Aidan Friederich, Naji Alibeji, Musa Audu, Ronald Triolo
An unmet need of the spinal cord injury population is reduced control of the trunk muscles which leads to instability when sitting. Neuroprostheses utilizing functional neuromuscular stimulation to the trunk muscles can restore dynamic trunk control and seated balance. Current feedback controllers use a simplified linear muscle recruitment curve to connect required changes in muscle activation to trunk orientation. To improve controller performance a functionally accurate recruitment curve of the trunk muscles needs to be experimentally determined. This can be achieved by measuring trunk muscle force output as a function of changing stimulus levels to the various muscles that mediate trunk stability. A device, The Trunk Muscle Transducer (TMT), was designed to interface with both a six-axis load cell and a subject to accurately determine trunk muscle forces as trunk orientation changes in the anterior/posterior (AP) and medial/lateral (ML) directions. The device is composed of aluminum beams with sliding joints to adjust to a variety of subject sizes along with a chair designed to stabilize the pelvis. The design was bench-tested by applying known loads with the device tilted in different orientations. The output forces from the sensor were accurate with errors not exceeding 10% in all cases. The device was further tested with able-bodied subjects and was able to determine various amounts of trunk forces in the AP and ML directions. The TMT can be additionally utilized in defining and treating trunk weaknesses evident in other conditions, such as people with hemiparesis or lower back pain.
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