Abstract
Many power-assist wearable exoskeletons have been developed to provide walking support and gait rehabilitation for elderly subjects and gait-disorder patients. Most designers have focused on a direct power-assist to the wearer's lower limbs. However, gait is a coordinated rhythmic movement of four limbs controlled intrinsically by central pattern generators, with the upper limbs playing an important role in walking. Maintaining a normal gait can become difficult as a person ages, because of decreases in limb coordination, stride length, and gait speed. It is known that coordination mechanisms can be governed by the principle of mutual entrainment, in which synchronization develops through the interaction between nonlinear phase oscillators in biological systems. This principle led us to hypothesize that interactive rhythmic stimulation to upper-limb movements might compensate for the age-related decline in coordination, thereby improving the gait in the elderly. To investigate this hypothesis, we developed a gait-assist wearable exoskeleton that employs interactive rhythmic stimulation to the upper limbs. In particular, we investigated the effects on spatial (i.e., hip-swing amplitude) and temporal (i.e., hip-swing period) gait parameters by conducting walking experiments with 12 healthy elderly subjects under one control condition and five upper-limb-assist conditions, where the output motor torque was applied at five different upper-limb swing positions. The results showed a statistically significant increase in the mean hip-swing amplitude, with a mean increment of about 7% between the control and upper-limb-assist conditions. They also showed a statistically significant decrease in the mean hip-swing period, with a mean decrement of about 2.3% between the control and one of the upper-limb-assist conditions. Although the increase in the hip-swing amplitude and the decrease in the hip-swing period were both small, the results indicate the possibility that interactive rhythmic stimulation to the upper limbs might have a positive effect on the gait of the elderly.
Highlights
The gait-assist wearable exoskeleton developed in this study, the WalkMate, applied interactive rhythmic stimulation to the elderly subjects’ upper limbs, aiming to support their gait based on the principle of mutual entrainment in human–robot interaction and upper–lower– limbs’ neural coupling as mediated by central pattern generators
We investigated the effect of such stimulation on spatial and temporal gait parameters by conducting walking experiments with healthy elderly subjects
The result indicates that interactive rhythmic stimulation to the upper limbs could increase the gait speed of the elderly to be comparable to the gait of healthy young adults. This decrease in the hip-swing period is small, the result indicates that interactive rhythmic stimulation to the upper limbs at an optimal arm-swing position can increase the arm-swing activity. Because it has been reported in previous studies that an increase in arm-swing activity increases the gait speed (Eke-Okoro et al, 1997; Marks, 1997; Long et al, 2011), the results indicate the possibility that interactive rhythmic stimulation to the upper limbs could increase the gait speed with these healthy elderly subjects due to an increase in armswing activity, at a 40% lag time
Summary
Many power-assist wearable exoskeletons have been developed to provide walking support and gait rehabilitation for elderly subjects (Kawamoto et al, 2003; Deng et al, 2017; Choi et al, 2018) and gait-disorder patients (Riener et al, 2005; Veneman et al, 2007; Kim et al, 2010; Strausser and Kazerooni, 2011; Barbareschi et al, 2015; Bortole et al, 2015; Chen et al, 2017; Lerner et al, 2017) Most of these exoskeletons provide direct power-assist support to the wearer’s lower limbs. The active leg exoskeleton, ALEX (Delaware, USA) uses a force-field controller and visual guidance on a treadmill to control hip and knee joint trajectories (Kim et al, 2010)
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