Cross education of movement function across the lifespan

The Context Older adults (> 65 years) already comprise a significant proportion (16% in 2008) of the UK population, yet their numbers will increase dramatically over the next twenty years. By 2033, those aged over 65 years will constitute 23% of the population. Between 30 and 40% of people over 65 years fall at least once annually. The proportion of falls resulting in a fracture increases markedly with age. In persons over 65 years, fractures are present in three-quarters of fall-related hospital admissions. In more than half of these cases a fracture of the arm is sustained. In most instances the arm is immobilised for an extended period, often in plaster. While this may allow the injury to heal, there are other less positive consequences. Immobilisation of a limb, even for a very short time, leads to a profound decrease in strength. The most significant risk associated with such a period of disuse is that the loss of physical capacity will leave an individual too frail to perform everyday activities, such as rising from a chair. The loss of independence that this represents has consequences not only for the person concerned, but also for their family, their caregivers and the community. This research is concerned with strategies that may be used to minimise the loss of function that would otherwise occur during recovery from upper limb injuries, particularly in older persons. The Aims and Objectives There is now a great deal of evidence that the older adult brain retains an extensive facility to undergo adaptive change or reorganisation. This capacity is referred to as plasticity. Adaptations within the brain play a significant role in relation to the gains that older adults derive from various forms of physical activity. In addition to contributing to the maintenance of strength, adaptations underpinned by brain plasticity form the basis of learning new strategies for performing tasks that compensate for loss of strength. The aims of the proposed research are to examine improvements in the functional capabilities of one limb that occur when only the other limb is trained, and to determine how brain plasticity may best be exploited in order to maximise the gains that can be achieved by such training. The Potential Applications and Benefits For many older people who suffer an injury such as a facture that requires casting, the scope of the treatment rarely extends beyond the injury itself. The potential consequences that arise when a limb is not used for an extended period of time are rarely considered. The proposed research project concerns the scientific basis of interventions that may be used harness brain plasticity during periods of limb immobilisation, with the aim of maintaining functional capacity in older persons. The knowledge gained through this research will have the potential for application to rehabilitation programs for those who undergo enforced periods of limb immobilisation, for example following fractures arising as a result of a fall. The benefits that may accrue from the application of this knowledge are likely to be expressed not only in terms of enhanced quality of life and functional life span for those who experience such injuries, but also as significantly more effective use of health care funds.

A significant risk associated with the fractures that arise from falls by older adults, is that the loss of specific muscle strength or general capacity resulting from limb immobilisation will leave the person below the level of capability necessary to perform everyday tasks, and thus maintain independent living. The phenomenon of cross-education, whereby practice with one arm enhances subsequent performance with the other arm has led to the supposition that the effects of disuse may be counteracted by training movements of the non-affected limb performed during the period of immobilisation. Although the phenomenon has been studied for more than a century, there is little consensus in relation to the neural mechanisms that mediate its effects. Two major theoretical models can be delineated: the 'cross-activation' model and the 'bilateral access' model. In order to provide a direct comparison of the explanatory power of these models, it is necessary to examine in the context of single tasks the relative impact upon cross-education of variations in the complexity of training movements, and the level of neural drive required for their execution. This unique approach is taken in the current project. In addition to theoretical considerations, a comprehensive understanding of the principles governing cross-education is required to ensure the optimum design of training programs that have as their aim the maintenance of functional capacity in older persons during limb immobilisation. Additional key objectives of the research are therefore to: establish the degree to which the balance that exists between factors that govern levels of cross-education varies across the lifespan; investigate the neural mechanisms that mediate their age-dependent influence; and assess age-related changes in the functional generalisation of cross-education to other movement tasks.

Who will benefit from this research? The proposed project comprises strategic pre-clinical science that focuses upon interventions to maintain functional capacity in older persons. The users of the research will be health-care professionals. The beneficiaries of the research will be individuals who have suffered injuries that require periods of limb immobilisation for their treatment. The most significant risk arising from such injuries, including fractures arising as a consequence of a fall, is that the loss of specific muscle strength or general capacity resulting from limb immobilisation will leave the person below the level of capability necessary to perform everyday tasks, and thus maintain independent living. The potential benefits of the research are therefore likely to extend beyond enhanced quality of life and functional life span for the individuals themselves, but also be expressed as a reduced level of burden on their families and care givers, and more effective use of health care funds. How will they benefit from this research? We will seek to determine the mechanisms that underpin improvements in the performance of an untrained limb induced by unilateral training of the opposite limb, and examine variations in the respective contributions of these mechanisms across the lifespan. In so doing, we aim to critically assess the potential for interventions based on the phenomenon of cross-education to be deployed in the treatment of individuals who undergo enforced periods of limb immobilisation. The knowledge thus derived will have the potential for direct application to the design of rehabilitation programs for older persons. What will be done to ensure that they benefit from this research? A number of strategies are already in place to increase the likelihood of impact, and encourage the uptake of the results arising from the research by users in the health services. The knowledge generated by the project will be disseminated to professional and community organisations, with the intent of enhancing the application of the findings in a manner that engages and informs the users and the beneficiaries. The team intend to pursue the policy that has been adopted successfully by the PI previously, of engaging directly with health-care professionals, particularly those working in Gerontology and Geriatrics, Rehabilitation Medicine, Physiotherapy, and Occupational Therapy, who deal with injuries in older person on a daily basis. The Principal Investigator is a member of the Department of Health (Northern Ireland) Mental Health, Ageing and Learning Disability Translational Research Group (TRG), and uniquely, he and his research group are also members of the Trauma and Rehabilitation Research TRG. These groups provide forums for the rapid exchange of knowledge between researchers and practitioners delivering front-line services. In addition to delivering regular talks at the Regional Acquired Brain Injury Unit in Belfast, the Applicant has since 2006 given two keynote presentations at meetings of the British Society of Rehabilitation Medicine, and recently addressed the Danish Society of Rehabilitation Medicine. By means of the networks thus established, the Applicant is confident of effective dissemination to clinicians and allied health professionals. The PI has established a close relationship with the Centre for Ageing Research and Development in Ireland (CARDI). In addition to providing a means of communicating to the wider community the outcomes of strategic research on ageing and older people that aims to improve quality of life, this partnership provides an ideal basis upon which to involve older people in all aspects of the research process. In this context, the research team has also been liasing with Go for Life an all-island (Ireland) programme for physical activity for older people, with a view to ensuring the direct communication of their research findings to the relevant sectors of the lay public.