Jeffrey Skidmore

Variable Stiffness Treadmill (VST): A novel tool for the investigation of gait

Locomotion is one of the humans most important functions that serve survival, progress and interaction. Gait requires kinematic and dynamic coordination of the limbs and muscles, multi-sensory fusion and robust control mechanisms. The force stimulus generated by the interaction of the foot with the walking surface is a vital part of the human gait. Although there have been many studies trying to decipher the load feedback mechanisms of gait, there is a need for the development of a versatile system that can advance research and provide new functionality. In this paper, we present the design and characterization of a novel system, called Variable Stiffness Treadmill (VST). The device is capable of controlling load feedback stimulus by regulating the walking surface stiffness in real time. The high range of available stiffness, the resolution and accuracy of the device, as well as the ability to regulate stiffness within the stance phase of walking, are some of the unique characteristics of the VST. We present experiments with healthy subjects in order to prove the concept of our device and preliminary findings on the effect of altered stiffness on gait kinematics. The developed system constitutes a uniquely useful research tool, which can improve our understanding of gait and create new avenues of research on gait analysis and rehabilitation.

Variable Stiffness Treadmill (VST): System Development, Characterization, and Preliminary Experiments

Locomotion is one of the humans most important functions that serve survival, progress, and interaction. Gait requires kinematic and dynamic coordination of the limbs and muscles, multisensory fusion, and robust control mechanisms. The force stimulus generated by the interaction of the foot with the walking surface is a vital part of human gait. Although there have been many studies trying to decipher the load feedback mechanisms of gait, there is a need for the development of a versatile system that can advance research and provide new functionality. In this paper, we present the design and characterization of a novel system, called variable stiffness treadmill (VST). The device is capable of controlling load feedback stimulus by regulating the walking surface stiffness in real time. The high range of available stiffness, the resolution and accuracy of the device, as well as the ability to regulate stiffness within the stance phase of walking, are some of the unique characteristics of the VST. We present experiments with healthy subjects in order to prove the concept of our device and show preliminary findings on the effect of altered stiffness on gait kinematics. The developed system constitutes a uniquely useful research tool, which can improve our understanding of gait and create new avenues of research on gait analysis and rehabilitation.

Unilateral Floor Stiffness Perturbations Systematically Evoke Contralateral Leg Muscle Responses: A New Approach to Robot-Assisted Gait Therapy

A variety of robotic rehabilitation devices have been proposed for gait rehabilitation after stoke, but have only produced moderate results when compared to conventional physiotherapy. We suggest a novel approach to robotic interventions which takes advantage of mechanisms of inter-limb coordination. In order to test the viability of this approach, we apply unilateral floor stiffness perturbations via a unique robotic device and observe evoked contralateral leg responses in kinematics, as well as muscle activations, in healthy subjects. The real-time control of floor stiffness is utilized to uniquely differentiate force and kinematic feedback, creating novel sensory perturbations. We present results of repeatable and scalable evoked kinematic and muscular response of the unperturbed leg in healthy subjects. Moreover, we provide insight into the fundamental sensorimotor mechanisms of inter-leg coordination. We also lay the foundation for model-based rehabilitation strategies for impaired walkers by presenting a mathematical model that accurately describes the relationship between the magnitude of the stiffness perturbation and the evoked muscle activity. One of the most significant advantages of this approach over current practices is the safety of the patient, since this does not require any direct manipulation of the impaired leg. The novel methods and results presented in this paper set the foundation for a paradigm shift in robotic interventions for gait rehabilitation.

Unilateral walking surface stiffness perturbations evoke brain responses: Toward bilaterally informed robot-assisted gait rehabilitation

Gait impairment due to neurological disorders has become an important problem of the 21st century. Stroke is a leading cause of long-term disability with approximately 90% of stroke survivors having some functional disability, with mobility being a major impairment. Despite the growing interest in using robotic devices for rehabilitation of sensorimotor function, their widespread use remains somewhat limited, as results so far in gait rehabilitation do not generally show improved outcomes over traditional treadmill-based therapy. This work focuses on understanding the mechanisms of inter-leg coordination, and based on that, proposing novel methods for gait rehabilitation. Using a novel robotic device, the Variable Stiffness Treadmill (VST), we apply walking surface stiffness perturbations to one leg, and analyze the response of the human nervous system in both low- (muscle) and high- (brain) levels, focusing on the mechanisms involved in the response of the other (unperturbed) leg. We show that the unperturbed leg uniquely responds to unilateral stiffness perturbations, while we provide solid evidence that the brain is involved in this observed inter-leg coordination. From a clinical prospective, the results of this study can be disruptive since they suggest that supraspinal neural activity can be evoked by altering the stiffness of the walking surface. Moreover, our methods provide a safe and targeted way to provide gait rehabilitation in hemiparesis since direct manipulation of the paretic side is not required. The present work provides for the first time evidence that specific robotic intervention in gait rehabilitation can have direct and predictable effects on the brain, opening a new avenue of research on targeted robot-assisted gait rehabilitation.

Leg muscle activation evoked by floor stiffness perturbations: A novel approach to robot-assisted gait rehabilitation

Robotic devices have been used in a variety of rehabilitation protocols, including gait rehabilitation after stroke. However, robotic intervention in gait therapy has only produced moderate results compared to conventional physiotherapy. We suggest a novel approach to robotic interventions which takes advantage of inter-limb coordination mechanisms. We hypothesize the existence of a mechanism of inter-leg coordination that may remain intact after a hemiplegic stroke that may be utilized to obtain functional improvement of the impaired leg. One of the most significant advantages of this approach is the safety of the patient, since this does not require any direct manipulation of the impaired leg. In this paper, we focus on designing and applying unilateral perturbations that evoke contralateral leg motions through mechanisms of inter-leg coordination. Real-time control of floor stiffness is utilized to uniquely differentiate force and kinematic feedback, creating novel perturbations. We present results of repeatable and scalable evoked muscle activity of the contralateral tibialis anterior muscle through unilateral stiffness perturbations. We also present a mathematical model that accurately describes the relationship between the magnitude of the stiffness perturbation and the evoked muscle activity, that could result in model-based rehabilitation strategies for impaired walkers. The novel methods and results presented in this paper set the foundation for a paradigm shift of robotic interventions for gait rehabilitation.

On the effect of walking surface stiffness on inter-limb coordination in human walking: toward bilaterally informed robotic gait rehabilitation

BackgroundRobotic devices have been utilized in gait rehabilitation but have only produced moderate results when compared to conventional physiotherapy. Because bipedal walking requires neural coupling and dynamic interactions between the legs, a fundamental understanding of the sensorimotor mechanisms of inter-leg coordination during walking, which are not well understood but are systematically explored in this study, is needed to inform robotic interventions in gait therapy.MethodsIn this study we investigate mechanisms of inter-leg coordination by utilizing novel sensory perturbations created by real-time control of floor stiffness on a split-belt treadmill. We systematically alter the unilateral magnitude of the walking surface stiffness and the timing of these perturbations within the stance phase of the gait cycle, along with the level of body-weight support, while recording the kinematic and muscular response of the uperturbed leg. This provides new insight into the role of walking surface stiffness in inter-leg coordination during human walking. Both paired and unpaired unadjusted t-tests at the 95 % confidence level are used in the approriate scernario to determine statistical significance of the results.ResultsWe present results of increased hip, knee, and ankle flexion, as well as increased tibialis anterior and soleus activation, in the unperturbed leg of healthy subjects that is repeatable and scalable with walking surface stiffness. The observed response was not impacted by the level of body-weight support provided, which suggests that walking surface stiffness is a unique stimulus in gait. In addition, we show that the activation of the tibialis anterior and soleus muscles is altered by the timing of the perturbations within the gait cycle.ConclusionsThis paper characterizes the contralateral leg’s response to ipsilateral manipulations of the walking surface and establishes the importance of walking surface stiffness in inter-leg coordination during human walking.

Investigation of contralateral leg response to unilateral stiffness perturbations using a novel device

The etymology of the word “Anthropos”, the Greek word for Human, includes one of the defining characteristics of human beings, which is the ability to stand upright and walk. Locomotion is one of the humans most important functions that serve survival, progress and interaction. The force stimulus generated by the interaction of the foot with the walking surface is a vital part of human gait. Although there have been many studies trying to decipher the load feedback mechanisms of gait, there is a need for the development of a versatile system that can advance research and provide new functionality. Moreover, the role of the load feedback in inter-leg coordination during walking is still not well understood. In this paper, we present a series of studies that attempt to shed light on the role of load feedback on inter-leg coordination using a novel system, called Variable Stiffness Treadmill (VST). The device is capable of controlling load feedback stimulus by regulating the walking surface stiffness in real time. We first present the main functionality of the VST, focusing on the real-time closed-loop control of stiffness. Using perturbations of the treadmill stiffness on one leg of healthy subjects, we investigate the inter-leg coordination mechanisms, in body-weight-supported gait. Results show that ipsilateral stiffness perturbations, affect the contralateral (unperturbed) leg in body-weight-supported gait, while their effect is dependent on the timing of the induced stiffness perturbations. The developed system and experimental protocols are uniquely useful for gait research, can improve our understanding of gait, and create new avenues of research on gait analysis, walking robots and gait rehabilitation.

Unilateral changes in walking surface compliance evoke dorsiflexion in paretic leg of impaired walkers

Introduction Gait impairments due to stroke impact millions of individuals throughout the world. Despite the growing interest in automating gait therapy with robotic devices, there is no clear evidence that robot-assisted gait therapy is superior to traditional treadmill-based therapy. Methods This work investigates the effect of perturbations to the compliance of the walking surface on the paretic leg of impaired walkers. Using a novel robotic device, the variable stiffness treadmill, we apply perturbations to the compliance of the walking surface underneath the non-paretic leg of two hemi-paretic walkers and analyze the kinematic and neuromuscular response of the contralateral (paretic) leg with motion capture and surface electromyography systems. Results We present results of evoked muscle activity (predominately tibialis anterior) and increased dorsiflexion in the paretic leg during the swing phase of gait at stiffness values of 60 kN/m and less for all subjects. Conclusions This work provides evidence for the first time of reducing the drop-foot effect in the impaired leg of hemiparetic walkers in response to unilateral perturbations to the compliance of the treadmill platform, thus providing direction for targeted robot-assisted gait rehabilitation.

Sudden changes in walking surface compliance evoke contralateral EMG in a hemiparetic walker: A case study of inter-leg coordination after neurological injury

Gait impairment due to neurological disorders is a significant problem around the world. Despite the growing interest in using robotic devices for gait rehabilitation, their widespread use remains limited as there is no clear evidence that robot-assisted gait therapy is superior to traditional treadmill-based therapy. This work is a case study that focuses on investigating the existence of mechanisms of inter-leg coordination after neurological injury, and based on that, proposing novel methods for gait rehabilitation. Using a novel robotic device, the Variable Stiffness Treadmill (VST), we apply perturbations to the compliance of the walking surface underneath the non-paretic leg, and analyze the response of the contralateral (paretic) leg. We show that muscle activity is evoked in the gastrocnemius of the paretic leg. From a clinical prospective, the results of this study can be disruptive because our methods provide a safe and targeted way to provide gait rehabilitation in hemiparesis since direct manipulation of the paretic side is not required. This work provides evidence for the first time that muscle activity can be evoked in the paretic leg of a hemiplegic walker in response to unilateral perturbations to the compliance of the walking surface, providing direction for targeted robot-assisted gait rehabilitation.