The Experts below are selected from a list of 282 Experts worldwide ranked by ideXlab platform
Alexander M. Dollar - One of the best experts on this subject based on the ideXlab platform.
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estimation of quasi stiffness of the human hip in the stance phase of walking
PLOS ONE, 2013Co-Authors: Kamran Shamaei, Gregory S Sawicki, Alexander M. DollarAbstract:Biomechanical data characterizing the quasi-stiffness of lower-limb joints during human locomotion is limited. Understanding joint stiffness is critical for evaluating gait function and designing devices such as Prostheses and Orthoses intended to emulate biological properties of human legs. The knee joint moment-angle relationship is approximately linear in the flexion and extension stages of stance, exhibiting nearly constant stiffnesses, known as the quasi-stiffnesses of each stage. Using a generalized inverse dynamics analysis approach, we identify the key independent variables needed to predict knee quasi-stiffness during walking, including gait speed, knee excursion, and subject height and weight. Then, based on the identified key variables, we used experimental walking data for 136 conditions (speeds of 0.75–2.63 m/s) across 14 subjects to obtain best fit linear regressions for a set of general models, which were further simplified for the optimal gait speed. We found R2 > 86% for the most general models of knee quasi-stiffnesses for the flexion and extension stages of stance. With only subject height and weight, we could predict knee quasi-stiffness for preferred walking speed with average error of 9% with only one outlier. These results provide a useful framework and foundation for selecting subject-specific stiffness for prosthetic and exoskeletal devices designed to emulate biological knee function during walking.
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Estimation of quasi-stiffness of the human knee in the stance phase of walking.
PloS one, 2013Co-Authors: Kamran Shamaei, Gregory S Sawicki, Alexander M. DollarAbstract:Biomechanical data characterizing the quasi-stiffness of lower-limb joints during human locomotion is limited. Understanding joint stiffness is critical for evaluating gait function and designing devices such as Prostheses and Orthoses intended to emulate biological properties of human legs. The knee joint moment-angle relationship is approximately linear in the flexion and extension stages of stance, exhibiting nearly constant stiffnesses, known as the quasi-stiffnesses of each stage. Using a generalized inverse dynamics analysis approach, we identify the key independent variables needed to predict knee quasi-stiffness during walking, including gait speed, knee excursion, and subject height and weight. Then, based on the identified key variables, we used experimental walking data for 136 conditions (speeds of 0.75-2.63 m/s) across 14 subjects to obtain best fit linear regressions for a set of general models, which were further simplified for the optimal gait speed. We found R(2) > 86% for the most general models of knee quasi-stiffnesses for the flexion and extension stages of stance. With only subject height and weight, we could predict knee quasi-stiffness for preferred walking speed with average error of 9% with only one outlier. These results provide a useful framework and foundation for selecting subject-specific stiffness for prosthetic and exoskeletal devices designed to emulate biological knee function during walking.
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estimation of quasi stiffness and propulsive work of the human ankle in the stance phase of walking
PLOS ONE, 2013Co-Authors: Kamran Shamaei, Gregory S Sawicki, Alexander M. DollarAbstract:Characterizing the quasi-stiffness and work of lower extremity joints is critical for evaluating human locomotion and designing assistive devices such as Prostheses and Orthoses intended to emulate the biological behavior of human legs. This work aims to establish statistical models that allow us to predict the ankle quasi-stiffness and net mechanical work for adults walking on level ground. During the stance phase of walking, the ankle joint propels the body through three distinctive phases of nearly constant stiffness known as the quasi-stiffness of each phase. Using a generic equation for the ankle moment obtained through an inverse dynamics analysis, we identify key independent parameters needed to predict ankle quasi-stiffness and propulsive work and also the functional form of each correlation. These parameters include gait speed, ankle excursion, and subject height and weight. Based on the identified form of the correlation and key variables, we applied linear regression on experimental walking data for 216 gait trials across 26 subjects (speeds from 0.75–2.63 m/s) to obtain statistical models of varying complexity. The most general forms of the statistical models include all the key parameters and have an R2 of 75% to 81% in the prediction of the ankle quasi-stiffnesses and propulsive work. The most specific models include only subject height and weight and could predict the ankle quasi-stiffnesses and work for optimal walking speed with average error of 13% to 30%. We discuss how these models provide a useful framework and foundation for designing subject- and gait-specific prosthetic and exoskeletal devices designed to emulate biological ankle function during level ground walking.
Kamran Shamaei - One of the best experts on this subject based on the ideXlab platform.
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estimation of quasi stiffness of the human hip in the stance phase of walking
PLOS ONE, 2013Co-Authors: Kamran Shamaei, Gregory S Sawicki, Alexander M. DollarAbstract:Biomechanical data characterizing the quasi-stiffness of lower-limb joints during human locomotion is limited. Understanding joint stiffness is critical for evaluating gait function and designing devices such as Prostheses and Orthoses intended to emulate biological properties of human legs. The knee joint moment-angle relationship is approximately linear in the flexion and extension stages of stance, exhibiting nearly constant stiffnesses, known as the quasi-stiffnesses of each stage. Using a generalized inverse dynamics analysis approach, we identify the key independent variables needed to predict knee quasi-stiffness during walking, including gait speed, knee excursion, and subject height and weight. Then, based on the identified key variables, we used experimental walking data for 136 conditions (speeds of 0.75–2.63 m/s) across 14 subjects to obtain best fit linear regressions for a set of general models, which were further simplified for the optimal gait speed. We found R2 > 86% for the most general models of knee quasi-stiffnesses for the flexion and extension stages of stance. With only subject height and weight, we could predict knee quasi-stiffness for preferred walking speed with average error of 9% with only one outlier. These results provide a useful framework and foundation for selecting subject-specific stiffness for prosthetic and exoskeletal devices designed to emulate biological knee function during walking.
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Estimation of quasi-stiffness of the human knee in the stance phase of walking.
PloS one, 2013Co-Authors: Kamran Shamaei, Gregory S Sawicki, Alexander M. DollarAbstract:Biomechanical data characterizing the quasi-stiffness of lower-limb joints during human locomotion is limited. Understanding joint stiffness is critical for evaluating gait function and designing devices such as Prostheses and Orthoses intended to emulate biological properties of human legs. The knee joint moment-angle relationship is approximately linear in the flexion and extension stages of stance, exhibiting nearly constant stiffnesses, known as the quasi-stiffnesses of each stage. Using a generalized inverse dynamics analysis approach, we identify the key independent variables needed to predict knee quasi-stiffness during walking, including gait speed, knee excursion, and subject height and weight. Then, based on the identified key variables, we used experimental walking data for 136 conditions (speeds of 0.75-2.63 m/s) across 14 subjects to obtain best fit linear regressions for a set of general models, which were further simplified for the optimal gait speed. We found R(2) > 86% for the most general models of knee quasi-stiffnesses for the flexion and extension stages of stance. With only subject height and weight, we could predict knee quasi-stiffness for preferred walking speed with average error of 9% with only one outlier. These results provide a useful framework and foundation for selecting subject-specific stiffness for prosthetic and exoskeletal devices designed to emulate biological knee function during walking.
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estimation of quasi stiffness and propulsive work of the human ankle in the stance phase of walking
PLOS ONE, 2013Co-Authors: Kamran Shamaei, Gregory S Sawicki, Alexander M. DollarAbstract:Characterizing the quasi-stiffness and work of lower extremity joints is critical for evaluating human locomotion and designing assistive devices such as Prostheses and Orthoses intended to emulate the biological behavior of human legs. This work aims to establish statistical models that allow us to predict the ankle quasi-stiffness and net mechanical work for adults walking on level ground. During the stance phase of walking, the ankle joint propels the body through three distinctive phases of nearly constant stiffness known as the quasi-stiffness of each phase. Using a generic equation for the ankle moment obtained through an inverse dynamics analysis, we identify key independent parameters needed to predict ankle quasi-stiffness and propulsive work and also the functional form of each correlation. These parameters include gait speed, ankle excursion, and subject height and weight. Based on the identified form of the correlation and key variables, we applied linear regression on experimental walking data for 216 gait trials across 26 subjects (speeds from 0.75–2.63 m/s) to obtain statistical models of varying complexity. The most general forms of the statistical models include all the key parameters and have an R2 of 75% to 81% in the prediction of the ankle quasi-stiffnesses and propulsive work. The most specific models include only subject height and weight and could predict the ankle quasi-stiffnesses and work for optimal walking speed with average error of 13% to 30%. We discuss how these models provide a useful framework and foundation for designing subject- and gait-specific prosthetic and exoskeletal devices designed to emulate biological ankle function during level ground walking.
Andrew H. Hansen - One of the best experts on this subject based on the ideXlab platform.
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Investigations of roll-over shape: implications for design, alignment, and evaluation of ankle-foot Prostheses and Orthoses.
Disability and rehabilitation, 2010Co-Authors: Andrew H. Hansen, Dudley S. ChildressAbstract:Purpose. The purpose of this article is to provide an overview of our previous work on roll-over shapes, which are the effective rocker shapes that the lower limb systems conform to during walking.Method. This article is a summary of several recently published articles from the Northwestern University Prosthetics Research Laboratory and Rehabilitation Engineering Research Program on the topic of roll-over shapes. The roll-over shape is a measurement of centre of pressure of the ground reaction force in body-based coordinates. This measurement is interpreted as the effective rocker shape created by lower limb systems during walking.Results. Our studies have shown that roll-over shapes in able-bodied subjects do not change appreciably for conditions of level ground walking, including walking at different speeds, while carrying different amounts of weight, while wearing shoes of different heel heights, or when wearing shoes with different rocker radii. In fact, results suggest that able-bodied humans will ac...
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Roll-over shapes of the ankle-foot and knee-ankle-foot systems of able-bodied children.
Clinical biomechanics (Bristol Avon), 2009Co-Authors: Andrew H. Hansen, Margrit R. MeierAbstract:Background: The roll-over shape is the effective rocker shape that a lower limb system conforms to during a step. The roll-over shape concept has been explored in detail in adults and has been successfully used in the design, evaluation, and alignment of lower limb Prostheses and Orthoses. No such analysis exists for the pediatric population. Therefore, the purpose of this study was to investigate the ankle-foot and knee-ankle-foot roll-over shapes in able-bodied children, values that could serve as tools for design and evaluation of lower limb pediatric Prostheses and Orthoses. Methods: This study describes a multi-center retrospective review of existing motion analysis data (n = 153 from three centers). Roll-over shapes were calculated by transforming center of pressure data from a laboratory-based coordinate system into two body-based coordinate systems. Roll-over shapes were then characterized using a circular arc model. Best-fit radii of roll-over shapes for children in three age groups (3-7 years, 8-11 years, and 12-17 years) were compared using the Kruskal-Wallis Test. Findings: No significant changes were found in roll-over shape radii between the three age groups (p = 0.54 for ankle-foot roll-over shape radii; p = 0.12 for knee-ankle-foot roll-over shape radii). The weighted mean of median radii for ankle-foot and knee-ankle-foot roll-over shapes from the three centers were approximately 22% and 17% of body stature, values similar to those seen in adults. Interpretation: Children produce nearly circular knee-ankle-foot roll-over shapes at a young age that are similar to those seen in adults when scaled by body stature. Keywords: foot, ankle, knee, rocker, cam, center of pressure, prosthetics
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Net external energy of the biologic and prosthetic ankle during gait initiation.
Gait & posture, 2009Co-Authors: Andrew H. Hansen, Steven A. Gard, Dudley S. Childress, Steve C. Miff, Margrit R. MeierAbstract:The net external energy of the biologic human ankle joint and of some lower limb prosthetic ankle-foot systems was examined during gait initiation. The purpose of the study was to better understand the ankle's behavior during the acceleration phase of walking for use in the design of improved lower limb Prostheses and Orthoses. Quantitative gait data were collected from 10 able-bodied subjects and 10 persons with unilateral transtibial amputations during gait initiation. The behaviors of the biologic and prosthetic 'ankle' joints were examined by analyzing the relationship between sagittal plane ankle angles and moments. Net external energy at the ankle was estimated by calculating the area under the moment versus angle curves (hysteresis) created during the loading and unloading phases. Results indicate that able-bodied persons utilize energy input from the trailing ankle after the first step is made in gait initiation, most likely to help transition the body into steady-state walking. The passive prosthetic ankle-foot systems tested were unable to put energy into the system during gait initiation.
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Effects of adding weight to the torso on roll-over characteristics of walking.
Journal of rehabilitation research and development, 2005Co-Authors: Andrew H. Hansen, Dudley S. ChildressAbstract:Ten participants without physical impairment walked with 0 kg, 11.5 kg, and 23.0 kg of added weight equally distributed about the torso in a harness. At each weight level, the participants walked at slow, normal, and fast self-selected walking speeds. We examined the roll-over characteristics by determining the ankle-foot and knee-ankle-foot roll-over shapes. These shapes, which are the effective rockers created by the respective lower-limb systems between heel contact and opposite heel contact of walking, are found if one transforms the center of pressure of ground reaction force into body coordinate systems. The roll-over shapes of the ankle-foot and knee-ankle-foot systems did not change appreciably with added weight at any of the three walking speeds. The invariance of these biologic systems to added weight should be considered when Prostheses and Orthoses are designed that intend to replace and augment their function in walking.
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Roll-over characteristics of human walking on inclined surfaces.
Human movement science, 2004Co-Authors: Andrew H. Hansen, Dudley S. Childress, Steve C. MiffAbstract:Abstract Roll-over characteristics of able-bodied human subjects walking on ramped surfaces were examined in this study. Ten subjects walked at their normal self-selected speed on a level surface, a 5-deg ramp, and a 10-deg ramped surface. Ramps were designed such that ground reaction forces and center of pressure of the ground reaction forces could be measured on their surfaces. This set-up facilitated calculation of the effective rockers that the ankle–foot (AF) and knee–ankle–foot (KAF) systems conformed to during single-limb stance (contralateral toe off to contralateral heel contact). Since our original “roll-over shapes” were characterized between heel contact and opposite heel contact, we label the shapes found during single-limb stance as “truncated roll-over shapes”. We hypothesized that the ankle–foot system would adapt to the various surfaces, creating a roll-over shape that would change in orientation with different levels of inclination. The truncated AF roll-over shapes supported this hypothesis for uphill walking but did not support the hypothesis for downhill walking. However, truncated roll-over shapes of the KAF system did adjust their orientation to match both the positive and negative levels of surface inclination. In general, the ankle appears to be the main adapting joint when walking up inclined surfaces while the knee becomes important for the overall adaptation in downhill walking. Knowledge of physiological lower-limb roll-over characteristics on ramped surfaces may help in the development of biomimetic Prostheses and Orthoses that will automatically adapt to changes in walking surface inclination.
Dudley S. Childress - One of the best experts on this subject based on the ideXlab platform.
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Investigations of roll-over shape: implications for design, alignment, and evaluation of ankle-foot Prostheses and Orthoses.
Disability and rehabilitation, 2010Co-Authors: Andrew H. Hansen, Dudley S. ChildressAbstract:Purpose. The purpose of this article is to provide an overview of our previous work on roll-over shapes, which are the effective rocker shapes that the lower limb systems conform to during walking.Method. This article is a summary of several recently published articles from the Northwestern University Prosthetics Research Laboratory and Rehabilitation Engineering Research Program on the topic of roll-over shapes. The roll-over shape is a measurement of centre of pressure of the ground reaction force in body-based coordinates. This measurement is interpreted as the effective rocker shape created by lower limb systems during walking.Results. Our studies have shown that roll-over shapes in able-bodied subjects do not change appreciably for conditions of level ground walking, including walking at different speeds, while carrying different amounts of weight, while wearing shoes of different heel heights, or when wearing shoes with different rocker radii. In fact, results suggest that able-bodied humans will ac...
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Net external energy of the biologic and prosthetic ankle during gait initiation.
Gait & posture, 2009Co-Authors: Andrew H. Hansen, Steven A. Gard, Dudley S. Childress, Steve C. Miff, Margrit R. MeierAbstract:The net external energy of the biologic human ankle joint and of some lower limb prosthetic ankle-foot systems was examined during gait initiation. The purpose of the study was to better understand the ankle's behavior during the acceleration phase of walking for use in the design of improved lower limb Prostheses and Orthoses. Quantitative gait data were collected from 10 able-bodied subjects and 10 persons with unilateral transtibial amputations during gait initiation. The behaviors of the biologic and prosthetic 'ankle' joints were examined by analyzing the relationship between sagittal plane ankle angles and moments. Net external energy at the ankle was estimated by calculating the area under the moment versus angle curves (hysteresis) created during the loading and unloading phases. Results indicate that able-bodied persons utilize energy input from the trailing ankle after the first step is made in gait initiation, most likely to help transition the body into steady-state walking. The passive prosthetic ankle-foot systems tested were unable to put energy into the system during gait initiation.
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Effects of adding weight to the torso on roll-over characteristics of walking.
Journal of rehabilitation research and development, 2005Co-Authors: Andrew H. Hansen, Dudley S. ChildressAbstract:Ten participants without physical impairment walked with 0 kg, 11.5 kg, and 23.0 kg of added weight equally distributed about the torso in a harness. At each weight level, the participants walked at slow, normal, and fast self-selected walking speeds. We examined the roll-over characteristics by determining the ankle-foot and knee-ankle-foot roll-over shapes. These shapes, which are the effective rockers created by the respective lower-limb systems between heel contact and opposite heel contact of walking, are found if one transforms the center of pressure of ground reaction force into body coordinate systems. The roll-over shapes of the ankle-foot and knee-ankle-foot systems did not change appreciably with added weight at any of the three walking speeds. The invariance of these biologic systems to added weight should be considered when Prostheses and Orthoses are designed that intend to replace and augment their function in walking.
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Roll-over characteristics of human walking on inclined surfaces.
Human movement science, 2004Co-Authors: Andrew H. Hansen, Dudley S. Childress, Steve C. MiffAbstract:Abstract Roll-over characteristics of able-bodied human subjects walking on ramped surfaces were examined in this study. Ten subjects walked at their normal self-selected speed on a level surface, a 5-deg ramp, and a 10-deg ramped surface. Ramps were designed such that ground reaction forces and center of pressure of the ground reaction forces could be measured on their surfaces. This set-up facilitated calculation of the effective rockers that the ankle–foot (AF) and knee–ankle–foot (KAF) systems conformed to during single-limb stance (contralateral toe off to contralateral heel contact). Since our original “roll-over shapes” were characterized between heel contact and opposite heel contact, we label the shapes found during single-limb stance as “truncated roll-over shapes”. We hypothesized that the ankle–foot system would adapt to the various surfaces, creating a roll-over shape that would change in orientation with different levels of inclination. The truncated AF roll-over shapes supported this hypothesis for uphill walking but did not support the hypothesis for downhill walking. However, truncated roll-over shapes of the KAF system did adjust their orientation to match both the positive and negative levels of surface inclination. In general, the ankle appears to be the main adapting joint when walking up inclined surfaces while the knee becomes important for the overall adaptation in downhill walking. Knowledge of physiological lower-limb roll-over characteristics on ramped surfaces may help in the development of biomimetic Prostheses and Orthoses that will automatically adapt to changes in walking surface inclination.
Gregory S Sawicki - One of the best experts on this subject based on the ideXlab platform.
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estimation of quasi stiffness of the human hip in the stance phase of walking
PLOS ONE, 2013Co-Authors: Kamran Shamaei, Gregory S Sawicki, Alexander M. DollarAbstract:Biomechanical data characterizing the quasi-stiffness of lower-limb joints during human locomotion is limited. Understanding joint stiffness is critical for evaluating gait function and designing devices such as Prostheses and Orthoses intended to emulate biological properties of human legs. The knee joint moment-angle relationship is approximately linear in the flexion and extension stages of stance, exhibiting nearly constant stiffnesses, known as the quasi-stiffnesses of each stage. Using a generalized inverse dynamics analysis approach, we identify the key independent variables needed to predict knee quasi-stiffness during walking, including gait speed, knee excursion, and subject height and weight. Then, based on the identified key variables, we used experimental walking data for 136 conditions (speeds of 0.75–2.63 m/s) across 14 subjects to obtain best fit linear regressions for a set of general models, which were further simplified for the optimal gait speed. We found R2 > 86% for the most general models of knee quasi-stiffnesses for the flexion and extension stages of stance. With only subject height and weight, we could predict knee quasi-stiffness for preferred walking speed with average error of 9% with only one outlier. These results provide a useful framework and foundation for selecting subject-specific stiffness for prosthetic and exoskeletal devices designed to emulate biological knee function during walking.
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Estimation of quasi-stiffness of the human knee in the stance phase of walking.
PloS one, 2013Co-Authors: Kamran Shamaei, Gregory S Sawicki, Alexander M. DollarAbstract:Biomechanical data characterizing the quasi-stiffness of lower-limb joints during human locomotion is limited. Understanding joint stiffness is critical for evaluating gait function and designing devices such as Prostheses and Orthoses intended to emulate biological properties of human legs. The knee joint moment-angle relationship is approximately linear in the flexion and extension stages of stance, exhibiting nearly constant stiffnesses, known as the quasi-stiffnesses of each stage. Using a generalized inverse dynamics analysis approach, we identify the key independent variables needed to predict knee quasi-stiffness during walking, including gait speed, knee excursion, and subject height and weight. Then, based on the identified key variables, we used experimental walking data for 136 conditions (speeds of 0.75-2.63 m/s) across 14 subjects to obtain best fit linear regressions for a set of general models, which were further simplified for the optimal gait speed. We found R(2) > 86% for the most general models of knee quasi-stiffnesses for the flexion and extension stages of stance. With only subject height and weight, we could predict knee quasi-stiffness for preferred walking speed with average error of 9% with only one outlier. These results provide a useful framework and foundation for selecting subject-specific stiffness for prosthetic and exoskeletal devices designed to emulate biological knee function during walking.
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estimation of quasi stiffness and propulsive work of the human ankle in the stance phase of walking
PLOS ONE, 2013Co-Authors: Kamran Shamaei, Gregory S Sawicki, Alexander M. DollarAbstract:Characterizing the quasi-stiffness and work of lower extremity joints is critical for evaluating human locomotion and designing assistive devices such as Prostheses and Orthoses intended to emulate the biological behavior of human legs. This work aims to establish statistical models that allow us to predict the ankle quasi-stiffness and net mechanical work for adults walking on level ground. During the stance phase of walking, the ankle joint propels the body through three distinctive phases of nearly constant stiffness known as the quasi-stiffness of each phase. Using a generic equation for the ankle moment obtained through an inverse dynamics analysis, we identify key independent parameters needed to predict ankle quasi-stiffness and propulsive work and also the functional form of each correlation. These parameters include gait speed, ankle excursion, and subject height and weight. Based on the identified form of the correlation and key variables, we applied linear regression on experimental walking data for 216 gait trials across 26 subjects (speeds from 0.75–2.63 m/s) to obtain statistical models of varying complexity. The most general forms of the statistical models include all the key parameters and have an R2 of 75% to 81% in the prediction of the ankle quasi-stiffnesses and propulsive work. The most specific models include only subject height and weight and could predict the ankle quasi-stiffnesses and work for optimal walking speed with average error of 13% to 30%. We discuss how these models provide a useful framework and foundation for designing subject- and gait-specific prosthetic and exoskeletal devices designed to emulate biological ankle function during level ground walking.
