scholarly journals Disentangling the energetic costs of step time asymmetry and step length asymmetry in human walking

2021 ◽  
Author(s):  
Jan Stenum ◽  
Julia T. Choi
Keyword(s):  
Energy Cost ◽  
Metabolic Cost ◽  
Step Length ◽  
Human Walking ◽  
Metabolic Power ◽  
Healthy Human ◽  
Time Asymmetry ◽  
Double Support ◽  
Post Stroke ◽  
The Cost

The metabolic cost of walking in healthy individuals increases with spatiotemporal gait asymmetries. Pathological gait, such as post-stroke, often has asymmetry in step lengths and step times which may contribute to an increased energy cost. But paradoxically, enforcing step length symmetry does not reduce metabolic cost of post-stroke walking. The isolated and interacting costs of asymmetry in step times and step lengths remain unclear, because previous studies did not simultaneously enforce spatial and temporal gait asymmetries. Here, we delineate isolated costs of asymmetry in step times and step lengths in healthy human walking. We first show that the cost of step length asymmetry is predicted by the cost of taking two non-preferred step lengths (one short and one long), but that step time asymmetry adds an extra cost beyond the cost of non-preferred step times. The metabolic power of step time asymmetry is about 2.5 times greater than the cost of step length asymmetry. Furthermore, the costs are not additive when walking with asymmetric step times and step lengths: metabolic power of concurrent asymmetry in step lengths and step times is driven by the cost of step time asymmetry alone. The metabolic power of asymmetry is explained by positive mechanical power produced during single support phases to compensate for a net loss of center of mass power incurred during double support phases. These data may explain why metabolic cost remains invariant to step length asymmetry in post-stroke walking and suggests how effects of asymmetry on energy cost can be attenuated.

scholarly journals A low-cost method for carrying loads during human walking

2020 ◽  
Vol 223 (23) ◽  
pp. jeb216119
Author(s):  
Christopher J. Arellano ◽  
Obioma B. McReynolds ◽  
Shernice A. Thomas
Keyword(s):  
Low Cost ◽  
Center Of Mass ◽  
Metabolic Cost ◽  
The Body ◽  
Human Walking ◽  
Metabolic Power ◽  
Arm Swing ◽  
Leg Motion ◽  
The Cost ◽  
Pendulum Dynamics

ABSTRACTHumans often perform tasks that require them to carry loads, but the metabolic cost of carrying loads depends on where the loads are positioned on the body. We reasoned that carrying loads at the arms’ center of mass (COM) during walking might be cheap because arm swing is thought to be dominated by passive pendulum dynamics. In contrast, we expected that carrying loads at the leg COM would be relatively expensive because muscular actuation is necessary to initiate and propagate leg swing. Therefore, we hypothesized that carrying loads at the arm COM while swinging would be cheaper than carrying loads at the leg COM. We further hypothesized that carrying loads at the arm COM while swinging would be more expensive than carrying loads at the waist, where the mass does not swing relative to the body. We measured net metabolic power, arm and leg motion, and the free vertical moment while subjects (n=12) walked on a treadmill (1.25 m s−1) without a load, and with 8 kg added to the arms (swinging versus not swinging), legs or waist. We found that carrying loads on the arms or legs altered arm swinging amplitude; however, the free vertical moment remained similar across conditions. Most notably, the cost of carrying loads on the swinging arms was 9% less than carrying at the leg COM (P<0.001), but similar to that at the waist (P=0.529). Overall, we found that carrying loads at the arm COM is just as cheap as carrying loads at the waist.

scholarly journals Feasibility of Using Foot–Ground Clearance Biofeedback Training in Treadmill Walking for Post-Stroke Gait Rehabilitation

2020 ◽  
Vol 10 (12) ◽  
pp. 978
Author(s):  
Hanatsu Nagano ◽  
Catherine M. Said ◽  
Lisa James ◽  
Rezaul K. Begg
Keyword(s):  
Real Time ◽  
Training Session ◽  
Step Length ◽  
Gait Training ◽  
Treadmill Walking ◽  
Biofeedback Training ◽  
Step Width ◽  
Double Support ◽  
Post Stroke ◽  
Foot Clearance

Hemiplegic stroke often impairs gait and increases falls risk during rehabilitation. Tripping is the leading cause of falls, but the risk can be reduced by increasing vertical swing foot clearance, particularly at the mid-swing phase event, minimum foot clearance (MFC). Based on previous reports, real-time biofeedback training may increase MFC. Six post-stroke individuals undertook eight biofeedback training sessions over a month, in which an infrared marker attached to the front part of the shoe was tracked in real-time, showing vertical swing foot motion on a monitor installed in front of the subject during treadmill walking. A target increased MFC range was determined, and participants were instructed to control their MFC within the safe range. Gait assessment was conducted three times: Baseline, Post-training and one month from the final biofeedback training session. In addition to MFC, step length, step width, double support time and foot contact angle were measured. After biofeedback training, increased MFC with a trend of reduced step-to-step variability was observed. Correlation analysis revealed that MFC height of the unaffected limb had interlinks with step length and ankle angle. In contrast, for the affected limb, step width variability and MFC height were positively correlated. The current pilot-study suggested that biofeedback gait training may reduce tripping falls for post-stroke individuals.

scholarly journals Persons post-stroke improve step length symmetry by walking asymmetrically

2020 ◽  
Author(s):  
Purnima Padmanabhan ◽  
Keerthana Sreekanth ◽  
Shivam Gulhar ◽  
Kendra M. Cherry-Allen ◽  
Kristan A. Leech ◽  
...  
Keyword(s):  
Center Of Mass ◽  
Metabolic Cost ◽  
Step Length ◽  
Gait Pattern ◽  
Future Research ◽  
Cost Of Transport ◽  
Post Stroke ◽  
Paretic Limb ◽  
Gait Parameters ◽  
The Many

Abstract Background Restoration of step length symmetry is a common rehabilitation goal after stroke. Persons post-stroke often retain the ability to walk with symmetric step lengths ("symmetric steps") at an elevated metabolic cost relative to healthy adults. Two key questions with direct implications for rehabilitation have emerged: 1) how do persons post-stroke generate symmetric steps, and 2) why do symmetric steps remain so effortful? Here, we aimed to understand how persons post-stroke generate symmetric steps and explored how the resulting gait pattern may relate to the metabolic cost of transport. Methods We recorded kinematic, kinetic, and metabolic data as nine persons post-stroke walked on an instrumented treadmill under two conditions: preferred walking and symmetric stepping (using visual feedback). Results Gait kinematics and kinetics remained markedly asymmetric even when persons post-stroke improved step length symmetry. Impaired paretic propulsion and abnormal movement of the center of mass were evident during both preferred walking and symmetric stepping. These deficits contributed to diminished positive work performed by the paretic limb on the center of mass in both conditions. Within each condition, decreased positive paretic work correlated with increased metabolic cost of transport and decreased walking speed across participants. Conclusions It is critical to consider the mechanics used to restore symmetric steps when designing interventions to improve walking after stroke. Future research should consider the many dimensions of asymmetry in post-stroke gait, and additional within-participant manipulations of gait parameters are needed to improve our understanding of the elevated metabolic cost of walking after stroke.

scholarly journals Simulated hemiparesis increases optimal spatiotemporal gait asymmetry but not metabolic cost

2021 ◽  
Author(s):  
Russell T Johnson ◽  
Nicholas August Bianco ◽  
James Finley
Keyword(s):  
Gait Speed ◽  
Metabolic Cost ◽  
The Body ◽  
Musculoskeletal Modeling ◽  
Cost Of Transport ◽  
Gait Patterns ◽  
Post Stroke ◽  
The Cost ◽  
Future Work ◽  
Isometric Muscle

Several neuromuscular impairments, such as weakness (hemiparesis), occur after an individual has a stroke, and these impairments primarily affect one side of the body more than the other. Predictive musculoskeletal modeling presents an opportunity to investigate how a specific impairment affects gait performance post-stroke. Therefore, our aim was to use to predictive simulation to quantify the spatiotemporal asymmetries and changes to metabolic cost that emerge when muscle strength is unilaterally reduced. We also determined how forced spatiotemporal symmetry affects metabolic cost. We modified a 2-D musculoskeletal model by uniformly reducing the peak isometric muscle force in all muscles unilaterally. We then solved optimal control simulations of walking across a range of speeds by minimizing the sum of the cubed muscle excitations across all muscles. Lastly, we ran additional optimizations to test if reducing spatiotemporal asymmetry would result in an increase in metabolic cost. Our results showed that the magnitude and direction of effort-optimal spatiotemporal asymmetries depends on both the gait speed and level of weakness. Also, the optimal metabolic cost of transport was 1.25 m/s for the symmetrical and 20% weakness models but slower (1.00 m/s) for the 40% and 60% weakness models, suggesting that hemiparesis can account for a portion of the slower gait speed seen in people post-stroke. Adding spatiotemporal asymmetry to the cost function resulted in small increases (~4%) in metabolic cost. Overall, our results indicate that spatiotemporal asymmetry may be optimal for people post-stroke, who have asymmetrical neuromuscular impairments. Additionally, the effect of speed and level of weakness on spatiotemporal asymmetry may explain the well-known heterogenous distribution of spatiotemporal asymmetries observed in the clinic. Future work could extend our results by testing the effects of other impairments on optimal gait strategies, and therefore build a more comprehensive understanding of the gait patterns in people post-stroke.

scholarly journals Persons post-stroke improve step length symmetry by walking asymmetrically

2020 ◽  
Author(s):  
Purnima Padmanabhan ◽  
Keerthana Sreekanth ◽  
Shivam Gulhar ◽  
Kendra M. Cherry-Allen ◽  
Kristan A. Leech ◽  
...  
Keyword(s):  
Center Of Mass ◽  
Metabolic Cost ◽  
Step Length ◽  
Gait Pattern ◽  
Future Research ◽  
Cost Of Transport ◽  
Post Stroke ◽  
Paretic Limb ◽  
Gait Parameters ◽  
The Many

Abstract Background Restoration of step length symmetry is a common rehabilitation goal after stroke. Persons post-stroke often retain the ability to walk with symmetric step lengths ("symmetric steps"); however, the resulting walking pattern remains effortful. Two key questions with direct implications for rehabilitation have emerged: 1) how do persons post-stroke generate symmetric steps, and 2) why do symmetric steps remain so effortful? Here, we aimed to understand how persons post-stroke generate symmetric steps and explored how the resulting gait pattern may relate to the metabolic cost of transport. Methods We recorded kinematic, kinetic, and metabolic data as nine persons post-stroke walked on an instrumented treadmill under two conditions: preferred walking and symmetric stepping (using visual feedback). Results Gait kinematics and kinetics remained markedly asymmetric even when persons post-stroke improved step length symmetry. Impaired paretic propulsion and aberrant movement of the center of mass were evident during both preferred walking and symmetric stepping. These deficits contributed to diminished positive work performed by the paretic limb on the center of mass in both conditions. Within each condition, decreased positive paretic work correlated with increased metabolic cost of transport and decreased walking speed across participants. Conclusions It is critical to consider the mechanics used to restore symmetric steps when designing interventions to improve walking after stroke. Future research should consider the many dimensions of asymmetry in post-stroke gait, and additional within-participant manipulations of gait parameters are needed to improve our understanding of the elevated metabolic cost of walking after stroke.

Negligible energetic cost of sonar jamming in a bat–moth interaction

2015 ◽  
Vol 93 (4) ◽  
pp. 331-335
Author(s):  
A.J. Corcoran ◽  
H.A. Woods
Keyword(s):  
Sound Production ◽  
Resting Metabolic Rate ◽  
Metabolic Cost ◽  
Energetic Cost ◽  
Metabolic Power ◽  
Model Species ◽  
Predator Prey ◽  
Acoustic Signaling ◽  
The Subject ◽  
The Cost

Energetic cost can constrain how frequently animals exhibit behaviors. The energetic cost of acoustic signaling for communication has been the subject of numerous studies; however, the cost of acoustic signaling for predator defense has not been addressed. We studied the energetic cost and efficiency of sound production for the clicks produced by the moth Bertholdia trigona (Grote, 1879) (Grote’s bertholdia) to jam the sonar of predatory bats. This moth is an excellent model species because of its extraordinary ability to produce sound—it clicks at the highest known rate of any moth, up to 4500 clicks·s–1. We measured the metabolic cost of clicking, resting, and flying from moths suspended in a respirometry chamber. Clicking was provoked by playing back an echolocation attack sequence. The cost of sound production for B. trigona was low (66% of resting metabolic rate) and the acoustic efficiency, or the percentage of metabolic power that is converted into sound, was moderately high (0.30% ± 0.15%) compared with other species. We discuss mechanisms that allow B. trigona to achieve their extraordinary clicking rates and high acoustic efficiency. Clicking for jamming bat sonar incurs negligible energetic cost to moths despite being the most effective known anti-bat defense. These results have implications for both the ecology of predator–prey interactions and the evolution of jamming signals.

scholarly journals Persons post-stroke restore step length symmetry by walking asymmetrically

2019 ◽  
Author(s):  
Purnima Padmanabhan ◽  
Keerthana Sreekanth Rao ◽  
Shivam Gulhar ◽  
Kendra M. Cherry-Allen ◽  
Kristan A. Leech ◽  
...  
Keyword(s):  
Center Of Mass ◽  
Metabolic Cost ◽  
Step Length ◽  
Gait Pattern ◽  
Vertical Movement ◽  
Cost Of Transport ◽  
Post Stroke ◽  
Paretic Limb ◽  
Rehabilitation Goal ◽  
Limb Kinematics

ABSTRACTBackgroundRestoration of step length symmetry is a common rehabilitation goal after stroke. Persons post-stroke often retain the capacity to walk with symmetric step lengths (“symmetric steps”); however, the resulting walking pattern remains effortful. Two key questions with direct implications for rehabilitation have emerged: 1) how do persons post-stroke generate symmetric steps, and 2) why do symmetric steps remain so effortful?ObjectiveTo understand how persons post-stroke generate symmetric steps and how the resulting gait pattern relates to the metabolic cost of transport.MethodsTen persons post-stroke walked on an instrumented treadmill under two conditions: preferred walking and symmetric stepping (using visual feedback). We recorded kinematic, kinetic, and metabolic data during both conditions.ResultsPersons post-stroke restored step length symmetry using energetically expensive, asymmetric patterns. Impaired paretic propulsion and abnormal vertical movement of the center of mass were evident during both preferred walking and symmetric stepping. These deficits contributed to diminished positive work performed by the paretic limb on the center of mass in both conditions. Decreased positive paretic work correlated with increased metabolic cost of transport, decreased self-selected walking speed, and increased asymmetry in limb kinematics.ConclusionsIt is important to consider the mechanics used to restore symmetric steps when designing interventions to improve walking after stroke. Facilitating symmetric steps via increased paretic propulsion or enabling paretic limb advancement without excessive vertical movement may enable persons post-stroke to walk with a less effortful, more symmetric gait pattern.

scholarly journals Individual differences in locomotor function predict the capacity to reduce asymmetry and modify the energetic cost of walking post-stroke

2017 ◽  
Author(s):  
Natalia Sánchez ◽  
James M. Finley
Keyword(s):  
Individual Differences ◽  
Visual Feedback ◽  
Metabolic Cost ◽  
Step Length ◽  
Energetic Cost ◽  
Stroke Survivors ◽  
Locomotor Function ◽  
Post Stroke ◽  
Paretic Limb ◽  
Over Ground Walking

AbstractChanges in the control of the lower extremities post-stroke lead to persistent biomechanical asymmetries during walking. These asymmetries are associated with an increase in energetic cost, leading to the possibility that reduction of asymmetry can improve economy. However, the influence of asymmetry on economy may depend on the direction and cause of asymmetry. For example, impairments with paretic limb advancement may result in shorter paretic steps while deficits in paretic support or propulsion result in shorter non-paretic steps. Given differences in the underlying impairments responsible for each type of step length asymmetry, the capacity to reduce asymmetry, and the associated changes in energetic cost may not be consistent across this population. Here, we identified factors explaining individual differences in the capacity to voluntarily reduce step length asymmetry and modify energetic cost during walking. Twenty-four individuals post-stroke walked on a treadmill with visual feedback of their step lengths to aid explicit modification of asymmetry. We found that individuals who naturally took longer paretic steps had a greater capacity to reduce asymmetry, and were better able to transfer the effects of training to over-ground walking. In addition, baseline energetic cost was negatively correlated with reductions in cost, such that participants with a more economical gait were more likely to reduce energetic cost by improving symmetry. These results demonstrate that many stroke survivors retain the capacity to voluntarily walk more symmetrically on a treadmill and over-ground. However, whether reductions in asymmetry reduce metabolic cost depends on individual differences in impairments affecting locomotor function.

scholarly journals Soft tissue deformations explain most of the mechanical work variations of human walking

2021 ◽  
Author(s):  
Tim J. van der Zee ◽  
Arthur D. Kuo
Keyword(s):  
Soft Tissue ◽  
Soft Tissues ◽  
Metabolic Cost ◽  
Step Length ◽  
Mechanical Work ◽  
Metabolic Energy ◽  
Whole Body ◽  
Human Walking ◽  
Negative Work ◽  
Tissue Deformations

AbstractHumans perform mechanical work during walking, some by leg joints actuated by muscles, and some by passive, dissipative soft tissues. Dissipative losses must be restored by active muscle work, potentially in amounts sufficient to cost substantial metabolic energy. The most dissipative, and therefore costly, walking conditions might be predictable from the pendulum-like dynamics of the legs. If pendulum behavior is systematic, it may also predict the work distribution between active joints and passive soft tissues. We therefore tested whether the overall negative work of walking, and the fraction due to soft tissue dissipation, are both predictable by a pendulum model across a wide range of conditions. The model predicts whole-body negative work from the leading leg’s impact with ground (termed the Collision), to increase with the squared product of walking speed and step length. We experimentally tested this in humans (N = 9) walking in 26 different combinations of speed (0.7 – 2.0 m·s-1) and step length (0.5 – 1.1 m), with recorded motions and ground reaction forces. Whole-body negative Collision work increased as predicted (R2= 0.73), with a consistent fraction of about 63% (R2= 0.88) due to soft tissues. Soft tissue dissipation consistently accounted for about 56% of the variation in total whole-body negative work. During typical walking, active work to restore dissipative losses could account for 31% of the net metabolic cost. Soft tissue dissipation, not included in most biomechanical studies, explains most of the variation in negative work of walking, and could account for a substantial fraction of the metabolic cost.Summary statementSoft tissue deformations dissipate substantial energy during human walking, as predicted by a simple walking model.

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