Biology subjects

Kreter, N.

Publications and source records attributed to Kreter, N..

6 recordsLinked to original sources

bioRxiv2025

Effects of Unexpected Underfoot Perturbations During Turning on Measures of Mediolateral Stability and Corresponding Recovery Strategies

Humans regularly walk across uneven terrain, which demands the use of reactive control strategies to maintain forward progress and stability. While reactive control during walking has been well described during straight gait, it is unclear how reactive control differs during turning gait. Because turning is asymmetrical, perturbations to the inside and outside limbs may elicit different reactive adjustments. This study investigates how unexpected underfoot perturbations alter stability measures during turning and how individuals alter their foot placement to maintain stability after such perturbations. Seven healthy adults completed walking trials around a circular track while wearing mechanized shoes that pseudo-randomly delivered underfoot perturbations to either the inside or outside limb. We calculated mediolateral margin of stability corrected for centripetal acceleration (ML MoSC), step width, and step length from kinematic data. Linear mixed effects models compared the effects of perturbation type (inversion vs eversion), perturbation limb (inside vs outside), and their interaction for each outcome measure. ML MoSC was affected by both perturbation type and perturbation limb, with larger changes observed during eversion, and outside, perturbations. Changes to step width and step time during two recovery steps after each perturbation were primarily influenced by the perturbation limb - outside perturbations elicited consistent changes during two recovery steps compared to one altered step after inside perturbations. Perturbations to the outside limb during turning disrupt gait longer than perturbations to the inside limb. This difference across perturbation limb may indicate that outside steps are more important to maintaining and recovering stability than inside ones during turning.

bioengineering↗

bioRxiv2024

Behavioral risk models explain locomotor and balance changes when walking at virtual heights

Walking in daily life requires humans to adapt to environments that can influence ones fear of falling and anxiety about a potential fall. In such environments, individuals may adopt compensatory locomotor and balance changes to maintain a constant expected risk function equal to the product of the probability of some event (e.g., a fall) and the cost of that event (e.g., injury or death). Here, we tested whether locomotor behaviors broadly align with this risk model in two experiments with height-related threats in immersive virtual reality. In Experiment 1, we examined how individuals change their locomotor trajectory while walking along a straight high-elevation walkway. In Experiment 2, we examined how individuals change trajectory and balance control during curved walking where the location of high elevation threat varied. Participants adopted two behaviors that decreased their probability of falling off the edge and aligned with the risk-based model: participants altered their proximity to perceived threats that pose high costs (e.g., a high-elevation ledge), and decreased mediolateral center of mass velocity when that was not possible. Taken together, our results suggest that individuals alter locomotor behavior to change the probability of falling based on the perceived cost of that fall.

neuroscience↗

bioRxiv2024

Sensory context of initiation-cue modulates action goal-relevant neural representations

The ability to produce goal-directed movement relies on the integration of diverse sources of sensory information specific to the task goal. Neural representations of goal-relevant features, such as target location and gaze direction, have been well studied in sensorimotor areas. It remains less clear whether goal-relevant motor representations are influenced by sensory changes to initiation-relevant information, such as a go-cue that provides no information about target location. We used Bayesian pattern component modelling of fMRI data during a delayed reach task with either visual or audiovisual go-cues to explore whether neural representations of goal-related features in sensorimotor areas are modulated by changes to initiation-relevant sensory information. We found that representations of target direction and gaze direction in the primary sensory areas, motor areas, and posterior parietal cortex, were sensitive to whether a reach was cued with a visual or audiovisual go-cue. These findings indicate that the central nervous system flexibly delegates the tasks of where to move and when to move based on available sensory context, even if initiation-relevant stimuli provide no additional information about target location.

neuroscience↗

bioRxiv2024

Bases for the selection of alternate foot placement during straight- and turning-gait

Humans typically plan foot placement strategy multiple steps in advance when walking across complex terrain. Planning steps in advance is beneficial for both upright stability and forward progress, but one drawback is that new obstacles can make planned foot placement location unsafe between planning and execution, necessitating a rapid shift to foot placement that impacts stability and progress. This study investigates the bases for selection of alternate foot placement during both straight- and turning-gait. Thirteen healthy young adults walked along a virtually projected walkway with precision footholds oriented in either a straight line or with a single 60{degrees}, 90{degrees}, or 120{degrees} turn to the right. On a subset of trials, participants were required to rapidly avoid stepping on select footholds. We found stereotyped alternate foot placement strategies across turn angles that differed by turn strategy. Alternate foot placement for step turns supported the walkers instantaneous kinematics but not the planned change in trajectory; whereas foot placement for disrupted spin turns supported the walkers anticipated change in trajectory. We conclude that when humans are forced to rapidly alter previously developed motor plans for foot placement, they utilize a rapid stereotyped behavior that changes based on the demand of the turn.

bioengineering↗

bioRxiv2022

The Choice of Reference Frame Alters Interpretations of Non-Linear Gait

IntroductionHumans regularly follow non-linear trajectories, such as turning, during everyday ambulation. However, globally-defined and locally-defined reference frames fall out of alignment during non- linear locomotion, which complicates spatiotemporal and biomechanical analyses of gait. Thus, the choice of the locally-defined reference frame is an important methodological consideration. This study investigated how different definitions of reference frame change the results and interpretations of common gait measures. MethodsNine healthy adults completed two walking trials around a circular track. Kinematic data were collected via motion capture and used to calculate step length, step width, anteroposterior margin of stability, and mediolateral margin of stability using three different locally-defined reference frames: walkway-fixed, body-fixed, and trajectory-fixed. Linear-mixed effects models compared the effect of reference frame on each gait measure, and the effect of reference frame on conclusions about a known effect of turning gait - asymmetrical stepping patterns. ResultsAll four gait measures differed significantly across the three reference frames. A significant interaction of reference frame and step type (i.e. inside vs outside step) on all four gait measures (p < 0.001) indicated conclusions about asymmetry differed based on the choice of reference frame. ConclusionThe choice of reference frame will change the calculated gait measures and may alter the conclusions of studies investigating non-linear gait. Care should be taken when comparing studies that used different reference frames, as results cannot be easily harmonized. Future studies of non-linear gait need to justify and detail their choice of reference frame.

bioengineering↗

bioRxiv2022

The effects of physical and temporal certainty on locomotion with discrete underfoot perturbations

BackgroundAmbulation over complex terrain requires active control of foot placement to maintain a normal kinematic relationship between the center of mass and base of support. Recent investigations have suggested that foot placement location may be selected to anticipate shifts to the underfoot center of pressure. However, it is unclear whether temporal affordance and physical certainty contribute to the selection of a perturbation-specific anticipatory strategy. This study investigates anticipatory and reactive locomotor strategies for repeated underfoot perturbations with varying levels of temporal certainty, temporal affordance, and physical certainty. MethodsThirteen healthy adults walked with random underfoot perturbations from a mechanized shoe. Temporal certainty was challenged by presenting the perturbations with or without warning. Temporal affordance was challenged by adjusting the timing of a warning tone before the perturbation. Physical certainty was challenged with conditions that included only eversion perturbations, only inversion perturbations, or both eversion and inversion perturbations. Linear-mixed effects models assessed the effect of each condition on the percent change of margin of stability and step width, respectively. ResultsFor temporally uncertain perturbations and perturbations with one stride or less of affordance, we observed few changes to step width or margin of stability. As affordance increased to two strides, participants adopted a wider step width in anticipation of the perturbation (p = 0.001). Physical certainty had little effect on gait for the step of the perturbation, but participants recovered normal gait sooner when the physical nature of the perturbation was predictable (p < 0.001). DiscussionDespite having information about the timing and magnitude of upcoming perturbations, individuals do not develop perturbation specific feedforward strategies but instead rely on feedback control to recover normal gait after a perturbation. However, physical certainty appears to improve the efficiency of the feedback controller and allows individuals to recover normal gait sooner.

neuroscience↗