Optimized hip-knee-ankle exoskeleton assistance reduces the metabolic cost of walking with worn loads.
Gwendolyn M Bryan, Patrick W Franks, Seungmoon Song and 4 others
PMID 34743714WHAT IT FOUND
Three expert users wearing a heavy hip-knee-ankle exoskeleton saw their walking effort drop by 41% to 48% while carrying loads of 15% and 30% body weight.
The device reduced metabolic cost significantly more than previous single-joint assists, but the worn mass of the device itself remains a major practical barrier.
Key findings
01Optimized assistance reduced the metabolic cost of walking by 48% with no load, 41% with a light load, and 43% with a heavy load compared to walking in the unpowered device.
02The exoskeleton applied similar positive power across all load conditions, with the hips and ankles contributing most of the assistance.
03Timing parameters for the assistance were consistent across participants and loads, but torque magnitudes varied, suggesting individual customization is needed for force but not for when to apply it.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTs
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What it does not show
The study included only three participants, all of whom were expert users with over 70 hours of experience with the device, so results may not generalize to naïve users. The exoskeleton emulator weighed 13.5 kg, which is significantly heavier than current autonomous devices, potentially offsetting some metabolic benefits in real-world scenarios. The study did not measure kinematics with motion capture due to occlusion issues, relying instead on exoskeleton joint angles. Long-term effects on joint health and injury risk are unknown, with some kinematic changes suggesting potential increased knee loading. The sample size was small due to the length of the experiment and pandemic-related safety concerns.
Declared interests
The study was supported by the U.S. Army Natick Soldier Research, Development and Engineering Center and the National Institutes of Health.
The easy way to misread this
Do not assume these metabolic reductions will translate directly to real-world use with lighter, autonomous exoskeletons. The device used here weighed 13.5 kg and was tethered to powerful offboard motors, meaning the net energy savings for a user wearing a commercially viable, lighter device may be substantially different.