A group of researchers from the Institute of Industrial Technologies and Automation and Villa Beretta Rehabilitation Center in Milan, Italy are studying the way upper limbs interact with exoskeletons intended for rehabilitation. Neurorehabilitation of the upper limbs is often implemented for patients with loss of motor function. Exoskeletons can be used for weight support during the training of upper limbs, allowing for a patient to engage with the movement at varying levels as needed and with semi-independence. Often the high cost of robotic exoskeletons conflicts with the accessibility of such technology. However, passive exoskeletons which utilize springs and counterweights offer a lower cost alternative such as the LIGHTarm.
One major consideration of exoskeleton use is transparency, or the torque the user of the system needs to apply to a robotic component to complete the desired task or movement driven by the user. Zero transparency is beneficial as it requires patients to experience the full motion and required force; however, transparency is reduced for applications in which patients require assistance and support to complete a task. Researchers are exploring the balance between transparency and assistance of the exoskeleton using muscle synergies. Muscle synergies are thought to be “activation patterns on which the CNS can rely on to execute a large number of different movements.” With this study, researchers set out to explore the methods of muscle synergies for evaluation of the use of muscles during movements assisted by a massive exoskeleton device- specifically the LIGHTarm.
The study was carried out on a small group of healthy subjects using the LIGHTarm which utilizes counterweights and springs for a hybrid solution for supporting the whole arm. Subjects were asked to complete movements of daily tasks: reaching against gravity, hand-to-mouth, and hand-to-nape of neck. These movements were repeated with the device and individualized weight compensation, with the device but without weight compensation and freely without the device. To evaluate the muscle activity during movement, surface EMG signals were recorded and analyzed with a FREEEMG 1000 system from BTS Bioengineering. Additionally, reflective markers were placed on anatomical landmarks of the upper limb using the SMART-DX infrared marker system from BTS Bioengineering for kinematics and analysis of movement. By utilizing these technologies, researchers were able to analyze the muscle activity at specific time points and movements during each session wirelessly, minimizing interference with the use of the assistive device.
The data from the system was then analyzed for user transparency through the framework of muscle synergies which takes into account spatial and temporal data on the activation of groups of muscles. Researchers observed differences in the muscle use between the free movement and use of the exoskeleton with compensation and were able to monitor the user transparency. The results demonstrated the potential for this analysis method in the rehabilitation field for monitoring and assessing the use of muscles. The innovative method of analysis allowed for the assessment of the exoskeleton use and interaction with the user.
Researchers of this study plan to continue exploring and quantifying the benefits of such analysis. It is clear that there is promise in these assistive devices to improve the rehabilitation of patients experiencing motor function loss.
For more information on the Villa Beretta Rehabilitation Center, please visit their BTS Motion Society profile.
This post was based on the following article, referenced:
Chiavenna, A., Scano, A., Malosio, M., Molinari Tosatti, L., & Molteni, F. (2018). Assessing User Transparency with Muscle Synergies during Exoskeleton-Assisted Movements: A Pilot Study on the LIGHTarm Device for Neurorehabilitation. Applied Bionics and Biomechanics, 2018, 7647562. http://doi.org/10.1155/2018/7647562