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Dzewaltowski AC, Antonellis P, Mohammadzadeh Gonabadi A, Song S, Malcolm P. Perturbation-based estimation of within-stride cycle metabolic cost. J Neuroeng Rehabil 2024; 21:131. [PMID: 39090735 PMCID: PMC11293076 DOI: 10.1186/s12984-024-01424-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Accepted: 07/17/2024] [Indexed: 08/04/2024] Open
Abstract
Metabolic cost greatly impacts trade-offs within a variety of human movements. Standard respiratory measurements only obtain the mean cost of a movement cycle, preventing understanding of the contributions of different phases in, for example, walking. We present a method that estimates the within-stride cost of walking by leveraging measurements under different force perturbations. The method reproduces time series with greater consistency (r = 0.55 and 0.80 in two datasets) than previous model-based estimations (r = 0.29). This perturbation-based method reveals how the cost of push-off (10%) is much smaller than would be expected from positive mechanical work (~ 70%). This work elucidates the costliest phases during walking, offering new targets for assistive devices and rehabilitation strategies.
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Affiliation(s)
- Alex C Dzewaltowski
- Department of Biomechanics and Center for Research in Human Movement Variability, University of Nebraska at Omaha, Omaha, NE, USA.
| | - Prokopios Antonellis
- Department of Biomechanics and Center for Research in Human Movement Variability, University of Nebraska at Omaha, Omaha, NE, USA
- Oregon Health & Science University, Portland, OR, USA
| | - Arash Mohammadzadeh Gonabadi
- Department of Biomechanics and Center for Research in Human Movement Variability, University of Nebraska at Omaha, Omaha, NE, USA
- Rehabilitation Engineering Center, Institute for Rehabilitation Science and Engineering, Madonna Rehabilitation Hospital, Lincoln, NE, USA
| | - Seungmoon Song
- Department of Mechanical and Industrial Engineering, Northeastern University, Boston, MA, USA
| | - Philippe Malcolm
- Department of Biomechanics and Center for Research in Human Movement Variability, University of Nebraska at Omaha, Omaha, NE, USA.
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2
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Cashaback JGA, Allen JL, Chou AHY, Lin DJ, Price MA, Secerovic NK, Song S, Zhang H, Miller HL. NSF DARE-transforming modeling in neurorehabilitation: a patient-in-the-loop framework. J Neuroeng Rehabil 2024; 21:23. [PMID: 38347597 PMCID: PMC10863253 DOI: 10.1186/s12984-024-01318-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Accepted: 01/25/2024] [Indexed: 02/15/2024] Open
Abstract
In 2023, the National Science Foundation (NSF) and the National Institute of Health (NIH) brought together engineers, scientists, and clinicians by sponsoring a conference on computational modelling in neurorehabiilitation. To facilitate multidisciplinary collaborations and improve patient care, in this perspective piece we identify where and how computational modelling can support neurorehabilitation. To address the where, we developed a patient-in-the-loop framework that uses multiple and/or continual measurements to update diagnostic and treatment model parameters, treatment type, and treatment prescription, with the goal of maximizing clinically-relevant functional outcomes. This patient-in-the-loop framework has several key features: (i) it includes diagnostic and treatment models, (ii) it is clinically-grounded with the International Classification of Functioning, Disability and Health (ICF) and patient involvement, (iii) it uses multiple or continual data measurements over time, and (iv) it is applicable to a range of neurological and neurodevelopmental conditions. To address the how, we identify state-of-the-art and highlight promising avenues of future research across the realms of sensorimotor adaptation, neuroplasticity, musculoskeletal, and sensory & pain computational modelling. We also discuss both the importance of and how to perform model validation, as well as challenges to overcome when implementing computational models within a clinical setting. The patient-in-the-loop approach offers a unifying framework to guide multidisciplinary collaboration between computational and clinical stakeholders in the field of neurorehabilitation.
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Affiliation(s)
- Joshua G A Cashaback
- Biomedical Engineering, Mechanical Engineering, Kinesiology and Applied Physiology, Biome chanics and Movement Science Program, Interdisciplinary Neuroscience Graduate Program, University of Delaware, 540 S College Ave, Newark, DE, 19711, USA.
| | - Jessica L Allen
- Department of Mechanical Engineering, University of Florida, Gainesville, USA
| | | | - David J Lin
- Division of Neurocritical Care and Stroke Service, Department of Neurology, Center for Neurotechnology and Neurorecovery, Massachusetts General Hospital, Harvard Medical School, Boston, USA
- Department of Veterans Affairs, Center for Neurorestoration and Neurotechnology, Rehabilitation Research and Development Service, Providence, USA
| | - Mark A Price
- Department of Mechanical and Industrial Engineering, Department of Kinesiology, University of Massachusetts Amherst, Amherst, USA
| | - Natalija K Secerovic
- School of Electrical Engineering, The Mihajlo Pupin Institute, University of Belgrade, Belgrade, Serbia
- Laboratory for Neuroengineering, Institute for Robotics and Intelligent Systems ETH Zürich, Zurich, Switzerland
| | - Seungmoon Song
- Mechanical and Industrial Engineering, Northeastern University, Boston, USA
| | - Haohan Zhang
- Department of Mechanical Engineering, University of Utah, Salt Lake City, USA
| | - Haylie L Miller
- School of Kinesiology, University of Michigan, 830 N University Ave, Ann Arbor, MI, 48109, USA.
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3
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Rong H, Ramezani S, Ambro A, Lei CH, Choi H. Design and characterization of a variable-stiffness ankle-foot orthosis. Prosthet Orthot Int 2024:00006479-990000000-00213. [PMID: 38180143 DOI: 10.1097/pxr.0000000000000323] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Accepted: 11/17/2023] [Indexed: 01/06/2024]
Abstract
BACKGROUND Ankle-foot orthoses (AFOs) are a type of assistive device that can improve the walking ability of individuals with neurological disorders. Adjusting stiffness is a common way to customize settings according to individuals' impairment. OBJECTIVE This study aims to design a variable-stiffness AFO by stiffness module and characterize the AFO stiffness range to provide subject-specific settings for the users. METHODS We modeled AFO using bending beams with varying fulcrum positions to adjust the stiffness. To characterize the stiffness range and profile, we used the superposition method to generate the theoretical model to analyze the AFO numerically. The intrinsic deformation of the bending beam in the AFO is considered a combination of 2 bending deformations to replicate actual bending conditions. The corresponding experiments in different fulcrum positions were performed to compare with and optimize the theoretical model. The curve fitting method was applied to tune the theoretical model by adding a fulcrum position-related coefficient. RESULTS The AFO stiffness increased as the fulcrum moved to the proximal position. The maximum stiffness obtained was 1.77 Nm/° at a 6-cm fulcrum position, and the minimum stiffness was 0.82 Nm/° at a 0.5-cm fulcrum position with a 0.43-cm thick fiberglass beam. The corresponding theoretical model had maximum and minimum stiffness of 1.71 and 0.80 Nm/°, respectively. The theoretical model had a 4.08% difference compared with experimental values. CONCLUSIONS The stiffness module can provide adjustable stiffness with the fulcrum position and different kinds of fiberglass bars, especially the thickness and material of the beam. The theoretical model with different fulcrum positions can be used to profile the real-time stiffness of the AFO in a dynamic motion and to determine the appropriate dimensions of the bending beam.
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Affiliation(s)
- Haochen Rong
- Department of Aerospace and Mechanical Engineering, Saint Louis University, St. Louis, MO
| | - Sepehr Ramezani
- Department of Mechanical and Aerospace Engineering, Biionix Cluster, University of Central Florida, Orlando, FL
| | - Alex Ambro
- Department of Aerospace and Mechanical Engineering, Saint Louis University, St. Louis, MO
| | - Chi Hou Lei
- Department of Aerospace and Mechanical Engineering, Saint Louis University, St. Louis, MO
| | - Hwan Choi
- Department of Mechanical and Aerospace Engineering, Biionix Cluster, University of Central Florida, Orlando, FL
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Koo YJ, Hwangbo J, Koo S. Higher coactivations of lower limb muscles increase stability during walking on slippery ground in forward dynamics musculoskeletal simulation. Sci Rep 2023; 13:22808. [PMID: 38129534 PMCID: PMC10739792 DOI: 10.1038/s41598-023-49865-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2023] [Accepted: 12/12/2023] [Indexed: 12/23/2023] Open
Abstract
The energy efficiency theory of human bipedal locomotion has been widely accepted as a neuro-musculoskeletal control method. However, coactivation of agonist and antagonist muscles in the lower limb has been observed during various limb movements, including walking. The emergence of this coactivation cannot be explained solely by the energy efficiency theory and remains a subject of debate. To shed light on this, we investigated the role of muscle coactivations in walking stability using a forward dynamics musculoskeletal simulation combined with neural-network-based gait controllers. Our study revealed that a gait controller with minimal muscle activations had a high probability of falls under challenging gait conditions such as slippery ground and uneven terrain. Lower limb muscle coactivations emerged in the process of gait controller training on slippery ground. Controllers with physiological coactivation levels demonstrated a significantly reduced probability of falls. Our results suggest that achieving stable walking requires muscle coactivations beyond the minimal level of muscle energy. This study implies that coactivations likely emerge to maintain gait stability under challenging conditions, and both coactivation and energy optimization of lower limb muscles should be considered when exploring the foundational control mechanisms of human walking.
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Affiliation(s)
- Young-Jun Koo
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Jemin Hwangbo
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea
| | - Seungbum Koo
- Department of Mechanical Engineering, Korea Advanced Institute of Science and Technology, 291 Daehak-ro, Yuseong-gu, Daejeon, 34141, Republic of Korea.
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Clancy CE, Gatti AA, Ong CF, Maly MR, Delp SL. Muscle-driven simulations and experimental data of cycling. Sci Rep 2023; 13:21534. [PMID: 38057337 PMCID: PMC10700567 DOI: 10.1038/s41598-023-47945-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2023] [Accepted: 11/20/2023] [Indexed: 12/08/2023] Open
Abstract
Muscle-driven simulations have provided valuable insights in studies of walking and running, but a set of freely available simulations and corresponding experimental data for cycling do not exist. The aim of this work was to develop a set of muscle-driven simulations of cycling and to validate them by comparison with experimental data. We used direct collocation to generate simulations of 16 participants cycling over a range of powers (40-216 W) and cadences (75-99 RPM) using two optimization objectives: a baseline objective that minimized muscle effort and a second objective that additionally minimized tibiofemoral joint forces. We tested the accuracy of the simulations by comparing the timing of active muscle forces in our baseline simulation to timing in experimental electromyography data. Adding a term in the objective function to minimize tibiofemoral forces preserved cycling power and kinematics, improved similarity between active muscle force timing and experimental electromyography, and decreased tibiofemoral joint reaction forces, which better matched previously reported in vivo measurements. The musculoskeletal models, muscle-driven simulations, simulation software, and experimental data are freely shared at https://simtk.org/projects/cycling_sim for others to reproduce these results and build upon this research.
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Affiliation(s)
- Caitlin E Clancy
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
| | - Anthony A Gatti
- Department of Radiology, Stanford University, Stanford, CA, USA.
| | - Carmichael F Ong
- Department of Bioengineering, Stanford University, Stanford, CA, USA
| | - Monica R Maly
- Department of Kinesiology and Health Sciences, University of Waterloo, Waterloo, ON, Canada
| | - Scott L Delp
- Department of Mechanical Engineering, Stanford University, Stanford, CA, USA
- Department of Bioengineering, Stanford University, Stanford, CA, USA
- Department of Orthopaedic Surgery, Stanford University, Stanford, CA, USA
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Chuang YC, Tsai YL, Lin TTL, Ou-Yang LJ, Lee YC, Cheng YY, Liu CC, Hsu CS. Effects of soft robotic exosuit on ambulation ability in stroke patients: a systematic review. Biomed Eng Online 2023; 22:88. [PMID: 37670316 PMCID: PMC10478336 DOI: 10.1186/s12938-023-01150-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2023] [Accepted: 08/28/2023] [Indexed: 09/07/2023] Open
Abstract
BACKGROUND Robot-assisted gait training is incorporated into guidelines for stroke rehabilitation. It is a promising tool combined with conventional therapy for low ambulatory patients. The heavy weight and bulky appearance of a robotic exoskeleton limits its practicality. On the other hand, soft robotic exosuit (SRE) based on its light weight and inconspicuous property, is better tolerated by patients in daily life. The aim of this study is to review the efficacy of the SRE with regard to walking ability and biomechanical properties in stroke patients. METHODS Electronic searches were carried out in PubMed, Embase, Cochrane Library, Web of Science, and the Physiotherapy Evidence Database. Clinical trials that investigated the effectiveness of SREs on ambulation ability in patients with post-stroke hemiparesis were eligible. Qualitative data synthesis was subsequently performed. RESULTS Nine studies were identified as relevant, involving a total of 83 patients. For the assessment of SRE efficacy, outcome measures were walking ability and biomechanical properties. In terms of both immediate effect and training effect, SREs improved the walking speed, walking distance, peak ankle dorsiflexion angle during swing phase, peak paretic propulsion, stride length and compensated gait in stroke patients. CONCLUSIONS SRE improved the ambulation ability of stroke patients in terms of walking ability and biomechanical properties. The small number of studies limits the generalizability of interpretation. More controlled studies with better quality are required to reach a more solid conclusion on this issue.
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Affiliation(s)
- Ya-Chi Chuang
- Department of Physical Medicine and Rehabilitation, Taichung Veterans General Hospital, No. 1650 Taiwan Boulevard Sect. 4, Taichung, 407219, Taiwan, ROC
| | - Yu-Lin Tsai
- Department of Physical Medicine and Rehabilitation, Taichung Veterans General Hospital, No. 1650 Taiwan Boulevard Sect. 4, Taichung, 407219, Taiwan, ROC
| | - Tony Tung-Liang Lin
- Department of Physical Medicine and Rehabilitation, Taichung Veterans General Hospital, No. 1650 Taiwan Boulevard Sect. 4, Taichung, 407219, Taiwan, ROC
| | - Liang-Jun Ou-Yang
- Department of Physical Medicine and Rehabilitation, Chang Gung Memorial Hospital, Linkou, Taoyuan, 333423, Taiwan, ROC
| | - Yu-Chun Lee
- Department of Physical Medicine and Rehabilitation, Taichung Veterans General Hospital, No. 1650 Taiwan Boulevard Sect. 4, Taichung, 407219, Taiwan, ROC
- Department of Exercise Health Science, National Taiwan University of Sport, Taichung, 404401, Taiwan, ROC
- Department of Industrial Engineering and Enterprise Information, Tunghai University, Taichung, 407224, Taiwan, ROC
| | - Yuan-Yang Cheng
- Department of Physical Medicine and Rehabilitation, Taichung Veterans General Hospital, No. 1650 Taiwan Boulevard Sect. 4, Taichung, 407219, Taiwan, ROC
- Department of Post-Baccalaureate Medicine, College of Medicine, National Chung Hsing University, Taichung, 402202, Taiwan
- School of Medicine, National Yang Ming Chiao Tung University, Taipei, 112202, Taiwan
| | - Chuan-Ching Liu
- Department of Physical Medicine and Rehabilitation, Taichung Veterans General Hospital, No. 1650 Taiwan Boulevard Sect. 4, Taichung, 407219, Taiwan, ROC.
| | - Chun-Sheng Hsu
- Department of Physical Medicine and Rehabilitation, Taichung Veterans General Hospital, No. 1650 Taiwan Boulevard Sect. 4, Taichung, 407219, Taiwan, ROC.
- Department of Post-Baccalaureate Medicine, College of Medicine, National Chung Hsing University, Taichung, 402202, Taiwan.
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7
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Price M, Huber ME, Hoogkamer W. Minimum effort simulations of split-belt treadmill walking exploit asymmetry to reduce metabolic energy expenditure. J Neurophysiol 2023; 129:900-913. [PMID: 36883759 PMCID: PMC10110733 DOI: 10.1152/jn.00343.2022] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2022] [Revised: 02/15/2023] [Accepted: 02/28/2023] [Indexed: 03/09/2023] Open
Abstract
Walking on a split-belt treadmill elicits an adaptation response that changes baseline step length asymmetry. The underlying causes of this adaptation, however, are difficult to determine. It has been proposed that effort minimization may drive this adaptation, based on the idea that adopting longer steps on the fast belt, or positive step length asymmetry (SLA), can cause the treadmill to exert net-positive mechanical work on a bipedal walker. However, humans walking on split-belt treadmills have not been observed to reproduce this behavior when allowed to freely adapt. To determine if an effort-minimization motor control strategy would result in experimentally observed adaptation patterns, we conducted simulations of walking on different combinations of belt speeds with a human musculoskeletal model that minimized muscle excitations and metabolic rate. The model adopted increasing amounts of positive SLA and decreased its net metabolic rate with increasing belt speed difference, reaching +42.4% SLA and -5.7% metabolic rate relative to tied-belt walking at our maximum belt speed ratio of 3:1. These gains were primarily enabled by an increase in braking work and a reduction in propulsion work on the fast belt. The results suggest that a purely effort minimization driven split-belt walking strategy would involve substantial positive SLA, and that the lack of this characteristic in human behavior points to additional factors influencing the motor control strategy, such as aversion to excessive joint loads, asymmetry, or instability.NEW & NOTEWORTHY Behavioral observations of split-belt treadmill adaptation have been inconclusive toward its underlying causes. To estimate gait patterns when driven exclusively by one of these possible underlying causes, we simulated split-belt treadmill walking with a musculoskeletal model that minimized its summed muscle excitations. Our model took significantly longer steps on the fast belt and reduced its metabolic rate below tied-belt walking, unlike experimental observations. This suggests that asymmetry is energetically optimal, but human adaptation involves additional factors.
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Affiliation(s)
- Mark Price
- Department of Kinesiology, University of Massachusetts, Amherst, Massachusetts, United States
- Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, Massachusetts, United States
| | - Meghan E Huber
- Department of Mechanical and Industrial Engineering, University of Massachusetts, Amherst, Massachusetts, United States
| | - Wouter Hoogkamer
- Department of Kinesiology, University of Massachusetts, Amherst, Massachusetts, United States
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Boyer KA, Hayes KL, Umberger BR, Adamczyk PG, Bean JF, Brach JS, Clark BC, Clark DJ, Ferrucci L, Finley J, Franz JR, Golightly YM, Hortobágyi T, Hunter S, Narici M, Nicklas B, Roberts T, Sawicki G, Simonsick E, Kent JA. Age-related changes in gait biomechanics and their impact on the metabolic cost of walking: Report from a National Institute on Aging workshop. Exp Gerontol 2023; 173:112102. [PMID: 36693530 PMCID: PMC10008437 DOI: 10.1016/j.exger.2023.112102] [Citation(s) in RCA: 16] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Revised: 01/09/2023] [Accepted: 01/19/2023] [Indexed: 01/22/2023]
Abstract
Changes in old age that contribute to the complex issue of an increased metabolic cost of walking (mass-specific energy cost per unit distance traveled) in older adults appear to center at least in part on changes in gait biomechanics. However, age-related changes in energy metabolism, neuromuscular function and connective tissue properties also likely contribute to this problem, of which the consequences are poor mobility and increased risk of inactivity-related disease and disability. The U.S. National Institute on Aging convened a workshop in September 2021 with an interdisciplinary group of scientists to address the gaps in research related to the mechanisms and consequences of changes in mobility in old age. The goal of the workshop was to identify promising ways to move the field forward toward improving gait performance, decreasing energy cost, and enhancing mobility for older adults. This report summarizes the workshop and brings multidisciplinary insight into the known and potential causes and consequences of age-related changes in gait biomechanics. We highlight how gait mechanics and energy cost change with aging, the potential neuromuscular mechanisms and role of connective tissue in these changes, and cutting-edge interventions and technologies that may be used to measure and improve gait and mobility in older adults. Key gaps in the literature that warrant targeted research in the future are identified and discussed.
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Affiliation(s)
- Katherine A Boyer
- Department of Kinesiology, University of Massachusetts Amherst, MA, USA; Department of Orthopedics and Physical Rehabilitation, University of Massachusetts Medical School, Worcester, MA, USA.
| | - Kate L Hayes
- Department of Kinesiology, University of Massachusetts Amherst, MA, USA
| | | | | | - Jonathan F Bean
- New England GRECC, VA Boston Healthcare System, Boston, MA, USA; Department of PM&R, Harvard Medical School, Boston, MA, USA; Spaulding Rehabilitation Hospital, Boston, MA, USA
| | - Jennifer S Brach
- Department of Physical Therapy, University of Pittsburgh, Pittsburgh, PA, USA
| | - Brian C Clark
- Ohio Musculoskeletal and Neurological Institute and the Department of Biomedical Sciences, Ohio University, Athens, OH, USA
| | - David J Clark
- Brain Rehabilitation Research Center, Malcom Randall VA Medical Center, Gainesville, FL, USA; Department of Physiology and Aging, University of Florida, Gainesville, FL, USA
| | - Luigi Ferrucci
- Intramural Research Program of the National Institute on Aging, NIH, Baltimore, MD, USA
| | - James Finley
- Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA, USA
| | - Jason R Franz
- Joint Department of Biomedical Engineering, University of North Carolina at Chapel Hill and North Carolina State University, Chapel Hill, NC, USA
| | - Yvonne M Golightly
- College of Allied Health Professions, University of Nebraska Medical Center, Omaha, NE, USA; Thurston Arthritis Research Center, Division of Rheumatology, Allergy, and Immunology, Department of Medicine, University of North Carolina, Chapel Hill, NC, USA
| | - Tibor Hortobágyi
- Hungarian University of Sports Science, Department of Kinesiology, Budapest, Hungary; Institute of Sport Sciences and Physical Education, University of Pécs, Hungary; Somogy County Kaposi Mór Teaching Hospital, Kaposvár, Hungary; Center for Human Movement Sciences, University of Groningen Medical Center, Groningen, the Netherlands
| | - Sandra Hunter
- Department of Physical Therapy, Marquette University, Milwaukee, WI, USA
| | - Marco Narici
- Neuromuscular Physiology Laboratory, Department of Biomedical Sciences, University of Padova, Padova, Italy
| | - Barbara Nicklas
- Section on Gerontology and Geriatric Medicine, Wake Forest University School of Medicine, USA
| | - Thomas Roberts
- Department of Ecology and Evolutionary Biology, Brown University, USA
| | - Gregory Sawicki
- George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, USA
| | - Eleanor Simonsick
- Intramural Research Program of the National Institute on Aging, NIH, Baltimore, MD, USA
| | - Jane A Kent
- Department of Kinesiology, University of Massachusetts Amherst, MA, USA
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