Ankle Exoskeletons May Reduce Feasible Standing Stability in Older Adults with Reduced Ankle Torque Capabilities

核心概念

Ankle exoskeletons can both enhance and hinder standing stability in older adults, depending on the user's ankle torque production capabilities and the velocity of the center of mass.

摘要

The study investigates the effects of ankle exoskeletons on standing balance in simple models of young and older adults. Key insights:

1. For young adults with full ankle strength, ankle exoskeletons moderately reduce the feasible stability boundaries, particularly at higher center of mass velocities.

2. For older adults with age-related deficits in maximum ankle torque (MT) and maximum rate of torque development (MRTD), there is a trade-off:

• At low center of mass velocities, exoskeletons can augment stability by compensating for reduced ankle torque capabilities.
• At higher velocities, exoskeletons can reduce stability in some conditions by further constraining the feasible stability region.

3. The effects of exoskeletons on stability depend on the specific control strategy used. A gravity compensation controller and a proportional-derivative controller were analyzed, with the gravity compensation strategy showing slightly larger reductions in stability boundaries.

4. Reductions in MT have a larger impact on stability than reductions in MRTD, but the exoskeleton can mitigate the effects of MT deficits at forward velocities.

5. A work-energy analysis provides additional insights into how the exoskeleton alters the zero-torque line, which delineates the boundary between forward and backward falls.

Overall, the results suggest that well-established control strategies for ankle exoskeletons must be experimentally validated, especially in older adult populations with impaired ankle function.

統計資料

"Ankle angle and angular velocity ranges for feasible stability are reduced by up to 17% with exoskeleton assistance in young adults, and increased by up to 18% in weak older adults."
"A 30% reduction in maximum ankle torque results in a 20% smaller stability region without exoskeleton, but only a 10% smaller region with exoskeleton assistance."
"A 30% reduction in maximum rate of torque development results in a 2.6% smaller stability region without exoskeleton, but a 10.4% smaller region with exoskeleton assistance."

引述

"Ankle exoskeletons may enhance stability at low center of mass velocities, but reduce stability in some high velocity conditions."
"Reductions in maximum ankle torque have a larger impact on stability than reductions in maximum rate of torque development."
"Well-established control strategies for ankle exoskeletons must be experimentally validated, especially in older adult populations with impaired ankle function."

從以下內容提煉的關鍵洞見

Ankle Exoskeletons May Hinder Standing Balance in Simple Models of Older and Younger Adults

by Daphna Raz, ... 於 arxiv.org 10-03-2024

https://arxiv.org/pdf/2408.05418.pdf

深入探究

How might the effects of ankle exoskeletons on standing balance change if the human user is able to actively modulate their own ankle torque production in response to the exoskeleton assistance?

If the human user can actively modulate their own ankle torque production in response to the exoskeleton assistance, the effects on standing balance could be significantly enhanced. Active modulation allows the user to dynamically adjust their torque output based on real-time feedback from their body and the environment. This adaptability could lead to several positive outcomes:

Improved Stability: Users could fine-tune their torque production to counteract the disturbances introduced by the exoskeleton, particularly in high-velocity conditions where the exoskeleton may otherwise hinder stability. By actively engaging their muscles, users can maintain a more stable center of mass (CoM) position, effectively expanding the stabilizable region (SR).

Enhanced Responsiveness: Active modulation would enable users to respond more effectively to perturbations, such as slips or shifts in weight. This responsiveness is crucial for maintaining balance, especially in older adults who may have slower reflexes or reduced proprioception.

Reduced Dependence on the Exoskeleton: By actively engaging their ankle muscles, users may become less reliant on the exoskeleton for stability. This could lead to a more natural gait and balance strategy, reducing the risk of over-reliance on the device, which can sometimes lead to decreased muscle activation and strength over time.

Personalized Control Strategies: Users could develop personalized control strategies that optimize the interaction between their natural torque production and the assistance provided by the exoskeleton. This could involve adjusting the level of assistance based on their current balance needs, leading to a more tailored and effective use of the device.

Overall, the ability to actively modulate ankle torque production could transform the interaction between the user and the exoskeleton, potentially leading to improved balance and mobility outcomes.

What other factors, beyond just age-related changes in ankle torque capabilities, might influence how an individual responds to ankle exoskeleton assistance during standing balance tasks?

Several factors beyond age-related changes in ankle torque capabilities can influence an individual's response to ankle exoskeleton assistance during standing balance tasks:

Physical Fitness Level: An individual's overall physical fitness, including strength, flexibility, and endurance, can significantly impact how they interact with an exoskeleton. Those with better fitness levels may adapt more quickly and effectively to the assistance provided by the device.

Neuromuscular Control: The ability of the nervous system to coordinate muscle activity plays a crucial role in balance. Individuals with better neuromuscular control may be more adept at utilizing exoskeleton assistance to enhance stability, while those with impaired control may struggle to integrate the device into their balance strategies.

Cognitive Factors: Cognitive load and attentional resources can affect balance performance. Individuals who are distracted or have cognitive impairments may find it more challenging to effectively use an exoskeleton, as maintaining balance requires both physical and mental resources.

Previous Experience with Assistive Devices: Familiarity with using assistive devices can influence how well an individual adapts to an ankle exoskeleton. Those with prior experience may have developed strategies that enhance their ability to use the device effectively.

Environmental Conditions: The context in which the exoskeleton is used, such as the surface type (e.g., slippery vs. stable) and the presence of obstacles, can affect balance performance. Different environments may require varying levels of torque production and modulation, influencing how the exoskeleton assists the user.

Psychological Factors: Confidence and fear of falling can also play a role. Individuals who are anxious about falling may be more hesitant to fully engage with the exoskeleton, potentially limiting its effectiveness.

These factors highlight the complexity of human-exoskeleton interactions and underscore the need for personalized approaches to exoskeleton design and control.

Given the complex and sometimes counterintuitive effects of ankle exoskeletons on standing stability, how might these devices be designed and controlled to reliably enhance balance and mobility in older adult populations?

To enhance balance and mobility in older adult populations through ankle exoskeletons, several design and control strategies can be implemented:

Adaptive Control Systems: Implementing adaptive control algorithms that can adjust the level of assistance based on real-time feedback from the user’s movements and environmental conditions can optimize performance. These systems should be capable of learning from user interactions to provide personalized assistance that evolves with the user’s capabilities.

User-Centric Design: The design of the exoskeleton should prioritize user comfort and ease of use. Lightweight materials, ergonomic shapes, and intuitive interfaces can encourage older adults to use the device more consistently. Additionally, the device should allow for easy donning and doffing to promote independence.

Variable Assistance Levels: Providing users with the ability to select different levels of assistance based on their current needs can enhance the effectiveness of the exoskeleton. For instance, users could choose higher assistance levels during challenging tasks or lower levels during routine activities to promote muscle engagement.

Integration of Sensory Feedback: Incorporating sensory feedback mechanisms, such as haptic feedback or visual cues, can help users better understand their balance status and the effects of the exoskeleton. This feedback can guide users in modulating their own torque production in response to the assistance provided.

Training and Rehabilitation Programs: Developing training programs that educate users on how to effectively use the exoskeleton can improve outcomes. These programs should focus on enhancing users’ awareness of their balance strategies and how to integrate the device into their movements.

Robust Safety Features: Safety features, such as automatic shut-off mechanisms or fall detection systems, can help mitigate risks associated with using exoskeletons. Ensuring that users feel safe while using the device is crucial for promoting confidence and encouraging regular use.

Customization for Individual Needs: Recognizing that older adults have diverse needs and capabilities, exoskeletons should be customizable to accommodate individual differences in strength, mobility, and balance strategies. This could involve adjustable torque settings or modular components that can be tailored to the user’s specific requirements.

By focusing on these design and control strategies, ankle exoskeletons can be made more effective tools for enhancing balance and mobility in older adult populations, ultimately reducing fall risk and improving quality of life.