Ongoing Projects

Proactive and Reactive Control of Balance during Walking in People Post-Stroke

Post-stroke motor and cognitive impairments can lead to falls, with approximately one-third of chronic stroke survivors reporting at least one fall within a one-year period. A gait perturbation, like a trip or slip, can result in a fall if an individual fails to use an appropriate balance control strategy. Balance is controlled using a combination of feedforward proactive control strategies and feedback-based reactive control strategies. Proactive strategies are used to modify the body’s state in advance of a perturbation, while reactive strategies generate motor commands based on movement errors. However, there are tradeoffs between the two balance control strategies; proactively preparing for a perturbation may require energetically costly changes to one’s gait – such as slower, wider steps – but can allow for a smaller subsequent reactive response. Relying solely on reactive control may be less energetically costly before the perturbation but then risks instability, especially for those with neurologic injury. Our ongoing work examines how perturbation predictability impacts proactive and reactive balance control during walking in older adults and people post-stroke.

Factors Influencing the Energetic Cost of Walking in People Post-Stroke
Hemiparetic gait, which is characterized by weakness on one side of the body, is associated with many walking abnormalities. For example, stroke survivors walk at slower speeds and with a higher metabolic cost than healthy individuals. Also, their gait is asymmetric, with different values of kinematic and kinetic parameters between the paretic and non-paretic sides, such as differences in stance and swing times, double support times, joint power, joint excursions, and step lengths. Typically, the spatiotemporal asymmetries observed during a hemiparetic gait are considered to be impairments or deviations at the level of body function and activity. However, in the absence of complete repair at the neural level, stroke survivors will always have a marked asymmetry in the neural circuits responsible for walking. As a result, it is possible that the symmetric movement patterns observed in healthy individuals may no longer be optimal given the constraints imposed by brain lesions.

Here, we aim to understand whether there are functional benefits to restoring spatiotemporal gait symmetry for stroke survivors to a level considered “normal” for non-impaired individuals. To answer this question, we must first select a set of metrics by which the “quality” of an individual’s walking pattern can be evaluated. We primarily use measures of walking economy, characterized by the metabolic cost of walking at a given speed, measures of dynamic stability, perceived effort, and patient preference to capture how changes in spatiotemporal coordination impact the quality of walking in people post-stroke. We ultimately hope that our work will be used to guide patient-specific interventions for gait rehabilitation. 

Publications

1. Sánchez N, Schweighofer N, Mulroy SJ, Roemmich RT, Kesar TM, Torres-Oviedo G, Fisher BE, Finley JM§, Winstein CJ§. (2023). Multi-site identification and generalization of clusters of walking impairment in individuals with chronic stroke. Neurorehabilitation and Neural Repair. 37: 810-822.
2. Kettlety SA, Finley JM, Reisman DS, Schweighofer S, and Leech KA. (2023). Speed-dependent biomechanical changes vary across individual gait metrics post-stroke relative to neurotypical adults. Journal of Neuroengineering and Rehabilitation. 20(1):14.
3. ​​Liu C, McNitt-Gray JL, Finley JM. (2022). Impairments in the mechanical effectiveness of reactive balance control strategies during walking in people post-stroke. Frontiers in Neurology. 13:1032417.
4. Johnson RT, Bianco NA, and Finley JM. (2022). Patterns of asymmetry and energy cost generated from predictive simulations of hemiparetic gait. PLOS Computational Biology. 18 (9) e1010466.
5. Sánchez N, Schweighofer N, Finley JM. (2021). Different biomechanical variables explain within-subjects versus between-subjects variance in step length asymmetry post-stroke. IEEE Trans Neural Syst Rehabil Eng. 2021;29:1188-1198. doi: 10.1109/TNSRE.2021.3090324.
6. S Park, C Liu, N Sánchez, JK. Tilson, SJ. Mulroy, and JM. Finley. Using biofeedback to reduce spatiotemporal asymmetry impairs dynamic balance in people post-stroke. Neurorehabil Neural Repair. 2021 Jun 1;:15459683211019346. doi: 10.1177/15459683211019346.
7. Buurke TJW, Liu C, Park S, den Otter R, Finley JM. (2020). Maintaining sagittal plane balance compromises frontal plane balance during reactive stepping in people post-stroke. Clinical Biomechanics, 80.
8. ​Sánchez, Natalia, and James M. Finley. (2018). Individual Differences in Locomotor Function Predict the Capacity to Reduce Asymmetry and Modify the Energetic Cost of Walking Poststroke. Neurorehabilitation and neural repair 32.8 (2018): 701-713.
9. J.M. Finley and A.J. Bastian. (2017). Associations between Foot Placement Asymmetries and Metabolic Cost of Transport in Hemiparetic Gait. Neurorehabilitation and Neural Repair. 31, 168-177. 
10. J.M. Finley, A. Long, A.J.Bastian, and G. Torres-Oviedo (2015). Spatial and Temporal Control Contribute to Step Length Asymmetry during Split-Belt Adaptation and Hemiparetic Gait. Neurorehabilitation and Neural Repair. 29:786-95.
11. R. D. Trumbower*, J. M. Finley*, J.Shemmell, C. F. Honeycutt, E. J. Perreault. (2013). Bilateral Impairments in Task-Dependent Modulation of the Long-Latency Stretch Reflex Following Stroke. Clinical Neurophysiology. 124,1373-1380 
12. J.M. Finley, E.J. Perreault, Y.Y. Dhaher.(2008). Stretch Reflex Coupling Between the Hip and Knee:Implications for Impaired Gait Following Stroke. Experimental Brain Research 131, 305-319

Funding