On the Effect of Walking Surface Stiffness on Inter-leg Coordination during Human Walking: a Unique Perspective to Robot-assisted Gait Rehabilitation

abstract: Millions of individuals suffer from gait impairments due to stroke or other neurological disorders. A primary goal of patients is to walk independently, but most patients only achieve a poor functional outcome five years after injury. Despite the growing interest in using robotic devices for rehabilitation of sensorimotor function, state-of-the-art robotic interventions in gait therapy have not resulted in improved outcomes when compared to traditional treadmill-based therapy. 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 is needed to inform robotic interventions in gait therapy. This dissertation presents a systematic exploration of sensorimotor mechanisms of inter-leg coordination by studying the effect of unilateral perturbations of the walking surface stiffness on contralateral muscle activation in healthy populations. An analysis of the contribution of several sensory modalities to the muscle activation of the opposite leg provides new insight into the sensorimotor control mechanisms utilized in human walking, including the role of supra-spinal neural circuits in inter-leg coordination. Based on these insights, a model is created which relates the unilateral deflection of the walking surface to the resulting neuromuscular activation in the opposite leg. Additionally, case studies with hemiplegic walkers indicate the existence of the observed mechanism in neurologically impaired walkers. The results of this dissertation suggest a novel approach to gait therapy for hemiplegic patients in which desired muscle activity is evoked in the impaired leg by only interacting with the healthy leg. One of the most significant advantages of this approach over current rehabilitation protocols is the safety of the patient since there is no direct manipulation of the impaired leg. Therefore, the methods and results presented in this dissertation represent a potential paradigm shift in robot-assisted gait therapy.Dissertation/ThesisDoctoral Dissertation Mechanical Engineering 201

Sensorimotor control of gait: a novel approach for the study of the interplay of visual and proprioceptive feedback

Sensorimotor control theories propose that the central nervous system exploits expected sensory consequences generated by motor commands for movement planning, as well as online sensory feedback for comparison with expected sensory feedback for monitoring and correcting, if needed, ongoing motor output. In our study, we tested this theoretical framework by quantifying the functional role of expected versus actual proprioceptive feedback for planning and regulation of gait in humans. We addressed this question by using a novel methodological approach to deliver fast perturbations of the walking surface stiffness, in conjunction with a virtual reality system that provided visual feedback of upcoming changes of surface stiffness. In the predictable experimental condition, we asked subjects to learn associating visual feedback of changes in floor stiffness (sand patch) during locomotion to quantify kinematic and kinetic changes in gait. In the unpredictable experimental condition, we perturbed floor stiffness at unpredictable instances during the gait to characterize the gait-phase dependent strategies in recovering the locomotor cycle. For the unpredictable conditions, visual feedback of changes in floor stiffness was absent or inconsistent with tactile and proprioceptive feedback. The investigation of these perturbation-induced effects on legs kinematics revealed that visual feedback of upcoming changes in floor stiffness allows for both early (preparatory) and late (post-perturbation) changes in leg kinematics. However, when proprioceptive feedback is not available, the early responses do not occur while the late responses are preserved although in a, slightly attenuated form. The methods proposed and the preliminary results of this study open new directions for the investigation of the relative role of visual, tactile, and proprioceptive feedback on gait control, with potential implications for designing novel robot-assisted gait rehabilitation approaches

Anticipatory Muscle Responses for Transitioning Between Rigid Surface and Surfaces of Different Compliance: Towards Smart Ankle-foot Prostheses

abstract: Locomotion is of prime importance in enabling human beings to effectively respond in space and time to meet different needs. Approximately 2 million Americans live with an amputation with most of those amputations being of the lower limbs. To advance current state-of-the-art lower limb prosthetic devices, it is necessary to adapt performance at a level of intelligence seen in human walking. As such, this thesis focuses on the mechanisms involved during human walking, while transitioning from rigid to compliant surfaces such as from pavement to sand, grass or granular media. Utilizing a unique tool, the Variable Stiffness Treadmill (VST), as the platform for human walking, rigid to compliant surface transitions are simulated. The analysis of muscular activation during the transition from rigid to different compliant surfaces reveals specific anticipatory muscle activation that precedes stepping on a compliant surface. There is also an indication of varying responses for different surface stiffness levels. This response is observed across subjects. Results obtained are novel and useful in establishing a framework for implementing control algorithm parameters to improve powered ankle prosthesis. With this, it is possible for the prosthesis to adapt to a new surface and therefore resulting in a more robust smart powered lower limb prosthesis.Dissertation/ThesisMasters Thesis Biomedical Engineering 201

OBJECTIVE EVALUATION OF FUNCTIONAL ANKLE INSTABILITY AND BALANCE EXERCISE TREATMENT

Functional ankle instability (FAI) is a poorly defined entity but commonly used to describe patients who sustain multiple ankle injuries with slight or no external provocation and have a subjective feeling of ankle "giving way". There have been conflicting results reported in literature regarding the role of suggested etiological factors of FAI including deficit in joint proprioception, strength, and stiffness (laxity). Diagnosis of FAI has been mainly relied on a subjective reporting, so is the assessment of FAI treatments. In spite of controversies regarding FAI factors, balance training has been widely used in sports medicine clinics for patients with FAI. Most of past studies reported its effect for FAI, but strong evidence with definitive result is still missing. Furthermore, the mechanism that explains the effect of balance training on FAI is still unclear. Recently, it was suggested that altered threshold to the unloading reaction may be behind ankle giving way episodes in patients with ankle instability. Therefore, we wanted to duplicate this finding in individuals with FAI during sudden ankle inversion test and examine the effects of a four-week balance training program on unloading reactions in individuals with FAI. Twenty four recreationally active individuals with unilateral FAI were evaluated for unloading reactions on the involved and uninvolved limbs using a sudden ankle inversion test. In seven out of twenty-four subjects, we observed a drastic reaction (hyper-reactivity) in that they were unable to maintain upright standing position when a combination of dynamic ankle stretching and nociceptive stimuli was applied on their affected ankles. The subjects were then randomized to either a control or intervention group. Subjects in the intervention group were trained on the affected limb with static and dynamic components using a Biodex balance stability system for 4-weeks. The control group received no intervention. The results suggested that balance training may desensitize the hyper-reactivity to unloading reaction in FAI subjects, suggesting a possible mechanism for reducing the ankle "giving way" episodes. In addition, balance training was found to improve the subjective self-reported ankle instability and passive ankle joint position sense. No effect was observed on isometric and isokinetic peroneal muscle strength and ankle stiffness (laxity). In summary, this dissertation work provides evidence that balance training is effective in patients with FAI, however a further study with more sample size and additional outcome measures is required to better understand the mechanism of balance training in these individuals. The findings of this work have implications for research/rehabilitation of not only individuals with FAI but also in individuals with functional joint instability, such as functional knee instability which shares many common symptoms with FAI

Motor Compensation During Lower Limb Pedaling After Stroke

Long-term motor dysfunction in the lower limb is common after stroke. One potential contributor is motor compensation, a behavior in which functions originally performed by the paretic limb are performed by the non-paretic limb. Compensation in chronic stroke may contribute to long-term motor dysfunction by limiting functional ability, impairing future recovery, and eliciting maladaptive neuroplasticity. The purpose of this dissertation was to describe the impact of compensation on motor function and brain activation during lower limb pedaling and identify elements that produce this behavior. To achieve this purpose, we evaluated muscle activation and motor performance when compensation was prevented. During unilateral pedaling, paretic muscle activation increased but motor performance deteriorated. During bilateral uncoupled pedaling, paretic muscle activation further increased. However, subjects were unable to coordinate movements of the legs, and motor performance further deteriorated. These results suggest that compensation improves motor performance but limits paretic motor output. Because motor performance was worse during bilateral uncoupled than unilateral pedaling, impaired interlimb coordination may be a primary factor leading to compensation. As a follow-up, we determined whether altered interlimb spinal reflex pathways contribute to impaired interlimb coordination after stroke. Interlimb cutaneous reflexes were elicited during pedaling, and we assessed whether the amplitude was altered. Interlimb reflex was altered, particularly in bifunctional muscles and at pedaling transitions. Reflex alterations were correlated with impairments in interlimb coordination and compensation. These data suggest that stroke-related changes in interlimb reflex pathways undermine interlimb coordination. Finally, we assessed whether altered motor commands and performance, such as seen with compensation, are related to decreased pedaling-related brain activation after stroke. Brain activation was measured during volitional pedaling and during passive pedaling, when between-group differences were minimized. Between-group differences in brain activation persisted during passive pedaling, suggesting that altered motor commands and pedaling performance do not account for reduced brain activation after stroke. Overall, these studies provide insight into rehabilitative interventions that may decrease long-term motor dysfunction in the lower limb after stroke. One potential strategy is to enhance paretic muscle activity by preventing compensation while simultaneously employing efforts to improve interlimb coordination, possibly by manipulating interlimb reflex pathways

Gait stability and balance strategies of both acquired and congenital lower limb prosthetic users in response to perturbations

Incorrect date on title page. Year of award is 2021.Falls are a health care problem for lower limb prosthetic users. The study of gait stability in lower limb prosthetic users facilitates improved insight and knowledge in different adaptation strategies of the human body in order to walk as functionally as possible with a prosthesis. The aim of this thesis was to determine how prosthetic users cope with unbalanced situations during walking and how these coping strategies may differ from able-bodied individuals. Improved understanding of such mechanisms may help reduce fall incidence. A number of prosthetic factors were considered including the use of a prosthetic foot incorporating an ankle joint, compared to a conventional prosthetic foot. Additionally, the effect of different alignments and the aetiology of the amputation or absence (congenital vs acquired amputation) was also considered. The study was conducted using an advanced dual-belt instrumented treadmill (CAREN). The protocol of perturbations in the study was adopted from a previous work by a group of researchers in University of Strathclyde (Roeles et al., 2018). Interventions used were anteroposterior (AP) perturbations by means of sudden changes in the walking speed to mimic a slip that can be faced in real-life situations. Main Outcome Measurements measured were AP and ML margins of stability (MoS) Hof et al. (2005). Step length, width and time were also measured to investigate the coping strategy following perturbation. Prosthetic users were less stable than able-bodied individuals. The involvement of the prosthetic side to recover stability was limited therefore, during rehabilitation stability training tasks for the intact side may help the prosthetic users enhance their overall stability and may reduce the fall incidence rate. Energy storing and return prosthetic feet may provide a sufficient level of stability compared to the feet which incorporate a moving ankle mechanism. The Ossur Pro-Flex foot demonstrated enhanced stability in the AP direction. Alignment changes from the optimal alignment may impose extra challenge to the stability. A short prosthesis was found to be the most challenging alignment change in response to perturbation. The prosthetic user with congenital related limb anomaly was found to be more stable than the prosthetic users with other lower limb loss. The outcomes of this study are novel and have potential to improve the understanding of how prosthetic users (acquired and congenital) react in when stability is compromised and the variables which may affect this further (foot design and alignment). It is envisaged that greater understanding of different adaptation strategies of the human body may help influence future prosthetic treatment, prescription, alignment and potentially component design.Falls are a health care problem for lower limb prosthetic users. The study of gait stability in lower limb prosthetic users facilitates improved insight and knowledge in different adaptation strategies of the human body in order to walk as functionally as possible with a prosthesis. The aim of this thesis was to determine how prosthetic users cope with unbalanced situations during walking and how these coping strategies may differ from able-bodied individuals. Improved understanding of such mechanisms may help reduce fall incidence. A number of prosthetic factors were considered including the use of a prosthetic foot incorporating an ankle joint, compared to a conventional prosthetic foot. Additionally, the effect of different alignments and the aetiology of the amputation or absence (congenital vs acquired amputation) was also considered. The study was conducted using an advanced dual-belt instrumented treadmill (CAREN). The protocol of perturbations in the study was adopted from a previous work by a group of researchers in University of Strathclyde (Roeles et al., 2018). Interventions used were anteroposterior (AP) perturbations by means of sudden changes in the walking speed to mimic a slip that can be faced in real-life situations. Main Outcome Measurements measured were AP and ML margins of stability (MoS) Hof et al. (2005). Step length, width and time were also measured to investigate the coping strategy following perturbation. Prosthetic users were less stable than able-bodied individuals. The involvement of the prosthetic side to recover stability was limited therefore, during rehabilitation stability training tasks for the intact side may help the prosthetic users enhance their overall stability and may reduce the fall incidence rate. Energy storing and return prosthetic feet may provide a sufficient level of stability compared to the feet which incorporate a moving ankle mechanism. The Ossur Pro-Flex foot demonstrated enhanced stability in the AP direction. Alignment changes from the optimal alignment may impose extra challenge to the stability. A short prosthesis was found to be the most challenging alignment change in response to perturbation. The prosthetic user with congenital related limb anomaly was found to be more stable than the prosthetic users with other lower limb loss. The outcomes of this study are novel and have potential to improve the understanding of how prosthetic users (acquired and congenital) react in when stability is compromised and the variables which may affect this further (foot design and alignment). It is envisaged that greater understanding of different adaptation strategies of the human body may help influence future prosthetic treatment, prescription, alignment and potentially component design

Lower limb kinematics, kinetics and coordination during a land and cut task; the role of gender and previous ACL injury

Anterior cruciate ligament (ACL) injury continues to be a constant adversary to field sports athletes. Females are widely acknowledged as being at an increased risk of ACL injury, in comparison to males. Athletes who are successful in rehabilitation after surgery and return to their sport are reported to have an increased risk of repeated ACL injury and the development of osteoarthritis. The current thesis utilised a novel, maximal drop-jump land and unanticipated cutting task to assess the lower limb biomechanics of uninjured male and females, and previously ACL injured subjects (ACLr). Discrete measures of lower limb kinematics and kinetics were firstly compared between uninjured males and females, and secondly between the previously injured (PI) leg of ACLr subjects and both the contralateral non-injured (NI) leg and an uninjured subject’s control leg. The results show that females had increased hip internal rotation, the PI leg was not significantly different to the NI leg but was different to the control subject’s leg with increased hip flexion, internal knee abduction moment and transverse plane knee ROM. Lower limb coordination was assessed in the ACLr subjects and both legs of the ACLr subjects had similar coordination patterns. The PI leg however showed different coordination patterns than the control subject’s leg for a number of couplings. Movement and coordination variability were also utilised for a gender and ACLr – control comparison. The female subjects and the PI leg had lower levels of movement and coordination variability than males and the contralateral non-injured leg respectively. The PI leg however, had higher levels of movement and coordination variability than the control subject’s leg. In conclusion, females and previously ACL injured subjects may be at an increased risk of initial ACL injury and the development of osteoarthritis on the PI leg respectively, due to lower levels of movement and coordination variability. Altered biomechanics at the hip were also highlighted as a potential mechanism increasing injury risk in females and ACLr subjects