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This study examined the effects of training with real-time auditory feedback in precision shooting. Top-level shooters (N=9) were randomly assigned to the feedback or nonfeedback group. Each group performed a pre-test, a 4-week training intervention and a post-test. The feedback group was provided with augmented real-time auditory feedback based on postural and rifle barrel stability during training sessions. Increases in performance were measured through changes in postural stability, rifle barrel stability, shot outcome and shot group diameter. Real-time auditory feedback did not increase postural or rifle barrel stability in the feedback group. No meaningful differences were found related to shot outcome or shot group diameter in air rifle testing. The feedback group was able to reduce shot group diameter during smallbore testing. In summary, the augmented real-time auditory feedback did not improve postural or rifle barrel stability. Future research should focus on examining the effects of auditory feedback on smallbore performance.

PURPOSE. To determine the influence of cataractous and refractive blur on postural stability and limb-load asymmetry (LLA) and to establish how postural stability changes with the spatial frequency and contrast of the visual stimulus. METHODS. Thirteen elderly subjects (mean age, 70.76 ± 4.14 [SD] years) with no history of falls and normal vision were recruited. Postural stability was determined as the root mean square [RMS] of the center of pressure (COP) signal in the anterior¿posterior (A-P) and medial¿lateral directions and LLA was determined as the ratio of the average body weight placed on the more-loaded limb to the less-loaded limb, recorded during a 30-second period. Data were collected under normal standing conditions and with somatosensory system input disrupted. Measurements were repeated with four visual targets with high (8 cyc/deg) or low (2 cyc/deg) spatial frequency and high (Weber contrast, 95%) or low (Weber contrast, 25%) contrast. Postural stability was measured under conditions of binocular refractive blur of 0, 1, 2, 4, and 8 D and with cataract simulation. The data were analyzed in a population-averaged linear model. RESULTS. The cataract simulation caused significant increases in postural instability equivalent to that caused by 8-D blur conditions, and its effect was greater when the input from the somatosensory system was disrupted. High spatial frequency targets increased postural instability. Refractive blur, cataract simulation, or eye closure had no effect on LLA. CONCLUSIONS. Findings indicate that cataractous and refractive blur increase postural instability, and show why the elderly, many of whom have poor vision along with musculoskeletal and central nervous system degeneration, are at greater risk of falling. Findings also highlight that changes in contrast sensitivity rather than resolution changes are responsible for increasing postural instability. Providing low spatial frequency information in certain environments may be useful in maintaining postural stability. Correcting visual impairment caused by uncorrected refractive error and cataracts could be a useful intervention strategy to help prevent falls and fall-related injuries in the elderly.

The overall aim of this thesis was to investigate postural balance, physical activity, physical capacity and their associations in young people (16-20 years) with intellectual disability (ID), mild to moderate. The aim was also to study the reliability and concurrent validity of postural balance tests. To evaluate postural balance, one assessor used five common postural balance tests and one new test. The tests were performed twice for 89 young people with ID (one to twelve days apart). Intraclass correlation coefficients greater than 0.80 were achieved for four of the common balance tests: Extended Timed Up and Go Test (ETUGT), Modified Forward Reach Test (MFRT), One-Leg Stance Test (OLS), and a Force Platform Test (FPT). The smallest real difference ranged from 12% to 40%; less than 20% is considered to be low. For the six balance tests, the concurrent validity varied between none to low. Falls are more common for young people with ID compared to young people without ID. One reason could be impaired postural balance. The postural balance for young people with ID has not been thoroughly investigated. Therefore, five balance tests and three muscle strength tests were used to compare young people with ID with an age-matched control group without ID (n=255). The young people with ID had significantly lower scores on most of the postural balance tests and muscle strength tests of the trunk and lower limbs. Muscle strength, height, and body mass index had no strong association with postural balance. The results also illustrated that young people with ID did not rely more on vision for their balance ability compared to peers without ID. It seems that postural balance is impaired for young people with ID when evaluated with common tests. An everyday situation is to react to unexpected balance disturbances to avoid falls by using different postural responses. Since young people with ID seem to fall more often than peers without ID, it is valuable to investigate if those postural responses are different between the groups. Therefore, young people with and without ID (n=99) were exposed to six backward surface translations and several postural muscle responses were evaluated: muscle synergies and strategies, muscle onset latency, time-to-peak amplitude, and adaptation. The responses of the investigated muscles – the gastrocnemius, the biceps femoris, and the erector spinae L4 level – were measured using electromyography. The results showed that there were no differences between the two groups with respect to synergies or strategies, muscle onset latency, and time-to-peak amplitude. An overall pattern was seen, that young people with ID adapted their muscle response slower in all three muscles than peers without ID, but this pattern was not statistically significant. Studies have shown that people with ID have impaired postural balance, a lower level of physical activity, and lower aerobic capacity compared to people without ID. The association is however not investigated. Therefore, postural balance (postural sway indirectly measured with the subjects standing on a force platform), physical activity (measured with a pedometer), and aerobic capacity (measured with a sub-maximal ergometer cycle test) were used to assess young people with and without ID (n=106). To investigate the subjects’ view of their own health, the subjects completed an adapted questionnaire that addressed their perceived health. The analysis showed no significant associations between postural balance, level of physical activity, and aerobic capacity. The subjects in the ID group, both men and women, had significantly lower aerobic capacity compared to subjects without ID. The answers from the health questionnaire did not correspond to the measured outcomes from the physical tests for young people with ID. In conclusion, ETUGT and MFRT can be used to evaluate change in postural balance over time in young people with mild to moderate ID. The low concurrent validity suggests that the postural balance tests probably challenge various subsystems. Young people with ID have impaired postural balance and perform lower on muscle strength tests than age-matched controls. Postural muscle responses after external perturbations seem to be similar for young people with and without ID, but the ability to adapt muscle responses after repeated perturbations appears to be slower for young people with ID. The studies in the thesis also indicate that young people with ID have reduced level of physical activity and lower aerobic capacity. The lack of association between the different physical functions indicates that they should be evaluated and exercised separately. Young persons with ID might have more difficulty realising the health advantage of being physically active, as they do not seem to make this connection. Because of this, it is important that parents/guardians, school staff, physiotherapists, and others encourage them to participate in physical activity.

Understanding the predisposing factors for older people falling is imperative as falls can lead to considerable medical and societal costs, loss of independence and reduced quality of life. In particular, it is important to understand more about the many possible intrinsic and extrinsic reasons why older people sometimes fail to maintain their postural stability and fall. Older people are increasingly being encouraged to maintain or increase their daily physical activity levels. Healthy older adults have been shown to have altered postural stability following high intensity physical activity; however it is not known whether postural stability is compromised during everyday levels of physical activity. If it were, it could expose them to greater risk of falling. The overall aim of this series of investigations was to determine whether postural stability was detrimentally affected immediately after moderate intensity physical activity. Five studies were undertaken. Study 1 was carried out to determine the typical duration of activity periods that occur during the daily lives of community-living older people. In this study, the activity period durations of older people living either at home or in an aged care facility were recorded over a continuous 72 hour period using an activity monitoring device. Study 2 determined the effect of an activity protocol, designed to be representative of routine daily activity of community-living older people, on clinical indicators of fatigue. These indicators included maximal voluntary torque from the knee extensor and hip abductor muscles, subjective feelings of fatigue and temporal and spatial gait variables. The physical activity protocol involved a series of tasks carried out continuously for 14 minutes, self-paced at moderate intensity. Tasks included walking, step-ups, mini-lunges and avoiding obstacles. The final three studies compared postural stability before and immediately after the moderate intensity physical activity protocol. Study 3 recorded centre of pressure (COP) displacement during quiet standing with feet together. Study 4 recorded forces and postural electromyographic (EMG) activity during a rapid forward step-up task. Study 5 recorded postural responses to a lateral waist-pull perturbation large enough to elicit a step response. Studies 2, 3 and 4 compared healthy young adults with healthy older and balance-impaired older adults, whilst the final study compared healthy young and old adults. Community-living older people were found to have a wide range of activity period durations and those living in aged care had significantly shorter activity periods compared to those living independently at home. As a result of the findings, an activity period duration of 14 minutes was considered representative of community-living older people’s physical activity exposure. In Study 2, immediately following the physical activity protocol, young, healthy old and balance-impaired older adults all showed no changes in leg strength. All groups felt generally tired and had sensations of local leg muscle fatigue but only the balance-impaired adults were still reporting feelings of fatigue 20 minutes after the activity ceased. This group were also the only group to show altered gait after the activity. Their cadence was reduced compared with before activity and remained reduced 20 minutes later. In quiet standing, all groups demonstrated larger COP displacement in the mediolateral direction following the physical activity. For the step-up task, all groups showed small improvements immediately following the physical activity. These included reductions in the duration of the weight-shift phase, lateral COP displacement during weight-shift and the stance leg hip abductor muscle onset times. Participants also showed a shift in COP position towards the stance side prior to the step following the physical activity. In the final study, the older participants used a cross-over step in response to the lateral perturbation more frequently after the activity than before. This response is a less optimal response compared with a faster and more stable single outward step. When older and younger participants did perform outward steps following the physical activity, they performed them as well as they did before activity. Small changes to some of the measures of postural stability were found during quiet standing, voluntary stepping and to the responses after a lateral perturbation following moderate intensity physical activity. These changes may have been due to the impact of subjective feelings of tiredness experienced by participants. The increased use of a cross-over step strategy to regain balance after a lateral perturbation among healthy older people may mean that older people are at greater risk of falling after physical activity. However, the findings from this series of studies do not convincingly support a clinically significant detrimental effect on older people’s postural stability immediately following routine daily physical activity. This thesis has begun to investigate the effect of physical activity at daily levels on older people’s postural stability, however further investigations are recommended.

Introdução: Com o aumento da idade, estudos demonstram que a população experimenta um declínio de sistemas fisiológicos participantes no controle da estabilidade postural. Dentre os métodos de avaliação descritos na literatura, encontra-se o Pull Test (PT), que é amplamente utilizado em escala mundial para avaliação do equilíbrio em indivíduos com doença de Parkinson. O teste examina a resposta do corpo a um deslocamento corporal posterior, oferecendo um identificador útil da estabilidade postural do indivíduo. O padrão de ativação muscular durante a realização do PT não foi ainda estudado. Objetivo: analisar o padrão da atividade eletromiográfica durante a realização do PT, em indivíduos hígidos acima de 40 anos de idade. Métodos: Vinte e três indivíduos hígidos realizaram o estudo eletromiográfico (EMG) de superfície dos músculos tibial anterior, gastrocnêmio medial e bíceps femoral durante a realização do PT. O PT e registros eletromiográficos foram realizados sucessivamente por 10 vezes em cada indivíduo. Os indivíduos foram também avaliados pelo Montreal Cognitive Assessment (MoCA). Resultados: O registro EMG mostrou que a atividade muscular inicia pelo tibial anterior, sendo seguida sucessivamente pelo gastrocnêmio medial e bíceps femoral. A frequência do número de passos para a manutenção da estabilidade postural foi de 93,9% para 1 ou 2 passos e 6,1% para 3 passos ou mais. A latência para ativação muscular foi relacionada com o desempenho cognitivo no MoCA. Pacientes com escores no MoCA inferior a 26 apresentavam maior latência do tibial anterior (p=0,03) e do bíceps femoral (p=0,02). Além disso, a amplitude do gastrocnêmio medial relacionou-se inversamente com o índice de massa corporal (IMC) (p=0,01). Conclusão: Constatou-se que o declínio da função executiva e o sobrepeso estão relacionados com mudanças nas respostas 12 neurofisiológicas durante a realização do PT. Os mesmos podem contribuir para prejuízos da estabilidade postural nestes indivíduos. / Background: Physiologic systems that participate of the postural stability control are impaired with aging. Pull Test (PT) is an assessment method widely worldwide utilized for evaluating the balance in individuals with Parkinson’s disease. The test examines the body’s response to a posterior bodily displacement, offering a useful identifier of the individual’s postural stability. The pattern of muscle activation during the PT has not yet been studied. Objective: the objective of this study was to analyze the pattern of electromyographic activity during the PT, in healthy individuals, over 40 years of age. Methods: Twenty three healthy individuals have carried out an electromyographic (EMG) study of the tibialis anterior, gastrocnemius medialis and biceps femoris muscles during the PT. The PT and the electromyographic recordings have been taken successively for 10 times in each individual. The individuals cognition have been assessed by the Montreal Cognitive Assessment (MoCA). Results: The EMG recording has showed that the muscle activity begins by the tibialis anterior, being successively followed by the gastrocnemius medialis and by the biceps femoris. The rate of the number of steps for keeping the postural stability was 93.9% for 1 or 2 steps, and 6.1% for 3 or more steps. The latency for muscle activation was related to the cognitive performance in the MoCA. Patients with MoCA scores lower than 26 have presented a larger latency in the tibialis anterior (p=0.03), and in the biceps femoris (p=0.02). Furthermore, the amplitude of the gastrocnemius medialis has been inversely related to the body mass index (BMI) (p=0.01). Conclusion: It has been found out that the decline in the executive function and overweight related to changes in the neurophysiologic 14 response during the taking of the PT. These may contribute for the losses of postural stability in such individuals.