Biology subjects

Finley, J. M.

Publications and source records attributed to Finley, J. M..

14 recordsLinked to original sources

bioRxiv2026

Competition Between Task Accuracy and Habitual Locomotor Behavior Underlies the Speed-Accuracy Trade-Off in Walking

The speed-accuracy trade-off is a hallmark feature of motor behavior, yet its underlying causes in cyclic, whole-body movements such as walking remain to be understood. In discrete, point-to-point movements, reduced accuracy at higher speeds is typically attributed to signal-dependent motor noise and an inability to use online error correction. Walking, however, may be governed by additional objectives, such as minimizing metabolic energy expenditure. To distinguish between these mechanisms, we tested young adults in a precision-walking task requiring them to match target step lengths across a range of treadmill speeds. Accuracy declined systematically as walking speed increased, demonstrating a locomotor speed-accuracy trade-off. Contrary to prevailing theory, removing online visual feedback of foot position did not affect this decline, indicating little contribution from visually guided error correction. Moreover, step-length variability, a task-specific measure of signal-dependent motor noise, decreased rather than increased with speed. Instead, faster walking produced progressively larger biases toward participants' habitual step lengths measured in the absence of targets. Because habitual step lengths are known to closely approximate energetically optimal values, these findings suggest energetic optimization, rather than motor noise or limitations associated with the use of online feedback, as the primary driver of the speed-accuracy trade-off during walking.

biophysics↗

bioRxiv2025

Proactive adjustments to cued gait perturbations in people with and without chronic stroke

Balance disturbances exist along a continuum from those that are fully unexpected to those that are predictable based on cues from the environment. When people experience predictable disturbances while walking, they may proactively adjust their gait to minimize losses of balance. However, ones ability to effectively implement these proactive control strategies may be impaired after a stroke due to a combination of motor and cognitive impairments that result from brain lesions. Here, we used explicit audiovisual cues to characterize the proactive and reactive control strategies implemented by people with and without stroke during unexpected versus expected gait perturbations. Following unexpected treadmill accelerations, both groups had smaller margins of stability on the recovery step than during unperturbed walking. When we provided audiovisual cues specifying the impending perturbation step, people without stroke performed less leg and joint work, especially at the ankle, during the cued perturbations and increased their subsequent margins of stability by approximately 3 cm on the recovery step. However, people post-stroke did not make the same proactive adjustments. Instead, after any perturbation, they modified their stepping to maintain their center of mass position within their base of support, and this strategy remained unchanged with audiovisual cues. Our findings suggest that people post-stroke rely on a general control strategy rather than proactively modifying push-off work, even when given precise timing information about the impending gait perturbations.

physiology↗

bioRxiv2025

Perceived risk of forward versus backward balance disturbances while walking in young and older adults

Falls, which often result from trips or slips, pose a major health concern, particularly among older adults. Experiencing falls or near-falls from balance disturbances can shape subsequent gait-related decisions, as individuals may avoid situations they perceive as risky. Here, we explore whether perceptions of risk are sensitive to the direction of previously experienced balance disturbances - forward or backward - and whether these perceptions change with age. Twenty young and twenty older adults walked on a split-belt treadmill while performing a two-alternative forced-choice task, where they indicated their preference between a forward-falling trip and a backward-falling slip. We varied the perturbation magnitudes using an adaptive staircase algorithm to obtain multiple trip-slip equivalence points. Using a mixed- effects linear model, we estimated the slope of the trip-slip relationship, which quantified the direction and strength of the sensitivity of perceived risk to perturbation type. To assess reliability, we repeated the procedure on a second day. Additionally, we investigated two potential reasons underlying any observed sensitivity - 1) emotional responses measured by state anxiety, and 2) physical responses measured by peak center of mass velocity. We found that both young and older adults perceived slips to be riskier than trips, with no group difference in sensitivity. The relative sensitivity to slips versus trips was moderately reliable across two days of testing, though most participants were less sensitive to perturbation direction on the second day. Neither state anxiety responses nor peak center of mass (CoM) velocity explained the directional sensitivity, though CoM velocity was higher during slips than trips for both age groups. These results suggest that the characteristics of experienced balance disturbances may influence behavioral decisions. Objectively measuring individual differences in the perceived risk of balance disturbances and the ability to recover from these disturbances, can potentially improve fall risk assessment and inform personalized training interventions.

neuroscience↗

bioRxiv2024

Identification of distinct subtypes of post-stroke and neurotypical gait behaviors using neural network analysis of kinematic time series data

BackgroundHeterogeneous types of gait impairment are common post-stroke. Studies used supervised and unsupervised machine learning on discrete biomechanical features to summarize the gait cycle and identify common patterns of gait behaviors. However, discrete features cannot account for temporal variations that occur during gait. Here, we propose a novel machine-learning pipeline to identify subgroups of gait behaviors post-stroke using kinematic time series data. MethodsWe analyzed ankle and knee kinematic data during treadmill walking data in 39 individuals post- stroke and 28 neurotypical controls. The data were first input into a supervised dual-stage Convolutional Neural Network-Temporal Convolutional Network, trained to extract temporal and spatial gait features. Then, we used these features to find clusters of different gait behaviors using unsupervised time series k-means. We repeated the clustering process using 10,000 bootstrap training data samples and a Gaussian Mixture Model to identify stable clusters representative of our dataset. Finally, we assessed the kinematic differences between the identified clusters using 1D statistical parametric mapping ANOVA. We then compared gait spatiotemporal and clinical characteristics between clusters using one-way ANOVA. ResultsWe obtained five clusters: two clusters of neurotypical individuals (C1 and C2) and three clusters of individuals post-stroke (S1, S2, S3). C1 had kinematics that resembled the normative gait pattern. Individuals in C2 had a shorter stride time than C1. Individuals in S1 had mild impairment and walked with increased bilateral knee flexion during the loading response. Individuals in S2 had moderate impairment, were the slowest among the clusters, took shorter steps, had increased knee flexion during stance bilaterally and reduced paretic knee flexion during swing. Individuals in S3 had mild impairment, asymmetric swing time, had increased ankle abduction during the gait cycle and reduced dorsiflexion bilaterally during loading response and stance. Every individual was assigned to a cluster with a cluster membership likelihood above 93%. ConclusionsOur results indicate that joint kinematics in individuals post-stroke are distinct from controls, even in those individuals with mild impairment. The three subgroups post-stroke showed distinct kinematic impairments during specific phases in the gait cycle, providing additional information to clinicians for gait retraining interventions.

bioengineering↗

bioRxiv2024

Stroke impairs the proactive control of dynamic balance during predictable treadmill accelerations

We maintain balance during gait using both proactive and reactive control strategies. Damage to the brain from a stroke impairs reactive balance, but little is known about how a stroke impacts proactive control during walking. Stroke-related impairments to proactive control could become targets for interventions designed to improve responses to predictable disturbances and reduce fall risk. Therefore, we determined if proactive strategies during predictable treadmill accelerations differed between people post-stroke (n=14) and people without stroke (n=14). Both groups walked with accelerations at random (every one to five strides) and regular (every three strides) intervals. We quantified the effects of the perturbations as changes to center of mass (COM) speed and used mechanical leg work to quantify the proactive strategies to slow the COM. Participants without stroke reduced peak COM speed better than those with stroke when perturbations were regular (-0.016 versus +0.004 m/s; p=0.007). They also reduced positive leg work more during the perturbation step than the group post-stroke (-5.7% versus +2.5%; p=0.003). One implication of these findings is that people post-stroke may be more susceptible to falls during predictable gait disturbances, and future work should identify the underlying impairments that cause these deficits.

physiology↗

bioRxiv2024

Uncovering locomotor learning dynamics in people with Parkinson's disease

Locomotor learning is important for improving gait and balance impairments in people with Parkinsons disease (PD). While PD disrupts neural networks involved in motor learning, there is a limited understanding of how PD influences the time course of locomotor learning and retention. Here, we used a virtual obstacle negotiation task to investigate whether the early stages of PD affect the acquisition and retention of locomotor skills. On Day 1, 15 participants with PD and 20 age-matched controls were instructed to achieve a specified level of foot clearance while repeatedly stepping over two different virtual obstacles on a treadmill. We assessed online performance improvement on Day 1 and overnight retention after at least 24 hours on Day 2. We used a hierarchical Bayesian state-space model to estimate the learning rate and the degree of interference between the two obstacles. There was a 93% probability that people with PD learned the locomotor skill faster than controls, but there was limited evidence of group differences in interference between the two heights of obstacles. Both groups improved their performance to a similar magnitude during skill acquisition and performed similarly during retention on Day 2. Notably, a slower learning rate was associated with greater online performance improvement, while lower interference was linked to better overnight retention, and this effect was strongest for the control group. These results highlight that people with early-stage PD retain the ability to use multisensory information to acquire and retain locomotor skills. In particular, our finding that people with early-stage PD learned faster than age-matched controls may reflect the emergence of compensatory motor learning strategies used to offset early motor impairments in people with PD.

neuroscience↗

bioRxiv2023

Generalizability of foot-placement control strategies during unperturbed and perturbed gait

Control of foot placement is an essential strategy for maintaining balance during walking. During unperturbed, steady-state walking, foot placement can be accurately described as a linear function of the bodys center of mass state at midstance. However, it is uncertain if this mapping from center of mass state to foot placement generalizes to larger perturbations that may be more likely to cause falls. These perturbations may cause balance disturbances and generate reactive control strategies not observed during unperturbed walking. Here, we used unpredictable changes in treadmill speed to assess the generalizability of foot placement mappings identified during unperturbed walking. We found that foot placement mappings generalized poorly from unperturbed to perturbed walking and differed for forward versus backward perturbations. We also used singular value decomposition of the mapping matrix to reveal that people were more sensitive to backward versus forward perturbations. Together, these results indicate that control of foot placement during losses of balance differs from the control strategies used during unperturbed walking. Better characterization of human balance control strategies could improve our understanding of why different neuromotor disorders result in heightened fall risk and inform the design of controllers for balance-assisting devices.

bioengineering↗

bioRxiv2023

Aging modulates the effects of scene complexity on visual search in naturalistic virtual environments

Processing task-relevant visual information is important for many everyday tasks. Prior work demonstrated that older adults are more susceptible to distraction by salient task-irrelevant stimuli, leading to less efficient visual search. However, these studies often used simple stimuli, and less is known about how aging influences visual attention in environments more representative of real-world complexity. Here, we test the hypothesis that aging impacts how the visual complexity of the environment influences visual search. Young and older adults completed a virtual reality-based visual search task in environments with increasing visual complexity. As visual complexity increased, all participants exhibited longer times to complete the task which resulted from increased time transferring gaze from one correct target to the next and increased delay between when correct targets were fixated and selected. The increase in time to completion can also be attributed to longer times spent re-fixating task-relevant objects and fixating task-irrelevant objects. These changes in visual search and target selection with increasing visual complexity were greater in older adults and working memory capacity was associated with multiple performance measures in the visual search task. These findings suggest that visual search performance could be integrated into assessments of working memory in dynamic environments.

neuroscience↗

bioRxiv2022

Impairments in the mechanical effectiveness of reactive balance control strategies during walking in people post-stroke

People post-stroke have an increased risk of falls compared to neurotypical individuals, partly resulting from an inability to generate appropriate reactions to restore balance. However, few studies investigated the effect of paretic deficits on the mechanics of reactive control strategies following forward losses of balance during walking. Here, we characterized the biomechanical consequences of reactive control strategies following perturbations induced by the treadmill belt accelerations. Thirty-eight post-stroke participants and thirteen age-matched and speed-matched neurotypical participants walked on a dual-belt treadmill while receiving perturbations that induced a forward loss of balance. We computed whole-body angular momentum and angular impulse using segment kinematics and reaction forces to quantify the effect of impulse generation by both the leading and trailing limbs in response to perturbations in the sagittal plane. We found that perturbations to the paretic limb led to larger increases in forward angular momentum during the perturbation step than perturbations to the non-paretic limb or to neurotypical individuals. To recover from the forward loss of balance, neurotypical individuals coordinated reaction forces generated by both legs to decrease the forward angular impulse relative to the pre-perturbation step. They first decreased the forward pitch angular impulse during the perturbation step. Then, during the first recovery step, they increased the backward angular impulse by the leading limb and decreased the forward angular impulse by the trailing limb. In contrast to neurotypical participants, people post-stroke did not reduce the forward angular impulse generated by the stance limb during the perturbed step. They also did not increase leading limb angular impulse or decrease the forward trailing limb angular impulse using their paretic limb during the first recovery step. Lastly, post-stroke individuals who scored poorer on clinical assessments of balance and had greater motor impairment made less use of the paretic limb to reduce forward momentum. Overall, these results suggest that paretic deficits limit the ability to recover from forward loss of balance. Future perturbation-based balance training targeting reactive stepping response in stroke populations may benefit from improving the ability to modulate paretic ground reaction forces to better control whole-body dynamics.

bioengineering↗

bioRxiv2022

Speed-dependent biomechanical changes vary across individual gait metrics post-stroke relative to neurotypical adults

BackgroundGait training at fast speeds is recommended to reduce walking activity limitations post-stroke. Fast walking may also reduce gait kinematic impairments post-stroke. However, the magnitude of speed-dependent kinematic impairment reduction in people post-stroke relative to neurotypical adult walking patterns is unknown. ObjectiveTo determine the effect of faster walking speeds on gait kinematics post-stroke relative to neurotypical adults walking at similar speeds. MethodsWe performed a secondary analysis with data from 28 people post-stroke and 50 neurotypical adults treadmill walking at multiple speeds. We evaluated the effects of speed and group on individual spatiotemporal and kinematic metrics and performed k-means clustering with all metrics at self-selected and fast speeds ResultsPeople post-stroke decreased step length asymmetry and trailing limb angle impairment, reducing between-group differences at fast speeds. Speed-dependent changes in peak swing knee flexion, hip hiking, and temporal asymmetries exaggerated between-group differences. Our clustering analyses revealed two clusters. One represented neurotypical gait behavior, composed of neurotypical and post-stroke participants. The other characterized stroke gait behavior, comprised entirely of participants post-stroke. Cluster composition was largely consistent at both speeds, and the distance between clusters increased at fast speeds ConclusionsThe biomechanical effect of fast walking post-stroke varied across individual gait metrics. For participants within the stroke gait behavior cluster, speed-dependent changes did not lead to an overall gait pattern more similar to neurotypical adults. This suggests that combining fast walking with an approach to strategically target gait metrics with smaller speed-dependent changes may potentiate the biomechanical benefits of fast walking.

neuroscience↗

bioRxiv2021

Using Bayesian Inference to Estimate Plausible Muscle Forces in Musculoskeletal Models

BackgroundMusculoskeletal modeling is currently a preferred method for estimating the muscle forces that underlie observed movements. However, these estimates are sensitive to a variety of assumptions and uncertainties, which creates difficulty when trying to interpret the muscle forces from musculoskeletal simulations. Here, we describe an approach that uses Bayesian inference to identify plausible ranges of muscle forces for a simple motion while representing uncertainty in the measurement of the motion and the objective function used to solve the muscle redundancy problem. MethodsWe generated a reference elbow flexion-extension motion by simulating a set of muscle excitation signals derived from the computed muscle control tool built into OpenSim. We then used a Markov Chain Monte Carlo (MCMC) algorithm to sample from a posterior probability distribution of muscle excitations that would result in the reference elbow motion trajectory. We constructed a prior over the excitation parameters which down-weighted regions of the parameter space with greater muscle excitations. We used muscle excitations to find the corresponding kinematics using OpenSim, where the error in position and velocity trajectories (likelihood function) was combined with the sum of the cubed muscle excitations integrated over time (prior function) to compute the posterior probability density. ResultsWe evaluated the muscle forces that resulted from the set of excitations that were visited in the MCMC chain (five parallel chains, 450,000 iterations per chain, runtime = 71 hours). The estimated muscle forces compared favorably with the reference motion from computed muscle control, while the elbow angle and velocity from MCMC matched closely with the reference with an average RMSE for angle and velocity equal to 0.008{degrees} and 0.18{degrees}/s, respectively. However, our rank plot analysis and potential scale reduction statistics, which we used to evaluate convergence of the algorithm, indicated that the parallel chains did not fully mix. ConclusionsWhile the results from this process are a promising step towards characterizing uncertainty in muscle force estimation, the computational time required to search the solution space with, and the lack of MCMC convergence indicates that further developments in MCMC algorithms are necessary for this process to become feasible for larger-scale models.

bioengineering↗

bioRxiv2019

Manual stabilization reveals a transient role for balance control during locomotor adaptation

A fundamental feature of human locomotor control is the need to adapt our walking pattern in response to changes in the environment. For example, when people walk on a split-belt treadmill which has belts that move at different speeds, they adapt to the asymmetric speed constraints by reducing their spatiotemporal asymmetry. Here, we aim to understand the role of stability as a potential factor driving this adaptation process. We recruited 24 healthy, young adults to adapt to walking on a split-belt treadmill while either holding on to a handrail or walking with free arm swing. We measured whole-body angular momentum and step length asymmetry as measures of dynamic balance and spatiotemporal asymmetry, respectively. To understand how changes in intersegmental coordination influenced measures of dynamic balance, we also measured segmental angular momenta and the coefficient of limb cancellation. When participants were initially exposed to the asymmetry in belt speeds, we observed an increase in whole-body angular momentum that was due to both an increase in the momentum of individual limb segments and a reduction in limb cancellation. Holding on to a handrail reduced the perturbation to asymmetry during the early phase of adaptation and resulted in a smaller after-effect during post-adaptation. In addition, the stabilization provided by holding on to a handrail led to reductions in the coupling between angular momentum and asymmetry. These results suggest that regulation of dynamic balance is most important during the initial, transient phase of adaptation to walking on a split-belt treadmill.\n\nSummary StatementRegulation of balance exhibits a transient effect on adaptation to imposed asymmetries during bipedal walking. External stabilization attenuates initial deviations in spatiotemporal asymmetry but has no effect on subsequent adaptation.

neuroscience↗

bioRxiv2018

Taking advantage of external mechanical work to reduce metabolic cost: the mechanics and energetics of split-belt treadmill walking

In everyday tasks such as walking and running, we exploit the work performed by external sources such as gravity to reduce the work performed by muscles. There has been considerable recent effort to design devices capable of performing mechanical work to improve walking function or reduce effort. The success of these devices relies on the user adapting their natural control strategies to take advantage of assistance provided by the device. Although locomotor adaptation is central to this process, the study of adaptation is often done using approaches that on the surface, seem to have little in common with the use of external assistance. Here, we show that one of the most common approaches for studying this process, which is adaptation to walking on a split-belt treadmill, can be understood from a perspective in which people learn to take advantage of mechanical work performed by the treadmill. During adaptation, people systematically adjust their step lengths, defined as the distance between the feet at heel strike, from one step to the next. Initially, the step length on the slow belt is longer than the step length on the fast belt, measured as a negative step length asymmetry, but people naturally reduce this asymmetry with practice. Here, we demonstrate that these modifications of step length asymmetry allow people to extract positive work from the treadmill belts to reduce the positive work performed by the legs and simultaneously reduce metabolic cost. Moreover, we show that walking with a positive step length asymmetry minimizes metabolic cost, and people prefer to walk in this manner when allowed to select their walking pattern. Together, our results suggest that split-belt adaptation can be interpreted as a process by which people learn to take advantage of mechanical work performed by an external device to improve walking economy.

neuroscience↗

bioRxiv2017

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

Changes 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.

physiology↗