Thesis (M. Med. Sc.)--University of Hong Kong, 200.

Background: Physical functioning and mobility of older populations are of increasing interest when populations are aging. Lower body functioning such as walking is a fundamental part of many actions in daily life. Limitations in mobility threaten independent living as well as quality of life in old age. In this study we examine differences in physical aging and convert those differences into the everyday measure of single years of age. Methods: We use the English Longitudinal Study of Ageing, which was collected biennially between 2002 and 2012. Data on physical performance, health as well as information on economics and demographics of participants were collected. Lower body performance was assessed with two timed walks at normal pace each of 8 ft (2.4 m) of survey participants aged at least 60 years. We employed growth curve models to study differences in physical aging and followed the characteristic-based age approach to illustrate those differences in single years of age. Results: First, we examined walking speed of about 11,700 English individuals, and identified differences in aging trajectories by sex and other characteristics (e.g. education, occupation, regional wealth). Interestingly, higher educated and non-manual workers outperformed their counterparts for both men and women. Moreover, we transformed the differences between subpopulations into single years of age to demonstrate the magnitude of those gaps, which appear particularly high at early older ages. Conclusions: This paper expands research on aging and physical performance. In conclusion, higher education provides an advantage in walking of up to 15 years for men and 10 years for women. Thus, enhancements in higher education have the potential to ensure better mobility and independent living in old age for a longer period. (author's Abstract)

Walking is an essential behavior across the animal kingdom. To navigate complex environments, animals must have highly robust, yet flexible locomotor behaviors. One crucial aspect of this process is the selection of an appropriate walking speed. Speed shifts entail not only the scaling of behavioral parameters (such as faster steps) but also changes in coordination to produce different gaits, and the details of how this switch occurs are currently unknown. Modulatory substances, particularly small biogenic amine neurotransmitters, can alter the output and even the connectivity of motor circuits. This work addresses the hypothesis that one such neuromodulator – serotonin (5HT) – is a key regulator of walking speed at the level of motor circuitry. To explore this question, I use the model organism Drosophila melanogaster which, like vertebrates, displays complex coordinated locomotion at a wide range of speeds. In Chapter 2, I will describe our efforts to characterize the anatomy of the serotonergic cell populations that provide direct input to motor circuitry. I find that innervation of the neuropil of the ventral nerve cord - a structure roughly analagous to the mammalian spinal cord - is provided primarily by local modulatory interneurons. Using stochastic single cell labeling techniques, I will detail the specific anatomy of individual neuromodulatory cells, and also the distribution of synapses across their processes. In Chapter 3, I will show that optogenetic activation or tonic inhibition of VNC serotonergic neurons produces opposing shifts in walking speed. To analyze behavior, I will use two complementary approaches. On the one hand, I will use an arena assay to holistically assess walking velocity and frequency. On the other, I will use a behavioral assay developed in the lab - the Flywalker - to assess walking kinematics at high resolution. The combination of these technique will give us a broad and specific picture of how the VNC serotonergic system modulates walking. In Chapter 4, I will identify natural behavioral contexts under which serotonin is used to shift walking behavior. I will use a variety of paradigms that induce animals to shift their speed, from changes in orientation and nutrition state, to pulses of light, odor, and a vibration. I will assess the requirement for the VNC serotonergic system under all of these conditions, to build a clearer picture of its role in modulating behavioral adaptation. In Chapter 5, I will describe our efforts, in collaboration with Pavan Ramdya's lab at EPFL, to functionally image VNC serotonergic cells while the animal is walking, to understand how activity is endogenously regulated in this population. Finally, in Chapter 6 I will characterize the circuit elements which might be responsible for serotonin's effect on walking. I will use recently developed mutant lines to identify the particular serotonergic receptors responsible for enacting shifts in walking behavior. Using genetic labeling tools, I will identify potential targets of serotonergic signaling in the VNC, and formulate a model by which action on these targets could adjust locomotor output. Altogether, this work seeks to characterize the anatomy and behavioral role of the VNC serotonergic system in Drosophila. I hope that through this work, I will gain a deeper understanding of not only this particular modulatory system in this particular behavioral context, but also of how static circuits are conferred with essential flexibility in behaving animals.

Study design is among the most fundamental factors influencing collection and interpretation of data. The purpose of this study is to understand the effect of design choices by evaluating gait mechanics in healthy control participants using three primary objectives: 1) determine the repeatability of marker placement, 2) determine the effect of set versus self-selected walking speed, and 3) examine the correlation between gait asymmetry and motor variability. Ten and fifty-one healthy control participants were recruited for aim 1 and aims 2/3, respectively. Reflective markers were placed on lower-extremity bony landmarks and participants walked on an instrumented treadmill while 3D motion capture data was collected. For aim 1, this procedure was repeated at two time points 30 minutes apart. For aims 2 and 3, participants completed set and self-selected speed trials. JMP Pro 13 was used to compare joint kinetics and gait kinematics for all aims. Marker placement was repeatable between time points. Participants walked slower in the self-selected walking speed trial, which resulted in both kinematic and kinetic gait mechanics alterations. Gait asymmetry was significantly correlated with motor variability for both spatial and temporal measures. Current study findings reiterated the importance of walking speed when evaluating gait symmetry, joint kinetics, and kinematics. The decision regarding whether to utilize a set or self-selected speed condition within a study design should be made based on whether the measures of interest are independent of walking speed. Gait asymmetry and motor variability are related and should not be treated as independent components of gait. / Master of Science / This study aims to evaluate gait mechanics in healthy young adults by evaluating the impact of multiple study design choices and relationships between different aspects of gait (walking). Loading and movement walking data was collected from a total of sixty-one participants. This data was then used to calculate several measures of gait including symmetry between limbs, joint ranges of motion, and variability of movement. The potential impact of study design choices including setting walking speed for all participants and evaluating loading asymmetry and movement variability independently are discussed based on the findings of the current study.

Student Number : 0414012 - MSc dissertation - School of Therapeutic Sciences - Faculty of Health Sciences / Aim: The aim of this study was to quantify the level of ability and in particular walking ability of a group of stroke survivors resident in Soweto, between 3-6 months post incident. Design: Descriptive study in which comfortable walking speed over ten metres is correlated with the distance covered in six minutes and two minutes. Subjects: Forty one subjects after stroke divided into two groups. Twenty six with a Barthel Index initial score of ≤60 and fifteen with a score >60. Main Outcome Measures: Walking speed and two and six minute distance were compared between groups. In addition actual distance walked in six minutes was compared with the distance predicted by the ten-metre walking speed test and the distance predicted by normative reference equations. Heart rate was measured during the six minute walking test. Functional ability was compared using the Barthel Index within ten days post stroke and three to six months. Results: Of those who survived 90% of subjects were able to walk independently after stroke. The mean walking speed of 0.55 m/s demonstrated a strong correlation with the distance walked in six minutes (R2=0.816). However it underestimated the distance walked in six minutes by 7.4%. There were no significant differences between groups for the walking tests. The two minute walking test distance accurately predicted the results of the six minute walking test distance (R2=0.97). The average distance walked in six minutes by subjects after stroke was 40% of the distance predicted for healthy adults. For the functional walk test 95.5% of subjects had a heart rate within normal recommended limits. The functional walk test together with a measure of exertion (heart rate) may indicate an individual's ability to sustain submaximal activity. Subjects had minimal rehabilitation training. Lower limb pain did not significantly lower the walking speed (p=0.18) or distance walked in six minutes (p=0.17). Mean Barthel Index score at three to six months was 85.78 indicative of independence with minimal assistance. Although the mortality rate for the Barthel Index group with a score less than 60 is 30.7%, the prognosis of survivors was not uniformly poor. Conclusion: This study demonstrates that though a high percentage of subjects recovered independent walking after stroke in the Soweto community with minimal rehabilitation, their walking speed and distance walked are indicative of limited walking capacity. Walking speed and the two minute walking test could be used to predict functional walk test performance. Pain in the paretic lower limb though commonly reported did not appear to affect walking speed or distance walked. The use of the Barthel Index to predict activities and/or survival merits further investigation.

This research investigates the effect of pedestrian countdown signals (PCS devices) on crossing walking speed of pedestrians at urban signalized intersections. The research considers two age groups: (1) younger pedestrians (ages 20 to 64); and (2) older pedestrians (ages 65 and older). Two pedestrian walking speeds were used for this research: (1) crossing walking speed (speed pedestrians walk crossing a signalized intersection); and (2) normal walking speed (speed pedestrians walk a segment of sidewalk). The research found that PCS devices have an effect on a pedestrians’ crossing walking speed, regardless of age, by decreasing the speed. Older pedestrians alter their walking speed after the installation of PCS devices more than younger pedestrians. Furthermore, after the installation of PCS devices the walking speed of pedestrians shifts from a faster crossing walking speed towards a slower normal walking speed.

Yes / Background Disruptions to the progress of the centre-of-pressure trajectory beneath prosthetic feet have been reported previously. These disruptions reflect how body weight is transferred over the prosthetic limb and are governed by the compliance of the prosthetic foot device and its ability to simulate ankle function. This study investigated whether using an articulating hydraulic ankle attachment attenuates centre-of-pressure trajectory fluctuations under the prosthetic foot compared to a fixed attachment. Methods Twenty active unilateral trans-tibial amputees completed walking trials at their freely-selected, comfortable walking speed using both their habitual foot with either a rigid or elastic articulating attachment and a foot with a hydraulic ankle attachment. Centre-of-pressure displacement and velocity fluctuations beneath the prosthetic foot, prosthetic shank angular velocity during stance, and walking speed were compared between foot conditions. Findings Use of the hydraulic device eliminated or reduced the magnitude of posteriorly directed centre-of-pressure displacements, reduced centre-of-pressure velocity variability across single-support, increased mean forward angular velocity of the shank during early stance, and increased freely chosen comfortable walking speed (P ≤ 0.002). Interpretation The attenuation of centre-of-pressure trajectory fluctuations when using the hydraulic device indicated bodyweight was transferred onto the prosthetic limb in a smoother, less faltering manner which allowed the centre of mass to translate more quickly over the foot.

In this study, we analyzed elderly people in Thailand to identify the validity of suggested cutoff points of physical measures, handgrip strength, usual walking speed, and a composite score of both measures to predict functional limitations. Moreover, we examined whether these physical performance measures are accurate indicators of the investigated health outcomes. Methods: Using Receiver Operating Characteristics (ROC) analysis, we investigated a sample of 8272 respondents aged 60 to 79 years. All data were based on the 2009 National Health Examination Survey (NHES IV) of Thailand. Results: For males aged 60 to 69 years, handgrip strength was used as an indicator of functional limitations. The cutoff point for disabilities in the activities of daily living (ADLs) was 29.5 kg, while in other limitations it ranged from 28.7 to 31.3 kg. In contrast, usual walking speed was able to indicate ADL disabilities at 0.7 m per second (m/s). As one might expect, the cutoff points for males aged 70 to 79 years were lower than for males in the 60 to 69 age group. For females, handgrip strength was able to indicate ADL disabilities at 16.5 kg for both the 60 to 69, and 70 to 79 age groups. Likewise, walking speed was indicative of ADL disabilities at 0.6 m/s for both age groups. Interestingly, the composite measure increases the ability to detect ADL disabilities in the younger group but not in the older group. The area under the curve (AUC) of cutoffs measuring the detection power of a diagnostic test was varied, ranging from 0.535 to 0.7386. Conclusions: The cutoff points of three measures varied according to sex and type of functional limitations. Our findings also showed that physical performance measures were useful for identifying people with an increased risk of functional limitations, particularly for ADL disabilities. However, although the AUC of the cutoffs of other functional limitations were relatively low, they should be considered with caution.

Introdução. Os pacientes com DPOC apresentam capacidade de exercício reduzida e limitação funcional para realização de suas atividades diárias, impactando a qualidade de vida desses indivíduos. Além disso, foi demonstrado para esses indivíduos um maior risco de queda em comparação a indivíduos saudáveis da mesma idade. Contudo, não se sabe o papel da intolerância ao exercício em variáveis relacionadas a locomoção dos pacientes com DPOC como o custo de transporte (C), a velocidade autosselecionada (VAS) e a estabilidade dinâmica, que podem auxiliar na dimensão da influência dessa intolerância na vida diária desses indivíduos. Objetivo. O presente estudo se propôs a investigar o comportamento do C, da eficiência ventilatória, do conforto ventilatório e da estabilidade dinâmica em diferentes velocidades de caminhada de indivíduos com DPOC e comparar com indivíduos sem a doença, além de verificar a possível correspondência entre a VAS e a velocidade ótima. Materiais e Métodos. Onze participantes com DPOC fizeram parte desse estudo e foram comparados com onze controles pareados por sexo e idade. Eles foram primeiramente submetidos a um teste de exercício cardiopulmonar e, em um segundo momento, a uma avaliação do C. No protocolo submáximo, os participantes caminharam em cinco velocidades diferentes, sendo uma a VAS e outras quatro ±20% e ±40% da VAS. Além disso, os participantes foram avaliados em uma velocidade pré-determinada igual a todos (isovelocidade). Para todas as velocidades do protocolo os participantes caminharam durante cinco minutos. A partir dos valores de consumo de oxigênio (VO2) obtidos, foram calculados os valores de C. Simultaneamente, foram realizados registro de vídeos dos participantes para posterior análise cinemática da marcha. Foram calculados a frequência de passada (FP), o comprimento de passada (CP) e o coeficiente de variação (CoV) referente a FP, como medida da estabilidade dinâmica. Resultados. Não houve diferença do C dos pacientes com DPOC em relação aos controles, nem mesmo quando caminhavam em isovelocidade (p=0,623). Em todas as velocidades, os pacientes demonstraram menor eficiência ventilatória. A VAS dos pacientes foi menor, no entanto observou-se menor valor de C nas velocidades mais altas de caminhada. Apesar de os indivíduos com DPOC apresentarem menor FP e CP, a estabilidade dinâmica não demonstrou-se prejudicada na amostra estudada. Conclusão. Pacientes com DPOC caminham em velocidades reduzidas, em relação aos controles, especialmente devido à dispneia acompanhada de uma menor eficiência ventilatória. Embora o C seja semelhante ao de indivíduos saudáveis, os participantes com DPOC apresentaram o índice de reabilitação inferior, sugerindo, portanto, que o mecanismo pendular não esteja otimizado na VAS. Além de não encontrar diferenças na economia de caminhada, foram observadas alterações mínimas na estabilidade dinâmica da marcha destes indivíduos. Terapias que tratem do conforto ventilatório são potenciais ferramentas para a melhora da locomoção de pacientes com DPOC. / Background. Subjects with COPD present reduced exercise capacity and functional limitation to perform daily activities, which affects their quality of life. Furthermore, it is known that this population has increased risk of falls when compared to health subjects. However, it is still unknown the role of exercise intolerance on important variables to assess locomotion, as the cost of transport (C), the self-selected speed (VAS) and the dynamic stability, which might be able to help to dimension the exercise intolerance on their daily life. Objective. To investigate the behaviour of C ventilatory efficiency, ventilatory comfort and dynamic stability at different walking speeds in COPD subjects and compare them to healthy controls, as well as to verify the possible correspondence of VAS and optimal speed. Methods and Materials. 11 patients with COPD participated in this study and were matched with 11 control subjects in terms of gender and age. They underwent a cardiopulmonary exercise test and an evaluation of C. In this last evaluation, participants walked at five different walking speeds, among them VAS and the others ±20% and ±40% of the VAS. There was also a sixth predetermined walking speed (isovelocity). The participants walked during five minutes in each speed. The C values were calculated from the oxygen consumption (VO2) values. Simultaneously, the subjects were filmed for later analysis of gait kinematics. The stride frequency (FP), stride length (CP) and the coefficient of variation (CoV) from FP as a measure of dynamic stability, were calculated. Results. There was no significant difference between the C of participants with COPD and control subjects, not even when walking at isovelocity (p=0,623). For all speeds investigated, the ventilatory efficiency of COPD subjects was impaired when compared to healthy individuals. The participants in COPD group walked at a slower VAS, but the lower value of C was found during faster walking speeds. Even though the COPD group had less FP and shorter strides, their dynamic stability showed minimal impairment. Conclusion. The patients with COPD walked at a reduced walking speed when compared to control subjects, specially caused by dyspnea and a lower ventilatory efficiency. In spite of a similar C between groups, the COPD subjects presented an inferior rehabilitation index, therefore suggesting that their pendulum-like mechanism is not optimal at VAS. Furthermore, besides a walking economy with no differences between groups, minimal impairments were found for dynamic stability in COPD group. Therapies that treat ventilatory comfort are a potential tool to improve locomotion of COPD subjects.

O objetivo deste estudo foi investigar o efeito do erro na localização do centro de pressão (5 e 10 mm) nas incertezas de momentos articulares dos membros inferiores em diferentes velocidades de marcha (1,0, 1,5 e 2,0 m/s). Nossas hipóteses foram que: as incertezas absolutas de momento articular diminuam de distal para o proximal e da condição de maior para a de menor velocidade. Os momentos articulares de cinco adultos jovens saudáveis foram calculados pelo método bottom-up de dinâmica inversa 3D, na dependência do qual estimamos as incertezas propagadas. Os resultados indicaram que existe uma relação diretamente proporcional entre os erros do centro de pressão e as incertezas de momento articular. As incertezas absolutas nos picos de momento expressas no sistema de referência anatômico diminuíram de distal para proximal, confirmando nossa primeira hipótese, exceto para o momento de abdução. Da menor para a maior velocidade de marcha ocorreu um aumento da incerteza no momento (de até 0,04 Nm/kg), confirmando agora nossa segunda hipótese, exceto, mais uma vez, para abduções de joelho e quadril. E ainda, as incertezas relativas variaram dependendo do plano e articulação (entre 5 e 31%), sendo os momentos articulares de joelho os mais afetados / The aim of this study was to investigate the effect of errors in the location of the center of pressure (5 and 10 mm) on lower limb joint moment uncertainties at different gait velocities (1.0, 1.5, and 2.0 m/s). Our hypotheses were that the absolute joint moment uncertainties would be gradually reduced from distal to proximal joints and from higher to lower velocities. Joint moments of five healthy young adults were calculated by inverse dynamics using the bottom-up approach, depending on which estimate the uncertainty propagated. Results indicated that there is a linear relationship between errors in center of pressure and joint moment uncertainties. The absolute moment peak uncertainties expressed on the anatomic reference frames decreased from distal to proximal joints, confirming our first hypothesis, except for the abduction moments. There was an increase in moment uncertainty (up to 0.04 Nm/kg for the 10 mm error in the center of pressure) from the lower to higher gait velocity, confirming our second hypothesis, although, once again, not for hip or knee abduction. Finally, depending on the plane of movement and the joint, relative uncertainties experienced variation (between 5 and 31%), and the knee joint moments were the most affected