Slip at the edge of complete contacts

We describe an asymptotic method for calculating the size of a zone of partial slip at the edge of a complete contact of arbitrary edge angle and coefficient of friction. Above a critical coefficient of friction the contact remains stuck, and this critical value is explored. A distributed dislocation method is used and the use of different types of numerical quadrature is explored. The size of the slip zone, and its dependence on the contact edge angle and coefficient of friction, are explored

Longer hospital stay, more complications, and increased mortality but substantially improved function after knee replacement in older patients

Background and purpose — Total knee replacement (TKR) is being increasingly performed in elderly patients, yet there is little information on specific requirements and complication rates encountered by this group. We assessed whether elderly patients undergoing TKR had different length of stay, requirements, complication rates, and functional outcomes compared to younger counterparts. Patients and methods — We analyzed prospectively gathered data on 3,144 consecutive primary TKRs (in 2,092 patients aged less than 75 years, 694 patients aged between 75 and 80 years, and 358 patients aged over 80 years at the time of surgery). Results — Incidence of blood transfusion, urinary catheterization, postoperative confusion, cardiac arrhythmia, and 1-year mortality increased with age, even after adjusting for confounding factors, whereas the incidences of chest infection and mortality at 1 month were highest in those aged 75–80. Rates of thromboembolism, prosthetic infection, and revision were similar in the 3 age groups. All groups showed similar substantial improvements in American Knee Society (AKS) knee scores, which were maintained at 5 years. Older patients had smaller improvements in AKS function score, which deteriorated between 3 and 5 years postoperatively, in contrast to the younger group. Interpretation — Elderly people stand to gain considerably from TKR, particularly in terms of pain relief, and they should not be denied surgery based solely on age. However, they should be warned that they can expect a longer length of stay, a higher requirement for blood transfusion and/or urinary catheterization, and more medical complications postoperatively. Mortality was also higher in the older age groups. The risks have been quantified to assist in perioperative counselling, informed consent, and healthcare planning.peer-reviewe

From both sides now: Crossover effects influence navigation in patients with unilateral neglect

Unilateral neglect is a challenging disorder that pervades a range of behaviours following stroke and hampers recovery. Although a preponderance of clinical studies measure performance on a range of bedside assessments, including line bisection and cancellation tasks, there have been calls for studies to embrace more relevant functional measures. Here, for the first time, we present data from two separate tasks that characterise the performance of seven patients with unilateral neglect when navigating a power wheelchair. The tasks involved negotiating an obstacle course and steering a central path between gaps of different sizes. Results from the obstacle course confirmed the clinical observation and predicted bias of contralesional errors. However, the second task revealed a robust "crossover" effect. Patients deviated to the ipsilesional side for large gaps but deviated increasingly contralesionally when steering through small gaps in behaviour that was analogous to that previously shown on line bisection tasks. Contrary to being seen as an unintuitive finding, further analysis of these errors suggests that patients are giving disproportionate weight to the location of the ipsilesional object when plotting a midline course between two objects. Our results provide a platform for further studies to investigate the modulation and rehabilitation of this important skill

Pattern discrimination in a human subject suffering visual agnosia

Since suffering a stroke some four years ago, H.J.A. has exhibited lack of visual pattern recognition, and CT scans show areas of neuronal damage localized bilaterally in the posterior cerebral cortex (Humphreys & Riddoch, 1984

Advancing the future of physical activity guidelines in Canada: an independent expert panel interpretation of the evidence

The Canadian Society for Exercise Physiology, in partnership with the Public Health Agency of Canada, has initiated a review of their physical activity guidelines to promote healthy active living for Canadian children, youth, adults and older adults; previous guidelines were released in 2002, 2002, 1998 and 1999 respectively. Several background papers from this project were published recently and provide foundation evidence upon which to base new guidelines. Furthermore, comprehensive systematic reviews were completed to ensure a rigorous evaluation of evidence informing the revision of physical activity guidelines for asymptomatic populations. The overall guideline development process is being guided and assessed by the AGREE II instrument. A meeting of experts was convened to present the evidence complied to inform the guideline revisions. An independent expert panel was assembled to review the background materials and systematic reviews; listen to the presentations and discussions at the expert meeting; ask for clarification; and produce the present paper representing their interpretation of the evidence including grading of the evidence and their identification of needs for future research. The paper includes also their recommendations for evidence-informed physical activity guidelines

MuRF-1 and Atrogin-1 Protein Expression and Quadriceps Fiber Size and Muscle Mass in Stable Patients with COPD

INTRODUCTION: Animal studies demonstrate the importance of the E3 ubiquitin ligases, Muscle RING-Finger Protein 1 (MuRF-1) and atrogin-1, in muscle protein degradation during acute muscle atrophy. Small clinical studies suggest MuRF-1 and atrogin-1 expression in the quadriceps muscle is also increased in stable patients with Chronic Obstructive Pulmonary Disease compared to controls. However, it remains unclear whether these ligases have a role in maintaining a muscle-wasted state in COPD patients. METHODS: 32 stable COPD patients (16 with a low fat-free mass index (FFMI), 16 with a normal FFMI) and 15 controls underwent lung function and quadriceps strength tests and a percutaneous quadriceps biopsy. Quadriceps MuRF-1 and atrogin-1 protein were quantified with western blotting. Quadriceps fiber cross-sectional area (CSA) and fiber proportions were determined by immunohistochemistry on muscle sections. MuRF-1 and atrogin-1 levels were compared between COPD patients with and without a low FFMI, and between patients and controls, and correlations between MuRF-1 and atrogin-1 levels and quadriceps fiber CSA in the patients were investigated. RESULTS: Atrogin-1 protein levels were lower in patients than controls, but similar in patients with a low and normal FFMI. MuRF-1 levels did not differ between any groups. MuRF-1 and atrogin-1 levels were not associated with quadriceps fiber CSA or quadriceps strength in patients. CONCLUSIONS: Chronic upregulation of ubiquitin ligases was not evident in the quadriceps muscle of stable COPD patients with a low muscle mass. This does not exclude the possibility of transient increases in ubiquitin ligases during acute catabolic episodes

Choice of activity-intensity classification thresholds impacts upon accelerometer-assessed physical activity-health relationships in children

It is unknown whether using different published thresholds (PTs) for classifying physical activity (PA) impacts upon activity-health relationships. This study explored whether relationships between PA (sedentary [SED], light PA [LPA], moderate PA [MPA], moderate-to-vigorous PA, vigorous PA [VPA]) and health markers differed in children when classified using three different PTs

Cardiorespiratory fitness is associated with hard and light intensity physical activity but not time spent sedentary in 10–14 year old schoolchildren: the HAPPY study

Sedentary behaviour is a major risk factor for developing chronic diseases and is associated with low cardiorespiratory fitness in adults. It remains unclear how sedentary behaviour and different physical activity subcomponents are related to cardiorespiratory fitness in children. The purpose of this study was to assess how sedentary behaviour and different physical activity subcomponents are associated with 10–14 year-old schoolchildren's cardiorespiratory fitness

Concurrent and prospective associations among biological maturation, and physical activity at 11 and 13 years of age

This study examined concurrent and prospective associations between objective measures of biological maturation, body composition and physical activity (PA) in adolescent males (n=671) and females (n=680). Participants born to women recruited to the Avon Longitudinal Study of Parents and Children birth cohort study were assessed at 11 and 13 years. Percentage of predicted adult stature was used as an estimate of biological maturation. PA and time sedentary was assessed over 7 consecutive days using Actigraph accelerometers. Body composition was assessed using whole-body DXA scans. At 11 and 13 years, maturity in males was inversely associated with accelerometer counts-per-minute (CPM) and time engaged in light PA, and positively associated with time sedentary. In females, maturity was inversely associated with accelerometer (CPM) at 11 but not 13 years. Adjusting for accelerometer wear times and corresponding activity levels at 11 years, maturity and percentage fat mass at 11 years did not predict any indices of PA or sedentary behavior in males or females at 13 years. Whereas advanced maturation in males is associated with less PA and more sedentary behavior at 11 and 13 years, maturity at 11 does not predict PA or sedentary behavior at 13 years in either sex

Does normal processing provide evidence of specialised semantic subsystems?

Category-specific disorders are frequently explained by suggesting that living and non-living things are processed in separate subsystems (e.g. Caramazza & Shelton, 1998). If subsystems exist, there should be benefits for normal processing, beyond the influence of structural similarity. However, no previous study has separated the relative influences of similarity and semantic category. We created novel examples of living and non-living things so category and similarity could be manipulated independently. Pre-tests ensured that our images evoked appropriate semantic information and were matched for familiarity. Participants were trained to associate names with the images and then performed a name-verification task under two levels of time pressure. We found no significant advantage for living things alongside strong effects of similarity. Our results suggest that similarity rather than category is the key determinant of speed and accuracy in normal semantic processing. We discuss the implications of this finding for neuropsychological studies. © 2005 Psychology Press Ltd