Determining the impact of lifestyle-related biomechanics on muscle in the ageing human arm

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Project summary (maximum of 4000 characters including spaces/returns) -from original proposal Summary: Normal ageing in humans is characterised by a reduction in muscle mass and strength, which results in reduced functional capacity in the musculoskeletal system. However, muscle ageing is characterised by more complex changes than simply a reduction in mass or fibre number. For example, ageing alters the spatial arrangement of muscle fibres, including muscle thickness, pennation angle and average muscle fascicle length. However, studies that have sought to track such changes have been biased towards lower limb (leg) muscles and have almost universally used an extremely small number of measurements per muscle to characterise their gross architectural properties. Recent application of high-resolution imaging and automated image analysis to measure a large number of fibres (>3000) in human leg muscles have not only demonstrated the potential inaccuracy of such approaches but also highlighted that important functional features, such high levels of inhomogeneity in fibre architecture in certain muscles, may have been missed from such analyses.In this project we will determine the long-term impacts of habitual arm use on age-related changes in muscle architecture and function using a combination state-of-the-art medical imaging, image analysis and experimental biomechanical approaches. We will use MRI scanning and deterministic fibre tractography to quantify age-related variation in muscle architecture in two cohorts with highly disparate forearm-hand use (office workers versus manual workers). The same subjects will also undergo a range of functional measurements related to forearm-hand muscle strength and movement precision, allowing similarities and differences in muscle architecture to be correlated with measures of musculoskeletal performance. Crucially, our analyses will go beyond 'first-order' relationships between architectural anatomy and muscle strength; based on our recent analyses of muscle architecture in the lower limb, we will test the novel hypotheses that inhomogeneity in fibre architecture is crucial to normal muscle function in the forearm and hand, and thus will be differentially expressed in the two cohorts leading to disparate trajectories in fibre architecture and functional performance over the life course. Finally, we will work with an industrial CASE partner to apply this new knowledge of forearm and hand muscle function to evaluate the performance and design of a medical implant using biplanar x-ray videography and a cadaveric forearm-hand motion simulator developed by the supervisory team. Thus, our basic science will provide new data on how lifestyle impacts (and might be used to mitigate) ageing in the human arm, as well as informing the development of new healthcare technologies.