Falls due to a loss of balance are a primary cause of injury and death in the elderly, and a debilitating symptom of a wide range of neurological, musculoskeletal, and cognitive deficits. However, because many neural and musculoskeletal elements can contribute to balance impairments - or equivalently to compensatory strategies - it is often difficult for clinicians to evaluate the severity of balance impairments, or to identify their underlying causes. The objective of this project is to understand the principles governing the modulation of feedforward and feedback neuromechanical elements contributing to postural stability during standing balance control. We have chosen to study the neuromechanical elements that can be rapidly modulated or selected by the nervous system, within the time frame of one session of data collection. We define feedforward neuromechanical elements to be those that adjust the intrinsic mechanical stability of the musculoskeletal system in anticipation of a postural perturbation, such as postural configuration and postural muscle tone. We define feedback neuromechanical elements to be those that activate muscles reactively following postural perturbations, and include task-level feedback gains, muscle synergies, and spinal reflexes. We hypothesize that the feedforward and feedback neuromechanical elements are modulated to achieve implicit performance goals such as stability, maneuverability, energy minimization, or robustness to uncertainty. Differing performance goals could explain variations in movement observed across trials, across individuals, across contexts, or across motor deficits. We predict that various combinations of neuromechanical elements may produce qualitatively similar movements, and yet quantitatively different functional and energetic consequences. We will study interactions between feedforward and feedback neuromechanical elements for standing balance control in normal and neurologically-impaired cats in Aim 1;during short- and long- term postural adaptations in intact animals in Aim 3.
In Aim 2, we will identify tradeoffs between functional and energetic costs and constraints that may drive postural adaptations in both health and disease using neuromechanical models of postural control. This proposal continues our development of a general scientific framework toward our long-term goal of understanding, diagnosing, and predicting optimal motor function in individuals with balance deficits, and motor impairments in general.

Public Health Relevance

Falls due to a loss of balance are the leading cause of injury leading to death in older adults. Loss of balance causing someone to fall can happen due to a number of neurological and musculoskeletal deficits. We will identify how specific neurological impairments alter subtle, but measurable changes in balance control. We also develop computer simulation and analysis tools that may eventually help physicians predict how best to treat balance impairments.

National Institute of Health (NIH)
Eunice Kennedy Shriver National Institute of Child Health & Human Development (NICHD)
Research Project (R01)
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Special Emphasis Panel (ZRG1-IFCN-H (03))
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Quatrano, Louis A
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Emory University
Biomedical Engineering
Schools of Medicine
United States
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Bartlett, Harrison L; Ting, Lena H; Bingham, Jeffrey T (2014) Accuracy of force and center of pressure measures of the Wii Balance Board. Gait Posture 39:224-8
Welch, Torrence D J; Ting, Lena H (2014) Mechanisms of motor adaptation in reactive balance control. PLoS One 9:e96440
Burkholder, Thomas J; van Antwerp, Keith W (2013) Practical limits on muscle synergy identification by non-negative matrix factorization in systems with mechanical constraints. Med Biol Eng Comput 51:187-96
Sohn, M Hongchul; McKay, J Lucas; Ting, Lena H (2013) Defining feasible bounds on muscle activation in a redundant biomechanical task: practical implications of redundancy. J Biomech 46:1363-8
Safavynia, Seyed A; Torres-Oviedo, Gelsy; Ting, Lena H (2011) Muscle Synergies: Implications for Clinical Evaluation and Rehabilitation of Movement. Top Spinal Cord Inj Rehabil 17:16-24
Bunderson, Nathan E; McKay, J Lucas; Ting, Lena H et al. (2010) Directional constraint of endpoint force emerges from hindlimb anatomy. J Exp Biol 213:2131-41
Chiel, Hillel J; Ting, Lena H; Ekeberg, Orjan et al. (2009) The brain in its body: motor control and sensing in a biomechanical context. J Neurosci 29:12807-14
Welch, Torrence D J; Ting, Lena H (2009) A feedback model explains the differential scaling of human postural responses to perturbation acceleration and velocity. J Neurophysiol 101:3294-309
Ting, Lena H; van Antwerp, Keith W; Scrivens, Jevin E et al. (2009) Neuromechanical tuning of nonlinear postural control dynamics. Chaos 19:026111
McKay, J Lucas; Ting, Lena H (2008) Functional muscle synergies constrain force production during postural tasks. J Biomech 41:299-306

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