A framework for feasible translation to enhance foot and ankle function in aging and mobility

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PROJECT SUMMARY This proposal will address the critical need for new and modifiable targets to enhance mobility and restore independence to those in our rapidly aging population. Due to reduced ankle push-off power, older adults walk slower and with higher metabolic energy cost than younger adults. As our central premise, we contend that hallmark age-associated deficits in push-off intensity during walking have been far too often mistakenly attributed solely to the plantarflexor muscles, and instead originate interdependently with those in the active, passive, and structural regulation of foot mechanical power. This premise paves the way for translational opportunities to augment foot structure and function to enhance independence and quality of life. This study combines the research agendas of two highly productive investigators and leverages the research infrastructure of two peer institutions. Aim 1 will be the first to study mechanical power interactions between the human foot and ankle in governing reduced push-off intensity and walking economy in older adults across a wide variety of everyday walking tasks. By combining metabolic measurements with state-of-the-art biomechanical and bioenergetic modeling, we will test the hypothesis that older adults exhibit higher mechanical energy losses via foot structures than young adults – aging effects that: (i) are larger for walking tasks that increase foot demand, (ii) misappropriate ankle moment and power during push-off, and thereby (iii) correlate with shorter 6 min walk distance and increased metabolic energy cost compared to young adults. Aim 2 will provide mechanistic insight into aging effects on the active, passive, and structural regulation of foot-ankle mechanical power interactions during walking. Using a series of controlled loading paradigms on a dynamometer combined with advanced in vivo ultrasound imaging and novel electromyographic biofeedback, we will test the hypotheses that older adults exhibit: (i) reduced foot and plantarflexor muscle strength and (ii) lower structural stiffness of and (iii) reduced structural connectivity between series elastic tissues spanning the foot and ankle – changes that require elevated plantar intrinsic muscle activation to maintain requisite foot stiffness and associate with reduced ankle moment and power output during push-off in walking. Finally, as a translational benchmark, Aim 3 will show that shoe- stiffness modifications that act in parallel with the plantar aponeurosis and intrinsic muscles can mitigate age- associated deficits in push-off function during walking. Supported by promising pilot data, we will test the hypotheses that older adults walking with increased shoe insole stiffness will exhibit: (i) smaller mechanical energy losses at the foot, (ii) more favorable plantarflexor muscle contractile dynamics, (iii) greater peak ankle moment and power output, and thus (iv) longer 6 min walk distance and reduced whole-body metabolic energy cost. Ultimately, this work will establish a paradigm shift in our biomechanical understanding and clinical management of age-related mobility impairment toward feasible and cost-effective devices to modify foot-ankle function – an outcome with significant potential to enhance independence and quality of life for millions.