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Pneumatically powered lower limb exoskeletons. We are building carbon-fiber lower limb orthoses powered by artificial pneumatic muscles (i.e. McKibben muscles) and controlled by myoelectrical signals. One aim is to build a bilateral hip-knee-ankle-foot orthosis to assist gait rehabilitation after stroke or spinal cord injury. A second aim is to build smaller one-joint and two-joint orthoses for investigating basic principles of motor adaptation during human locomotion. A third aim is to determine if powered exoskeletons can reduce the metabolic cost of human locomotion.
CAREER: Biomechanics and energetics of human locomotion with powered exoskeletons. This five-year CAREER Development project will examine the biomechanics and energetics of human locomotion with powered lower limb exoskeletons. The Human Neuromechanics Laboratory at The University of Michigan has developed carbon fiber lower limb exoskeletons that can comfortably supply active torque assistance at the ankle, knee, and hip during walking and running. Artificial pneumatic muscles attached to a carbon fiber shell provide high power outputs while minimizing exoskeleton weight. Myoelectrical signals from biological muscles control force in the artificial muscles in a physiologically appropriate manner. Although the exoskeletons are limited to laboratory use because they require a large source of compressed air, they are ideal for studying human responses to powered locomotor assistance.
The objective of the research plan is to quantify the effects of powered assistance on the energetics of walking and running. We will measure the metabolic efficiency of external power assistance at the ankle, knee, and hip during walking and running over a range of speeds and added loads. The intellectual merit of these studies will be in two separate areas. From a physiological perspective, the results will provide important insight into the mechanical factors that determine the metabolic cost of locomotion. There is considerable debate among biomechanists and physiologists as to the mechanical actions and functions of lower limb muscles during walking and running. The exoskeleton allows us to selectively manipulate artificial flexor and extensor strength and then relate their force and work to changes in metabolic energy consumption. From an engineering perspective, the results will provide much needed guidance for creation of future lower limb exoskeletons. We will be able to quantify the biomechanical and metabolic benefit of adding external power to the ankle vs. knee vs. hip. These data will be instrumental in performing cost-benefit analyses of actuator and exoskeleton design for gait rehabilitation and human performance augmentation.
The objective of the educational plan is to use exoskeleton research to introduce problem-based discovery learning into the curriculum of students preparing for health science careers (e.g. physician, physical/occupational therapist, prosthetist/orthotist). The plan includes: a) creating an upper division course on gait biomechanics that incorporates hands-on experimentation and testing related to exoskeletons for human augmentation and rehabilitation, b) recruiting and training female and minority undergraduate students for exoskeleton research projects in the Human Neuromechanics Laboratory, and c) creating an interactive web page on robotic exoskeletons that can be used as an educational resource for secondary and undergraduate students. Thus, the broader impacts of these activities will be to enhance science and technology education of students at the college and high school level, increase participation of underrepresented groups in biomechanics research, and advance scientific and technological understanding of the public by broadly disseminating state of the art research on robotic exoskeletons.
Motor Adaptation During Human Locomotion. The aim of the project is to determine if healthy human subjects alter their muscle activity patterns and/or limb kinematics when walking with powered ankle-foot orthoses.
Recent research suggests that locomotor training can improve human walking ability after neurological injury. When stroke and spinal cord injury patients practice stepping with manual assistance, they recover mobility more quickly due to task-specific motor learning. Although multiple studies support the efficacy of this rehabilitation method, there is considerable debate about the extent of motor adaptation possible in the human locomotor pattern. Some animal and clinical studies indicate that muscle activation patterns during locomotion are hardwired into the nervous system and incapable of substantial modification. This would suggest that there are limits to locomotor training as a therapeutic tool. The proposed research project will use powered ankle-foot orthoses to study human locomotor adaptation. The powered orthoses will exert a torque about the ankle joint, altering normal lower limb kinematics if muscle activity patterns are not modified. As a result, these studies will test the relative invariance of muscle activity patterns and lower limb kinematics during human locomotion. This will not only provide the opportunity to study human locomotor adaptation under controlled experimental conditions, it will also provide a means to test whether the nervous system controls lower limb movements during locomotion based on kinematics.
The overall objectives of the proposed research are 1) to determine the extent of motor adaptation possible in the human locomotor pattern and 2) to test an hypothesized neural control strategy for human walking. Healthy human subjects will walk while wearing carbon fiber ankle-foot orthoses that are powered by artificial pneumatic muscles and controlled via proportional myoelectrical control. The studies will test the hypothesis that subjects will modify their muscle activity patterns when walking with powered orthoses to maintain joint kinematics similar to normal walking. In addition to providing important insight into the neural control of human locomotion, the project will advance robotic technologies for assisting gait rehabilitation and controlling powered lower limb prostheses.