Advances in robotic technology have allowed for the development of powered lower-limb prostheses that rely on intrinsic-sensing approaches to improve ambulation for individuals with amputations via the ability to interject mechanical power into the gait cycle to replace the mechanical power that is lost due to missing biological muscles. However, a study published August 10 in the Journal of Neuroengineering and Rehabilitation concludes that as an alternative, robotic lower-limb prostheses could use myoelectric signals recorded from surface electrodes within the socket-limb interface to derive feedforward commands from the amputee’s nervous system. In feedforward control, people act in anticipation of their actions-a combination of inherent patterns and reflexive actions-in the absence of external cues.
The purpose of the study was to determine if muscle activation signals could be recorded from residual lower-limb muscles within the prosthetic socket-limb interface during walking. The researchers recorded surface electromyography (EMG) from three lower-leg muscles and four upper-leg muscles of 12 unilateral transtibial amputee subjects and 12 non-amputee subjects during treadmill walking at 0.7, 1.0, 1.3, and 1.6 meters per second. Muscle signals were recorded from the residual limb of amputee subjects and the right leg of control subjects. For amputee subjects, lower-leg muscle signals were recorded from within the limb-socket interface and from muscles above the knee. Differences were quantified in the muscle-activation profile between amputee and control groups during treadmill walking. The step-to-step inter-subject variability of these profiles were also assessed.
According to study authors, Daniel Ferris, PhD, and graduate student Stephanie Huang, MS, both with the Human Neuromechanics Lab, University of Michigan, Ann Arbor, the main finding of this study is that during walking, most amputee subjects had residual lower-leg muscle activation patterns that were entrained to the gait cycle but highly variable across subjects. However, muscle-activation profile variability was higher for amputee subjects than for control subjects. Another finding of this study is that many, but not all, amputee subjects had robust volitional control of residual lower-leg muscle activation. Ferris and Huang stated that their results support the potential control of powered lower-limb prosthesis using EMG from the residual-limb muscles.
The researchers said they plan to expand their study to include lower-limb EMG patterns of transtibial amputees and non-amputees during over-ground walking at self-selected walking speeds to provide a better understanding of how signals recorded from residual muscles in transtibial amputees can be utilized to control robotic lower-limb prostheses.
Editor’s note: This story has been adapted from materials provided by the Journal of Neuroengineering and Rehabilitation.
