Varying negative work assistance at the ankle with a soft exosuit during loaded walking.
Philippe Malcolm, Sangjun Lee, Simona Crea and 6 others
PMID 28651596WHAT IT FOUND
Adding negative work assistance to a soft exosuit did not add a clear metabolic benefit beyond positive work assistance.
All powered conditions lowered cost 11 to 15% versus powered-off, but the negative-work dose was not shown.
Key findings
01All powered conditions reduced metabolic rate versus Powered-Off by 11 to 15%, but increasing negative ankle work assistance did not significantly change that reduction.
02Increasing negative ankle work assistance reduced ankle dorsiflexion around mid-stance and peak plantarflexion, and reduced peak biological ankle moment.
03The suit also passively applied work at the hip, and hip assistance was not kept constant, so ankle negative work alone cannot be separated.
STILL TO COME
How it was doneWhat they found
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What it does not show
The study included eight healthy male experienced load carriers or endurance athletes, not patients or people with mobility problems. One participant was excluded because the waist belt slipped, and two participants could not complete the High condition. All powered conditions provided positive ankle work assistance and passive hip work along with negative ankle work assistance, so the effect of any single component cannot be separated. The suit was driven by off-board motors, not a fully autonomous wearable device. The comparison was against a powered-off suit, not against no suit, so some effects may reflect wearing the suit hardware. Hip assistance changed as ankle negative work assistance changed, and hip forces were estimated rather than directly measured during the main test. The task was fast loaded walking at 1.5 m/s with a 23-kg backpack, which may not apply to clinical walking tasks.
Declared interests
The supplied text lists Defense Advanced Research Projects Agency, Samsung, and National Science Foundation as funders. It does not give further conflict-of-interest declarations.
The easy way to misread this
Do not read the 11 to 15% metabolic reductions as evidence that negative-work assistance works. Every powered condition also gave positive-work assistance and passive hip-work assistance, and the negative-work dose effect was not significant (p = 0.083).