You'll need your doctors and stroke hospital to initiate research with this in stroke patients. Walking cost in stroke patients is vastly higher than normal so help is needed. Will your stroke doctors do one damn thing to initiate research? Or will they sit on their asses doing nothing like usual?
cost of walking (1 post to July 2020)
Optimized hip-knee-ankle exoskeleton assistance reduces the metabolic cost of walking with worn loads
Journal of NeuroEngineering and Rehabilitation volume 18, Article number: 161 (2021)
Abstract
Background
Load carriage is common in a wide range of professions, but prolonged load carriage is associated with increased fatigue and overuse injuries. Exoskeletons could improve the quality of life of these professionals by reducing metabolic cost to combat fatigue and reducing muscle activity to prevent injuries. Current exoskeletons have reduced the metabolic cost of loaded walking by up to 22% relative to walking in the device with no assistance when assisting one or two joints. Greater metabolic reductions may be possible with optimized assistance of the entire leg.
Methods
We used human-in the-loop optimization to optimize hip-knee-ankle exoskeleton assistance with no additional load, a light load (15% of body weight), and a heavy load (30% of body weight) for three participants. All loads were applied through a weight vest with an attached waist belt. We measured metabolic cost, exoskeleton assistance, kinematics, and muscle activity. We performed Friedman’s tests to analyze trends across worn loads and paired t-tests to determine whether changes from the unassisted conditions to the assisted conditions were significant.
Results
Exoskeleton assistance reduced the metabolic cost of walking relative to walking in the device without assistance for all tested conditions. Exoskeleton assistance reduced the metabolic cost of walking by 48% with no load (p = 0.05), 41% with the light load (p = 0.01), and 43% with the heavy load (p = 0.04). The smaller metabolic reduction with the light load may be due to insufficient participant training or lack of optimizer convergence. The total applied positive power was similar for all tested conditions, and the positive knee power decreased slightly as load increased. Optimized torque timing parameters were consistent across participants and load conditions while optimized magnitude parameters varied.
Conclusions
Whole-leg exoskeleton assistance can reduce the metabolic cost of walking while carrying a range of loads. The consistent optimized timing parameters across participants and conditions suggest that metabolic cost reductions are sensitive to torque timing. The variable torque magnitude parameters could imply that torque magnitude should be customized to the individual, or that there is a range of useful torque magnitudes. Future work should test whether applying the load to the exoskeleton rather than the person’s torso results in larger benefits.
Introduction
Exoskeletons could reduce the effort associated with loaded walking. Load carriage is a common task in many professions, for example military personnel will carry loads over 80% of their body weight [1]. When applied to the waist or back, each kilogram of additional load will increase metabolic cost by about 2%, and the metabolic impact increases as the load is applied further from the participant’s center of gravity [2]. In addition to increased metabolic cost, prolonged load carriage is associated with overuse injuries such as stress fractures, back strain, and knee pain [3]. Exoskeletons could assist loaded walking by reducing the user’s metabolic cost and could, over the longer term, prevent overuse injuries.
Some exoskeletons have reduced the metabolic cost of loaded walking when assisting one to two joints. Exoskeletons are typically evaluated by their ability to augment user performance, and reducing metabolic cost is an important evaluation metric [4]. Exoskeleton assistance has reduced the metabolic cost of loaded walking by up to 22% compared to walking in the device without assistance and up to 15% compared to walking without the device [5]. Many of the devices that have reduced the metabolic cost of loaded walking have assisted hip extension [6, 7], ankle plantarflexion [8,9,10,11], hip flexion and ankle plantarflexion [12, 13] or hip flexion, hip extension, and ankle plantarflexion [5, 7]. Some of these experiments applied the same mass to all participants, up to 24.5 kg in addition to the weight of the device [5,6,7,8, 11, 12, 14], while others have applied the load as a percentage of body weight, up to 30% [9, 10, 13]. Exoskeletons can reduce the metabolic cost during load carriage, but there has been limited research into optimal assistance or comparing assistance with different loads.
With increasing worn load, exoskeleton assistance has produced similar absolute metabolic reductions and decreasing metabolic reductions as a percent of control conditions. Compared to walking in the unpowered device, a hip-ankle exosuit can reduce the metabolic cost of walking by 23% (1.02 W/kg) with no load when assisting hip flexion and ankle plantarflexion [15], by 22% (1.04 W/kg) with a 7 kg load when assisting hip flexion, hip extension, and ankle plantarflexion [5] and by 15% (0.67 W/kg) with a 24 kg load when assisting hip flexion, hip extension, and ankle plantarflexion [7]. In a single-participant pilot study with bilateral ankle exoskeletons, assistance reduced the metabolic cost of walking relative to walking in the device without assistance by 33% with no load and by 15% with a 20% body weight load [9]. It is unclear if the decreasing metabolic reductions with increasing worn load is a biological trend, a result of limited actuation capabilities, or a product of assisting only one or two joints. There may be greater metabolic reductions possible when assisting the hips, knees and ankle simultaneously.
Providing assistance at all three joints (hips, knees, and ankles) may result in larger metabolic reductions for loaded walking. Biological hip extension, knee extension and ankle plantarflexion joint moments all increase with worn load [16], and optimal exoskeleton assistance may follow a similar pattern. Simulations of exoskeleton assistance when walking with a heavy load found the greatest metabolic reductions when assisting hip flexion, knee flexion, or hip abduction [17]. These simulations assume that the exoskeleton is massless, has a lossless transmission, and has unlimited torque and power capabilities. In unloaded walking, a comparison of optimized assistance for one joint, two joint, and three joint configurations found the greatest metabolic reductions when the hips, knees and ankles were assisted simultaneously [18]. The same may be true for loaded walking where optimized hip-knee-ankle exoskeleton assistance could produce greater metabolic reductions than assistance at one or two joints.
We optimized hip-knee-ankle exoskeleton assistance to reduce the metabolic cost of loaded walking. We hypothesized that exoskeleton assistance would reduce metabolic cost for all loaded conditions and that the optimized extension torques would increase with load. Three participants wore a hip-knee-ankle exoskeleton emulator [19] while we used human-in-the-loop optimization to reduce the metabolic cost of walking with no load [18, 20], while carrying 15% of body weight, and while carrying 30% of body weight. The loads were applied with a weight vest with an attached waist strap such that the majority of the load was applied to the user’s iliac crests. We measured changes in metabolic cost, muscle activity, exoskeleton assistance and kinematics across loads. We used biomechanics measurements to gain insights into the mechanisms underlying changes in metabolic rate. We expected the results of this study to be used to prescribe effective load-dependent assistance for future exoskeleton products.
No comments:
Post a Comment