When humans hop or run on compliant surfaces they alter the stiffness of their legs so that the overall stiffness of the leg-surface system remains the same. Adding a spring in parallel to the ankle joint incites a similar neuromuscular response; humans decrease their biological ankle stiffness such that the overall ankle stiffness remains unchanged. These results suggest that an elastic exoskeleton could be effective at reducing the metabolic cost of locomotion. To further increase our understanding of human response we have developed an elastic knee brace that adds a stiff spring in parallel to the knee. It will be used as a test platform in ascertaining the neuromuscular effects of adding a parallel knee spring while hopping on one leg. This paper focuses primarily on the mechanical design and implementation of our elastic knee orthosis. Results of the forthcoming studies of human subjects wearing this knee orthosis will be presented in a separate article that will focus on the biomechanics and the neuromuscular adaptations of the human body. Prior research found that the neuromuscular response to hopping on compliant surfaces was the same when running on compliant surfaces. We expect that our results from hopping with springs in parallel with the knee will also be applicable to running. This elastic knee brace represents the first phase of an ongoing research project to develop a passive compliant lower-body exoskeleton to assist in human running. It is expected that this research will benefit healthy individuals as well as those with disabilities causing decreased muscle function.

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