This paper presents the design, analysis, and a clinical application of a reconfigurable, parallel mechanism based, force feedback exoskeleton for the human ankle. The device can either be employed as a balance/proprioception trainer or configured to accommodate range of motion (RoM)/strengthening exercises. The exoskeleton can be utilized as a clinical measurement tool to estimate dynamic parameters of the ankle and to assess ankle joint properties in physiological and pathological conditions. Kinematic analysis and control of the device are detailed and a protocol for utilization of the exoskeleton to determine ankle impedance is discussed. The prototype of the device is also presented.

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The ability to walk is important for independent living and when this capacity is affected by neurological injury, gait therapy is the traditional approach to re-train the nervous system. The importance of this problem is illustrated by the approximately 5.8 million stroke survivors alive in the US today and an estimated additional 700,000 strokes occurring each year, many requiring gait therapy. This manuscript presents the design and proof-of-concept testing for a novel device to deliver gait therapy. While robotic devices to train gait therapy exist, none of them take advantage of the concept of passive walkers and most of them impose the kinematics of unimpaired gait on impaired walkers. Yet research has found that proper neural input and stimulation is a critical factor for an efficacious therapy program. This novel device might afford a more ecological gait therapy including heel-strike.

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Studies have shown locomotor adaptation of the ankle to assistive torques, but the ability of the knee to adapt to assistive forces has not yet been explored. Understanding how humans modulate knee joint kinematics during gait could be valuable for designing assistive devices for stroke patients. In this study we examined how healthy subjects adapt to knee flexion torque assistance during gait. We hypothesized that 1) when given assistance subjects would adapt their locomotor patterns to walk with kinematics similar to baseline values and 2) removal of assistance following adaptation would result in substantially reduced knee flexion. Contrary to expectations, data from the five subjects show a weak adaptation and an increase in knee flexion kinematics after forces were removed. These results suggest that neuromuscular control of the knee joint during walking is not strongly modulated by feedforward mechanisms.

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Background: How space suits affect the preferred walk-run transition is an open question with relevance to human biomechanics and planetary extravehicular acti-vity. Walking and running energetics differ; in reduced gravity (,0.5 g), running, unlike on Earth, uses less energy per distance than walking. Methodology/Principal Findings: The walk-run transition (denoted *) correlates with the Froude Number (Fr = v2/gL, velocity v, gravitational acceleration g, leg length L). Hu-man unsuited Fr* is relatively constant (,0.5) with gravity but increases substantially with decreasing gravity below ,0.4 g, rising to 0.9 in 1/6 g; space suits appear to lower Fr*. Because of pressure forces, space suits partially (1 g) or completely (lunar-g) support their own weight. We define the Apollo Number (Ap = Fr/M) as an expected invariant of locomotion under manipulations of M, the ratio of human-supported to total transported mass. We hypothesize that for lunar suited conditions Ap* but not Fr* will be near 0.9, because the Apollo Number captures the effect of space suit self-support. We used the Apollo Lunar Surface Journal and other sources to identify 38 gait events during lunar exploration for which we could determine gait type (walk/lope/run) and calculate Ap. We estimated the binary transition between walk/lope (0) and run (1), yielding Fr* (0.3660.11, mean695% CI) and Ap* (0.6860.20). Conclusions/Significance: The Apollo Number explains 60% of the difference between suited and unsuited Fr*, appears to capture in large part the effects of space suits on the walk-run transition, and provides several testable predictions for space suit locomotion and, of increasing relevance here on Earth, exoskeleton locomotion. The knowledge of how space suits affect gait transitions can be used to optimize space suits for use on the Moon and Mars.

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Current changes in aging demographics poses new challenges: people require to keep their quality of life even after circumstances that threatened their movement and function. This increases the demand for new physical rehabilitation facilities that go beyond the traditional patient-therapist, one-to-one rehabilitation sessions. Two promising solutions rely on virtual reality and on the development of autonomous active orthoses, or exoskeletons. Whatever is the chosen approach, there is a requirement for a robust human-machine interface for the control, able to understand patient’s intention and to produce an immediate activation of the device. This paper presents a biomechanical model, a possible solution able to predict joint torque from the surface electromyography signals emitted by muscles during their activation. The main objective of the research is to investigate the benefits and efficacy of this model and to lay down the basis of our current research, whose main goal is to make possible a rehabilitation process either with active orthoses or virtual reality. Experiments involving all the steps of our model demonstrate the viability and effectiveness of our approach.

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