subjects were measured during WBV exposure using surface electromyography (EMG). Maximal voluntary contractions (MVCs) were conducted prior to the measurements to normalise the EMG signals. A three-way mixed ANOVA was performed to analyse the different effects of the biomechanical variables on muscle activity. Study 2 (S2) represents a randomised controlled trial to assess the results of S1 implemented in a WBV training protocol and therefore to evaluate the feasibility and effectiveness of a six-week WBV intervention (H2, H3, and H4). A total of 21 subjects was allocated randomly into either a WBV training or control group. While the WBV group completed a six-week WBV training programme the control group was asked not to change their current level of physical activity during the study. Before and after the intervention period, jump height was measured during a countermovement jump (CMJ). In addition, isokinetic knee extension and flexion strength parameters were recorded using a motor-driven dynamometer. The Borg scale for ratings of perceived exertion (RPE scale) was used to evaluate the intensity of WBV exercises within each training session. Changes from pre- to posttest were analysed by a paired sample t-test (within-group comparisons) and independent sample t-test (between-group comparisons). The intention of study 3 (S3) was to analyse the impact of biomechanical variables on neuromuscular activity of different trunk and neck muscles during WBV (H5) filling the lack of information in current literature. Those biomechanical variables were assumed, which current literature suggests as having the lowest risk of negative side effects on the head. Surface EMG was used to record the neuromuscular activity in 28 healthy subjects. EMG signals were normalised to prior measured MVC. Different effects of the biomechanical variables were analysed by an ANOVA for repeated measurements. Results The findings of S1 showed that the biomechanical variables affect the level of neuromuscular activity of thigh muscles in older adults in different dimensions which confirms H1. The maximum levels of muscle activity were significantly reached at high amplitude and high frequency, whereas the factor “knee angle” only significantly affected the quadriceps femoris. Furthermore, WBV led to a higher muscle activation of the quadriceps femoris (74.1 % MVC) than of the hamstring muscles (27.3 % MVC). The main findings in S2 were an increased multi-joint strength performance of the lower limbs during a countermovement jump in the WBV group, whereas values of the control group remained unchanged after the intervention, thus confirming H2. There were no statistically significant differences in isokinetic maximal strength, mean power, or work values in knee extension or flexion in both groups (rejecting H3). In addition, the subjective perceived exertion of the WBV exercises and respective training parameters ranged between moderate rating levels of 7 and 13 of the Borg scale and indicate WBV intervention as a feasible and safe training program for elderly people, which is consistent with H4. Finally, the outcomes of S3 confirmed H5 as the biomechanical variables affect the level of neuromuscular activity of the trunk and neck in different dimensions. The maximum levels of muscle activity were significantly reached at high amplitude and high frequency, while knee angles had similar effects on the VbL. WBV led to a higher muscle activation of the lower back muscles (27.2% MVC) than of neck muscles (8.5 % MVC) and the abdominal muscles (3.6 % MVC). Conclusion A maximised VbL for WBV training in older adults depends on specific combinations of the biomechanical variables (vibration frequency, vibration amplitude, and knee angle). In addition, a WBV training based on this age-specific high VbL is a feasible, suitable and effective training program for elderly people to prevent age-related reduction of muscle performance in the lower extremities. Furthermore, the combination of biomechanical variables recommended in literature as safe for preventing harmful transmissions to the head, only elicit low to moderate muscle activation of the upper body. The findings of this thesis represent fundamental research in the field of WBV and may help to improve further research in this area. Finally, this thesis may help coaches and therapists to enhance the quality of WBV training in practical application.
Hintergrund Ganzkörpervibration (Whole-Body Vibration, WBV) hat sich als Trainingsanwendung im Sport-, Fitness, Rehabilitationsbereich und klinischen Bereich etabliert, wobei die Übungen dabei im Stehen auf einer Vibrationsplatte durchgeführt werden. In diesem Zusammenhang ist auch das wissenschaftliche Interesse am Vibrationstraining ein stetig wachsendes Feld in den Bereichen der Sportwissenschaft und Forschung. Bisher konnte gezeigt werden, dass Vibrationstraining verschiedene biologische als auch physiologische Reaktionen beim Menschen hervorruft. Dennoch gibt es nur wenige Untersuchungen, die sich mit den Auswirkungen des Vibrationstrainings auf die neuromuskuläre Leistung der unteren Extremitäten bei älteren Menschen beschäftigen. Des Weiteren weißen die Ergebnisse dieser wenigen Studien viele Widersprüchlichkeiten auf, welche durch die unterschiedlich verwendeten Trainingsvorgaben und Vibrationsbelastungen verursacht sein könnten. Darüber hinaus besteht noch ein großes Defizit an grundlegenden Informationen hinsichtlich effektiver, aber dennoch sicherer Vorgaben in der Anwendung des Vibrationstrainings im Bereich der Rumpf- und Nackenmuskulatur. Vor diesem Hintergrund beschäftigt sich die vorliegende Dissertation mit drei wesentlichen Aspekten des Vibrationstrainings: (1) die Empfehlung von optimalen Vibrationsbelastungen (VbL) als wesentlicher Bestandteil des Vibrationstrainingsplans der unteren Extremitäten älterer Menschen, (2) die Evaluierung dieser VbL anhand einer auf Vibrationstraining basierter Intervention mit älteren Menschen hinsichtlich Durchführbarkeit und Auswirkungen auf die neuromuskuläre Leistung der unteren Gliedmaßen, und (3) Angaben für effektive und sichere VbL für Rumpf- und Nackenmuskulatur bereitzustellen. Mit der Aufarbeitung von Ergebnissen und Defiziten des aktuellen Forschungsstands werden diese Aspekte durch die Formulierung von fünf Hypothesen (H1, H2, H3, H4, and H5) weiter spezifiziert. Methodik Die fünf Hypothesen werden in drei wissenschaftlichen Veröffentlichungen (Studie 1 bis 3) untersucht. Die erste Studie (S1) befasste sich mit der optimalen VbL für ältere Personen (H1), welche durch die Kombination von drei biomechanischen Variablen (Vibrationsfrequenz, Vibrationsamplitude und Kniewinkel) bestimmt wird. Hierzu wurde die neuromuskuläre Aktivität der vorderen und hinteren Oberschenkelmuskulatur von 51 gesunden Probanden unter Vibration mittels Oberflächen-Elektromyografie (EMG) gemessen. Vor den Messungen wurden maximale muskuläre Kontraktionen durchgeführt, um die EMG zu normalisieren. Um die unterschiedlichen Auswirkungen der biomechanischen Variablen zu analysieren wurde eine drei-faktorielle Varianzanalyse durchgeführt. Studie 2 (S2) entspricht einer randomisierten kontrollierten Studie, welche die Ergebnisse aus S1 in einem Trainingsplan verwendet, um die Durchführbarkeit und Effektivität eines sechs wöchigen Vibrationstrainings zu untersuchen (H2, H3, und H4). Hierfür wurden 21 Probanden zufällig einer Vibrationstrainings- oder einer Kontrollgruppe zugeteilt. Während die Vibrationsgruppe ein sechs wöchiges Vibrationstraining absolvierte, wurden die Teilnehmer der Kontrollgruppe gebeten ihre körperliche Aktivität während des Studienzeitraums nicht zu verändern. Vor und nach dem Untersuchungszeitraums wurde die Sprunghöhe während eines „countermovement jump“ (CMJ) erfasst. Weiterhin wurden isokinetische Kraftmessgrößen der Kniegelenkbeugung und –streckung an einem Dynamometer ermittelt. Die Borgskala zur Erfassung des subjektiven Belastungsempfindens wurde eingesetzt, um die Intensität der Übungen des Vibrationstrainings innerhalb einer Trainingseinheit zu messen. Veränderungen der Messgrößen zwischen Eingangs- und Abschlusstest wurden statistisch mit einem t-Test für abhängige (innerhalb einer Gruppe) und einem t-Test für unabhängige Stichproben (zwischen den Gruppen) untersucht. Ziel der dritten Studie (S3) war es den Einfluss der biomechanischen Variablen auf die muskuläre Aktivierung verschiedener Rumpf- und Nackenmuskeln (H5). Hierzu wurden solche biomechanische Variablen ausgesucht, welche laut derzeitigem Wissensstand jeweils das geringste Risiko von Nebenwirkungen für den Kopf ausüben. Mittels Oberflächen-EMG wurde die muskuläre Aktivität von 28 Probanden erfasst. EMG Signale wurden zu vorangegangenen MVC Messungen normalisiert. Die Unterschiedlichen Effekte der biomechanischen Variablen wurden mittels einer Varianzanalyse für Messwiederholungen analysiert. Ergebnisse Die Ergebnisse von S1 konnten zeigen, dass die biomechanischen Variablen den neuromuskulären Aktivierungsgrad der Oberschenkelmuskulatur bei älteren Personen unterschiedlich beeinflussen und somit H1 bestätigen. Der höchste Grad der Aktivierung wurde deutlich mit einer großen Amplitude und hohen Frequenz erreicht, wobei der Kniewinkel ausschließlich die vordere Oberschenkelmuskulatur beeinflusst. Zudem, führte der Vibrationseinfluss zu einer größeren Muskelaktivität der Oberschenkelvorderseite (74.1 % MVC) als der –rückseite (27.3 % MVC). Die Resultate von S2 hinsichtlich des CMJ Tests bestätigen H2, da es in der Vibrationstrainingsgruppe zu einer gesteigerten gelenksübergreifender Kraftleistung in den Beinen kam, aber keine Veränderungen in der Kontrollgruppe feststellbar waren. Hingegen kam es in keiner Gruppe zu statistisch signifikanten Veränderungen der isokinetischen Messgrößen (Maximalkraft, Kraftleistung, Muskelarbeit), wodurch H3 abgelehnt wird. Das subjektive Belastungsempfinden der Übungen und des Belastungsgefüges des Vibrationstrainings liegt zwischen moderaten Bewertungsstufen von 7 bis 13 der Borgskala und weist daraufhin, dass Vibrationstraining ein praktikables und sicheres Übungsprogramm für ältere Menschen ist und somit H4 bestätigt. Die Ergebnisse von S3 konnten H5 bestätigen, da die biomechanischen Variablen den neuromuskulären Rumpf- und Nackenmuskulatur unterschiedlich beeinflussen. Der höchste Grad der Aktivierung wurde deutlich mit einer großen Amplitude und hohen Frequenz erreicht, wobei der Kniewinkel sich ähnlich auf die VbL auswirkt. Der Vibrationsstimulus führte zudem zu einer höheren Aktivierung der unteren Rückenmuskulatur (27.2% MVC) als der Nacken- (8.5 % MVC) und Bauchmuskulatur (3.6 % MVC). Schlussfolgerungen Die maximale muskuläre Belastung älterer Personen in einem Vibrationstrainings hängt von bestimmten Kombinationen der biomechanischen Variablen (Vibrationsfrequenz, Vibrationsamplitude und Kniewinkel). Zudem ist ein Vibrationstraining, das auf altersspezifischen Vibrationsbelastungen basiert ein machbares, angemessenes und effektives Trainingsprogramm für älteren Menschen, um einem altersbedingten Abnehmen der muskulären Leistungsfähigkeit vorzubeugen. Weiterhin führt die Verbindung von biomechanischen Variablen, welche laut bisherigem Forschungsstand als sicher gegen schädliche Vibrationsübertragungen zum Kopf gelten, nur zu leichten bis moderaten Muskelaktivierung im Oberkörper. Die Ergebnisse dieser Dissertation liefern einen Beitrag zur Grundlagenforschung auf dem Gebiet des Vibrationstrainings und können weiteren Forschungsarbeiten hilfreich sein. Darüber hinaus kann diese Arbeit helfen die Qualität von Vibrationstrainingsangeboten zu verbessern und somit zum praktischen Nutzen beitragen.

No
When descending stairs bodyweight becomes supported on a single limb while the forwards-reaching contralateral limb is lowered in order to make contact with the step below. This is associated with lowering of the centre of mass (CoM), which in order to occur in a controlled manner, requires increased ankle and knee joint torque production relative to that in overground walking. We have previously shown that when descending steps or stairs older people operate at a higher proportion of their maximum eccentric capacity and at, or in excess of the maximum passive reference joint range of motion. This suggests they have reduced and/or altered control over their CoM and we hypothesised that this would be associated with alterations in muscle activity patterns and in the CoM vertical acceleration and velocity profiles during both the lowering and landing phases of stair descent. 15 older (mean age 75 years) and 17 young (mean age 25 years) healthy adults descended a 4-step staircase, leading with the right limb on each stair, during which CoM dynamics and electromyographic activity patterns for key lower-limb muscles were assessed. Maximum voluntary eccentric torque generation ability at the knee and ankle was also assessed. Older participants compared to young participants increased muscle co-contraction relative duration at the knee and ankle of the trailing limb so that the limb was stiffened for longer during descent. As a result older participants contacted the step below with a reduced downwards CoM velocity when compared to young participants. Peak downwards and peak upwards CoM acceleration during the descent and landing phases respectively, were also reduced in older adults compared to those in young participants. In contrast, young participants descended quickly onto the step below but arrested their downward CoM velocity sooner following landing; a strategy that was associated with longer relative duration lead-limb plantar flexor activity, increased peak upwards CoM acceleration, and a reduced landing duration. These results suggest that a reduced ability to generate high eccentric torque at the ankle in the forward reaching limb is a major factor for older participants adopting a cautious movement control strategy when descending stairs. The implications of this CoM control strategy on the incidences of falling on stairs are discussed.