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

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.

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

10.1101/2021.03.26.437212 ◽

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.

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Influence of walking speed on locomotor time production

10.1101/001156 ◽

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.

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

10.21203/rs.2.20510/v1 ◽

2020 ◽

Cited By ~ 2

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.

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

10.21203/rs.2.20510/v2 ◽

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.

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THE ENERGETIC COSTS OF CALLING IN THE BUSHCRICKET REQUENA VERTICALIS (ORTHOPTERA: TETTIGONIIDAE: LISTROSCELIDINAE)

Journal of Experimental Biology ◽

10.1242/jeb.178.1.21 ◽

1993 ◽

Vol 178 (1) ◽

pp. 21-37 ◽

Cited By ~ 4

Author(s):

W. J. Bailey ◽

P. C. Withers ◽

M. Endersby ◽

K. Gaull

Keyword(s):

Body Mass ◽

Sound Pressure ◽

Metabolic Cost ◽

Acoustic Power ◽

Metabolic Energy ◽

Energetic Cost ◽

Metabolic Efficiency ◽

Metabolic Costs ◽

Sound Pressure Levels ◽

The Relationship

1. The metabolic costs of calling for male Requena verticalis Walker (Tettigoniidae: Listroscelidinae) were measured by direct recordings of oxygen consumption. The acoustic power output was measured by sound pressure levels around the calling bushcricket. 2. The average metabolic cost of calling was 0.143 ml g-1 h-1 but depended on calling rate. The net metabolic cost of calling per unit call, the syllable, was calculated to be 4.34×10-6+/−8.3×10-7 ml O2 syllable-1 g-1 body mass (s.e.) from the slope of the relationship between total V(dot)O2 and rate of syllable production. The resting V(dot)O2, calculated as the intercept of the relationship, was 0.248 ml O2 g-1 body mass h-1. 3. The energetic cost of calling for R. verticalis (average mass 0.37 g) was estimated at 31.85×10-6 J syllable-1. 4. Sound pressure levels were measured around calling insects. The surface area of a sphere of uniform sound pressure level [83 dB SPL root mean square (RMS) acoustic power] obtained by these measurements was used to calculate acoustic power. This was 0.20 mW. 5. The metabolic efficiency of calling, based on total metabolic energy utilisation, was 6.4 %. However, we propose that the mechanical efficiency for acoustic transmission is closer to 57 %, since only about 10 % of muscle metabolic energy is apparently available for sound production. 6. R. verticalis emits chirps formed of several syllables within which are discrete sound pulses. Wing stroke rates, when the insect is calling at its maximal rate, were approximately 583 min-1. This is slow compared to the rates observed in conehead tettigoniids, the only other group of bushcrickets where metabolic costs have been measured. The thoracic temperatures of males that had been calling for 5 min were not significantly different from those of non-calling males. 7. For R. verticalis, calling with relatively slow syllable rates may reduce the total cost of calling, and this may be a compensatory mechanism for their other high energetic cost of mating (a large spermatophylax).

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Walking Speed at Self-Selected Exercise Pace Is Lower but Energy Cost Higher in Older Versus Younger Women

Journal of Physical Activity and Health ◽

10.1123/jpah.6.3.327 ◽

2009 ◽

Vol 6 (3) ◽

pp. 327-332 ◽

Cited By ~ 18

Author(s):

Lynnette M. Jones ◽

Debra L. Waters ◽

Michael Legge

Keyword(s):

Older Women ◽

Energy Cost ◽

Walking Speed ◽

Metabolic Cost ◽

Energetic Cost ◽

Energy Costs ◽

Energy Equivalent ◽

Younger Women ◽

Exercise Modality ◽

Walking Speeds

Background:Walking is usually undertaken at a speed that coincides with the lowest metabolic cost. Aging however, alters the speed–cost relationship, as preferred walking speeds decrease and energy costs increase. It is unclear to what extent this relationship is affected when older women undertake walking as an exercise modality. The aim of this study was to compare the energetic cost of walking at a self-selected exercise pace for 30 min in older and younger women.Methods:The energetic cost of walking was assessed using the energy equivalent of oxygen consumption measured in 18 young (25 to 49 y) and 20 older (50 to 79 y) women who were asked to walk at their “normal” exercise pace on a motorized treadmill for 30 min.Results:The mass-specific net cost of walking (Cw) was 15% higher and self-selected walking speed was 23% lower in the older women than in the younger group. When speed was held constant, the Cw was 0.30 (J · .kg−1 · m−1) higher in the older women.Conclusions:Preferred exercise pace incurs a higher metabolic cost in older women and needs be taken into consideration when recommending walking as an exercise modality.

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Simulating bipedal walking using a translating center of pressure

10.1101/723445 ◽

2019 ◽

Author(s):

Karna Potwar ◽

Dongheui Lee

Keyword(s):

Steady State ◽

Walking Speed ◽

Center Of Pressure ◽

Reaction Force ◽

Bipedal Walking ◽

Upper Body ◽

Foot Placement ◽

Fast Walking ◽

Walking Speeds ◽

Steady State Solutions

AbstractDuring walking, foot orientation and foot placement allow humans to stabilize their gait and to move forward. Consequently the upper body adapts to the ground reaction force (GRF) transmitted through the feet. The foot-ground contact is often modeled as a fixed pivot in bipedal models for analysis of locomotion. The fixed pivot models, however, cannot capture the effect of shift in the pivot point from heel to toe. In this study, we propose a novel bipedal model, called SLIPCOP, which employs a translating center of pressure (COP) in a spring loaded inverted pendulum (SLIP) model. The translating COP has two modes: one with a constant speed of translation and the other as the weighted function of the GRF in the fore aft direction. We use the relation between walking speed and touchdown (TD) angle as well as walking speed and COP speed, from existing literature, to restrict steady state solutions within the human walking domain. We find that with these relations, SLIPCOP provides steady state solutions for very slow to very fast walking speeds unlike SLIP. SLIPCOP for normal to very fast walking speed shows good accuracy in estimating COM amplitude and swing stance ratio. SLIPCOP is able to estimate the distance traveled by the COP during stance with high precision.

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Comparing optimized exoskeleton assistance of the hip, knee, and ankle in single and multi-joint configurations

Wearable Technologies ◽

10.1017/wtc.2021.14 ◽

2021 ◽

Vol 2 ◽

Author(s):

Patrick W. Franks ◽

Gwendolyn M. Bryan ◽

Russell M. Martin ◽

Ricardo Reyes ◽

Ava C. Lakmazaheri ◽

...

Keyword(s):

Human Mobility ◽

Metabolic Cost ◽

Metabolic Energy ◽

Maximum Effect ◽

Loop Optimization ◽

Human In The Loop ◽

Ankle Joints ◽

Individual Effects ◽

Single Well ◽

Ankle Exoskeleton

Abstract Exoskeletons that assist the hip, knee, and ankle joints have begun to improve human mobility, particularly by reducing the metabolic cost of walking. However, direct comparisons of optimal assistance of these joints, or their combinations, have not yet been possible. Assisting multiple joints may be more beneficial than the sum of individual effects, because muscles often span multiple joints, or less effective, because single-joint assistance can indirectly aid other joints. In this study, we used a hip–knee–ankle exoskeleton emulator paired with human-in-the-loop optimization to find single-joint, two-joint, and whole-leg assistance that maximally reduced the metabolic cost of walking. Hip-only and ankle-only assistance reduced the metabolic cost of walking by 26 and 30% relative to walking in the device unassisted, confirming that both joints are good targets for assistance (N = 3). Knee-only assistance reduced the metabolic cost of walking by 13%, demonstrating that effective knee assistance is possible (N = 3). Two-joint assistance reduced the metabolic cost of walking by between 33 and 42%, with the largest improvements coming from hip-ankle assistance (N = 3). Assisting all three joints reduced the metabolic cost of walking by 50%, showing that at least half of the metabolic energy expended during walking can be saved through exoskeleton assistance (N = 4). Changes in kinematics and muscle activity indicate that single-joint assistance indirectly assisted muscles at other joints, such that the improvement from whole-leg assistance was smaller than the sum of its single-joint parts. Exoskeletons can assist the entire limb for maximum effect, but a single well-chosen joint can be more efficient when considering additional factors such as weight and cost.

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Interlimb Coordination During Slow Walking in the Cockroach: I. Effects of Substrate Alterations

Journal of Experimental Biology ◽

10.1242/jeb.78.1.233 ◽

1979 ◽

Vol 78 (1) ◽

pp. 233-243 ◽

Cited By ~ 1

Author(s):

CARL P. SPIRITO ◽

DANIEL L. MUSHRUSH

Keyword(s):

Control System ◽

Walking Speed ◽

Interlimb Coordination ◽

Steering Control ◽

Inclined Plane ◽

Slow Walking ◽

Tripod Gait ◽

Walking Speeds

In this study, interlimb coordination in the cockroach during slow walking (2–7 steps/s) is described for a variety of substrate conditions. During normal free-walking, the animal utilizes an alternating tripod gait (both ipsilateral and contralateral phase close to 0.50). The protraction/retraction ratio varies linearly with walking speed. When tethered on a supported ball, the ipsilateral phase ranges from 0.32 to 0.46 at walking speeds of 2-7 steps/s, and contralateral phase is constant at 0.53. Protraction/retraction ratios are normal in this case. Blind free-walking animals use a gait which is indistinguishable from normal, but the protraction/retraction ratio is constant over speeds of 2-7 steps/s. When walking down an inclined plane (45°), the gait resembles ball-walking, with an average ipsilateral phase of 0.43 and contralateral phase of 0.53. These alterations of gait under different substrate conditions can be related to the animal's responses to loading, gravity, and steering control system.

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Comparing optimized exoskeleton assistance of the hip, knee, and ankle in single and multi-joint configurations

10.1101/2021.02.19.431882 ◽

2021 ◽

Author(s):

Patrick W. Franks ◽

Gwendolyn M. Bryan ◽

Russell M. Martin ◽

Ricardo Reyes ◽

Steven H. Collins

Keyword(s):

Human Mobility ◽

Metabolic Cost ◽

Metabolic Energy ◽

Maximum Effect ◽

Loop Optimization ◽

Human In The Loop ◽

Ankle Joints ◽

Individual Effects ◽

Single Well ◽

Ankle Exoskeleton

Exoskeletons that assist the hip, knee, and ankle joints have begun to improve human mobility, particularly by reducing the metabolic cost of walking. However, direct comparisons of optimal assistance of these joints, or their combinations, have not yet been possible. Assisting multiple joints may be more beneficial than the sum of individual effects, because muscles often span multiple joints, or less effective, because single-joint assistance can indirectly aid other joints. In this study, we used a hip-knee-ankle exoskeleton emulator paired with human-in-the-loop optimization to find single-joint, two-joint, and whole-leg assistance that maximally reduced the metabolic cost of walking for three participants. Hip-only and ankle-only assistance reduced the metabolic cost of walking by 26% and 30% relative to walking in the device unassisted, confirming that both joints are good targets for assistance. Knee-only assistance reduced the metabolic cost of walking by 13%, demonstrating that effective knee assistance is possible. Two-joint assistance reduced the metabolic cost of walking by between 34% and 42%, with the largest improvements coming from hip-ankle assistance. Assisting all three joints reduced the metabolic cost of walking by 50%, showing that at least half of the metabolic energy expended during walking can be saved through exoskeleton assistance. Changes in kinematics and muscle activity indicate that single-joint assistance indirectly assisted muscles at other joints, such that the improvement from whole-leg assistance was smaller than the sum of its single-joint parts. Exoskeletons can assist the entire limb for maximum effect, but a single well-chosen joint can be more efficient when considering additional factors such as weight and cost.

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