This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
With the recent conflicts in Afghanistan and Iraq, it is increasingly evident that the demands of... more With the recent conflicts in Afghanistan and Iraq, it is increasingly evident that the demands of warfare are changing and the need for innovative mobility systems is growing. In the rough, unstructured terrain that the soldiers encounter, they have reverted to using mules and donkeys to move stealthily and quickly. In light of the growing need for autonomous systems, the Army is looking at the possibility of legged mobility options such as gasoline powered quadrupeds to traverse the off-road terrain. As technology advances, the era of military bipeds may well be in sight. However, current bipedal robotic technology is far too inefficient for battlefield use. Much of this inefficiency stems from actuated control of each limb's motion throughout the entire gait cycle. An alternative approach is to exploit the passive pendular dynamics of legs and legged bodies for energy savings. This paper compares and contrasts fully-actuated walking with passive walking. Simulations of passive and quasi-passive walking are analyzed to evaluate their stability regions and their initial responses on uneven terrain functions are compared.
The U.S. Army is seeking to develop autonomous off-road mobile robots to perform tasks in the fie... more The U.S. Army is seeking to develop autonomous off-road mobile robots to perform tasks in the field such as supply delivery and reconnaissance in dangerous territory. A key problem to be solved with these robots is off-road mobility, to ensure that the robots can accomplish their tasks without loss or damage. We have developed a computer model of one such concept robot, the small-scale "T-1" omnidirectional vehicle (ODV), to study the effects of different control strategies on the robot's mobility in off-road settings. We built the dynamic model in ADAMS/Car and the control system in Matlab/Simulink. This paper presents the template-based method used to construct the ADAMS model of the T-1 ODV. It discusses the strengths and weaknesses of ADAMS/Car software in such an application, and describes the benefits and challenges of the approach as a whole. The paper also addresses effective linking of ADAMS/Car and Matlab for complete control system development. Finally, this paper includes a section describing the extension of the T-1 templates to other similar ODV concepts for rapid development.
Muscle-tendon units about the ankle joint generate a burst of positive power during the step-to-s... more Muscle-tendon units about the ankle joint generate a burst of positive power during the step-to-step transition in human walking, termed ankle push-off, but there is no scientific consensus on its functional role. A central question embodied in the biomechanics literature is: does ankle push-off primarily contribute to leg swing, or to center of mass (COM) acceleration? This question has been debated in various forms for decades. However, it actually presents a false dichotomy, as these two possibilities are not mutually exclusive. If we ask either question independently, the answer is the same: yes! (1) Does ankle push-off primarily contribute to leg swing acceleration? Yes. (2) Does ankle push-off primarily contribute to COM acceleration? Yes. Here, we summarize the historical debate, then synthesize the seemingly polarized perspectives and demonstrate that both descriptions are valid. The principal means by which ankle push-off affects COM mechanics is by a localized action that increases the speed and kinetic energy of the trailing push-off limb. Because the limb is included in body COM computations, this localized segmental acceleration also accelerates the COM, and most of the segmental energy change also appears as COM energy change. Interpretation of ankle mechanics should abandon an either/ or contrast of leg swing versus COM acceleration. Instead, ankle push-off should be interpreted in light of both mutually consistent effects. This unified perspective informs our fundamental understanding of the role of ankle push-off, and has important implications for the design of clinical interventions (e.g. prostheses, orthoses) intended to restore locomotor function to individuals with disabilities.
The U.S. Army is seeking to develop autonomous off-road mobile robots to perform tasks in the fie... more The U.S. Army is seeking to develop autonomous off-road mobile robots to perform tasks in the field such as supply delivery and reconnaissance in dangerous territory. A key problem to be solved with these robots is off-road mobility. We have developed a computer model of one concept robot, the "T1" omnidirectional vehicle (ODV), to study the effects of different control strategies on the robot's off-road mobility. The T1 is a lightweight robot with an innovative running-gear and control strategy to enhance mobility characteristics. We built the dynamic model of T1 in ADAMS/Car and the control system in MATLAB/Simulink. This paper presents the template-based method used to construct the ADAMS model of the T1 ODV. It also discusses effective linking of ADAMS and MATLAB for control system development. Finally, this paper includes a section describing the extension of the T1 templates to other similar ODV concepts for rapid development.
The current process of prescribing prosthetic feet is hampered by imprecise classifications based... more The current process of prescribing prosthetic feet is hampered by imprecise classifications based on self-assessment, recommendations based on subjective prediction, burdensome justification requirements, and slow, costly testing of devices. These problems have been exacerbated by the introduction of robotic prostheses, which can improve gait performance for some individuals, but are very expensive. We propose an alternative process, in which a versatile robotic emulator is used to preview patient interactions with a range of prostheses, while objective data related to effort, stability, speed and preference are collected, all prior to prescription. Results from pilot testing with a prototype emulator system demonstrate accurate haptic rendering of a wide range of prosthesis classes and differentiation of user performance across these classes. Eventually, emulation-based prescription could reduce bias, cost and waste in the prescription process, while simultaneously improving patient outcomes.
Robotic prostheses can improve walking performance for amputees, but prescription of these device... more Robotic prostheses can improve walking performance for amputees, but prescription of these devices has been hindered by their high cost and uncertainty about the degree to which individuals will benefit. The typical prescription process cannot well predict how an individual will respond to a device they have never used because it bases decisions on subjective assessment of an individual's current activity level. We propose a new approach in which individuals 'test drive' candidate devices using a prosthesis emulator while their walking performance is quantitatively assessed and results are distilled to inform prescription. In this system, prosthesis behavior is controlled by software rather than mechanical implementation, so users can quickly experience a broad range of devices. To test the viability of the approach, we developed a prototype emulator and assessment protocol, leveraging hardware and methods we previously developed for basic science experiments. We demonstrated emulations across the spectrum of commercially available prostheses, including traditional (e.g. SACH), dynamic-elastic (e.g. FlexFoot), and powered robotic (e.g. BiOM ® T2) prostheses. Emulations exhibited low error with respect to reference data and provided subjectively convincing representations of each device. We demonstrated an assessment protocol that differentiated device classes for each individual based on quantitative performance metrics, providing feedback that could be used to make objective, personalized device prescriptions.
During human walking, the center of pressure under the foot progresses forward smoothly during ea... more During human walking, the center of pressure under the foot progresses forward smoothly during each step, creating a wheel-like motion between the leg and the ground. This rolling motion might appear to aid walking economy, but the mechanisms that may lead to such a benefit are unclear, as the leg is not literally a wheel. We propose that there is indeed a benefit, but less from rolling than from smoother transitions between pendulum-like stance legs. The velocity of the body center of mass (COM) must be redirected in that transition, and a longer foot reduces the work required for the redirection. Here we develop a dynamic walking model that predicts different effects from altering foot length as opposed to foot radius, and test it by attaching rigid, arc-like foot bottoms to humans walking with fixed ankles. The model suggests that smooth rolling is relatively insensitive to arc radius, whereas work for the step-to-step transition decreases approximately quadratically with foot length. We measured the separate effects of arc-foot length and radius on COM velocity fluctuations, work performed by the legs and metabolic cost. Experimental data (N=8) show that foot length indeed has much greater effect on both the mechanical work of the step-to-step transition (23% variation, P=0.04) and the overall energetic cost of walking (6%, P=0.03) than foot radius (no significant effect, P>0.05). We found the minimum metabolic energy cost for an arc foot length of approximately 29% of leg length, roughly comparable to human foot length. Our results suggest that the foot's apparently wheel-like action derives less benefit from rolling per se than from reduced work to redirect the body COM.
IEEE Transactions on Neural Systems and Rehabilitation Engineering, Sep 1, 2015
Unilateral lower-limb amputees exhibit asymmetry in many gait features, such as ground force, ste... more Unilateral lower-limb amputees exhibit asymmetry in many gait features, such as ground force, step time, step length, and joint mechanics. Although these asymmetries result from weak prosthetic-side push-off, there is no proven mechanistic explanation of how that impairment propagates to the rest of the body. We used a simple dynamic walking model to explore possible consequences of a unilateral impairment similar to that of a transtibial amputee. The model compensates for reduced push-off work from one leg by performing more work elsewhere, for example during the middle of stance by either or both legs. The model predicts several gait abnormalities, including slower forward velocity of the body center-of-mass (COM) during intactside stance, greater energy dissipation in the intact side, and more positive work overall. We tested these predictions with data from unilateral transtibial amputees (N = 11) and non-amputee control subjects (N = 10) walking on an instrumented treadmill. We observed several predicted asymmetries, including forward velocity during stance phases and energy dissipation from the two limbs, as well as greater work overall. Secondary adaptations, such as to reduce discomfort, may exacerbate asymmetry, but these simple principles suggest that some asymmetry may be unavoidable in cases of unilateral limb loss.
The current process of prescribing prosthetic feet is hampered by imprecise classifications based... more The current process of prescribing prosthetic feet is hampered by imprecise classifications based on self-assessment, recommendations based on subjective prediction, burdensome justification requirements, and slow, costly testing of devices. These problems have been exacerbated by the introduction of robotic prostheses, which can improve gait performance for some individuals, but are very expensive. We propose an alternative process, in which a versatile robotic emulator is used to preview patient interactions with a range of prostheses, while objective data related to effort, stability, speed and preference are collected, all prior to prescription. Results from pilot testing with a prototype emulator system demonstrate accurate haptic rendering of a wide range of prosthesis classes and differentiation of user performance across these classes. Eventually, emulation-based prescription could reduce bias, cost and waste in the prescription process, while simultaneously improving patient outcomes.
The work the legs perform on the body center of mass (COM) is an important determinant of the met... more The work the legs perform on the body center of mass (COM) is an important determinant of the metabolic cost of walking. Much COM work is performed to redirect the center of mass from a downward to an upward velocity during transitions between successive stance legs, termed step-to-step transitions. We elucidate the links between COM velocity fluctuation, COM work, and metabolic cost through several experimental manipulations of gait. We show that foot length and foot bottom curvature affect COM work and metabolic cost in fixed-ankle walking. In dynamic walking models, longer feet lead to decreased work requirements for gait. We measured COM work and metabolic cost while subjects walked with locked ankles and artificial foot bottom shapes. COM work decreases with increasing foot length, because longer feet reduce the angular redirection of COM viii velocity during the step-to-step transition. Foot bottom curvature has no significant effect for humanlike foot sizes. In this range, COM work using arc shapes is less than for normal walking, though metabolic cost is higher. Metabolic cost is minimized by feet having length 28% of leg length. We also show that COM work for mechanically unconstrained walking depends on COM speed and angular redirection of COM velocity during the step-to-step transition. We measured variations in COM velocity while subjects walked at a wide range of speeds and step lengths. COM work scales quadratically with COM speed at heel strike times angular redirection of COM velocity. We introduce a sagittal plane plot of COM velocity trajectory, called a hodograph, to visualize these variables and understand abnormal gait. We use these hodographs to show that unilateral transtibial amputees walk asymmetrically with respect to several kinetic variables of gait. Amputees exhibit higher mid-stance COM speed and weaker push-off on the prosthetic side, and more positive and negative step-to-step transition COM work on the intact side. Finally, we introduce the Rock'N'Lock foot, a reconfigurable foot prosthesis that implements a rigid foot bottom shape with the goal of reducing metabolic cost. In preliminary results this foot has cost equal to other prostheses', but forthcoming design improvements may lower the cost further.
IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2022
1 home balance therapy is essential to promote long-term 2 adherence to unsupervised training and... more 1 home balance therapy is essential to promote long-term 2 adherence to unsupervised training and to foster indepen-3 dence. We developed a portable interactive balance training 4 system that provides real-world visual cues on balance 5 performance using wobble board tilt angles to control the 6 speed of a robotic car platform in a three-dimensional 7 environment. The goal of this study was to validate this 8 mobile balance therapy system for home use across the 9 lifespan. Twenty younger (18-39 years) and nineteen older 10 (58-74 years) healthy adults performed balance training with 11 and without visual feedback while standing on a wobble 12 board instrumented with a consumer-grade inertial mea-13 surement unit (IMU) and optical motion tracking markers. 14 Participants performed feedback trials based on either 15 the robotic car's movements or a commercially-available 16 virtual game. Wobble board tilt measurements were 17 highly correlated between IMU and optical measurement 18 systems (R>0.84), with high agreement in outcome metrics 19 (ICC>0.99) and small bias (mean<3%). Both measurement 20 systems identified similar aging, feedback, and stance type 21 effects including (1) altered movement control when older 22 adults performed tilting trials with either robotic or virtual 23 feedback compared to without feedback, (2) twofold greater 24 wobble board oscillations in older vs. younger adults during 25 steady standing, (3) no difference in board oscillations 26 during steady standing in narrow vs. wide double support, 27 and (4) greater wobble board oscillations for single com-28 pared to double support. These findings demonstrate the 29 feasibility of implementing goal-directed robotic balance
The human ankle produces a large burst of 'push-off' mechanical power late in the stance phase of... more The human ankle produces a large burst of 'push-off' mechanical power late in the stance phase of walking, reduction of which leads to considerably poorer energy economy. It is, however, uncertain whether the energetic penalty results from poorer efficiency when the other leg joints substitute for the ankle's push-off work, or from a higher overall demand for work due to some fundamental feature of push-off. Here, we show that greater metabolic energy expenditure is indeed explained by a greater demand for work. This is predicted by a simple model of walking on pendulum-like legs, because proper push-off reduces collision losses from the leading leg. We tested this by experimentally restricting ankle push-off bilaterally in healthy adults (N=8) walking on a treadmill at 1.4 m s −1 , using ankle-foot orthoses with steel cables limiting motion. These produced up to ∼50% reduction in ankle pushoff power and work, resulting in up to ∼50% greater net metabolic power expenditure to walk at the same speed. For each 1 J reduction in ankle work, we observed 0.6 J more dissipative collision work by the other leg, 1.3 J more positive work from the leg joints overall, and 3.94 J more metabolic energy expended. Loss of ankle push-off required more positive work elsewhere to maintain walking speed; this additional work was performed by the knee, apparently at reasonably high efficiency. Ankle push-off may contribute to walking economy by reducing dissipative collision losses and thus overall work demand.
The elastic stretch-shortening cycle of the Achilles tendon during walking can reduce the active ... more The elastic stretch-shortening cycle of the Achilles tendon during walking can reduce the active work demands on the plantarflexor muscles in series. However, this does not explain why or when this ankle work, whether by muscle or tendon, needs to be performed during gait. We therefore employ a simple bipedal walking model to investigate how ankle work and series elasticity impact economical locomotion. Our model shows that ankle elasticity can use passive dynamics to aid push-off late in single support, redirecting the body's center-of-mass (COM) motion upward. An appropriately timed, elastic push-off helps to reduce dissipative collision losses at contralateral heelstrike, and therefore the positive work needed to offset those losses and power steady walking. Thus, the model demonstrates how elastic ankle work can reduce the total energetic demands of walking, including work required from more proximal knee and hip muscles. We found that the key requirement for using ankle elasticity to achieve economical gait is the proper ratio of ankle stiffness to foot length. Optimal combination of these parameters ensures proper timing of elastic energy release prior to contralateral heelstrike, and sufficient energy storage to redirect the COM velocity. In fact, there exist parameter combinations that theoretically yield collision-free walking, thus requiring zero active work, albeit with relatively high ankle torques. Ankle elasticity also allows the hip to power economical walking by contributing indirectly to push-off. Whether walking is powered by the ankle or hip, ankle elasticity may aid walking economy by reducing collision losses.
The labor-intensive nature of the construction industry requires workers to frequently perform ph... more The labor-intensive nature of the construction industry requires workers to frequently perform physically demanding manual work, thereby exposing them to the risk of musculoskeletal injury (approximately 31.2 cases per 10,000 full-time equivalent workers). Exoskeletons and exosuits (collectively called EXOs here) are designed to protect workers from these injuries by reducing exertion and muscle fatigue during work. However, the usability of EXOs in construction is still not clear. This is because extant EXO assessments in construction were mainly conducted in laboratory environments with test participants who are not construction professionals. In this research, we conducted a pilot study to investigate the usability of EXOs in a real construction workplace. Four experienced workers were recruited to push/empty construction gondolas with and without a Back-Support EXO, HeroWear Apex. Three workers were recruited to install/remove wooden blocks between steel studs with and without t...
The current process of prescribing prosthetic feet is hampered by imprecise classifications based... more The current process of prescribing prosthetic feet is hampered by imprecise classifications based on self-assessment, recommendations based on subjective prediction, burdensome justification requirements, and slow, costly testing of devices. These problems have been exacerbated by the introduction of robotic prostheses, which can improve gait performance for some individuals, but are very expensive. We propose an alternative process, in which a versatile robotic emulator is used to preview patient interactions with a range of prostheses, while objective data related to effort, stability, speed and preference are collected, all prior to prescription. Results from pilot testing with a prototype emulator system demonstrate accurate haptic rendering of a wide range of prosthesis classes and differentiation of user performance across these classes. Eventually, emulation-based prescription could reduce bias, cost and waste in the prescription process, while simultaneously improving patient outcomes.
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
With the recent conflicts in Afghanistan and Iraq, it is increasingly evident that the demands of... more With the recent conflicts in Afghanistan and Iraq, it is increasingly evident that the demands of warfare are changing and the need for innovative mobility systems is growing. In the rough, unstructured terrain that the soldiers encounter, they have reverted to using mules and donkeys to move stealthily and quickly. In light of the growing need for autonomous systems, the Army is looking at the possibility of legged mobility options such as gasoline powered quadrupeds to traverse the off-road terrain. As technology advances, the era of military bipeds may well be in sight. However, current bipedal robotic technology is far too inefficient for battlefield use. Much of this inefficiency stems from actuated control of each limb's motion throughout the entire gait cycle. An alternative approach is to exploit the passive pendular dynamics of legs and legged bodies for energy savings. This paper compares and contrasts fully-actuated walking with passive walking. Simulations of passive and quasi-passive walking are analyzed to evaluate their stability regions and their initial responses on uneven terrain functions are compared.
The U.S. Army is seeking to develop autonomous off-road mobile robots to perform tasks in the fie... more The U.S. Army is seeking to develop autonomous off-road mobile robots to perform tasks in the field such as supply delivery and reconnaissance in dangerous territory. A key problem to be solved with these robots is off-road mobility, to ensure that the robots can accomplish their tasks without loss or damage. We have developed a computer model of one such concept robot, the small-scale "T-1" omnidirectional vehicle (ODV), to study the effects of different control strategies on the robot's mobility in off-road settings. We built the dynamic model in ADAMS/Car and the control system in Matlab/Simulink. This paper presents the template-based method used to construct the ADAMS model of the T-1 ODV. It discusses the strengths and weaknesses of ADAMS/Car software in such an application, and describes the benefits and challenges of the approach as a whole. The paper also addresses effective linking of ADAMS/Car and Matlab for complete control system development. Finally, this paper includes a section describing the extension of the T-1 templates to other similar ODV concepts for rapid development.
Muscle-tendon units about the ankle joint generate a burst of positive power during the step-to-s... more Muscle-tendon units about the ankle joint generate a burst of positive power during the step-to-step transition in human walking, termed ankle push-off, but there is no scientific consensus on its functional role. A central question embodied in the biomechanics literature is: does ankle push-off primarily contribute to leg swing, or to center of mass (COM) acceleration? This question has been debated in various forms for decades. However, it actually presents a false dichotomy, as these two possibilities are not mutually exclusive. If we ask either question independently, the answer is the same: yes! (1) Does ankle push-off primarily contribute to leg swing acceleration? Yes. (2) Does ankle push-off primarily contribute to COM acceleration? Yes. Here, we summarize the historical debate, then synthesize the seemingly polarized perspectives and demonstrate that both descriptions are valid. The principal means by which ankle push-off affects COM mechanics is by a localized action that increases the speed and kinetic energy of the trailing push-off limb. Because the limb is included in body COM computations, this localized segmental acceleration also accelerates the COM, and most of the segmental energy change also appears as COM energy change. Interpretation of ankle mechanics should abandon an either/ or contrast of leg swing versus COM acceleration. Instead, ankle push-off should be interpreted in light of both mutually consistent effects. This unified perspective informs our fundamental understanding of the role of ankle push-off, and has important implications for the design of clinical interventions (e.g. prostheses, orthoses) intended to restore locomotor function to individuals with disabilities.
The U.S. Army is seeking to develop autonomous off-road mobile robots to perform tasks in the fie... more The U.S. Army is seeking to develop autonomous off-road mobile robots to perform tasks in the field such as supply delivery and reconnaissance in dangerous territory. A key problem to be solved with these robots is off-road mobility. We have developed a computer model of one concept robot, the "T1" omnidirectional vehicle (ODV), to study the effects of different control strategies on the robot's off-road mobility. The T1 is a lightweight robot with an innovative running-gear and control strategy to enhance mobility characteristics. We built the dynamic model of T1 in ADAMS/Car and the control system in MATLAB/Simulink. This paper presents the template-based method used to construct the ADAMS model of the T1 ODV. It also discusses effective linking of ADAMS and MATLAB for control system development. Finally, this paper includes a section describing the extension of the T1 templates to other similar ODV concepts for rapid development.
The current process of prescribing prosthetic feet is hampered by imprecise classifications based... more The current process of prescribing prosthetic feet is hampered by imprecise classifications based on self-assessment, recommendations based on subjective prediction, burdensome justification requirements, and slow, costly testing of devices. These problems have been exacerbated by the introduction of robotic prostheses, which can improve gait performance for some individuals, but are very expensive. We propose an alternative process, in which a versatile robotic emulator is used to preview patient interactions with a range of prostheses, while objective data related to effort, stability, speed and preference are collected, all prior to prescription. Results from pilot testing with a prototype emulator system demonstrate accurate haptic rendering of a wide range of prosthesis classes and differentiation of user performance across these classes. Eventually, emulation-based prescription could reduce bias, cost and waste in the prescription process, while simultaneously improving patient outcomes.
Robotic prostheses can improve walking performance for amputees, but prescription of these device... more Robotic prostheses can improve walking performance for amputees, but prescription of these devices has been hindered by their high cost and uncertainty about the degree to which individuals will benefit. The typical prescription process cannot well predict how an individual will respond to a device they have never used because it bases decisions on subjective assessment of an individual's current activity level. We propose a new approach in which individuals 'test drive' candidate devices using a prosthesis emulator while their walking performance is quantitatively assessed and results are distilled to inform prescription. In this system, prosthesis behavior is controlled by software rather than mechanical implementation, so users can quickly experience a broad range of devices. To test the viability of the approach, we developed a prototype emulator and assessment protocol, leveraging hardware and methods we previously developed for basic science experiments. We demonstrated emulations across the spectrum of commercially available prostheses, including traditional (e.g. SACH), dynamic-elastic (e.g. FlexFoot), and powered robotic (e.g. BiOM ® T2) prostheses. Emulations exhibited low error with respect to reference data and provided subjectively convincing representations of each device. We demonstrated an assessment protocol that differentiated device classes for each individual based on quantitative performance metrics, providing feedback that could be used to make objective, personalized device prescriptions.
During human walking, the center of pressure under the foot progresses forward smoothly during ea... more During human walking, the center of pressure under the foot progresses forward smoothly during each step, creating a wheel-like motion between the leg and the ground. This rolling motion might appear to aid walking economy, but the mechanisms that may lead to such a benefit are unclear, as the leg is not literally a wheel. We propose that there is indeed a benefit, but less from rolling than from smoother transitions between pendulum-like stance legs. The velocity of the body center of mass (COM) must be redirected in that transition, and a longer foot reduces the work required for the redirection. Here we develop a dynamic walking model that predicts different effects from altering foot length as opposed to foot radius, and test it by attaching rigid, arc-like foot bottoms to humans walking with fixed ankles. The model suggests that smooth rolling is relatively insensitive to arc radius, whereas work for the step-to-step transition decreases approximately quadratically with foot length. We measured the separate effects of arc-foot length and radius on COM velocity fluctuations, work performed by the legs and metabolic cost. Experimental data (N=8) show that foot length indeed has much greater effect on both the mechanical work of the step-to-step transition (23% variation, P=0.04) and the overall energetic cost of walking (6%, P=0.03) than foot radius (no significant effect, P>0.05). We found the minimum metabolic energy cost for an arc foot length of approximately 29% of leg length, roughly comparable to human foot length. Our results suggest that the foot's apparently wheel-like action derives less benefit from rolling per se than from reduced work to redirect the body COM.
IEEE Transactions on Neural Systems and Rehabilitation Engineering, Sep 1, 2015
Unilateral lower-limb amputees exhibit asymmetry in many gait features, such as ground force, ste... more Unilateral lower-limb amputees exhibit asymmetry in many gait features, such as ground force, step time, step length, and joint mechanics. Although these asymmetries result from weak prosthetic-side push-off, there is no proven mechanistic explanation of how that impairment propagates to the rest of the body. We used a simple dynamic walking model to explore possible consequences of a unilateral impairment similar to that of a transtibial amputee. The model compensates for reduced push-off work from one leg by performing more work elsewhere, for example during the middle of stance by either or both legs. The model predicts several gait abnormalities, including slower forward velocity of the body center-of-mass (COM) during intactside stance, greater energy dissipation in the intact side, and more positive work overall. We tested these predictions with data from unilateral transtibial amputees (N = 11) and non-amputee control subjects (N = 10) walking on an instrumented treadmill. We observed several predicted asymmetries, including forward velocity during stance phases and energy dissipation from the two limbs, as well as greater work overall. Secondary adaptations, such as to reduce discomfort, may exacerbate asymmetry, but these simple principles suggest that some asymmetry may be unavoidable in cases of unilateral limb loss.
The current process of prescribing prosthetic feet is hampered by imprecise classifications based... more The current process of prescribing prosthetic feet is hampered by imprecise classifications based on self-assessment, recommendations based on subjective prediction, burdensome justification requirements, and slow, costly testing of devices. These problems have been exacerbated by the introduction of robotic prostheses, which can improve gait performance for some individuals, but are very expensive. We propose an alternative process, in which a versatile robotic emulator is used to preview patient interactions with a range of prostheses, while objective data related to effort, stability, speed and preference are collected, all prior to prescription. Results from pilot testing with a prototype emulator system demonstrate accurate haptic rendering of a wide range of prosthesis classes and differentiation of user performance across these classes. Eventually, emulation-based prescription could reduce bias, cost and waste in the prescription process, while simultaneously improving patient outcomes.
The work the legs perform on the body center of mass (COM) is an important determinant of the met... more The work the legs perform on the body center of mass (COM) is an important determinant of the metabolic cost of walking. Much COM work is performed to redirect the center of mass from a downward to an upward velocity during transitions between successive stance legs, termed step-to-step transitions. We elucidate the links between COM velocity fluctuation, COM work, and metabolic cost through several experimental manipulations of gait. We show that foot length and foot bottom curvature affect COM work and metabolic cost in fixed-ankle walking. In dynamic walking models, longer feet lead to decreased work requirements for gait. We measured COM work and metabolic cost while subjects walked with locked ankles and artificial foot bottom shapes. COM work decreases with increasing foot length, because longer feet reduce the angular redirection of COM viii velocity during the step-to-step transition. Foot bottom curvature has no significant effect for humanlike foot sizes. In this range, COM work using arc shapes is less than for normal walking, though metabolic cost is higher. Metabolic cost is minimized by feet having length 28% of leg length. We also show that COM work for mechanically unconstrained walking depends on COM speed and angular redirection of COM velocity during the step-to-step transition. We measured variations in COM velocity while subjects walked at a wide range of speeds and step lengths. COM work scales quadratically with COM speed at heel strike times angular redirection of COM velocity. We introduce a sagittal plane plot of COM velocity trajectory, called a hodograph, to visualize these variables and understand abnormal gait. We use these hodographs to show that unilateral transtibial amputees walk asymmetrically with respect to several kinetic variables of gait. Amputees exhibit higher mid-stance COM speed and weaker push-off on the prosthetic side, and more positive and negative step-to-step transition COM work on the intact side. Finally, we introduce the Rock'N'Lock foot, a reconfigurable foot prosthesis that implements a rigid foot bottom shape with the goal of reducing metabolic cost. In preliminary results this foot has cost equal to other prostheses', but forthcoming design improvements may lower the cost further.
IEEE Transactions on Neural Systems and Rehabilitation Engineering, 2022
1 home balance therapy is essential to promote long-term 2 adherence to unsupervised training and... more 1 home balance therapy is essential to promote long-term 2 adherence to unsupervised training and to foster indepen-3 dence. We developed a portable interactive balance training 4 system that provides real-world visual cues on balance 5 performance using wobble board tilt angles to control the 6 speed of a robotic car platform in a three-dimensional 7 environment. The goal of this study was to validate this 8 mobile balance therapy system for home use across the 9 lifespan. Twenty younger (18-39 years) and nineteen older 10 (58-74 years) healthy adults performed balance training with 11 and without visual feedback while standing on a wobble 12 board instrumented with a consumer-grade inertial mea-13 surement unit (IMU) and optical motion tracking markers. 14 Participants performed feedback trials based on either 15 the robotic car's movements or a commercially-available 16 virtual game. Wobble board tilt measurements were 17 highly correlated between IMU and optical measurement 18 systems (R>0.84), with high agreement in outcome metrics 19 (ICC>0.99) and small bias (mean<3%). Both measurement 20 systems identified similar aging, feedback, and stance type 21 effects including (1) altered movement control when older 22 adults performed tilting trials with either robotic or virtual 23 feedback compared to without feedback, (2) twofold greater 24 wobble board oscillations in older vs. younger adults during 25 steady standing, (3) no difference in board oscillations 26 during steady standing in narrow vs. wide double support, 27 and (4) greater wobble board oscillations for single com-28 pared to double support. These findings demonstrate the 29 feasibility of implementing goal-directed robotic balance
The human ankle produces a large burst of 'push-off' mechanical power late in the stance phase of... more The human ankle produces a large burst of 'push-off' mechanical power late in the stance phase of walking, reduction of which leads to considerably poorer energy economy. It is, however, uncertain whether the energetic penalty results from poorer efficiency when the other leg joints substitute for the ankle's push-off work, or from a higher overall demand for work due to some fundamental feature of push-off. Here, we show that greater metabolic energy expenditure is indeed explained by a greater demand for work. This is predicted by a simple model of walking on pendulum-like legs, because proper push-off reduces collision losses from the leading leg. We tested this by experimentally restricting ankle push-off bilaterally in healthy adults (N=8) walking on a treadmill at 1.4 m s −1 , using ankle-foot orthoses with steel cables limiting motion. These produced up to ∼50% reduction in ankle pushoff power and work, resulting in up to ∼50% greater net metabolic power expenditure to walk at the same speed. For each 1 J reduction in ankle work, we observed 0.6 J more dissipative collision work by the other leg, 1.3 J more positive work from the leg joints overall, and 3.94 J more metabolic energy expended. Loss of ankle push-off required more positive work elsewhere to maintain walking speed; this additional work was performed by the knee, apparently at reasonably high efficiency. Ankle push-off may contribute to walking economy by reducing dissipative collision losses and thus overall work demand.
The elastic stretch-shortening cycle of the Achilles tendon during walking can reduce the active ... more The elastic stretch-shortening cycle of the Achilles tendon during walking can reduce the active work demands on the plantarflexor muscles in series. However, this does not explain why or when this ankle work, whether by muscle or tendon, needs to be performed during gait. We therefore employ a simple bipedal walking model to investigate how ankle work and series elasticity impact economical locomotion. Our model shows that ankle elasticity can use passive dynamics to aid push-off late in single support, redirecting the body's center-of-mass (COM) motion upward. An appropriately timed, elastic push-off helps to reduce dissipative collision losses at contralateral heelstrike, and therefore the positive work needed to offset those losses and power steady walking. Thus, the model demonstrates how elastic ankle work can reduce the total energetic demands of walking, including work required from more proximal knee and hip muscles. We found that the key requirement for using ankle elasticity to achieve economical gait is the proper ratio of ankle stiffness to foot length. Optimal combination of these parameters ensures proper timing of elastic energy release prior to contralateral heelstrike, and sufficient energy storage to redirect the COM velocity. In fact, there exist parameter combinations that theoretically yield collision-free walking, thus requiring zero active work, albeit with relatively high ankle torques. Ankle elasticity also allows the hip to power economical walking by contributing indirectly to push-off. Whether walking is powered by the ankle or hip, ankle elasticity may aid walking economy by reducing collision losses.
The labor-intensive nature of the construction industry requires workers to frequently perform ph... more The labor-intensive nature of the construction industry requires workers to frequently perform physically demanding manual work, thereby exposing them to the risk of musculoskeletal injury (approximately 31.2 cases per 10,000 full-time equivalent workers). Exoskeletons and exosuits (collectively called EXOs here) are designed to protect workers from these injuries by reducing exertion and muscle fatigue during work. However, the usability of EXOs in construction is still not clear. This is because extant EXO assessments in construction were mainly conducted in laboratory environments with test participants who are not construction professionals. In this research, we conducted a pilot study to investigate the usability of EXOs in a real construction workplace. Four experienced workers were recruited to push/empty construction gondolas with and without a Back-Support EXO, HeroWear Apex. Three workers were recruited to install/remove wooden blocks between steel studs with and without t...
The current process of prescribing prosthetic feet is hampered by imprecise classifications based... more The current process of prescribing prosthetic feet is hampered by imprecise classifications based on self-assessment, recommendations based on subjective prediction, burdensome justification requirements, and slow, costly testing of devices. These problems have been exacerbated by the introduction of robotic prostheses, which can improve gait performance for some individuals, but are very expensive. We propose an alternative process, in which a versatile robotic emulator is used to preview patient interactions with a range of prostheses, while objective data related to effort, stability, speed and preference are collected, all prior to prescription. Results from pilot testing with a prototype emulator system demonstrate accurate haptic rendering of a wide range of prosthesis classes and differentiation of user performance across these classes. Eventually, emulation-based prescription could reduce bias, cost and waste in the prescription process, while simultaneously improving patient outcomes.
Uploads
Papers by Peter Adamczyk