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1. Effects of protective step training on proactive and reactive motor adaptations in Parkinson’s disease patients

   https://doi.org/10.3389/fneur.2023.1211441  

   Lockhart, Thurmon; Frames, Chris; Olson, Markey; Moon, Seong H; Peterson, Dan; Lieberman, Abraham (October 2023, Frontiers in Neurology)

   The aim of this study was to investigate to what extent PD affects the ability to walk, respond to balance perturbations in a single training session, and produce acute short-term effects to improve compensatory reactions and control of unperturbed walking stability. Understanding the mechanism of compensation and neuroplasticity to unexpected step perturbation training during walking and static stance can inform treatment of PD by helping to design effective training regimens that remediate fall risk. Current rehabilitation therapies are inadequate at reducing falls in people with Parkinson’s disease (PD). While pharmacologic and surgical treatments have proved largely ineffective in treating postural instability and gait dysfunction in people with PD, studies have demonstrated that therapy specifically focusing on posture, gait, and balance may significantly improve these factors and reduce falls. The primary goal of this study was to assess the effectiveness of a novel and promising intervention therapy (protective step training – i.e., PST) to improve balance and reduce falls in people with PD. A secondary goal was to understand the effects of PST on proactive and reactive feedback responses during stance and gait tasks. Multiple-baseline, repeated measures analyses were performed on the multitude of proactive and reactive performance measures to assess the effects of PST on gait and postural stability parameters. In general, the results indicate that participants with PD were able to use experiences with perturbation training to integrate and adapt feedforward and feedback behaviors to reduce falls. The ability of the participants with PD to adapt to changes in task demands suggests that individuals with PD could benefit from the protective step training to facilitate balance control during rehabilitation. 

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2. Real-time feedback control of split-belt ratio to induce targeted step length asymmetry

   https://doi.org/10.1186/s12984-022-01044-0  

   Carr, Sean; Rasouli, Fatemeh; Kim, Seok Hun; Reed, Kyle B. (December 2022, Journal of NeuroEngineering and Rehabilitation)

   Abstract Introduction Split-belt treadmill training has been used to assist with gait rehabilitation following stroke. This method modifies a patient’s step length asymmetry by adjusting left and right tread speeds individually during training. However, current split-belt training approaches pay little attention to the individuality of patients by applying set tread speed ratios (e.g., 2:1 or 3:1). This generalization results in unpredictable step length adjustments between the legs. To customize the training, this study explores the capabilities of a live feedback system that modulates split-belt tread speeds based on real-time step length asymmetry. Materials and methods Fourteen healthy individuals participated in two 1.5-h gait training sessions scheduled 1 week apart. They were asked to walk on the Computer Assisted Rehabilitation Environment (CAREN) split-belt treadmill system with a boot on one foot to impose asymmetrical gait patterns. Each training session consisted of a 3-min baseline, 10-min baseline with boot, 10-min feedback with boot (6% asymmetry exaggeration in the first session and personalized in the second), 5-min post feedback with boot, and 3-min post feedback without boot. A proportional-integral (PI) controller was used to maintain a specified step-length asymmetry by changing the tread speed ratios during the 10-min feedback period. After the first session, a linear model between baseline asymmetry exaggeration and post-intervention asymmetry improvement was utilized to develop a relationship between target exaggeration and target post-intervention asymmetry. In the second session, this model predicted a necessary target asymmetry exaggeration to replace the original 6%. This prediction was intended to result in a highly symmetric post-intervention step length. Results and discussion Eleven out of 14 participants (78.6%) developed a successful relationship between asymmetry exaggeration and decreased asymmetry in the post-intervention period of the first session. Seven out of the 11 participants (63.6%) in this successful correlation group had second session post-intervention asymmetries of < 3.5%. Conclusions The use of a PI controller to modulate split-belt tread speeds demonstrated itself to be a viable method for individualizing split-belt treadmill training. 

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3. Evoking Cutaneous Reflexes During Human Walking II. An Open‐Source Pseudo‐Randomization Approach

   https://doi.org/10.1002/cpz1.70219  

   Benites, Colin E; Espinoza, Francisco; Arellano, Christopher J (November 2025, Current Protocols)

   Abstract This paper, the second in a two‐part series, outlines a low‐cost, open‐source, pseudo‐randomization approach for measuring cutaneous reflexes during human walking. The protocol guides users through integrating an Arduino Uno microcontroller, a VICON data acquisition system, and an electrical stimulation device. A custom code was developed in C++, and steps are provided to guide users in downloading and integrating it with an Arduino. This setup provides researchers the ability to define key experimental parameters such as the number of gait cycles to include in quantifying the average time of the subject's walking gait cycle, the number of bins to partition the human walking gait cycle, and the number of stimuli per bin—all while maintaining real‐time stimulation capability. During a walking trial, the system is designed to (1) deliver stimuli pseudo‐randomly using instances when the foot makes initial contact with the treadmill surface and (2) deliver an even distribution of stimuli across all bins. Real‐time feedback mechanisms and data monitoring are enabled via an integrated Arduino and VICON framework, allowing researchers to conduct controlled, repeatable experiments that aim to measure cutaneous reflexes during human walking. This protocol provides a flexible and accessible solution for researchers aiming to investigate phase‐dependent modulation of reflexes during normal and perturbed walking conditions. Its modularity and integration with existing motion capture systems make it a powerful tool for both basic and clinical research within the fields of neuroscience, biomechanics, and gait rehabilitation. © 2025 Wiley Periodicals LLC. Basic Protocol 1: Integrating Arduino to VICON data acquisition and stimulator Basic Protocol 2: Downloading and running pseudo‐randomized Arduino code 

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4. Treadmill vs. overground walking: different response to physical interaction

   https://doi.org/10.1152/jn.00176.2017  

   Ochoa, Julieth; Sternad, Dagmar; Hogan, Neville (October 2017, Journal of Neurophysiology)

   Rehabilitation of human motor function is an issue of growing significance, and human-interactive robots offer promising potential to meet the need. For the lower extremity, however, robot-aided therapy has proven challenging. To inform effective approaches to robotic gait therapy, it is important to better understand unimpaired locomotor control: its sensitivity to different mechanical contexts and its response to perturbations. The present study evaluated the behavior of 14 healthy subjects who walked on a motorized treadmill and overground while wearing an exoskeletal ankle robot. Their response to a periodic series of ankle plantar flexion torque pulses, delivered at periods different from, but sufficiently close to, their preferred stride cadence, was assessed to determine whether gait entrainment occurred, how it differed across conditions, and if the adapted motor behavior persisted after perturbation. Certain aspects of locomotor control were exquisitely sensitive to walking context, while others were not. Gaits entrained more often and more rapidly during overground walking, yet, in all cases, entrained gaits synchronized the torque pulses with ankle push-off, where they provided assistance with propulsion. Furthermore, subjects entrained to perturbation periods that required an adaption toward slower cadence, even though the pulses acted to accelerate gait, indicating a neural adaptation of locomotor control. Lastly, during 15 post-perturbation strides, the entrained gait period was observed to persist more frequently during overground walking. This persistence was correlated with the number of strides walked at the entrained gait period (i.e., longer exposure), which also indicated a neural adaptation. NEW & NOTEWORTHY We show that the response of human locomotion to physical interaction differs between treadmill and overground walking. Subjects entrained to a periodic series of ankle plantar flexion torque pulses that shifted their gait cadence, synchronizing ankle push-off with the pulses (so that they assisted propulsion) even when gait cadence slowed. Entrainment was faster overground and, on removal of torque pulses, the entrained gait period persisted more prominently overground, indicating a neural adaptation of locomotor control. 

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5. Using robot-assisted stiffness perturbations to evoke aftereffects useful to post-stroke gait rehabilitation

   https://doi.org/10.3389/frobt.2022.1073746  

   Chambers, Vaughn; Artemiadis, Panagiotis (January 2023, Frontiers in Robotics and AI)

   Stroke is a major global issue, affecting millions every year. When a stroke occurs, survivors are often left with physical disabilities or difficulties, frequently marked by abnormal gait. Post-stroke gait normally presents as one of or a combination of unilaterally shortened step length, decreased dorsiflexion during swing phase, and decreased walking speed. These factors lead to an increased chance of falling and an overall decrease in quality of life due to a reduced ability to locomote quickly and safely under one’s own power. Many current rehabilitation techniques fail to show lasting results that suggest the potential for producing permanent changes. As technology has advanced, robot-assisted rehabilitation appears to have a distinct advantage, as the precision and repeatability of such an intervention are not matched by conventional human-administered therapy. The possible role in gait rehabilitation of the Variable Stiffness Treadmill (VST), a unique, robotic treadmill, is further investigated in this paper. The VST is a split-belt treadmill that can reduce the vertical stiffness of one of the belts, while the other belt remains rigid. In this work, we show that the repeated unilateral stiffness perturbations created by this device elicit an aftereffect of increased step length that is seen for over 575 gait cycles with healthy subjects after a single 10-min intervention. These long aftereffects are currently unmatched in the literature according to our knowledge. This step length increase is accompanied by kinematics and muscle activity aftereffects that help explain functional changes and have their own independent value when considering the characteristics of post-stroke gait. These results suggest that repeated unilateral stiffness perturbations could possibly be a useful form of post-stroke gait rehabilitation. 

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