Littérature scientifique sur le sujet « Biomechanical variable »

Background and Purpose. Previous studies suggest that individuals poststroke can achieve substantial gains in walking function following high-intensity locomotor training (LT). Recent findings also indicate practice of variable stepping tasks targeting locomotor deficits can mitigate selected impairments underlying reduced walking speeds. The goal of this study was to investigate alterations in locomotor biomechanics following 3 different LT paradigms. Methods. This secondary analysis of a randomized trial recruited individuals 18 to 85 years old and >6 months poststroke. We compared changes in spatiotemporal, joint kinematics, and kinetics following up to 30 sessions of high-intensity (>70% heart rate reserve [HRR]) LT of variable tasks targeting paretic limb and balance impairments (high-variable, HV), high-intensity LT focused only on forward walking (high-forward, HF), or low-intensity LT (<40% HRR) of variable tasks (low-variable, LV). Sagittal spatiotemporal and joint kinematics, and concentric joint powers were compared between groups. Regressions and principal component analyses were conducted to evaluate relative contributions or importance of biomechanical changes to between and within groups. Results. Biomechanical data were available on 50 participants who could walk ≥0.1 m/s on a motorized treadmill. Significant differences in spatiotemporal parameters, kinematic consistency, and kinetics were observed between HV and HF versus LV. Resultant principal component analyses were characterized by paretic powers and kinematic consistency following HV, while HF and LV were characterized by nonparetic powers. Conclusion. High-intensity LT results in greater changes in kinematics and kinetics as compared with lower-intensity interventions. The results may suggest greater paretic-limb contributions with high-intensity variable stepping training that targets specific biomechanical deficits. Clinical Trial Registration. https://clinicaltrials.gov/ Unique Identifier: NCT02507466

OBJECTIVE Concussion is a common topic of research as a result of the short- and long-term effects it can have on the affected individual. Of particular interest is whether previous concussions can lead to a biomechanical susceptibility, or vulnerability, to incurring further head injuries, particularly for youth populations. The purpose of this research was to compare the impact biomechanics of a concussive event in terms of acceleration and brain strains of 2 groups of youths: those who had incurred a previous concussion and those who had not. It was hypothesized that the youths with a history of concussion would have lower-magnitude biomechanical impact measures than those who had never suffered a previous concussion. METHODS Youths who had suffered a concussion were recruited from emergency departments across Canada. This pool of patients was then separated into 2 categories based on their history of concussion: those who had incurred 1 or more previous concussions, and those who had never suffered a concussion. The impact event that resulted in the brain injury was reconstructed biomechanically using computational, physical, and finite element modeling techniques. The output of the events was measured in biomechanical parameters such as energy, force, acceleration, and brain tissue strain to determine if those patients who had a previous concussion sustained a brain injury at lower magnitudes than those who had no previously reported concussion. RESULTS The results demonstrated that there was no biomechanical variable that could distinguish between the concussion groups with a history of concussion versus no history of concussion. CONCLUSIONS The results suggest that there is no measureable biomechanical vulnerability to head impact related to a history of concussions in this youth population. This may be a reflection of the long time between the previous concussion and the one reconstructed in the laboratory, where such a long period has been associated with recovery from injury.

The variable prescription is widely described under the clinical aspect: the clinics is the result of the evolution of the state-of-the-art, aspect that is less considered in the daily literature. The state-of-the-art is the key to understand not only how we reach where we are but also to learn how to manage propely the torque, focusing on the technical and biomechanical purpos-es that led to the change of the torque values over time. The aim of this study is to update the clinicians on the aspects that affect the torque under the biomechanical sight, helping them to understand how to managing it, following the “timeline changes” in the different techniques so that the Variable Prescription Orthodontic (VPO) would be a suitable tool in every clinical case.

Background Concussion is an injury that occurs in non-sporting and sporting environments. To determine improved clinical methods for identifying this injury, it is important to develop and understand how the impact event results in quantifiable differences in brain functioning—functioning that has been quantified in the past using saccadic measures. The purpose of this research was to examine the relationships between oculomotor deficits, specifically antisaccade responses, and the biomechanics of impact for a concussion. Methods Participants underwent a diffusion tensor imaging protocol as well as saccadic testing to determine differences in brain functioning in comparison to controls. The injury event was then reconstructed in laboratory using physical and finite element models to determine the biomechanics of the impact and brain tissue strain. Relationships between the biomechanical variables and antisaccade responses were then examined. Results The diffusion tensor imaging analyses found that there was a decrease in radial diffusivity and axial diffusivity found in the cerebral peduncle (p < 0.05) and cingulum hippocampus (p < 0.05), respectively. There was an increase in the axial diffusivity for the corona radiata (p < 0.05). The saccadic testing found an increase in mean latency for the concussed group (p < 0.05). The results indicated no significant relationship between mean latency, duration, amplitude and peak velocity antisaccade measures and the biomechanical variables. This may have been influenced not only by a lack of sensitivity in biomechanical variable to antisaccade responses, but also to these responses being affected by factors other than injury such as attentiveness and wakefulness. Conclusion While the sample of this research was small, this research suggests that to improve the understanding of the relationship between impact biomechanics and concussion, methods that can quantify the damage to brain structures through imaging, such as diffusion tensor imaging, may be more appropriate.

Optimization is frequently employed in biomechanics research to solve system identification problems, predict human movement, or estimate muscle or other internal forces that cannot be measured directly. Unfortunately, biomechanical optimization problems often possess multiple local minima, making it difficult to find the best solution. Furthermore, convergence in gradient-based algorithms can be affected by scaling to account for design variables with different length scales or units. In this study we evaluate a recently- developed version of the particle swarm optimization (PSO) algorithm to address these problems. The algorithm’s global search capabilities were investigated using a suite of difficult analytical test problems, while its scale-independent nature was proven mathematically and verified using a biomechanical test problem. For comparison, all test problems were also solved with three off-the-shelf optimization algorithms—a global genetic algorithm (GA) and multistart gradient-based sequential quadratic programming (SQP) and quasi-Newton (BFGS) algorithms. For the analytical test problems, only the PSO algorithm was successful on the majority of the problems. When compared to previously published results for the same problems, PSO was more robust than a global simulated annealing algorithm but less robust than a different, more complex genetic algorithm. For the biomechanical test problem, only the PSO algorithm was insensitive to design variable scaling, with the GA algorithm being mildly sensitive and the SQP and BFGS algorithms being highly sensitive. The proposed PSO algorithm provides a new off-the-shelf global optimization option for difficult biomechanical problems, especially those utilizing design variables with different length scales or units.

Abstract Running biomechanics and its evolution that occurs over intensive trials are widely studied, but few studies have focused on the reproducibility of stride evolution in these runs. The purpose of this investigation was to assess the reproducibility of changes in eight biomechanical variables during exhaustive runs, using three-dimensional analysis. Ten male athletes (age: 23 ± 4 years; maximal oxygen uptake: 57.5 ± 4.4 ml02·min-1·kg-1; maximal aerobic speed: 19.3 ± 0.8 km·h-1) performed a maximal treadmill test. Between 3 to 10 days later, they started a series of three time-to-exhaustion trials at 90% of the individual maximal aerobic speed, seven days apart. During these trials eight biomechanical variables were recorded over a 20-s period every 4 min until exhaustion. The evolution of a variable over a trial was represented as the slope of the linear regression of these variables over time. Reproducibility was assessed with intraclass correlation coefficients and variability was quantified as standard error of measurement. Changes in five variables (swing duration, stride frequency, step length, centre of gravity vertical and lateral amplitude) showed moderate to good reproducibility (0.48 ≤ ICC ≤ 0.72), while changes in stance duration, reactivity and foot orientation showed poor reproducibility (-0.71 ≤ ICC ≤ 0.04). Fatigue-induced changes in stride biomechanics do not follow a reproducible course across the board; however, several variables do show satisfactory stability: swing duration, stride frequency, step length and centre of gravity shift.

Abstract Study aim: This study aims to identify biomechanical gait variables explaining clinical test results in institutionalized elderly people. Material and methods: Twenty-nine elderly (82.0 ± 6.3 years) residents in a nursing home were assessed. They were able to walk 10 meters without walking aids. First, the spontaneous gait was assessed using inertial measurement units in a 10-meter long corridor. Fifteen biomechanical gait variables were analyzed. Then, three clinical tests usually used in elderly subjects were applied: the Timed Up and Go (TUG) test, the Tinetti Scale and the Sit to Stand (STS) test. A correlation matrix using Pearson’s correlation coefficient between clinical and biomechanical variables was performed, obtaining a total of 45 potential correlations. A stepwise multiple linear regression analysis was then performed to determine the influence of each variable. Results: TUG, Tinetti and STS were significantly correlated with similar biomechanical variables, including temporal, temporo-spatial and kinematic variables. Adults over 80 years old and women showed stronger correlations. Single support and ankle angle at takeoff were the two most important variables in stepwise regression analysis. Conclusions: In institutionalized elderly subjects, clinical variables for gait and postural stability are correlated with the biomechanical gait variables, especially in women and adults aged over 80 years.

Background: Despite an abundance of literature regarding construct strength for a myriad of anchors and anchor configurations in the shoulder, there remains a paucity of biomechanical studies detailing the efficacy of these implants for proximal hamstring repair. Purpose: To biomechanically evaluate the ultimate failure load and failure mechanism of knotless and knotted anchor configurations for hamstring repair. Study Design: Controlled laboratory study. Methods: A total of 17 cadaveric specimens divided into 3 groups composed of intact hamstring tendons as well as 2 different anchor configurations (all-knotted and all-knotless) underwent first cyclic loading and subsequent maximal loading to failure. This protocol entailed a 10-N preload, followed by 100 cycles incrementally applied from 20 to 200 N at a frequency of 0.5 Hz, and ultimately followed by a load to failure with a loading rate of 33 mm/s. The ultimate failure load and mechanism of failure were recorded for each specimen, as was the maximal displacement of each bone-tendon interface subsequent to maximal loading. Analysis of variance was employed to calculate differences in the maximal load to failure as well as the maximal displacement between the 3 study groups. Holm-Sidak post hoc analysis was applied when necessary. Results: The all-knotless suture anchor construct failed at the highest maximal load of the 3 groups (767.18 ± 93.50 N), including that for the intact tendon group (750.58 ± 172.22 N). There was no statistically significant difference between the all-knotless and intact tendon groups; however, there was a statistically significant difference in load to failure when the all-knotless construct was compared with the all-knotted technique (549.56 ± 20.74 N) ( P = .024). The most common mode of failure in both repair groups was at the suture-tendon interface, whereas the intact tendon group most frequently failed via avulsion of the tendon from its insertion site. Conclusion: Under biomechanical laboratory testing conditions, proximal hamstring repair using all-knotless suture anchors outperformed the all-knotted suture anchor configuration with regard to elongation during cyclic loading and maximal load to failure. Failure in the all-knotted repair group was at the suture-tendon interface in most cases, whereas the all-knotless construct failed most frequently at the musculotendinous junction. Clinical Relevance: No biomechanical studies have clearly identified the optimal anchor configuration to avert proximal hamstring repair failure. Delineating this ideal suture anchor construct and its strength compared with an intact hamstring tendon may alter the current standards for postoperative rehabilitation, which remain extremely conservative and onerous for these patients.

This paper examines the mechanics of the tibiotalocalcaneal construct made with a PHILOS plating system. A failed device consisting of the LCP plate and cortical, locking, and cannulated screws was used to perform the analysis. Visual, microstructure, and fractographic examinations were carried out to characterize the fracture surface topology. These examinations revealed the presence of surface scratching, inclusions, discoloration, corrosion pits, beach marks, and cleavage and striations on the fracture surface. Further examination of the material crystallography and texture revealed an interaction of S, Ni, and Mo-based inclusions that may have raised pitting susceptibility of the device made with Stainless Steel 316L. These features suggest that the device underwent damage by pitting the corrosion-fatigue mechanism and overloading towards the end to fail the plate and screws in two or more components. The screws failed via conjoint bending and torsion fatigue mechanisms. Computer simulations of variable angle locking screws were performed in this paper. The material of construction of the device was governed by ASTM F138-8 or its ISO equivalent 5832 and exhibited inconsistencies in chemistry and hardness requirements. The failure conditions were matched in finite element modeling and those boundary conditions discussed in this paper.

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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Pain emanating from the cervical spine represents a significant diagnostic and therapeutic challenge for clinicians. The precise etiology of the pain may be difficult to identify because there are many potential pain-generating structures in the cervical spine and surrounding region. It is helpful to delineate the patient’s symptoms as axial- or radicular-predominant in order to guide the investigation prior to initiating treatment. The evidence for many commonly used treatment regimens is variable, and therefore an individualized plan is often necessary. Although it is conceptually accommodating to compartmentalize the etiology of cervical spine pain from a single source, the reality is that multiple structures are often involved, given the complex anatomy of the cervical spine. This chapter discusses cervical spine anatomy and biomechanics, as well as the etiology, pathophysiology, and management options for axial and radicular neck pain.

One of the great limitations in applying research involving the military population is that data are taken from other studies that do not reflect the specific characteristics or conditions of Colombian soldiers. Regardless, the outcomes are applied and appropriated as if these soldiers were, in fact, the sample of the study. In response to this situation, this work publishes the results of research involving the physical performance of Colombian military personnel to provide the academic community with descriptions of the variables that make up this population’s physical fitness training. This work is a first attempt to characterize their physical, physiological, and biomechanical capabilities using the best available evidence and state-of-the-art technology. One of this book’s main contributions to military physical training knowledge is that it is the first initiative to evaluate Colombian military personnel’s level of physical training. The scientific rigor of the studies in this compilation allows the reproducibility of the tests (external validity). It paves the way for a series of studies in military physical performance and health-related factors concerning active members of the National Army, seeking to characterize, evaluate, and determine training programs to optimize the institution’s pillars of doctrine. The ultimate goal is to drive the improvement of soldiers’ physical conditions, favoring a better quality of life and safety in operational performance.

Government recommendations have been made to place children into the rear seating areas of motor vehicles in order to alleviate airbag hazards in frontal impact. In most moderate to severe rear impacts, however, the adult occupied front seats will “yield” or “collapse” into the rear seat area and thus pose another potential head and chest injury hazard to the rear seated children. Numerous factors or variables, each with a wide parameter range, influence whether or not an occupied collapsing front seat will result in engagement with the rear occupant, and whether that engagement is likely to cause injury to the rear-seated occupant. A combined experimental and analytical method, employing instrumented surrogates in a sled-buck test set-up, has been utilized to study the multivariable potential injury problem of the rear-seated child in rear impact. A 3 year-old H-III surrogate, seated in the built-in booster seat of a minivan, was used as the rear seat passenger in this study. Five tests were utilized. The experimental surrogate data from the test method is combined into a “polynomial response function” that expresses “injury levels” (i.e. HIC and chest G) as a function of the many variables, and allows for analytical “interpolation and extrapolation” at variable combinations and ranges not tested. Actual accident cases were compared with the biomechanical injury measures. The present study presents a methodology to delineate the biomechanics of injuries using multivariate analysis.

Vulnerable plaques are inflamed, active, and growing lesions which are prone to complications such as rupture, luminal and mural thrombosis, intraplaque hemorrhage, and rapid progression to stenosis. It remains difficult to assess what factors influence the biomechanical stability of vulnerable plaques and promote some of them to rupture while others remain intact. The rupture of thin fibrous cap overlying the necrotic core of a vulnerable plaque is the principal cause of acute coronary syndrome. The mechanism or mechanisms responsible for the sudden conversion of a stable atherosclerotic plaque to a life threatening athero-thrombotic lesion are not fully understood. It has been widely assumed that plaque morphology is the major determinant of clinical outcome [1, 2]. Thin-cap fibroatheroma with a large necrotic core and a fibrous cap of < 65μm was describes as a more specific precursor of plaque rupture due to tissue stress.

Coronary atherosclerotic plaques are frequently focal lesions that have variable rates of progression. Wall shear stresses (WSS) create a number of responses in endothelial cells that can lead to the localization and progression of these lesions, and in vivo coronary segments with low WSS have been found to develop greater plaque progression than segments of higher WSS.

The ability to track and predict the onset of physiologic fatigue using easily measurable variables is of great importance to both civilian and military activities. In this paper, biomechanical gait variables are used to reconstruct fatigue evolution in subjects walking with a 40 kg load on a level treadmill for two hours. Fatigue is reconstructed in two steps: (1) phase space warping based feature vectors are estimated from gait variable time series; and (2) smooth orthogonal decomposition is used to extract fatigue related trends from these features. These results are verified using independently obtained measures of fatigue from breath-by-breath oxygen consumption (V˙O2) and surface electromyography (EMG) from a set of leg muscles. V˙O2 based measures for some subjects show no discernable trends. However, for a subject showing monotonically increasing oxygen consumption, the reconstructed dominant fatigue variable closely track V˙O2 measure reflecting global systemic fatigue. For the muscles showing variation in EMG-based fatigue measures, the reconstructed fatigue variables also closely track these local muscle trends. The results show that kinematic angles, which are easier quantities to measure in the field, can be used to track and predict the onset of fatigue.

Biomechanical response is often influenced by the geometry (shape) of a system. Numerical techniques such as the finite element (FE) method offer the possibility of incorporating geometric details of a system into a mathematical model with a greater level of detail than is generally achievable with purely analytical models. In this vein, FE models of biological structures tend to fall into two broad categories: generic models and specimen-specific models. Generic models are attractive because the geometric features of interest may be cast as variable parameters that simplify analysis of factor influence, but may be limited in what can be predicted about a specific specimen. In contrast, specimen-specific models may contain a high level of geometric detail, but analysis of the influence of geometry can be more complicated.

In two-wheeled vehicles the mass of the rider is a significant part of the total mass of the system and the rider influences the dynamic behavior both by means of the voluntary control actions and by means of the passive response of his body to the oscillations of the vehicle. The passive response of the rider’s body has a particular influence on roll motion, which is typical of two-wheeled vehicles. Roll oscillations generate inertia forces on the rider’s body, which moves with respect to the vehicle. Forces and torques generated by the rider on the handlebars, saddle and foot rests are different from the ones that would be generated if the body was rigidly fixed to the vehicle. Therefore, advanced simulation of two wheeled vehicles requires passive biomechanical models of the rider. This paper proposes a novel approach for the study of the passive response of the rider’s body that is based on measurements in the laboratory of the interaction forces between the rider and the vehicle. A special motorcycle mock-up is developed, it is driven by a hydraulic shaker that generates roll excitation with variable frequency. A system of load cells measures the lateral force and torque between the rider and the motorcycle mock-up. The study is carried out in the frequency domain, the passive response of rider’s body is represented by means of three frequency response functions (FRFs): lateral force FRF and torque FRF are the ratios between the lateral force/torque and the roll input; motion FRF is the ratio between the roll motion of the rider’s trunk and the roll input. The biomechanical models of the rider’s body that are developed in this work are able to simulate its response both in terms of interaction forces and motion. These models are composed by some rigid bodies with lumped stiffness and damping parameters in the articulations and in this way they represent a good compromise between accuracy and complexity. The biomechanical parameters of the models are identified by means of a genetic algorithm that aims to minimize a penalty function based on the difference between the three FRFs predicted by the model and the measured FRFs. Results show that a 5 degree of freedom model of the rider is able to represent the measured behavior both in terms of interaction forces and trunk motion.

A seven degree-of-freedoms human body-seat-suspension model was built for multi-objective optimization of vehicle ride dynamics behavior. Biomechanical models of human body and elastic model of seat cushion were integrated with classical 1/4 car model. The root mean square values of head acceleration of human body, together with suspension work space and dynamic tire load, were selected as objective functions of optimization. Non-dimension method was introduced into the formulation of objective functions so that optimization could be independent of different running conditions. Parameter sensitivity analysis was utilized to explore the relation between objective functions and parameters of suspension and seat cushion. Based on the results of analysis, design variables were determined. Non-dominated Sorting Genetic Algorithm - II was used in this multi-objective optimization problem to compute Pareto optimal set and Pareto frontier. Results indicate that Pareto frontier includes two parts. These two parts have the nearly same range of dynamic tire load and share partial range of suspension work space in objective function space. In design variable space, two parts respectively correspond to two different distribution areas of Pareto optimal solution set. So, for the same expected objective, parameters of suspension and seat cushion usually have at least one available combination, which improves the flexibility of optimal design.

Structural and biomechanical parameters of Edible Frog, Pelophylax esculentus (Linnaeus, 1758), limb bones, namely, mass, linear dimensions, parameters of the shaft ’s cross-sectional shape (cross-sectional area, moments of inertia, radiuses of inertia) were investigated. Some coeffi cients were also estimated: diameters ratio (df/ds), cross-sectional index (ik), principal moments of inertia ratio (Imax/Imin). Coeffi cients of variation of linear dimensions (11.9–20.0 %) and relative bone mass (22–35 %) were established. Moments of inertia of various bones are more variable (CV = 41.67–56.35 %) in relation to radii of inertia (CV = 9.68–14.67 %). Shaft ’s cross-sectional shape is invariable in all cases. However, there is high individual variability of structural and biomechanical parameters of P. esculentus limb bones. Variability of parameters was limited by the certain range.We suggest the presence of stable norm in bone structure. Stylopodium bones have the primary biomechanical function among the elements of limb skeleton, because their parameters most clearly responsiveto changes in body mass.

This technical report presents the new numerical modeling capabilities for simulating wave attenuation and mean water level changes through flexible vegetation such as smooth cordgrass in coastal and marine wetlands. These capabilities were implemented into the Cross-SHORE (CSHORE) numerical model. The biomechanical properties of vegetation such as dimensions, flexibility, and bending strength are parameterized in terms of the scaling law. Correspondingly, a new formulation of the vegetation drag coefficient, CD, is developed using field data from a salt marsh in Terrebonne Bay, LA, by considering spatially varying effective stem and blade heights of species. This report also presents a general procedure for using the model to simulate hydrodynamic variables (i.e., waves, currents, mean water levels) at vegetated coasts, which are used to quantify the effects of wave attenuation and reduction of surge and runup due to vegetation. Preliminary model validation was conducted by simulating a set of laboratory experiments on synthetic vegetation, which mimicked the flexibility of Spartina alterniflora. The validation results indicate that the newly developed vegetation capabilities enable CSHORE to predict changes of wave heights and water levels through marshes by considering species-specific biomechanical features. The model is also applicable to assess vegetation effectiveness against waves and surges.