4461 Rockfish Creek Lane
Using Ultrasound to Detect Muscle Fatigue
Joseph Majdi, M.S., Bioengineering, George Mason University
Abstract: Functional electrical stimulation (FES) is often used for rehabilitation in movement disorders and in assistive devices such as exoskeletons. However, FES can rapidly cause muscle fatigue, which limits the induced force production. At present there exists no reliable, real time indicator for FES-induced muscle fatigue. We believe that functional muscle physiology associated with muscle fatigue can be inferred from ultrasound imaging. In this study, we utilized tissue Doppler imaging (TDI) to quantify FES-induced twitch responses in the gastrocnemius muscle, at baseline and after inducing fatigue through repeated voluntary isometric contractions. We estimated muscle velocities using M-mode TDI to quantify differences in the twitch response before and after fatigue. Preliminary results indicate that fatigue induces a higher muscle acceleration during twitch, and the muscle contracts for a longer duration. These results could potentially be used as a real-time indicator for muscle fatigue. We are investigating the use of such a system integrated into an external hybrid walking exoskeleton that can switch from FES-induced force generation to external motors for force generation once the muscle fatigues. Further, it may be possible to replace TDI imaging with a wearable single-element continuous wave Doppler instrument for these measurements, reducing computational complexity and power requirements.
Biography: Joe received his BSE and MS in biomedical engineering at Tulane University in 2012 under Dr. Michael Moore. For his thesis, he built and tested a digital micromirror device to selectively activate neurons using optogenetics. He then did a research fellowship at the Food and Drug Administration studying electrical stimulation and neurotoxins in the retina. In 2017 he completed an MS in electrical and computer engineering at George Mason University, specializing in signal processing. He then joined the the Biomedical Imaging Laboratory as a PhD student with Dr. Siddhartha Sikdar in 2017.
The relationship between embodiment and functional performance with assistive devices: a discussion of upper limb prostheses
Susannah Engdahl, Ph.D., Bioengineering, George Mason University
Abstract: In order to understand patient performance with assistive devices, researchers often use biomechanical methods to quantify whether the device helps restore natural movement patterns. There is growing recognition of the need to include additional methods that characterize the user’s interaction with the device from a psychological standpoint. In particular, quantifying embodiment (perception of the device as part of the body) in conjunction with biomechanics may lead to a valuable understanding of what factors promote functional success with assistive devices. In this presentation, I will discuss my research on understanding how the design of an upper limb prosthesis can affect both the user’s experience of embodiment and their functional outcomes.
Biography: Dr. Engdahl is a postdoctoral researcher in the Biomedical Imaging Laboratory at George Mason University. She earned her BS in Physics from Wittenberg University and her MS and PhD in Biomedical Engineering from the University of Michigan. Her research focuses on upper limb prostheses, including kinematic analysis of prosthesis use and quantifying prosthesis embodiment. She has a strong interest in translating her research into evidence-based treatment practices to improve quality of care for patients.