Biomechanics and energetics of walking in powered ankle exoskeletons using myoelectric control versus mechanically intrinsic control.
Jeffrey R Koller, C David Remy, Daniel P Ferris
PMID 29801451WHAT IT FOUND
Metabolic work rate did not differ significantly between two powered ankle exoskeleton control methods in eight healthy adults.
Both powered methods reduced metabolic work rate compared with unpowered exoskeleton walking. The main differences were calf muscle activity and ankle power.
Key findings
01The primary comparison found no significant difference in net metabolic work rate between the timing-based controller and the proportional myoelectric controller.
02Both powered controllers reduced net metabolic work rate compared with unpowered walking: 2.95±0.14 W kg^-1 for timing-based and 2.95±0.12 W kg^-1 for proportional myoelectric control.
03The timing-based controller produced a significantly lower peak soleus linear envelope than the proportional myoelectric controller (P=0.026), and the proportional myoelectric controller produced significantly larger positive and negative total ankle power (P=0.005 and P=0.001).
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
Only eight healthy young men were tested, so the results do not show what would happen in people with neurological or musculoskeletal conditions. All walking was on a treadmill at a fixed speed of 1.2 m/s, so it may not reflect overground walking or variable walking speeds. The powered conditions were compared with walking in the exoskeleton without actuation, not with walking without the exoskeleton. The study tested one myoelectric controller and one timing-based controller, not a broad set of control strategies. The paper does not report randomisation or blinding of controller order; the order was fixed after training and calibration. The exoskeleton hardware was limited in torque output.
Declared interests
The paper states funding from the U.S. Department of Defense and the Horace H. Rackham School of Graduate Studies, University of Michigan.
The easy way to misread this
Do not conclude that myoelectric control is clinically better for rehabilitation. The primary metabolic work-rate difference between controllers was not significant, and the study tested only eight healthy adults walking at a fixed speed on a treadmill. The rehabilitation suggestion appears only as an untested interpretation.