A Cable-Driven Pelvic Robot: Human Gait Adaptation and Rehabilitation Studies

Walking is a state of continuous imbalance that requires a complex control strategy and cyclic activation of leg muscles to achieve successful inter‐limb coordination. Neuro‐musculoskeletal impairments, such as stroke, cerebral palsy, and spinal cord injury, affect one's ability to voluntarily contract muscles to normal amplitudes. This change in muscle activation pattern reduces the joint level torque generation and as a result impairs the ability to walk normally. Technological advances over the last two decades have resulted in the development of rigid link robotic exoskeletons that aim to improve gait deficits. These devices reduce repetitive and manual labor of therapists while providing objective measurement of the therapy during the gait rehabilitation. Despite the development of these robotic devices, no consensus has emerged about the superiority of robot-aided gait rehabilitation over the traditional methods. This may be because of the inherent complexity of the human musculoskeletal system and the constraints that rigid linked systems impose on the human movement. In this work, we present a cable-driven Active Tethered Pelvic Assist Device (A-TPAD) for gait rehabilitation that can apply a controlled external wrench to the human pelvis in any direction and at any point of the gait cycle for a specified duration. The A-TPAD does not add undesirable inertia on the user and does not constrain the user's motion during training. The A-TPAD provides a technological platform to scientifically study human adaptation in gait due to externally applied forces and moments on the pelvis. Human studies with the A-TPAD can motivate new gait rehabilitation paradigms which can potentially be used to correct gait deficits in human walking. The human nervous system is capable of modifying the motor commands in response to alterations in the movement conditions. Several studies have demonstrated the flexibility of human locomotion despite motor impairments and have shown the potential of using such paradigms for gait rehabilitation. In this work, we present a number of human experiments using the cable-driven A-TPAD to propose novel force interventions that induce adaptation in human gait kinematics and kinetics. In particular, stance phase gait interventions have been developed for gait rehabilitation of hemiparetic patients. In these interventions, the external force vector was applied to the pelvis to target weight bearing during walking and to promote longer stance durations. A single-session force training experiment with hemiparetic stroke patients was also conducted as a part of this work. It is shown that hemiparetic stroke patients improved the ground reaction force symmetry, forward propulsion effort, and stance phase symmetry during walking. In this work, the A-TPAD is also used to develop an intervention to apply external gait synchronized forces on the pelvis to reduce the user's effort during walking. The external forces were directed in the sagittal plane to assist the trailing leg during the forward propulsion and vertical deceleration of the pelvis during the gait cycle. A pilot experiment with five healthy subjects was conducted. This study provides a novel approach to study the role of external forces in altering the walking effort, such understanding is important while designing assistive devices for individuals who spend higher than normal effort during walking

The Integration of Principles of Motor Learning to Reduce Gait Asymmetry Using a Novel Robotic Device in Individuals Chronically Post-Stroke

Unilateral deficits resulting from stroke manifest as reduced velocity, decreased cadence and asymmetries in temporal, spatial and force parameters during ambulation. Gait asymmetries and compensatory strategies employed during gait result in a higher mechanical energy cost that limits activity and community participation. Despite conventional rehabilitation efforts, individuals often remain with chronic gait deficits after stroke. Robotic-based therapies have been developed as an alternative to conventional rehabilitation. These therapies offer the means to provide task-specific training at an intensity greater than that of conventional approaches; however, to date outcomes have been similar to that of conventional training. One factor potentially contributing to the limited efficacy of robotic training is the active-assist control strategy that is often employed. This type of training strategy reduces the users’ engagement in the learning process and limits skilled learning. The tethered pelvic assist device (TPAD) is a robotic device that employs actuated tethers at the pelvis to guide the user along a pre-set movement trajectory. While other robotic devices restrict movement to a fixed trajectory, the TPAD promotes shifting weight onto the paretic limb, but permits users to freely move the limb to navigate spatiotemporal aspects of training independently. This allows individuals to participate in the problem-solving process required for motor learning to occur, facilitating a more active role in the motor task itself, and thus promoting learning. Earlier work utilized the TPAD to reduce gait asymmetry in a population of individuals in the chronic phase after stroke in a single training session (Bishop et al., 2015; Vashista, 2015). Results demonstrated an increase in propulsive forces of the affected limb as a result of the intervention, but these gains did not transfer to overground gait. A follow up study explored the feasibility and efficacy of two different training strategies using the TPAD (Bishop et al., 2017). Both training strategies proved feasible and similarly efficacious. The current work examines the feasibility and preliminary efficacy of a five-day intervention using the TPAD with faded visual feedback and a short bout of task-specific overground training to reduce gait asymmetry in a population of individuals at least six months after stroke. Participants underwent a series of three Pre Test assessments within a one-week interval prior to initiating the intervention. Training occurred over five consecutive days, with a Post Test assessment administered on conclusion of Day 5 of training. A one-week Follow Up assessment was also recorded. Results demonstrated this intervention coupling TPAD training with additional tenets of motor learning including visual feedback and salient task-specific overground training was feasible in terms of safety, tolerance and adherence. Further, while participant’s load asymmetry was not significantly reduced on the treadmill from Baseline to Post Training (p >0.05), there was a significant improvement in stance symmetry during overground gait (F = 8.498, p = 0.002). These results suggest that the integration of motor learning tenets with robotic TPAD training was useful in facilitating gains to overground walking. Implications to the broader scope of robotic training suggest that creating an environment in which the user plays a more active role is useful at maximizing effects of robotic training. Future work should include comparison groups (TPAD treadmill training, overground training, and combined TPAD and overground training) with a more robust sample size for a longer duration of training to parse out contributing factors to overground gains. Future work should also consider a longer training and follow up interval in an effort to determine whether individuals are able to maintain improvements longer than the immediate post training period

Metabolic Cost and Stability of Locomotion in People with Lower Limb Amputation

It is generally accepted that metabolic energy expenditure and gait stability are key factors that influence the selection of able-bodied locomotor patterns. It is unclear how energy expenditure and gait stability are prioritized during walking in people with lower limb amputation. People with lower limb amputation generally have greater metabolic energy expenditure during walking and increased incidence of falls. People with unilateral lower limb amputation spend more time on the intact limb compared with the prosthetic limb, while able-bodied individuals generally walk with symmetrical timing between limbs. Restoring symmetry is often a goal of rehabilitation and assistive devices, yet the gait differences for people with unilateral amputation relative to able-bodied walkers could in fact be optimal for metabolic energy expenditure and stability. The purpose of this dissertation was to determine how metabolic energy expenditure and gait stability are affected by inter-limb gait asymmetry in people with and without unilateral transtibial amputation. To the best of my knowledge, this is the first set of studies to have people with amputation walk with preferred (i.e., asymmetrical) and non-preferred (i.e., symmetrical and greater asymmetry) inter-limb stance timing in order to understand how metabolic energy expenditure and gait stability are affected by asymmetry. Results from the first study found that subjects with amputation walked with more time on intact side compared with the prosthetic side, while able-bodied subjects walked with near symmetry

Trunk Rehabilitation Using Cable-Driven Robotic Systems

Upper body control is required to complete many daily tasks. One needs to stabilize the head and trunk over the pelvis, as one shifts the center of mass to interact with the world. While healthy individuals can perform activities that require leaning, reaching, and grasping readily, those with neurological and musculoskeletal disorders present with control deficits. These deficits can lead to difficulty in shifting the body center of mass away from the stable midline, leading to functional limitations and a decline in the quality of activity. Often these patient groups use canes, walkers, and wheelchairs for support, leading to occasional strapping or joint locking of the body for trunk stabilization. Current rehabilitation strategies focus on isolated components of stability. This includes strengthening, isometric exercises, hand-eye coordination tasks, isolated movement, and proprioceptive training. Although all these components are evidence based and directly correlate to better stability, motor learning theories such as those by Nikolai Bernstein, suggest that task and context specific training can lead to better outcomes. In specific, based on our experimentation, we believe functional postural exploration, while encompassing aspects of strengthening, hand-eye coordination, and proprioceptive feedback can provide better results. In this work, we present two novel cable robotic platforms for seated and standing posture training. The Trunk Support Trainer (TruST) is a platform for seated posture rehabilitation that provides controlled external wrench on the human trunk in any direction in real-time. The Stand Trainer is a platform for standing posture rehabilitation that can control the trunk, pelvis, and knees, simultaneously. The system works through the use of novel force-field algorithms that are modular and user-specific. The control uses an assist-as-needed strategy to apply forces on the user during regions of postural instability. The device also allows perturbations for postural reactive training. We have conducted several studies using healthy adult populations and pilot studies on patient groups including cerebral palsy, cerebellar ataxia, and spinal cord injury. We propose new training methods that incorporate motor learning theory and objective interventions for improving posture control. We identify novel methods to characterize posture in form of the “8-point star test”. This is to assess the postural workspace. We also demonstrate novel methods for functional training of posture and balance. Our results show that training with our robotic platforms can change the trunk kinematics. Specifically, healthy adults are able to translate the trunk further and rotate the trunk more anteriorly in the seated position. In the standing position, they can alter their reach strategy to maintain the upper trunk more vertically while reaching. Similarly, Cerebral Palsy patients improve their trunk translations, reaching workspace, and maintain a more vertical posture after training, in the seated position. Our results also showed that an Ataxia patient was able to improve their reaching workspace and trunk translations in the standing position. Finally, our results show that the robotic platforms can successfully reduce trunk and pelvis sway in spinal cord injury patients. The results of the pilot studies suggest that training with our robotic platforms and methods is beneficial in improving trunk control

Postural strategies in skilled riders

For optimal horse-rider communication, high-levels of technical riding-skills are needed which requires both self-coordination of the rider and coordination with the body of the horse. The scientific documentation of the optimal postural position and the technical skills for a rider is limited. It is generally agreed that good riders should be highly symmetric and must continue to develop symmetry in themselves and their horses for optimal performance in riding. On the other hand, asymmetry in riders is recognized as a negative trait. To improve the technical skills needed to develop high-level performance, the kinematics of the core segments of the rider’s body must be understood and objectively characterized. The aim of this thesis was to target the intersegmental postural strategies of the foot, pelvis, trunk and head in skilled riders under three conditions: riding, walking and rocking a balance chair. 3D high-speed motion capture and inertial measurement unit techniques were used. The individual studies acquired and analyzed data from 7 to 20 high-skilled riders. Sagittal-plane riders kinematics were compared between passive and active riding situations; three different intersegmental strategies were found in active riding. Most of the riders applied increased pressure on the withers area during active riding and with increased collection of the horse. Furthermore, associations were found between intersegmental postural strategies while riding, sitting on a balance chair, and walking. During walking the foot with the higher degree of eversion/pronation was associated with greater contralateral pelvic drop in early stance. Skilled riders showed a higher degree of trunk movement compared to pelvic movement while rocking a balance chair. The results suggested high degrees of movement asymmetry in these skilled riders, when comparing the individual segmental strategies on left versus right directions both when seated but unmounted and during riding. It is well accepted in the equestrian community that skilled riders should communicate with the horse through pelvic movements. The ability to characterize the intersegmental postural strategies of the rider´s seat may enhance the possibilities to train body awareness and improve equestrian performance in the future. The long-term goal should be to produce healthier individuals and better performance and the results from this thesis may promote this development

WALKING FOR OBJECT TRANSPORT: AN EXAMINATION OF THE COORDINATIVE ADAPTATIONS TO LOCOMOTOR, PERCEPTUAL, AND MANUAL TASK CONSTRAINTS

The goal of this dissertation was to understand how the intrinsic dynamics of gait adapt to support the performance of an ecologically relevant object transport task. A common object transport task is walking with a cup of water. Because the water can move relatively independent of the cup, the cup and water system is classified as a complex object. To model this task participants carried a cup with a wooden lid placed on top. On the lid there was a circular region with the same circumference as the cup and a ball. The object of the task was to keep the ball inside the circular region. We explored two questions: 1) how do the intrinsic coordinative gait dynamics adapt to support object transport during walking? And 2) how do individuals adapt to manually control a complex object when asked to concurrently attend to visual information? To address question 1, participants walked on a treadmill at six speeds (0.4 - 1.4 m/s) and performed three conditions: normal walking, walking with a cup only (Cup), and walking with the cup and ball (Cup-Ball). When performing the Cup-Ball condition, as gait speed increased, pelvis-thorax coordination was more in-phase compared to the normal walking and the Cup conditions. Arm-leg coordination was affected by the performance of the Cup-Ball condition. On the constrained side arm-leg coordination was 2:1 while a 1:1 relationship was maintained on the unconstrained side. A correlation between the amplitude of the unconstrained arm and manual task performance revealed a significant negative correlation as gait speed increased, indicating that individuals who reduced their arm swing performed better. To address question 2, participants walked on a treadmill at three gait speeds under four task conditions: normal walking, walking with the cup and ball system (Cup-Ball), walking while identifying visual stimuli (Visual), and a combined condition where participants walked with the cup and ball system while identifying visual stimuli (Cup-Ball-Vis). The addition of the visual task in study 2 resulted in the head orientation to be more extended relative to the trunk with a larger range of motion compared to the manual task only condition; participants optimized on the visual task at the expense of manual task performance. In both manual task conditions pelvis-thorax coordination was more in-phase as gait speed increased and more variable compared to the walking only condition. The latter result demonstrates the functionality of increased coordination variability during object transport tasks. The amplitude of the unconstrained arm decreased as the system became more constrained (i.e., going from walking only to Cup-Ball to Cup-Ball-Vis tasks). Although the arm amplitude decreased, the unconstrained arm maintained a 1:1 arm-leg coordination while the constrained arm was in a 2:1 relationship for both manual task conditions. This result demonstrates that the unconstrained arm continues to move to counteract angular momentum imparted by the legs while the arm carrying the object is coupled to the step frequency, counteracting disturbances imposed by heel contacts. The overall results from both studies demonstrate that the body’s natural walking dynamics adapt to support manual task performance. The segments not directly involved in the task continue to interact to maintain intrinsic gait dynamics. This dissertation makes significant contributions to the literature by demonstrating: 1) asymmetries in arm-leg coordination are exploited by the body to maintain manual task performance and intrinsic gait dynamics; 2) amplitude of the freely swinging arm is an important factor in task performance during object transport; and 3) increased variability at the level of the pelvis-thorax interaction plays a functional role in maintaining both manual and visual task performance. The significance of the findings here is that they demonstrate how task constraints alter intrinsic coordination dynamics during walking in order to support performance while at the same time maintaining gait stabilit

Gait analyses of a portuguese child with cerebroretinal microangiopathy with calcifications and cysts under specific walking conditions : barefoot, orthoses with shoe, insole with shoe : a case study

The objective of this case study was to describe and compare differences in gait patterns of a child suffering from Cerebroretinal Microangiophaty with Calcifications and Cysts, along the time (three data collections) under different conditions (barefoot, foot orthoses and insole). We performed a biomechanical analysis collecting spatio-temporal parameters and kinematic data, at free walking speed, during his 4th and 5th years of life. Different conditions were compared to verify the efficiency of the foot orthoses and insoles prescribed by doctors who assist him, and the effects over barefoot walking. Using an adapted set-up of markers based on Oxford multi-segmented foot, adapted to the child’s condition, data collection took place at the Biomechanics and Functional Morphology Laboratory, with 14 infrared cameras Qualisys Oqus 300, the collection was made with Qualisys Track Manager, and data was processed with Visual 3D. Data were collected according to the adaptation or prescription of foot orthoses, after a period of adaptation to their use. In each data collection, it was observed that new adaptations in foot orthoses benefit ankle movement under the three planes and adaptations in the lower limb joints. However, the effect of other kind of stimulus, such as physiotherapy, is unknown, as well as the direct effects of the disease evolution under his gait pattern, due to neural plasticity, loss of vision, individual’s ability to adapt to conditions. By maintaining regular data collection, it will be possible to contribute with more information about this rare and poorly described disease development, clarifying the importance of different factors influence under his gait patterns, as well as contributing to adaptations that will benefit him and improve his quality of life