New ex­oskele­ton re­ally puts spring in your step


Mil­lions of years of evo­lu­tion have en­abled hu­man be­ings to de­velop a smooth, en­ergy-ef­fi­cient way of walk­ing.

But, biome­chan­i­cal en­gi­neers sug­gested on Wed­nes­day, there’s al­ways room for im­prove­ment.

They un­veiled an un­pow­ered ex­oskele­ton — a small, light, springac­ti­vated de­vice that fits on the lower leg and re­duces the en­ergy cost of walk­ing by around seven per­cent.

“The dif­fer­ence might seem small, but it makes a sig­nif­i­cant dif­fer­ence for hu­mans,” said Steve Collins of Carnegie Mel­lon Uni­ver­sity in Pitts­burgh, Penn­syl­va­nia.

It’s the rough equiv­a­lent of an in­fantry­man be­ing able to march seven per­cent more in terms of time and dis­tance for the same en­ergy ex­pen­di­ture, or a trekker freed of the en­ergy cost of tot­ing a 4-kilo (10-pound) back­pack, he said.

Ex­oskele­tons — ex­ter­nally-worn de­vices in­tended to aug­ment phys­i­cal ac­tions or strength — have a long his­tory.

Back in the late 19th cen­tury, pi­o­neer­ing in­ven­tors toyed with coiled springs tucked into the heels of cow­boy boots, or har­nesses with rub­ber bands that were at­tached to the legs and sought to make walk­ing eas­ier.

But the weight and de­sign of the gad­gets were of­ten an en­ergy drain in them­selves.

Partly as a re­sult of such set­backs, ex­oskele­ton de­sign to­day fa­vors pow­ered de­vices, but in turn has to strug­gle with chal­lenges such as bat­tery range and bulk.

The new gad­get, de­scribed in the science jour­nal Na­ture, is a car­bon­fiber me­chan­i­cal de­vice weigh­ing about 500 grams (1.1 pounds) for each leg.

It com­prises a spring that is at­tached at one end to a strap around the top of the calf, and, at the other end, to the heel of the shoe.

When the heel meets the ground, the spring be­comes ex­tended, and a tiny me­chan­i­cal clutch en­gages to en­sure that the spring briefly re­tains this en­ergy.

When the heel is lifted, the clutch dis­en­gages and the spring is re­leased, thus giv­ing up its stored en­ergy and pro­vid­ing dis­creet help for the calf mus­cles as they lift the lower leg.

It’s Spring Time

There’s no mo­tor, no bat­tery and no com­puter, the in­ven­tors said proudly.

“The un­pow­ered ex­oskele­ton is like a cat­a­pult,” said Collins’ team­mate, Gre­gory Saw­icki of North Carolina State Uni­ver­sity.

“It has a spring that mim­ics the ac­tion of your Achilles’ ten­don, and works in par­al­lel with your calf mus­cles to re­duce the load placed upon them.”

The pro­to­type was de­vel­oped through tests on nine able-bod­ied vol­un­teers, who wore an ex­oskele­ton on both calves.

They were placed on a tread­mill and filmed in or­der to find a spring whose ten­sion of­fered the best sav­ings in en­ergy cost.

The re­duc­tion av­er­ages 7.2 per­cent, plus or or mi­nus 2.6 per­cent, for healthy adults who used it un­der nat­u­ral con­di­tions wear­ing nor­mal ath­letic shoes. The per­for­mance is com­pa­ra­ble to sav­ings with pow­ered ex­oskele­tons, ac­cord­ing to the pa­per.

The de­vice has been patented, and the hope is that it can be adapted for peo­ple with re­duced mo­bil­ity as a re­sult of in­jury, stroke or age­ing.

Fur­ther re­search is needed to en­sure that long-term use of the de­vice does not have an im­pact on body me­chan­ics else­where, Collins said in an email ex­change.

“The body is very com­plex, and it is dif­fi­cult to pre­dict such ef­fects,” he said.

Walk­ing takes up a big chunk of our daily en­ergy use.

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