Is natural variability in gait sufficient to initiate spontaneous energy optimization in human walking?

In new walking contexts, the nervous system can adapt preferred gaits to minimize energetic cost. During treadmill walking, this optimization is not usually spontaneous but instead requires experience with the new energetic cost landscape. Experimenters can provide subjects with the needed experience by prescribing new gaits or instructing them to explore new gaits. Yet in familiar walking contexts, people naturally prefer energetically optimal gaits: the nervous system can optimize cost without an experimenter’s guidance. Here we test the hypothesis that the natural gait variability of overground walking provides the nervous system with sufficient experience with new cost landscapes to initiate spontaneous minimization of energetic cost. We had subjects walk over paths of varying terrain while wearing knee exoskeletons that penalized walking as a function of step frequency. The exoskeletons created cost landscapes with minima that were, on average, 8% lower than the energetic cost at the initially preferred gaits and achieved at walking speeds and step frequencies that were 4% lower than the initially preferred values. We found that our overground walking trials amplified gait variability by 3.7-fold compared with treadmill walking, resulting in subjects gaining greater experience with new cost landscapes, including frequent experience with gaits at the new energetic minima. However, after 20 min and 2.0 km of walking in the new cost landscapes, we observed no consistent optimization of gait, suggesting that natural gait variability during overground walking is not always sufficient to initiate energetic optimization over the time periods and distances tested in this study. NEW & NOTEWORTHY While the nervous system can continuously optimize gait to minimize energetic cost, what initiates this optimization process during every day walking is unknown. Here we tested the hypothesis that the nervous system leverages the natural variability in gait experienced during overground walking to converge on new energetically optimal gaits created using exoskeletons. Contrary to our hypothesis, we found that participants did not adapt toward optimal gaits: natural variability is not always sufficient to initiate spontaneous energy optimization.

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Energy Optimization is a Major Objective in the Real-Time Control of Step Width in Human Walking

10.1101/506808 ◽

2018 ◽

Author(s):

Sabrina J. Abram ◽

Jessica C. Selinger ◽

J. Maxwell Donelan

Keyword(s):

Nervous System ◽

Real Time ◽

Energy Optimization ◽

Energetic Cost ◽

Step Width ◽

Real Time Control ◽

Step Frequency ◽

Major Objective ◽

Cost Shifting ◽

Time Control

People prefer to move in energetically optimal ways during walking. We have recently found that this preference arises not just through evolution and development, but that the nervous system will continuously optimize step frequency in response to new energetic cost landscapes. Here we test whether energy optimization is also a major objective in the nervous system's real-time control of step width. To accomplish this, we use a device that can reshape the relationship between step width and energetic cost, shifting the energy optimal width wider than that initially preferred. We find that the nervous system doesn't spontaneously initiate energy optimization, but instead requires experience with a lower energetic cost step width. After initiating optimization, people converge towards their new energy optimal width within hundreds of steps and update this as their new preferred width, rapidly returning to it when perturbed away. However, energy optimization was incomplete as this new preferred width was slightly narrower than the energetically optimal width. This suggests that the nervous system may determine its preferred width by optimizing energy simultaneously with other objectives such as stability or maneuverability. Collectively, these findings indicate that the nervous systems of able-bodied people continuously optimize energetic cost to determine preferred step width.

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Walking Dynamics in Preadolescents With and Without Down Syndrome

Physical Therapy ◽

10.2522/ptj.20140210 ◽

2015 ◽

Vol 95 (5) ◽

pp. 740-749 ◽

Cited By ~ 12

Author(s):

Jianhua Wu ◽

Matthew Beerse ◽

Toyin Ajisafe ◽

Huaqing Liang

Keyword(s):

Down Syndrome ◽

Elastic Property ◽

Motor Task ◽

Muscular Activity ◽

Cross Sectional Study ◽

Treadmill Walking ◽

Overground Walking ◽

Cross Sectional ◽

Walking Speeds ◽

G Ratio

Background A force-driven harmonic oscillator (FDHO) model reveals the elastic property of general muscular activity during walking. Objective This study aimed to investigate whether children with Down syndrome (DS) have a lower K/G ratio, a primary variable derived from the FDHO model, compared with children with typical development during overground and treadmill walking and whether children with DS can adapt the K/G ratio to walking speeds, external ankle load, and a treadmill setting. Design A cross-sectional study design was used that included 26 children with and without DS, aged 7 to 10 years, for overground walking and 20 of them for treadmill walking in a laboratory setting. Methods During overground walking, participants walked at 2 speeds: normal and fastest speed. During treadmill walking, participants walked at 75% and 100% of their preferred overground speed. Two load conditions were manipulated for both overground and treadmill walking: no load and an ankle load that was equal to 2% of body mass on each side. Results Children with DS showed a K/G ratio similar to that of their healthy peers and increased this ratio with walking speed regardless of ankle load during overground walking. Children with DS produced a lower K/G ratio at the fast speed of treadmill walking without ankle load, but ankle load helped them produce a K/G ratio similar to that of their healthy peers. Limitations The FDHO model cannot specify what muscles are used or how muscles are coordinated for a given motor task. Conclusions Children with DS show elastic property of general muscular activity similar to their healthy peers during overground walking. External ankle load helps children with DS increase general muscular activity and match their healthy peers while walking fast on a treadmill.

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The Relationship Between Walking Speed and the Energetic Cost of Walking in Persons With Multiple Sclerosis and Healthy Controls: A Systematic Review

Neurorehabilitation and Neural Repair ◽

10.1177/15459683211005028 ◽

2021 ◽

pp. 154596832110050

Author(s):

Kyra Theunissen ◽

Guy Plasqui ◽

Annelies Boonen ◽

Bente Brauwers ◽

Annick Timmermans ◽

...

Keyword(s):

Multiple Sclerosis ◽

Healthy Subjects ◽

Walking Speed ◽

Included Study ◽

Treadmill Walking ◽

Energetic Cost ◽

Overground Walking ◽

Blood Institute ◽

National Heart Lung ◽

The Relationship

Background Persons with multiple sclerosis (pwMS) experience walking impairments, characterized by decreased walking speeds. In healthy subjects, the self-selected walking speed is the energetically most optimal. In pwMS, the energetically most optimal walking speed remains underexposed. Therefore, this review aimed to determine the relationship between walking speed and energetic cost of walking (Cw) in pwMS, compared with healthy subjects, thereby assessing the walking speed with the lowest energetic cost. As it is unclear whether the Cw in pwMS differs between overground and treadmill walking, as reported in healthy subjects, a second review aim was to compare both conditions. Method PubMed and Web of Science were systematically searched. Studies assessing pwMS, reporting walking speed (converted to meters per second), and reporting oxygen consumption were included. Study quality was assessed with a modified National Heart, Lung and Blood Institute checklist. The relationship between Cw and walking speed was calculated with a second-order polynomial function and compared between groups and conditions. Results Twenty-nine studies were included (n = 1535 pwMS) of which 8 included healthy subjects (n = 179 healthy subjects). PwMS showed a similar energetically most optimal walking speed of 1.44 m/s with a Cw of 0.16, compared with 0.14 mL O2/kg/m in healthy subjects. The most optimal walking speed in treadmill was 1.48 m/s, compared with 1.28 m/s in overground walking with a similar Cw. Conclusion Overall, the Cw is elevated in pwMS but with a similar energetically most optimal walking speed, compared with healthy subjects. Treadmill walking showed a similar most optimal Cw but a higher speed, compared with overground walking.

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Comparison of Treadmill and Overground Walking in Children and Adolescents

Perceptual and Motor Skills ◽

10.1177/0031512521993102 ◽

2021 ◽

pp. 003151252199310

Author(s):

Taeyou Jung ◽

Yumi Kim ◽

Luke E. Kelly ◽

Mayumi Wagatsuma ◽

Youngok Jung ◽

...

Keyword(s):

Children And Adolescents ◽

Stride Length ◽

Pediatric Population ◽

Treadmill Walking ◽

Gait Velocity ◽

Overground Walking ◽

Common Error ◽

Gait Parameters ◽

Analysis System ◽

Walking Speeds

The primary purpose of this study was to compare biomechanical gait variables and perceived gait velocity between overground and treadmill walking conditions among typically developing children and adolescents. Twenty children and adolescents ( Mage = 11.4, SD = 2.9 years) walked overground and on a treadmill at a matched comfortable walking speed while a 3-D motion analysis system captured spatiotemporal and kinematic gait parameters. In order to compare perceived gait velocities, we acquired data at self-selected comfortable and fastest walking speeds. Paired t-tests comparing the children’s speed and gait in these two different walking conditions revealed significantly higher cadence ( p < .001) and shorter stride length ( p < .002), during treadmill versus overground walking. In addition, treadmill walking showed statistically significant differences in joint kinematics of ankle excursion and pelvic rotation excursions ( p < .001). Participants chose slower speeds on the treadmill than for overground walking when they were asked to select their comfortable and fastest walking speeds ( p < .001). Our findings suggest that these differences between treadmill and overground walking in cadence, stride length, and perceived gait velocity should be considered whenever a treadmill is used for gait research within the pediatric population. However, the differences we found in gait kinematics between these two walking conditions appear to be relatively trivial and fell within the common error range of kinematic analysis.

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Speed-related but not detrended gait variability increases with more sensitive self-paced treadmill controllers at multiple slopes

PLoS ONE ◽

10.1371/journal.pone.0251229 ◽

2021 ◽

Vol 16 (5) ◽

pp. e0251229

Author(s):

Cesar R. Castano ◽

Helen J. Huang

Keyword(s):

Step Length ◽

Gait Variability ◽

The Self ◽

Step Width ◽

Step Frequency ◽

Gait Biomechanics ◽

Treadmill Speed ◽

Gait Parameters ◽

Walking Speeds ◽

Speed Fluctuations

Self-paced treadmills are being used more frequently to study humans walking with their self-selected gaits on a range of slopes. There are multiple options to purchase a treadmill with a built-in controller, or implement a custom written self-paced controller, which raises questions about how self-paced controller affect treadmill speed and gait biomechanics on multiple slopes. This study investigated how different self-paced treadmill controller sensitivities affected gait parameters and variability on decline, level, and incline slopes. We hypothesized that increasing self-paced controller sensitivity would increase gait variability on each slope. We also hypothesized that detrended variability could help mitigate differences in variability that arise from differences in speed fluctuations created by the self-paced controllers. Ten young adults walked on a self-paced treadmill using three controller sensitivities (low, medium, and high) and fixed speeds at three slopes (decline, -10°; level, 0°; incline, +10°). Within each slope, average walking speeds and spatiotemporal gait parameters were similar regardless of self-paced controller sensitivity. With higher controller sensitivities on each slope, speed fluctuations, speed variance, and step length variance increased whereas step frequency variance and step width variance were unaffected. Detrended variance was not affected by controller sensitivity suggesting that detrending variability helps mitigate differences associated with treadmill speed fluctuations. Speed-trend step length variances, however, increased with more sensitive controllers. Further, detrended step length variances were similar for self-paced and fixed speed walking, whereas self-paced walking included substantial speed-trend step length variance not present in fixed speed walking. In addition, regardless of the self-paced controller, subjects walked fastest on the level slope with the longest steps, narrowest steps, and least variance. Overall, our findings suggest that separating gait variability into speed-trend and detrended variability could be beneficial for interpreting gait variability among multiple self-paced treadmill studies and when comparing self-paced walking with fixed speed walking.

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Speed-related but not detrended gait variability increases with more sensitive self-paced treadmill controllers at multiple slopes

10.1101/2021.01.27.428459 ◽

2021 ◽

Author(s):

Cesar R. Castano ◽

Helen J. Huang

Keyword(s):

Step Length ◽

Gait Variability ◽

The Self ◽

Step Width ◽

Step Frequency ◽

Gait Biomechanics ◽

Treadmill Speed ◽

Gait Parameters ◽

Walking Speeds ◽

Speed Fluctuations

AbstractSelf-paced treadmills are being used more and more to study humans walking with their self-selected gaits on a range of slopes. There are multiple options to purchase a treadmill with or implement a custom written self-paced controller, which raises questions about how self-paced controller affect treadmill speed and gait biomechanics on multiple slopes. This study investigated how different self-paced treadmill controller sensitivities affected gait parameters and variability on a decline, level, and incline slopes. We hypothesized that increasing self-paced controller sensitivity would increase gait variability on each slope. We also hypothesized that detrended variability could help mitigate differences in variability that arise from differences in speed fluctuations created by the self-paced controllers. Ten young adults walked on a self-paced treadmill using three self-paced controller sensitivities (low, medium, and high) and fixed speeds at three slopes (decline, −10°; level, 0°; incline, +10°). Within each slope, average walking speeds and spatiotemporal gait parameters were similar regardless of self-paced controller sensitivity. With higher controller sensitivities on each slope, speed fluctuations, speed variance, and step length variance increased whereas step frequency variance and step width variance were unaffected. Detrended variance was not affected by controller sensitivity suggesting that detrending variability helps mitigate differences associated with treadmill speed fluctuations. Speed-trend step length variances, however, increased with more sensitive controllers. Further, detrended step length variances were similar for self-paced and fixed speed walking, whereas self-paced walking included substantial speed-trend step length variance not present in fixed speed walking. In addition, regardless of the self-paced controller, subjects walked fastest on the level slope with the longest steps, widest steps, and least variance. Overall, our findings suggest that separating gait variability into speed-trend and detrended variability could be beneficial for interpreting gait variability among multiple self-paced treadmill studies and when comparing self-paced walking with fixed speed walking.

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Fast visual prediction and slow optimization of preferred walking speed

Journal of Neurophysiology ◽

10.1152/jn.00866.2011 ◽

2012 ◽

Vol 107 (9) ◽

pp. 2549-2559 ◽

Cited By ~ 35

Author(s):

Shawn M. O'Connor ◽

J. Maxwell Donelan

Keyword(s):

Nervous System ◽

Healthy Subjects ◽

Walking Speed ◽

Prior Experience ◽

Sensory Information ◽

Energetic Cost ◽

The Subject ◽

Walking Speeds ◽

Visual Speed ◽

Direction Opposite

People prefer walking speeds that minimize energetic cost. This may be accomplished by directly sensing metabolic rate and adapting gait to minimize it, but only slowly due to the compounded effects of sensing delays and iterative convergence. Visual and other sensory information is available more rapidly and could help predict which gait changes reduce energetic cost, but only approximately because it relies on prior experience and an indirect means to achieve economy. We used virtual reality to manipulate visually presented speed while 10 healthy subjects freely walked on a self-paced treadmill to test whether the nervous system beneficially combines these two mechanisms. Rather than manipulating the speed of visual flow directly, we coupled it to the walking speed selected by the subject and then manipulated the ratio between these two speeds. We then quantified the dynamics of walking speed adjustments in response to perturbations of the visual speed. For step changes in visual speed, subjects responded with rapid speed adjustments (lasting <2 s) and in a direction opposite to the perturbation and consistent with returning the visually presented speed toward their preferred walking speed, when visual speed was suddenly twice (one-half) the walking speed, subjects decreased (increased) their speed. Subjects did not maintain the new speed but instead gradually returned toward the speed preferred before the perturbation (lasting >300 s). The timing and direction of these responses strongly indicate that a rapid predictive process informed by visual feedback helps select preferred speed, perhaps to complement a slower optimization process that seeks to minimize energetic cost.

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Increasing the gradient of energetic cost does not initiate adaptation in human walking

Journal of Neurophysiology ◽

10.1152/jn.00311.2020 ◽

2021 ◽

Author(s):

Surabhi N Simha ◽

Jeremy D. Wong ◽

Jessica C Selinger ◽

Sabrina J Abram ◽

J. Maxwell Donelan

Keyword(s):

Nervous System ◽

Lower Cost ◽

Cost Savings ◽

Control Policy ◽

Human Walking ◽

Energetic Cost ◽

Mechatronic System ◽

Step Frequency ◽

Normalized Units ◽

New Situation

When in a new situation, the nervous system may benefit from adapting its control policy. In determining whether or not to initiate this adaptation, the nervous system may rely on some features of the new situation. Here we tested whether one such feature is salient cost savings. We changed cost saliency by manipulating the gradient of participants' energetic cost landscape during walking. We hypothesized that steeper gradients would cause participants to spontaneously adapt their step frequency to lower costs. To manipulate the gradient, a mechatronic system applied controlled fore-aft forces to the waist of participants as a function of their step frequency as they walked on a treadmill. These forces increased the energetic cost of walking at high step frequencies and reduced it at low step frequencies. We successfully created three cost landscapes of increasing gradients, where the natural variability in participants' step frequency provided cost changes of 3.6% (shallow), 7.2% (intermediate) and 10.2% (steep). Participants did not spontaneously initiate adaptation in response to any of the gradients. Using metronome-guided walking-a previously established protocol for eliciting initiation of adaptation-participants next experienced a step frequency with a lower cost. Participants then adapted by -1.41±0.81 (p=0.007) normalized units away from their originally preferred step frequency obtaining cost savings of 4.80±3.12% That participants would adapt under some conditions, but not in response to steeper cost gradients, suggests that the nervous system does not solely rely on the gradient of energetic cost to initiate adaptation in novel situations.

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A mechatronic system for studying energy optimization during walking.

10.1101/496489 ◽

2018 ◽

Cited By ~ 1

Author(s):

Surabhi N Simha ◽

J. Maxwell Donelan

Keyword(s):

Nervous System ◽

System Design ◽

Human Movement ◽

Human Walking ◽

Energetic Cost ◽

Mechatronic System ◽

Step Frequency ◽

Coordination Strategies ◽

Design Build ◽

Optimal Coordination

A general principle of human movement is that our nervous system is able to learn optimal coordination strategies. However, how our nervous system performs this optimization is not well understood. Here we design, build, and test a mechatronic system to probe the algorithms underlying optimization of energetic cost in walking. The system applies controlled fore-aft forces to a hip-belt worn by a user, decreasing their energetic cost by pulling forward or increasing it by pulling backward. The system controls the forces, and thus energetic cost, as a function of how the user is moving. In testing, we found that the system can quickly, accurately, and precisely apply target forces within a walking step. We next controlled the forces as a function of the user's step frequency and found that we could predictably reshape their energetic cost landscape. Finally, we tested whether users adapted their walking in response to the new cost landscapes created by our system, and found that users shifted their step frequency towards the new energetic minima. Our system design appears to be effective for reshaping energetic cost landscapes in human walking to study how the nervous system optimizes movement.

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Increasing the gradient of energetic cost does not initiate adaptation in human walking

10.1101/2020.05.20.107250 ◽

2020 ◽

Author(s):

Surabhi N. Simha ◽

Jeremy D. Wong ◽

Jessica C. Selinger ◽

Sabrina J. Abram ◽

J. Maxwell Donelan

Keyword(s):

Nervous System ◽

Lower Cost ◽

Cost Savings ◽

Control Policy ◽

Human Walking ◽

Energetic Cost ◽

Mechatronic System ◽

Step Frequency ◽

Normalized Units ◽

New Situation

AbstractWhen in a new situation, the nervous system may benefit from adapting its control policy. In determining whether or not to initiate this adaptation, the nervous system may rely on some features of the new situation. Here we tested whether one such feature is salient cost savings. We changed cost saliency by manipulating the gradient of participants’ energetic cost landscape during walking. We hypothesized that steeper gradients would cause participants to spontaneously adapt their step frequency to lower costs. To manipulate the gradient, a mechatronic system applied controlled fore-aft forces to the waist of participants as a function of their step frequency as they walked on a treadmill. These forces increased the energetic cost of walking at high step frequencies and reduced it at low step frequencies. We successfully created three cost landscapes of increasing gradients, where the natural variability in participants’ step frequency provided cost changes of 3.6% (shallow), 7.2% (intermediate) and 10.2% (steep). Participants did not spontaneously initiate adaptation in response to any of the gradients. Using metronome-guided walking— a previously established protocol for eliciting initiation of adaptation—participants next experienced a step frequency with a lower cost. Participants then adapted by −1.41±0.81 (p=0.007) normalized units away from their originally preferred step frequency obtaining cost savings of 4.80±3.12%. That participants would adapt under some conditions, but not in response to steeper cost gradients, suggests that the nervous system does not solely rely on the gradient of energetic cost to initiate adaptation in novel situations.

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