Advanced Techniques in Gait Adaptation and Perturbation Training
Introduction to Gait Adaptation and Perturbation Training
With the global focus on fall prevention and maintaining community independence, assessment of gait asymmetries and perturbation responses have been the subject of rehabilitation research over the past decade. Task-specific stepping interventions are effective in reducing fall rates by 52% across healthy, those with high fall risk, community-dwelling, and institutionalized elders compared to exercise interventions (16%) or exercise and balance training (38%) alone (Okubo, 2016). Therefore, gait adaptation and perturbation training are valuable components in rehabilitation. This blog post explores approaches to gait adaptation and perturbation training using visual and platform perturbations on the Bertec CDP and split-belt perturbations on the FIT5 Instrumented treadmill.
Importance of Gait Adaptation in Fall Prevention
Walking is a highly adaptable motor skill, constantly adjusting to task and environmental demands to maintain rhythmic and stable steps. These movement patterns include both rapid reactive automatic responses and slower adaptive strategies. For example, when walking on an unfamiliar slippery surface, we must react quickly to overcome unpredictable perturbations to avoid a slip and fall; these automatic reactive sensory feedback strategies involve the vestibulospinal and spinal reflexes. With practice (e.g. taking smaller, slower steps when encountering a slippery surface), adaptation occurs through voluntary feedforward predictive anticipatory motor control involving the cerebellum. Task-specific split-belt gait adaptation training targets both the automatic and adaptive motor control strategies (Ogawa, 2015), while perturbation training targets the reactive responses.
Split-Belt Treadmill Training for Gait Asymmetries
Gait asymmetries occurring in neurological disorders (e.g. Parkinson’s Disease, Stroke) often result in functional impairments that can be addressed via split-belt treadmill rehabilitation. During split-belt training, the belts either move together (tied-belt) or at different speeds (split-belt). Gait training focusing on adaptation typically starts with the tied-belt condition, followed by split-belt conditions to facilitate motor learning, and finishing with the tied-belt conditions. To correct the asymmetry, the limb with the shorter step length is placed on the fast belt. The blog introducing the FIT5 instrumented treadmill highlighted such a gait adaptation protocol (Sato and Choi, 2019).
Types of Perturbation Training: Trips and Slips
Balance challenges simulating trips or slips can be induced by unexpected surface perturbations using either a moving platform (like the Bertec CDP) or instrumented treadmills such as the FIT5. Trips contribute more to falls than slips although slips are more demanding for gait recovery than trips due to the smaller margin of backward stability. Stopping the treadmill belt causes a trip perturbation, requiring a compensatory forward step. Slip perturbations lead to a backward loss of balance and prompt a quicker initial step with the opposite limb compared to trip perturbations. Accelerating the belt (e.g., from 10 m/s² to 20 m/s²) causes a slip perturbation, leading to a backward loss of balance and prompting a quicker initial step with the opposite limb, compared to a trip.
Implementing Perturbation Protocols with the FIT5 Treadmill
The FIT5 user can utilize the advanced remote control API interface with external devices to precisely time treadmill perturbations. This can be done randomly during quiet standing or at specific points in the gait cycle such as just after heel strike or at midstance. For example, Shih’s (2023) trip perturbation protocol was triggered by a vertical GRF (20-25% body weight) during the early stance phase of gait to precisely deliver a sudden deceleration of the belt for 50 ms to simulate a trip perturbation, followed by an acceleration for 270 ms, and finally deceleration for another 220 ms to return to the initial comfortable walking speed.
Visual and Surface Perturbations in Training
Recovery responses are more consistent for slips and trips induced by treadmill perturbations compared to overground perturbations by therapist-applied techniques. Overground generalized strength and balance training programs often fail to effectively translate into task-specific fall prevention training due to the distinct biomechanical responses required for balance recovery. These programs lack the rapid, sequential changes in joint kinetics and the coordinated nervous system responses needed for lower extremity muscle activation during automatic stepping responses. An earlier blog post introduced task-specific perturbation training and provided examples of perturbation training design using platform and visual perturbations (https://www.bertec.com/blog/perturbation-training-part-1).
The immersive visual environment provided by the CDP or the fully immersive head-mounted display (HMD) can deliver visual perturbations of a given scene, offering inadequate or conflicting visual feedback. Users can select from a variety of scenes and variables to control the patient's visual environment. Sway-referenced platform tilt or translation perturbations can be introduced to increase complexity and task specificity. Combining surface and visual perturbations creates more realistic and task-specific stimuli for motor learning. Conversely, during treadmill slip and trip perturbations, sensory information is primarily perceived through the somatosensory system. To be effective, perturbation types (tilt, translation, split belt slip or trip), as well as their magnitude and direction, should be carefully considered when designing a perturbation training program to leverage learning principles effectively. The CDP and the split-belt treadmill provide various combinations to manipulate sensory information for the visual and proprioceptive systems. The harness system on both devices provides a safe and controlled environment, especially in patients with high anxiety levels and fear of falling.
Benefits of Task-Specific Perturbation Training
Trip-specific split-belt treadmill training has been shown to significantly reduce the relative risk of falls within just two weeks of twice-weekly sessions (Grabiner, 2014). Larger split-belt perturbations provide greater challenges, resulting in enhanced motor learning and metabolic efficiency (Bogard, 2021). While many treadmill or platform-based environmental perturbations are large and fast to elicit a stepping response to quickly increase the base of support, some individuals may not have the ability or space to step or execute a complex reflexive movement. Voluntary tasks such as bending over to pick up an object, turning, or reaching with an extended arm generate movements that disrupt balance but don’t result in a stepping response. For example, an alternate perturbation protocol involves training non-stepping postural responses by establishing a stepping threshold, followed by a block training paradigm of 60 perturbations just below the stepping threshold during each session over 6-8 sessions (Barnes, 2023). Task learning specificity that occurs with repeated perturbations enhances postural control by shifting it from a reactive feedback loop to a predictive, anticipatory motor control strategy.
Conclusion and Key Points
Two motor control strategies targeted with split-belt treadmill adaptation training:
Rapid, reactive automatic responses; feedback; vestibulospinal and spinal reflex loops
Voluntary, predictive control; feedforward; cerebellum
Two perturbation types:
Trip: stop treadmill belt or translate the balance plate backward, compensatory forward step
Slip: accelerate treadmill belt or translate the balance plate forward, backward loss of balance
A wide range of perturbation paradigms have been used to successfully train both reactive and predictive responses (McCrum, 2017). The CDP platform and its immersive surround offer the ability to perform multisensory perturbation training while the FIT5 allows the user flexibility to design and implement a variety of adaptation and perturbation protocols in the clinical and research settings.
For more information, contact [email protected].
References:
Barnes, J. H., Eftekhar, A., Fake, T. T., Carmack, C. S., Greenberg, E. W., Crenshaw, J. R., & Wolpaw, J. R. (2023). Treadmill-based system for postural studies: Design and validation. Medical engineering & physics, 122, 104071. https://doi.org/10.1016/j.medengphy.2023.104071
Bogard, A. T., Hembree, T. G., Pollet, A. K., Smith, A. C., Ryder, S. C., Marzloff, G., & Tan, A. Q. (2024). Intermittent Hypoxia-Induced Enhancements in Corticospinal Excitability Predict Gains in Motor Learning and Metabolic Efficiency. Research Square, rs.3.rs-4259378. https://doi.org/10.21203/rs.3.rs-4259378/v1
Grabiner, M. D., Crenshaw, J. R., Hurt, C. P., Rosenblatt, N. J., & Troy, K. L. (2014). Exercise-Based Fall Prevention: Can You Be a Bit More Specific? Exercise and Sport Sciences Reviews, 42(4), 161–168. https://doi.org/10.1249/JES.0000000000000023
Lee, P.-Y., Gadareh, K., & Bronstein, A. M. (2014). Forward-backward postural protective stepping responses in young and elderly adults. Human Movement Science, 34, 137–146. https://doi.org/10.1016/j.humov.2013.12.010
McCrum, C., Gerards, M. H. G., Karamanidis, K., Zijlstra, W., & Meijer, K. (2017). A systematic review of gait perturbation paradigms for improving reactive stepping responses and falls risk among healthy older adults. European review of aging and physical activity : official journal of the European Group for Research into Elderly and Physical Activity, 14, 3. https://doi.org/10.1186/s11556-017-0173-7
Ogawa, T., Kawashima, N., Obata, H., Kanosue, K., & Nakazawa, K. (2015). Distinct motor strategies underlying split-belt adaptation in human walking and running. PloS one, 10(3), e0121951. https://doi.org/10.1371/journal.pone.0121951
Sato, S., & Choi, J. T. (2019). Increased intramuscular coherence is associated with temporal gait symmetry during split-belt locomotor adaptation. Journal of neurophysiology, 122(3), 1097–1109. https://doi.org/10.1152/jn.00865.2018
Shih, H.-T., Gregor, R., & Lee, S.-P. (2023). Description, reliability and utility of a ground-reaction-force triggered protocol for precise delivery of unilateral trip-like perturbations during gait. PloS One, 18(4), e0284384. https://doi.org/10.1371/journal.pone.0284384
Yoo, D., An, J., Seo, K. H., & Lee, B. C. (2021). Aging Affects Lower Limb Joint Moments and Muscle Responses to a Split-Belt Treadmill Perturbation. Frontiers in sports and active living, 3, 683039. https://doi.org/10.3389/fspor.2021.683039
