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<p> Centre of pressure (CP) excursion frequency characteristics of normal and visually impaired children were examined. Thirty-six normal (N) children and 12 visually impaired (VI) children stood on a force platform under 4 conditions (eyes open or closed, normal or foam surface). CP excursions were analyzed by fast Fourier transformation. Total power was calculated between 0-4 Hz, and percent of total power was calculated in the low (0-1 Hz) and high (1-4 Hz) bands. Linear regression was performed on logarithmically transformed data and the slope was used to compare the relative power at low and high frequencies. Analysis of covariance removed the variance due to height in the N children. The Mann-Whitney test compared theN and VI children. Total power decreased with age. Young children (4-7 years) had more high frequency power. Young children may respond intermittently to feedback with ballistic type movements while older children may continuously monitor and respond to sensory feedback. Vision helped control CP adjustments, but power did not increase between 0-1 Hz with eyes closed. VI had higher total power on the normal surface. With eyes closed the differences were more obvious in the older children (10-12 years) which suggests vision is important in development to fine-tune the sensory systems. The foam reduced pressor receptor feedback, reducing the advantage of more finely tuned somatosense in N children. VI children had more low frequency power than N children (A-P). Young VI children did not have a large amount of high frequency power, as the N children did, suggesting that VI children may adapt at a younger age to continuously monitor and respond to feedback without relying on intermittent ballistic type responses. </p> / Thesis / Master of Science (MSc)

Falls from heights are the fourth leading cause of occupational injury and fatality in the United States. In particular, construction workers such as roofers are often exposed to high risk environments. Recent research has reported that a leading cause of falls among workers is a loss of balance. Therefore, in moving towards reducing the number of occupational falls, further investigation of balance and factors that influence postural control is necessary. The effect of neuromuscular fatigue has been addressed by many investigators; however, few studies have examined the effect of localized fatigue in muscles not located in the lower extremities. Because low back fatigue is so prevalent during manual labor, this investigation determined to study the effects of lumbar extensor fatigue on balance. Chapter 1 includes a complete review of current literature addressing the effects of muscular fatigue on measures of balance. Chapter 2 details an initial investigation of lumbar extensor fatigue on center of pressure (COP) based measures of postural sway and examines the effect of fatiguing rate. Chapter 3 examines the effects of different levels of lumbar extensor fatigue and expands on the previous investigation by examining center of mass (COM) movement and incorporating additional measures of postural control. The results of these investigations indicate that lumbar extensor fatigue affects both COP and COM measures of postural sway, and might also lead to an increased reliance on feedforward postural control mechanisms. These findings contribute to understanding of effects of fatigue on balance and may aid the future design of interventions aimed at fall prevention. / Master of Science

Falls in the workplace are a major cause of injuries and fatalities. Muscle fatigue is one important factor that has been linked to a decrement in postural control and a potential increased falling risk. However, potential interactive effects of muscle fatigue with other risk factors remain unclear, and practical interventions are needed to mitigate the adverse effects of muscle fatigue. The current work was conducted to address these research needs through three experimental studies. The first study investigated how muscle fatigue affects postural control during quiet standing on inclined surfaces. Inclined surfaces compromised postural control, with the most deleterious effects found while standing in a lateral direction. Fatigue did not result in further decrements in postural control during standing on inclined surfaces. The second study investigated the effects of muscle fatigue on postural control while lifting unexpected loads. Lifting an object with unexpected mass compromised postural control, with a more substantial effect found in the unexpectedly light load condition. Fatigue-related effects were not consistent, though there was evidence that lumbar muscle fatigue did not compound the adverse effects of lifting an object in unexpected mass conditions. The last study evaluated the efficacy of three interventions (two auditory stimulations and periodic rest breaks) at mitigating the adverse effects of muscle fatigue on postural control. Allowance of rest breaks did not improve postural control during the fatiguing work, though it was indicated that benefits may be present for some individuals. Both a static pure tone and moving conversation appeared to offset fatigue-induced postural instability. The current research provides a more comprehensive understanding of the contribution of muscle fatigue to fall risks during occupationally relevant tasks and assessed the efficacy of practical interventions to reduce the risk of falls. These findings may facilitate the development of strategies to prevent occupational falls related to muscle fatigue, inclined surfaces, and manual material handling tasks. / Ph. D.

In North America ice hockey is considered to be the fastest of all teamsports with high demands on leg strength and power. These two factors are crucial for acceleration and the total speed performance during a hockeygame. Skating performance requires a muscle engagement which also occurs during the Y-Balance Test (YBT). Some of the most active muscles during ice skating are biceps femoris, tibialis anterior and vastus medialis , these muscles are also some of the most active muscles during the YBT. The similarities between those two activities enable a possible relationship between skating velocity and YBT. This study investigated the relationship between dynamic postural control and on ice performance which includes 52 meter forward skating. The purpose of this study was to see if there is a significant correlation between skating velocity and the performance on YBT. Methods: 7 male ice hockey players in ages between 18-19 years performed a 52 meter forward skating test and a test for evaluating their dynamic postural control. The method used for measuring the dynamic postural control was the YBT. Results: There was no significant correlation between the YBT longitudinal directions, the total score and 52 meter forward skating. The strongest association (0,570) was shown between the YBT anterior longitudinal direction and 52 meter forward skating. The total score on YBT did not show a significant correlation with 52 meter forward skating, with a correlationcoefficient of 0,251. Conclusion: Due to several management errors during the YBT the results showed no significance. We can not for certain say that there is no significant correlation due to for instance management errors and the deficiency pf power. Future studies are needed to determine if there is a significant correlation between skating velocity and the performance on YBT.

An increase in postural sway is one of the risk factors that have been linked to an increased incidence of falls in the older adult population. Researchers have shown that peripheral sensation is crucial in maintaining a static posture for adults of all ages. It has been reported that older adults have decreased tactile sensation of the plantar surface of their feet. and when the sensory feedback was increased older adults had improved postural control. It was hypothesized that facilitation of the sole of the foot with the use of a semirigid foot orthotic would result in improved postural stability in older adults. Twenty-seven volunteers (19 females, 8 males, mean age: 87 ± 5 yrs) were recruited as subjects from a retirement community. All subjects were supplied with the SmartStep™ Stabilization System. There were a total of 5 Test Days for each subject. The first 2 Test Days were performed while the subjects wore their own shoes, while the last 3 Test Days were performed while the subjects wore the SmartStep™. Test Days 1 and 2 were performed 48 hours apart. Test Day 3 occurred 2 to 4 weeks after Test 2. Test Days 4 and 5 occurred 4-weeks after the prior Test Day. During the 8-weeks between Test Days 3 and 5, subjects were asked to wear the SmartStep™ as their daily shoe. Clinical measures of balance, force plate measurements, sensation testing, and confidence and activity scales were collected on all subjects throughout the eight week test period. Statistical significance was found for 3 of the clinical measures. The Timed “Up & Go” improved from 17.25 to 15.47 sec. The Functional Reach and Lateral Reach Tests demonstrated a decline in scores during the eight weeks. There was only 1 statistically significant finding for the force plate measures. The center of pressure displacement in the anteriorposterior direction was increased from 4.6 to 5.3 cm. No significant differences where reported for any other dependent variable. The results did not indicate statistically that the in-shoe orthotic enhanced postural stability in this group of subjects. However, there were indications that there was a subset of the current population that benefited from the intervention and this needs to be investigated further.

The rollator is a mobility aid commonly used to facilitate balance and mobility for individuals with cardiorespiratory, musculoskeletal, or neurological deficits. Despite its popularity, there are also reports of adverse effects related to walker use linked to increased fall risks. Studies examining the effectiveness and consequences of rollator use have employed standard laboratory-based measurement methods that rely on performing specific tasks within a short time period and under controlled conditions, potentially limiting generalization to mobility in the everyday context. An instrumented rolling walker (iWalker) was developed as an ambulatory measurement tool applicable to the assessment of balance outside of the lab or clinic for assistive device users. The iWalker autonomously collects measurements of the upper and lower limb behaviour related to balance, walker kinematics, and video of the immediate spatial environment. The design and development of the iWalker is first described, followed by two studies characterizing the involvement of the upper limbs for balance in standing and walking that served to address gaps in the literature and evaluate the utility of the upper limb measures. Overall, the upper limbs can become the primary effectors of balancing forces when lower limb capabilities are compromised. When lower limb involvement was experimentally constrained, the upper limbs became the primary effectors of balance control in healthy, young adults. In older adults, individuals demonstrating the highest upper limb usage during walking were associated with the largest reduction in frontal plane stepping parameters (i.e., step width). A third study evaluated the applicability of the iWalker to assess everyday mobility in a series of in-patients recovering from neurological injury (i.e., stroke, traumatic brain injury). Patients demonstrated significantly different upper limb balancing behaviour in everyday situations compared to in-laboratory assessments. Furthermore, the iWalker captured behaviours that may be precursors to falling, such as collisions, stumbling and lifting the assistive device. The implications of these studies on assessing the effectiveness of rollators and feasibility of using the iWalker in follow-up efforts are discussed.

The purpose of the current research was to examine how a novel balance task is learnt by individuals with a mature neurological system, and to investigate the responses of experienced hand balancers to mechanical and sensory perturbations. Balance in each posture was assessed by various techniques, including: traditional measures of centre of pressure, nonlinear time series analysis of centre of pressure, estimates of feedback time delay from cross correlations and delayed regression models, and calculation of small, medium, and large movement corrections. Data from this study suggests that the best balance metric for distinguishing between each of the balance conditions was the traditional balance measure of sway velocity. However, sway velocity cannot provide any further information on the underlying process of balance. Nonlinear measures of balance offer insight into the underlying deterministic processes that control balance, offering measures of system determinism, complexity, and predictability. Assessments of feedback time delay and movement corrections provide both an insight into the control of posture and help distinguish one condition from another. Both feedback time delay and movement corrections and magnitudes may be used simultaneously to delve further into the control of posture. Delayed regression models seem to be an appropriate and useful tool for estimating feedback time delays during balance. Findings support the use of the third term in the adapted regression model as a means of estimating the effect of passive stiffness on feedback time delay. Generally, with increased duration in handstand subjects displayed reduced sway as measured by traditional measures of balance. A more marked change in nonlinear measures of balance can be seen, with quicker reductions in variance for some nonlinear measures of balance than in the traditional measures. It may be that more pronounced changes in nonlinear measures represent changes in the subjects underlying process of postural control, whereas less pronounced changes in traditional measures relate more to their general ability or performance in the balance task.

A entorse de tornozelo pode ocorrer pela amplitude exagerada de inversão e flexão plantar. Lacuna importante no controle postural é a ação do ajuste postural antecipatório (APA) e compensatório (APC) para estabilizar a articulação do tornozelo. O reflexo de estiramento (M1) e as reações pré-programadas (M2 e M3) foram pouco exploradas em pessoas com instabilidade crônica de tornozelo (CAI). A co-ativação e inibição são fenômenos modulados em nível medular por neurônios excitatórios e inibitórios, mas as informações sobre esses fenômenos atuam na CAI são escassas. A fadiga muscular afeta negativamente as pessoas na condição de CAI. Logo, qual é a relação entre APA e APC no movimento de entorse de tornozelo? A CAI pode alterar as respostas M1, M2 e M3 por lesões osteomioarticulares do tornozelo? A fadiga pode alterar todas estas variáveis em pessoas com CAI? Esta dissertação de mestrado teve por objetivo geral analisar o sinal EMG no movimento simulado da inversão de tornozelo em atletas universitárias de futsal que possuem e que não possuem a CAI. A amostra foi composta por 24 atletas de futsal feminino universitário e foram divididos em dois grupos: controle e instabilidade. A simulação do movimento de entorse do tornozelo foi feita por meio de uma plataforma mecânica que simula o movimento de inversão de tornozelo. Foi utilizado um sistema de aquisição de sinais de 8 canais, onde foram utilizados 4 canais para registro EMG e 3 canais para o registro do sinal do acelerômetro. Para determinar o início e final do movimento da plataforma foi fixado um acelerômetro 3D em uma das bordas da plataforma de inversão. Foram realizar quedas aleatórias na plataforma de inversão antes e depois do protocolo de fadiga. Foram monitorados os músculos tibial anterior, fibular longo e curto e gastrocnêmio lateral. Os períodos analisados foram os APA, APC, reflexo de estiramento muscular e reações pré-programadas. Parece que durante os períodos M1, M2 e M3 há um fator de desproteção no grupo instabilidade, apesar de haver em alguns pares de músculos uma maior coerência, comparado com o grupo controle. Durante o APA os músculos eversores não foram alterados no grupo instabilidade, mas no APC os eversores foram menores comparados com o grupo controle, sugerindo um fator de desproteção. Na correlação cruzada, todos os pares de músculos foram maiores no grupo controle, uma forma de se opor ao movimento de inversão maior que o grupo instabilidade. A co-ativação e inibição recíproca foram alteradas com a fadiga, aumentando após a fadiga, mas a inibição recíproca foi maior somente no grupo controle, podendo mover a articulação do tornozelo de uma forma mais facilitada que o grupo instabilidade. A coerência de pares de músculos foi diferente somente nos grupos, sendo que durante o APC os músculos não sincronizaram de forma satisfatória no grupo instabilidade, somente durante APA e período M / Ankle sprain is an injury associated with sports and exercise and may be used for the exaggerated amplitude of inversion and plantar flexion. An important gap in postural control is the anticipatory (APA) and compensatory (CPA) postural adjustments to stabilize the ankle joint. The stretch reflex (M1) and the pre-programmed reactions (M2 and M3) were poorly explored in people with chronic ankle instability (CAI). Coactivation and recíprocal inhibition are phenomena modulated at the spinal level by excitatory and inhibitory neurons, but the information about these phenomena in CAI is scarce. Negative effects of muscular fatigue affect persons with CAI. Therefore, What is the relationship between APA and CPA in the movement of ankle sprain? Can CAI change the M1, M2 and M3 responses due to osteomyoarticular ankle injuries? Can fatigue change all these variables in people with CAI? This dissertation aimed at analysing the EMG signal in the simulated ankle inversion movement task in female indoor soccer university athletes who have and do not have the CAI. Participants were 24 female indoor soccer college athletes divided in two groups: control and instability. Simulation of ankle sprain was performed with a mechanical platform that simulated the ankle inversion movement. An 8-channel signal acquisition system was used, which 4 channels were used for EMG recording and 3 channels to record accelerometer signal. For determine the beginning and end of the movement of the inversion platform a 3D accelerometer was fixed to one of the edges of the inversion platform. We performed random falls on the inversion platform before and after the fatigue protocol. Muscles monitored were mm. tibialis anterior, fibularis longus, fibularis brevis and gastrocnemius lateralis. Data epochs were APA, CPA, muscle stretching reflex and preprogramed reactions. During M1, M2 and M3 epochs, there was an unprotection factor for instability group, although in some muscle pairs there were more coherence compared to control group. The eversor muscles were not changed in instability group compared with control group during APA epoch, it suggests an unprotect factor. All pair of muscles, the cross correlation were greater in control group to oppose the inversion movement greater in control group than instability group. Coactivation and reciprocal inhibition were changed with fatigue, increasing after fatigue, but reciprocal inhibition was greater only in control group, and could move the ankle joint more easily than for instability group. Coherence of muscle pairs was different only between groups, and during CPA the muscles did not synchronize satisfactorily for instability group, only during APA and M epochs