Robotic resistance

In recent years, there has been a growing interest in creating wearable robotic exoskeletons for children, especially those with conditions like cerebral palsy (CP). The Agilik smart orthosis is one of these pediatric devices. These exoskeletons hold the promise of improving various aspects of walking, such as step length, walking speed, and muscle activity. This is crucial for children with CP because they often experience difficulties with walking as they grow, and current treatments have their limitations. One of the challenges in addressing these walking difficulties in CP is the need to target both muscle weakness and problems with motor control. While strength training has shown some effectiveness in addressing certain aspects, it doesn’t fully tackle the issues related to motor control.

To tackle this challenge, researchers at the NIH Clinical Center are exploring robotic exoskeletons that can provide both resistance and assistance within a single stride or across multiple strides. The aim is to harness the benefits of exoskeleton assistance while simultaneously offering targeted resistance to enhance specific aspects of walking. This study focuses on the development and validation of such an innovative control strategy for a wearable exoskeleton designed to address knee extension problems in children with crouch gait associated with CP. The researchers’ hypothesis is that this approach will not only improve knee extension during the stance phase but also enhance muscle activation during the swing phase extension. This innovative approach holds great promise for enhancing the mobility and function of children with CP, especially those with more severe impairments.

The study employed a pediatric exoskeleton called P.REX, specifically designed to provide support to the knee and ankle. It features a custom thigh-mounted actuator (the Agilik smart orthosis) responsible for controlling knee movement. Various sensors measure angles and forces, and it’s powered by a battery that can be worn on one’s back. A user-friendly computer application allows operators to configure the exoskeleton and monitor data.

The control system in the P.REX exoskeleton breaks down the walking cycle into five distinct phases, making real-time adjustments based on sensor feedback. Within each phase, the exoskeleton can apply torque and control its direction. The study examined three different modes: one that provided knee extension assistance, another with an interleaved strategy involving resistance, and a third mode without any assistance.

The data for this study were collected from a 13-year-old female participant who underwent multiple visits. This study is part of a larger ongoing project that assesses various exoskeleton modes in children with crouch gait due to CP or other neuromotor disorders, all using the Agilik. Each participant undergoes ten visits, including medical assessments, exoskeleton fitting, practice sessions, and data collection. Data were collected through motion capture and electromyography (EMG) from specific muscles during walking sessions.

The primary objective of the study was to validate a new exoskeleton mode called AssistStResistSw, which combines assistance and resistance for knee extension, and compare it with an assistive mode (AssistStSw) and a baseline mode (Zero). The study verified the accuracy of exoskeleton control by comparing sensor data with motion capture data. It also assessed the flexibility of limb movement relative to the exoskeleton by comparing knee angles.

The effects of the exoskeleton mode on walking were evaluated using motion capture and EMG data from the last session. Key measures included joint angles and muscle activity, compared to the baseline mode (Zero). The study used a statistical analysis method called the two standard deviation method due to the study’s specific conditions.

The participant met the inclusion criteria, had mild spasticity, and successfully completed all 10 study visits without any issues. The study confirmed the accuracy of the controller in segmenting the gait cycle and providing appropriate torques. It also noted improvements in crouch gait during both the assistive and interleaved modes, without affecting walking speed. The study observed increased activity in knee extensor muscles during late swing extension in the interleaved mode, suggesting potential for improved strength and motor control. However, it’s essential to exercise caution when interpreting these results, and further research is required to investigate the long-term therapeutic effects. In summary, this study demonstrates the feasibility and potential benefits of this innovative exoskeleton-based gait training strategy for children with crouch gait associated with CP.

Any reference to the NIH or to Dr. Bulea should not be viewed as an endorsement of Bionic Power, Inc., its products or services.

For a link to the complete text and other studies related to the Agilik, please check out our Published Papers page.

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