scholarly journals Optimized hip-knee-ankle exoskeleton assistance at a range of walking speeds

2021 ◽  
Author(s):  
Gwendolyn M Bryan ◽  
Patrick W. Franks ◽  
Seungmoon Song ◽  
Alexandra S Voloshina ◽  
Ricardo Reyes ◽  
...  
Keyword(s):  
Muscle Activity ◽  
Metabolic Cost ◽  
Positive Power ◽  
Fast Walking ◽  
Know How ◽  
Ankle Torque ◽  
Slow Walking ◽  
Limited Success ◽  
Ankle Exoskeleton ◽  
Walking Speeds

Background: Effective autonomous exoskeletons will need to be useful at a variety of walking speeds, but we do not know how optimal exoskeleton assistance should change with speed. Optimal exoskeleton assistance may increase with speed similar to biological torque changes or a well-tuned assistance profile may be effective at a variety of speeds. Methods: We optimized hip-knee-ankle exoskeleton assistance to reduce metabolic cost for three participants walking at 1.0 m/s, 1.25 m/s and 1.5 m/s. We measured metabolic cost, muscle activity, exoskeleton assistance and kinematics. We performed two tailed paired t-tests to determine significance. Results: Exoskeleton assistance reduced the metabolic cost of walking compared to wearing the exoskeleton with no torque applied by 26%, 47% and 50% at 1.0, 1.25 and 1.5 m/s, respectively. For all three participants, optimized exoskeleton ankle torque was the smallest for slow walking, while hip and knee torque changed slightly with speed in ways that varied across participants. Total applied positive power increased with speed for all three participants, largely due to increased joint velocities, which consistently increased with speed. Conclusions: Exoskeleton assistance is effective at a range of speeds and is most effective at medium and fast walking speeds. Exoskeleton assistance was less effective for slow walking, which may explain the limited success in reducing metabolic cost for patient populations through exoskeleton assistance. Exoskeleton designers may have more success when targeting activities and groups with faster walking speeds. Speed-related changes in optimized exoskeleton assistance varied by participant, indicating either the benefit of participant-specific tuning or that a wide variety of torque profiles are similarly effective.

scholarly journals Optimized hip–knee–ankle exoskeleton assistance at a range of walking speeds

2021 ◽  
Vol 18 (1) ◽  
Author(s):  
Gwendolyn M. Bryan ◽  
Patrick W. Franks ◽  
Seungmoon Song ◽  
Alexandra S. Voloshina ◽  
Ricardo Reyes ◽  
...  
Keyword(s):  
Walking Speed ◽  
Metabolic Cost ◽  
Metabolic Energy ◽  
Positive Power ◽  
Fast Walking ◽  
Slow Walking ◽  
Limited Success ◽  
Ankle Exoskeleton ◽  
Walking Speeds ◽  
The Relationship

Abstract Background Autonomous exoskeletons will need to be useful at a variety of walking speeds, but it is unclear how optimal hip–knee–ankle exoskeleton assistance should change with speed. Biological joint moments tend to increase with speed, and in some cases, optimized ankle exoskeleton torques follow a similar trend. Ideal hip–knee–ankle exoskeleton torque may also increase with speed. The purpose of this study was to characterize the relationship between walking speed, optimal hip–knee–ankle exoskeleton assistance, and the benefits to metabolic energy cost. Methods We optimized hip–knee–ankle exoskeleton assistance to reduce metabolic cost for three able-bodied participants walking at 1.0 m/s, 1.25 m/s and 1.5 m/s. We measured metabolic cost, muscle activity, exoskeleton assistance and kinematics. We performed Friedman’s tests to analyze trends across walking speeds and paired t-tests to determine if changes from the unassisted conditions to the assisted conditions were significant. Results Exoskeleton assistance reduced the metabolic cost of walking compared to wearing the exoskeleton with no torque applied by 26%, 47% and 50% at 1.0, 1.25 and 1.5 m/s, respectively. For all three participants, optimized exoskeleton ankle torque was the smallest for slow walking, while hip and knee torque changed slightly with speed in ways that varied across participants. Total applied positive power increased with speed for all three participants, largely due to increased joint velocities, which consistently increased with speed. Conclusions Exoskeleton assistance is effective at a range of speeds and is most effective at medium and fast walking speeds. Exoskeleton assistance was less effective for slow walking, which may explain the limited success in reducing metabolic cost for patient populations through exoskeleton assistance. Exoskeleton designers may have more success when targeting activities and groups with faster walking speeds. Speed-related changes in optimized exoskeleton assistance varied by participant, indicating either the benefit of participant-specific tuning or that a wide variety of torque profiles are similarly effective.

scholarly journals Optimized hip-knee-ankle exoskeleton assistance reduces the metabolic cost of walking with worn loads

2021 ◽  
Vol 18 (1) ◽  
Author(s):  
Gwendolyn M. Bryan ◽  
Patrick W. Franks ◽  
Seungmoon Song ◽  
Ricardo Reyes ◽  
Meghan P. O’Donovan ◽  
...  
Keyword(s):  
Body Weight ◽  
Muscle Activity ◽  
Metabolic Cost ◽  
Load Carriage ◽  
Heavy Load ◽  
Human In The Loop ◽  
Light Load ◽  
Wide Range ◽  
Ankle Exoskeleton ◽  
The Individual

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.

scholarly journals Influence of walking speed on locomotor time production

2013 ◽  
Author(s):  
Fabrice MEGROT ◽  
Carole MEGROT
Keyword(s):  
Healthy Subjects ◽  
Walking Speed ◽  
The Other ◽  
Temporal Perception ◽  
Time Production ◽  
Fast Walking ◽  
Slow Walking ◽  
Perception Of Time ◽  
Walking Speeds

The aim of the present study was to determine whether or not walking speed affects temporal perception. It was hypothesized that fast walking would reduce the perceived length of time while slow walking increase production estimates. 16 healthy subjects were included. After a first « calibration » phase allowing the determination of different walking speeds, the subjects were instructed to demonstrate periods of time or « target times » of 3s and 7s, by a walking movement. Then, subjects were asked to simulate walking by raising one foot after the other without advancing. Finally, a third condition, Motionless, involved producing the target times while standing without movement. The results of this study suggest that movement does influence the perception of time, causing an overestimation of time. In agreement with the results of Denner et al. (1963) the subjects produced times which were longer than the target times.

scholarly journals Optimized Hip-Knee-Ankle Exoskeleton Assistance Reduces the Metabolic Cost of Walking With Worn Loads

2021 ◽  
Author(s):  
Gwendolyn M Bryan ◽  
Patrick Franks ◽  
Seungmoon Song ◽  
Ricardo Reyes ◽  
Meghan O’Donovan ◽  
...  
Keyword(s):  
Body Weight ◽  
Muscle Activity ◽  
Metabolic Cost ◽  
Load Carriage ◽  
Heavy Load ◽  
Human In The Loop ◽  
Light Load ◽  
Wide Range ◽  
Ankle Exoskeleton ◽  
Load Conditions

Abstract BackgroundLoad carriage is a typical activity 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 23% when assisting one or two joints. Greater metabolic reductions may be possible with optimized assistance of the entire leg. MethodsWe 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 one-tailed paired t-tests to determine significant reductions for metabolic cost and muscle activity, and we performed an analysis of variance (ANOVA) to determine significant changes across load conditions for metabolic cost and applied power. ResultsExoskeleton 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 47% with no load (p = 0.02), 35% with the light load (p = 0.03), and 43% with the heavy load (p = 0.02). 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. ConclusionsWhole-leg exoskeleton assistance can reduce the metabolic cost of walking while carrying a range of loads. The consistent optimized timing parameters 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.

scholarly journals Speed related changes in muscle activity from normal to very slow walking speeds

2004 ◽  
Vol 19 (3) ◽  
pp. 270-278 ◽  
Author(s):  
A.R den Otter ◽  
A.C.H Geurts ◽  
T Mulder ◽  
J Duysens
Keyword(s):  
Muscle Activity ◽  
Slow Walking ◽  
Walking Speeds

scholarly journals Triceps surae torque-length relationships relevant for walking activity levels with and without an ankle exoskeleton

2019 ◽  
Author(s):  
Anthony L. Hessel ◽  
Brent J. Raiteri ◽  
Michael J. Marsh ◽  
Daniel Hahn
Keyword(s):  
Muscle Activity ◽  
Metabolic Cost ◽  
Activity Levels ◽  
Plantar Flexor ◽  
Plantar Flexors ◽  
Flexor Muscle ◽  
Fascicle Length ◽  
Lateral Gastrocnemius ◽  
Work Requirements ◽  
Ankle Exoskeleton

AbstractAnkle exoskeletons have been developed to assist walking by offloading the plantar flexors work requirements, which reduces muscle activity level. However, reduced muscle activity alters plantar flexor muscle-tendon unit dynamics in a way that is poorly understood. We therefore evaluated torque-fascicle length properties of the soleus and lateral gastrocnemius during voluntary contractions at simulated activity levels typical during late stance with and without an ankle exoskeleton. Soleus activity levels (100, 30, and 22% maximal voluntary activity) were produced by participants via visual electromyography feedback at ankle angles ranging from −10° plantar flexion to 35° dorsiflexion. Using dynamometry and ultrasound imaging, torque-fascicle length data of the soleus and lateral gastrocnemius were produced. The results indicate that muscle activity reductions observed with an exoskeleton shift the torque-angle and torque-fascicle length curves to more dorsiflexed ankle angles and longer fascicle lengths where no descending limb is physiologically possible. This shift is in line with previous simulations that predicted a similar increase in the operating fascicle range when wearing an exoskeleton. These data suggest that a small reduction in muscle activity causes changes to torque-fascicle length properties, which has implications for the design and testing of future ankle exoskeletons for assisted walking.Significance StatementAssistive lower-limb exoskeletons reduce the metabolic cost of walking by reducing the positive work requirements of the plantar flexor muscles. However, if the exoskeleton reduces plantar flexor muscle activity too much, then the metabolic benefit is lost. The biological reasons for this are unclear and hinder further exoskeleton development. This research study is the first to directly evaluate if a reduction in plantar flexor muscle activity similar to that caused by wearing an exoskeleton affects muscle function. We found that reduced muscle activity changes the torque-length properties of two plantar flexors, which could explain why reducing muscle activity too much can increase metabolic cost.

scholarly journals Effect of Walking Speeds on Complexity of Plantar Pressure Patterns

Complexity ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Ben-Yi Liau ◽  
Fu-Lien Wu ◽  
Yameng Li ◽  
Chi-Wen Lung ◽  
Ayman A. Mohamed ◽  
...  
Keyword(s):  
Plantar Pressure ◽  
Repeated Measures ◽  
Multiscale Entropy ◽  
Fast Walking ◽  
Slow Walking ◽  
Significant Difference ◽  
Nonlinear Features ◽  
Plantar Pressure Measurement ◽  
Walking Speeds ◽  
Pressure Measurement System

Various walking speeds may induce different responses on the plantar pressure patterns. Current methods used to analyze plantar pressure patterns are linear and ignore nonlinear features. The purpose of this study was to analyze the complexity of plantar pressure images after walking at various speeds using nonlinear bidimensional multiscale entropy (MSE2D). Twelve participants (age: 27.1 ± 5.8 years; height: 170.3 ± 10.0 cm; and weight: 63.5 ± 13.5 kg) were recruited for walking at three speeds (slow at 1.8 mph, moderate at 3.6 mph, and fast at 5.4 mph) for 20 minutes. A plantar pressure measurement system was used to measure plantar pressure patterns. Complexity index (CI), a summation of MSE2D from all time scales, was used to quantify the changes of complexity of plantar pressure images. The analysis of variance with repeated measures and Fisher’s least significant difference correction were used to examine the results of this study. The results showed that CI of plantar pressure images of 1.8 mph (1.780) was significantly lower compared with 3.6 (1.790) and 5.4 mph (1.792). The results also showed that CI significantly increased from the 1st min (1.780) to the 10th min (1.791) and 20th min (1.791) with slow walking (1.8 mph). Our results indicate that slow walking at 1.8 mph may not be good for postural control compared with moderate walking (3.6 mph) and fast walking (5.4 mph). This study demonstrates that bidimensional multiscale entropy is able to quantify complexity changes of plantar pressure images after different walking speeds.

scholarly journals Impact of elastic ankle exoskeleton stiffness on neuromechanics and energetics of human walking across multiple speeds

2020 ◽  
Author(s):  
Richard W. Nuckols ◽  
Gregory S. Sawicki
Keyword(s):  
Metabolic Rate ◽  
Muscle Activation ◽  
Walking Speed ◽  
Metabolic Cost ◽  
Weighted Sum ◽  
Joint Mechanics ◽  
Metabolic Demand ◽  
Muscle Dynamics ◽  
Ankle Exoskeleton ◽  
Walking Speeds

Abstract Background: Elastic ankle exoskeletons with springs of intermediate stiffness springs in parallel with the human plantarflexors can reduce the metabolic cost of walking by ~7% at 1.25 m s-1. In a move toward ‘real-world’ application, we examined whether the unpowered approach has metabolic benefit across a range of walking speeds, and if so, whether the optimal exoskeleton stiffness was speed dependent. We hypothesized that there is an ‘optimal’ exoskeleton stiffness for any speed which minimizes the user’s metabolic rate and that the metabolically optimal exoskeleton stiffness will also increase with walking speed. Methods: Eleven participants walked on a level treadmill at 1.25, 1.50, and 1.75 m s-1 while we used a state-of-the-art exoskeleton emulator system to apply bilateral ankle exoskeleton assistance at five controlled rotational stiffnesses (kexo = 0, 50, 100, 150, 250 Nm rad-1). We measured metabolic cost, lower limb joint mechanics, and EMG of muscles crossing the ankle, knee, and hip. Results: We measured significant reductions in metabolic cost at the lowest exoskeleton stiffness (50 Nm rad-1) for assisted walking at both 1.25 (4.2%; p = 0.032) and 1.75 m s-1 (4.7%; p = 0.009). At these speeds, the metabolically optimal ankle exoskeleton stiffness provided peak assistive torques of ~0.20 Nm kg-1 that resulted in reduced biological ankle moment of ~12% and reduced soleus muscle activity of ~10%. We found no spring stiffness that could reduce the metabolic cost of walking at 1.5 m s-1. Across all speeds, the non-weighted sum of soleus and tibialis anterior activation rate explained the change metabolic rate due to exoskeleton assistance (p < .05; R2 > 0.56)). Conclusions: Elastic ankle exoskeletons with low rotational stiffness reduce users’ metabolic cost of walking at slow and fast walking speeds but not at intermediate walking speed. The relationship between the non-weighted sum of soleus and tibialis activation and metabolic cost (R2 > 0.56) indicates that muscle activation may drive metabolic demand. Future work using computer simulations and ultrasound imaging will get ‘under the skin’ and examine the interaction between exoskeleton stiffness and plantarflexor muscle dynamics to better inform stiffness selection in human-machine systems.

scholarly journals Impact of elastic ankle exoskeleton stiffness on neuromechanics and energetics of human walking across multiple speeds

2020 ◽  
Author(s):  
Richard W. Nuckols ◽  
Gregory S. Sawicki
Keyword(s):  
Metabolic Rate ◽  
Muscle Activation ◽  
Walking Speed ◽  
Metabolic Cost ◽  
Weighted Sum ◽  
Joint Mechanics ◽  
Muscle Dynamics ◽  
Activation Rate ◽  
Ankle Exoskeleton ◽  
Walking Speeds

Abstract Background: Elastic ankle exoskeletons with springs of intermediate stiffness in parallel with the human plantarflexors can reduce the metabolic cost of walking by ~7% at 1.25 m s -1 . In a move toward ‘real-world’ application, we examined whether the unpowered approach has metabolic benefit across a range of walking speeds, and if so, whether the optimal exoskeleton stiffness was speed dependent. We hypothesized that, for any walking speed, there would be an optimal ankle exoskeleton stiffness - not too compliant and not too stiff - that minimizes the user’s metabolic rate. In addition, we expected the optimal exoskeleton stiffness to increase with walking speed. Methods: Eleven participants walked on a level treadmill at 1.25, 1.50, and 1.75 m s -1 while we used a state-of-the-art exoskeleton emulator system to apply bilateral ankle exoskeleton assistance at five controlled rotational stiffnesses (k exo = 0, 50, 100, 150, 250 Nm rad -1 ). We measured metabolic cost, lower limb joint mechanics, and EMG of muscles crossing the ankle, knee, and hip. Results: We measured significant reductions in metabolic cost at the lowest exoskeleton stiffness (50 Nm rad -1 ) for assisted walking at both 1.25 (4.2%; p = 0.032) and 1.75 m s -1 (4.7%; p = 0.009). At these speeds, the metabolically optimal ankle exoskeleton stiffness provided peak assistive torques of ~0.20 Nm kg -1 that resulted in reduced biological ankle moment of ~12% and reduced soleus muscle activity of ~10%. We found no spring stiffness that could reduce the metabolic cost of walking at 1.5 m s -1 . Across all speeds, the non-weighted sum of soleus and tibialis anterior activation rate explained the change metabolic rate due to exoskeleton assistance ( p < .05; R 2 > 0.56)). Conclusions: Elastic ankle exoskeletons with low rotational stiffness reduce users’ metabolic cost of walking at slow and fast walking speeds but not at intermediate walking speed. The relationship between the non-weighted sum of soleus and tibialis activation rate and metabolic cost (R 2 > 0.56) indicates that muscle activation may drive metabolic demand. Future work using computer simulations and ultrasound imaging will get ‘under the skin’ and examine the interaction between exoskeleton stiffness and plantarflexor muscle dynamics to better inform stiffness selection in human-machine systems.

Do humans exploit the metabolic and mechanical benefits of arm swing across slow to fast walking speeds?

2021 ◽  
Vol 115 ◽  
pp. 110181
Author(s):  
Shernice A. Thomas ◽  
Daisey Vega ◽  
Christopher J. Arellano
Keyword(s):  
Arm Swing ◽  
Fast Walking ◽  
Walking Speeds
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