We examined the metabolic cost of plantar flexor muscle–tendon mechanical work during human walking. Nine healthy subjects walked at constant step frequency on a motorized treadmill at speeds corresponding to 80% (1.00ms–1), 100% (1.25ms–1), 120% (1.50ms–1) and 140% (1.75ms–1) of their preferred step length (L*) at 1.25ms–1. In each condition subjects donned robotic ankle exoskeletons on both legs. The exoskeletons were powered by artificial pneumatic muscles and controlled using soleus electromyography (i.e. proportional myoelectric control). We measured subjects’ metabolic energy expenditure and exoskeleton mechanics during both unpowered and powered walking to test the hypothesis that ankle plantarflexion requires more net metabolic power (Wkg–1) at longer step lengths for a constant step frequency (i.e. preferred at 1.25ms–1). As step length increased from 0.8 L to 1.4 L, exoskeletons delivered ~25% more average positive mechanical power (P=0.01; +0.20±0.02Wkg–1 to +0.25±0.02Wkg–1, respectively). The exoskeletons reduced net metabolic power by more at longer step lengths (P=0.002; –0.21±0.06Wkg–1 at 0.8 L* and –0.70±0.12Wkg–1 at 1.4 L*). For every 1 J of exoskeleton positive mechanical work subjects saved 0.72 J of metabolic energy (‘apparent efficiency’=1.39) at 0.8 L and 2.6 J of metabolic energy (‘apparent efficiency’=0.38) at 1.4 L. Declining ankle muscle–tendon ‘apparent efficiency’ suggests an increase in ankle plantar flexor muscle work relative to Achilles’ tendon elastic energy recoil during walking with longer steps. However, previously stored elastic energy in Achilles’ tendon still probably contributes up to 34% of ankle muscle–tendon positive work even at the longest step lengths we tested. Across the range of step lengths we studied, the human ankle muscle–tendon system performed 34–40% of the total lower-limb positive mechanical work but accounted for only 7–26% of the net metabolic cost of walking.

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The demand for rehabilitation robots is increasing for the upcoming aging society. Power-assisting devices are considered promising for enhancing the mobility of elderly and disabled people. Other potential applications are for muscle rehabilitation and sports training. The main focus of this paper is to control the load of selected muscles by using a power-assisting device, thus enabling “pinpointed” motion support, rehabilitation, and training by explicitly specifying the target muscles. By taking into account the physical interaction between human muscle forces and actuator drivingforces during power-assisting, the feasibility of this muscle force control is analyzed as a constrained optimization problem. A prototype power-assisting device driven by pneumatic rubber actuators is developed. A control system is developed with a graphical user interface that provides an easy operation to designate desired forces for target muscles. The validity of the method is confirmed by experiments by measuring surface electromyographic (EMG) signals for target muscles.

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In this paper we describe the design and preliminary evaluation of an energetically-autonomous powered knee exoskeleton to facilitate running. The device consists of a knee brace in which a motorized mechanism actively places and removes a spring in parallel with the knee joint. This mechanism is controlled such that the spring is in parallel with the knee joint from approximately heel-strike to toe-off, and is removed from this state during the swing phase of running. In this way, the spring is intended to store energy at heel-strike which is then released when the heel leaves the ground, reducing the effort required by the quadriceps to exert this energy, thereby reducing the metabolic cost of running.

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A Stroke can affect different parts of the human body depending on the area of brain affected; our research focuses on upper limb motor dysfunction for stroke patients. In current practice, ordinal scale systems are used for conducting physical assessment of upper limb impair-ment. The reliability of these assessments is questionable, since their coarse ratings cannot reliably distinguish between the different levels of performance. This thesis describes the design, implementation and evaluation of a novel system to facilitate stroke diagnosis which relies on data collected with an innovative KINARM robotic tool. This robotic tool allows for an objective quantification of motor function and performance assessment for stroke patients. The main methodology for the research is Case Based Rea-soning (CBR) — an effective paradigm of artificial intelligence that relies on the principle that a new problem is solved by observing similar, previously encountered problems and adapting their known solu-tions. A CBR system was designed and implemented for a repository of stroke subjects who had an explicit diagnosis and prognosis. For a new stroke patient, whose diagnosis was yet to be confirmed and who had an indefinite prognosis, the CBR model was effectively used to retrieve analogous cases of previous stroke patients. These similar cases provide useful information to the clinicians, facilitating them in reaching a potential solution for stroke diagnosis and also a means to validate other imaging tests and clinical assessments to confirm the diagnosis and prognosis.

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This article discusses the pros and cons of compliant actuation for rehabilitation robots on the example of LOPES, focusing on the cons. After illustrating the bandwidth limitations, a new result has been derived: if stability in terms of passivity of the haptic device is desired, the renderable stiffness is bounded by the stiffness of the SEA’s elastic component. In practical experiments with the VMC, the aforementioned limitations affected the control performance. Desired gait modifications were not tracked exactly, because the subjects were able to deviate from the prescribed pattern even in the stiffest possible configuration. Despite the limitations, the practical experiments also demonstrated the general effectiveness of the realization. Manipulation of selected gait parameters is possible, whereby other parameters are left unaffected. This high selectivity is made possible by the low level of undesired interaction torques, which is achieved by elastic decoupling of motor mass and a lightweight exoskeleton. The discrepancy between theoretical bounds and rendered stiffness indicated that healthy subjects might represent a stabilizing component of the coupled system, which could be different for patients. In light of the theoretical stability analysis and with the focus on patients, the LOPES actuation was slightly modified. The robot was equipped with stiffer springs to obtain sufficient stiffness and to ensure stability without relying on stabilizing effects of the human. For this application, the disadvantages of compliant actuation can thus be tolerated or dealt with, and they are small compared with the advantages. Given that a rehabilitation robot, in the first place, is supposed to imitate therapist action, the limitations of bandwidth and stiffness do not pose severe problems. In contrast, safety and backdrivability are highly relevant, and they can be ensured easier with a compliant actuator. Therefore, we conclude that compliant actuation and a lightw- — eight exoskeleton provide effective means to accomplish the desired AAN behavior of a rehabilitation robot. The next step is to evaluate the robot behavior, control performance, and therapeutic effectiveness in patient studies.

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