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):  
Muscle Activation ◽  
Walking Speed ◽  
Metabolic Cost ◽  
Weighted Sum ◽  
Joint Mechanics ◽  
Metabolic Demand ◽  
Muscle Dynamics ◽  
Activation Rate ◽  
Ankle Exoskeleton ◽  
All Speeds

Abstract Background: Elastic ankle exoskeletons with 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, 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 cost. In addition, we expected the optimal 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 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: Metabolic cost was significantly reduced at the lowest exoskeleton stiffness (50 Nm rad -1 ) for assisted walking at both 1.25 (4.2%; p = 0.0162) and 1.75 m s -1 (4.7%; p = 0.0045). At these speeds, the metabolically optimal 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 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 in 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 but not 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 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 ◽  
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.

scholarly journals Associations Between Foot Placement Asymmetries and Metabolic Cost of Transport in Hemiparetic Gait

2016 ◽  
Vol 31 (2) ◽  
pp. 168-177 ◽  
Author(s):  
James M. Finley ◽  
Amy J. Bastian
Keyword(s):  
Walking Speed ◽  
Metabolic Cost ◽  
Positive Association ◽  
Stroke Survivor ◽  
Gas Analysis ◽  
Stroke Survivors ◽  
Cost Of Transport ◽  
Foot Placement ◽  
Hemiparetic Gait ◽  
All Speeds

Stroke survivors often have a slow, asymmetric walking pattern. They also walk with a higher metabolic cost than healthy, age-matched controls. It is often assumed that spatial-temporal asymmetries contribute to the increased metabolic cost of walking poststroke. However, elucidating this relationship is made challenging because of the interdependence between spatial-temporal asymmetries, walking speed, and metabolic cost. Here, we address these potential confounds by measuring speed-dependent changes in metabolic cost and implementing a recently developed approach to dissociate spatial versus temporal contributions to asymmetry in a sample of stroke survivors. We used expired gas analysis to compute the metabolic cost of transport (CoT) for each participant at 4 different walking speeds: self-selected speed, 80% and 120% of their self-selected speed, and their fastest comfortable speed. We also computed CoT for a sample of age- and gender-matched control participants who walked at the same speeds as their matched stroke survivor. Kinematic data were used to compute the magnitude of a number of variables characterizing spatial-temporal asymmetries. Across all speeds, stroke survivors had a higher CoT than controls. We also found that our sample of stroke survivors did not choose a self-selected speed that minimized CoT, contrary to typical observations in healthy controls. Multiple regression analyses revealed negative associations between speed and CoT and a positive association between asymmetries in foot placement relative to the trunk and CoT. These findings suggest that interventions designed to increase self-selected walking speed and reduce foot-placement asymmetries may be ideal for improving walking economy poststroke.

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.

Factors contributing to lower metabolic demand of eccentric compared with concentric cycling

2017 ◽  
Vol 123 (4) ◽  
pp. 884-893 ◽  
Author(s):  
Luis Peñailillo ◽  
Anthony J. Blazevich ◽  
Kazunori Nosaka
Keyword(s):  
Oxygen Consumption ◽  
Muscle Activity ◽  
Muscle Activation ◽  
Vastus Lateralis ◽  
Oxygenation Index ◽  
Metabolic Cost ◽  
Rectus Femoris ◽  
Biceps Femoris ◽  
Metabolic Demand ◽  
Length Changes

This study compared muscle-tendon behavior, muscle oxygenation, and muscle activity between eccentric and concentric cycling exercise at the same work output to investigate why metabolic demand is lower during eccentric cycling than with concentric cycling. Eleven untrained men (27.1 ± 7.0 y) performed concentric cycling (CONC) and eccentric cycling (ECC) for 10 min (60 rpm) at 65% of the maximal concentric cycling power output (191 ± 45 W) 4 wk apart. During cycling, oxygen consumption (V̇o2), heart rate (HR), vastus lateralis (VL) tissue total hemoglobin (tHb), and oxygenation index (TOI) were recorded, and muscle-tendon behavior was assessed using ultrasonography. The surface electromyogram (EMG) was recorded from VL, vastus medialis (VM), rectus femoris (RF), and biceps femoris (BF) muscles, and cycling torque and knee joint angle during each revolution were also recorded. Average V̇o2 (−65 ± 7%) and HR (−35 ± 9%) were lower and average TOI was greater (16 ± 1%) during ECC than CONC, but tHb was similar between bouts. Positive and negative cycling peak crank torques were greater (32 ± 21 and 48 ± 24%, respectively) during ECC than CONC, but muscle-tendon unit and fascicle and tendinous tissue length changes during pedal revolutions were similar between CONC and ECC. VL, VM, RF, and BF peak EMG amplitudes were smaller (24 ± 15, 22 ± 18, 16 ± 17, and 18 ± 9%, respectively) during ECC than CONC. These results suggest that the lower metabolic cost of eccentric compared with concentric cycling was due mainly to a lower level of muscle activation per torque output. NEW & NOTEWORTHY This study shows that lower oxygen consumption of eccentric compared with concentric cycling at the same workload is explained by lower muscle activity of agonist and antagonist muscles during eccentric compared with during concentric cycling.

An experimental comparison of the relative benefits of work and torque assistance in ankle exoskeletons

2015 ◽  
Vol 119 (5) ◽  
pp. 541-557 ◽  
Author(s):  
Rachel W. Jackson ◽  
Steven H. Collins
Keyword(s):  
Metabolic Rate ◽  
Center Of Mass ◽  
Metabolic Cost ◽  
Whole Body ◽  
Experimental Comparison ◽  
Joint Mechanics ◽  
Cascading Effects ◽  
Double Support ◽  
Muscle Dynamics ◽  
Work Input

Techniques proposed for assisting locomotion with exoskeletons have often included a combination of active work input and passive torque support, but the physiological effects of different assistance techniques remain unclear. We performed an experiment to study the independent effects of net exoskeleton work and average exoskeleton torque on human locomotion. Subjects wore a unilateral ankle exoskeleton and walked on a treadmill at 1.25 m·s−1 while net exoskeleton work rate was systematically varied from −0.054 to 0.25 J·kg−1·s−1, with constant (0.12 N·m·kg−1) average exoskeleton torque, and while average exoskeleton torque was systematically varied from approximately zero to 0.18 N·m·kg−1, with approximately zero net exoskeleton work. We measured metabolic rate, center-of-mass mechanics, joint mechanics, and muscle activity. Both techniques reduced effort-related measures at the assisted ankle, but this form of work input reduced metabolic cost (−17% with maximum net work input) while this form of torque support increased metabolic cost (+13% with maximum average torque). Disparate effects on metabolic rate seem to be due to cascading effects on whole body coordination, particularly related to assisted ankle muscle dynamics and the effects of trailing ankle behavior on leading leg mechanics during double support. It would be difficult to predict these results using simple walking models without muscles or musculoskeletal models that assume fixed kinematics or kinetics. Data from this experiment can be used to improve predictive models of human neuromuscular adaptation and guide the design of assistive devices.

scholarly journals Metabolic cost of calcification in bivalve larvae under experimental ocean acidification

2016 ◽  
Vol 74 (4) ◽  
pp. 941-954 ◽  
Author(s):  
Christina A. Frieder ◽  
Scott L. Applebaum ◽  
T.-C. Francis Pan ◽  
Dennis Hedgecock ◽  
Donal T. Manahan
Keyword(s):  
Ocean Acidification ◽  
Climate Change Impacts ◽  
Metabolic Cost ◽  
Shell Formation ◽  
Metabolic Demand ◽  
Shell Size ◽  
Saturation State ◽  
Shell Mass ◽  
Energy Limitation ◽  
Endogenous Reserves

Abstract Physiological increases in energy expenditure frequently occur in response to environmental stress. Although energy limitation is often invoked as a basis for decreased calcification under ocean acidification, energy-relevant measurements related to this process are scant. In this study we focus on first-shell (prodissoconch I) formation in larvae of the Pacific oyster, Crassostrea gigas. The energy cost of calcification was empirically derived to be ≤ 1.1 µJ (ng CaCO3)−1. Regardless of the saturation state of aragonite (2.77 vs. 0.77), larvae utilize the same amount of total energy to complete first-shell formation. Even though there was a 56% reduction of shell mass and an increase in dissolution at aragonite undersaturation, first-shell formation is not energy limited because sufficient endogenous reserves are available to meet metabolic demand. Further studies were undertaken on larvae from genetic crosses of pedigreed lines to test for variance in response to aragonite undersaturation. Larval families show variation in response to ocean acidification, with loss of shell size ranging from no effect to 28%. These differences show that resilience to ocean acidification may exist among genotypes. Combined studies of bioenergetics and genetics are promising approaches for understanding climate change impacts on marine organisms that undergo calcification.

Effects of activation pattern on nonisometric human skeletal muscle performance

2007 ◽  
Vol 102 (5) ◽  
pp. 1985-1991 ◽  
Author(s):  
Ryan D. Maladen ◽  
Ramu Perumal ◽  
Anthony S. Wexler ◽  
Stuart A. Binder-Macleod
Keyword(s):  
Skeletal Muscle ◽  
Instantaneous Frequency ◽  
Muscle Activation ◽  
Motor Units ◽  
Muscle Performance ◽  
Variable Frequency ◽  
Constant Frequency ◽  
Muscle Activation Patterns ◽  
Activation Rate ◽  
Discharge Patterns

During volitional muscle activation, motor units often fire with varying discharge patterns that include brief, high-frequency bursts of activity. These variations in the activation rate allow the central nervous system to precisely control the forces produced by the muscle. The present study explores how varying the instantaneous frequency of stimulation pulses within a train affects nonisometric muscle performance. The peak excursion produced in response to each stimulation train was considered as the primary measure of muscle performance. The results showed that at each frequency tested between 10 and 50 Hz, variable-frequency trains that took advantage of the catchlike property of skeletal muscle produced greater excursions than constant-frequency trains. In addition, variable-frequency trains that could achieve targeted trajectories with fewer pulses than constant-frequency trains were identified. These findings suggest that similar to voluntary muscle activation patterns, varying the instantaneous frequency within a train of pulses can be used to improve muscle performance during functional electrical stimulation.

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.

Sign in / Sign up

Export Citation Format

Share Document